This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

## 26 May 2010

### 2010 Move An Asteroid Technical Paper Competition

From the Space Generation Advisory Council (SGAC) announcement about their 2010  Move An Asteroid Technical Paper Competition...

SGAC's Near Earth Object Working Group is happy to announce its third annual Move an Asteroid technical paper competition.

While previous years’ competitions asked contestants how to move an asteroid, this edition of the competition challenges students and young professionals worldwide to come up with ideas for a global asteroid impact early warning system. The perfect warning system would bring together the four elements of early detection, deflection technology, warning methods, and decision-making to best meet the threat of asteroids. Contestants are asked to address some or all of these issues in their submissions of ten pages or fewer.

One skilled winner will earn a fully paid trip to Prague, Czech Republic to present the findings at the 2010 Space Generation Congress (SGC) and the International Astronautical Congress (IAC). The prize will include round-trip airfare, as well as hotel and registration for both the SGC and IAC

Submissions are due 30 July, 2010.

For full details on the competition please see: http://www.spacegeneration.org/asteroid

For more information on SGAC’s Near Earth Object Working Group and how to join it, please see:
http://www.spacegeneration.org/index.php/activities/current-projects/neo-working-group

For more information on the Space Generation Congress please see: http://www.explorerswanted.com

## 25 May 2010

### ESA Advanced Concepts Team (ACT) Analysis of Potential Asteroids to Visit

Figure 1: Orbits of the best 10 asteroids for human missions (Source: ESA ACT).

The Advanced Concepts Team (ACT) of the European Space Agency (ESA) has been looking at potential asteroids to visit. From their news release...

Human missions to asteroids (as recently announced by US President Obama* on April 15 at the Kennedy Space Centre) are in several aspects different from those to Mars or to the Moon, among others because of the wide choice: there are millions of them in the Asteroid belt between the orbits of Jupiter and Mars and thousands in the Near Earth vicinity (NEAs). Not all of these are equally easy and safe to reach – and return from.

The team has taken up the challenge of filtering the good ones out finding possible return trajectories to all known asteroids.

For a first human mission to an asteroid after 2020, one can assume some basic requirements in order to help downselecting a list of interesting asteroids:
• The asteroid should be not too small in order to be able to eventually land and take samples;
• A minimum stay on the asteroid should be guaranteed to allow for a useful scientific return.
Furthermore, it is reasonable to assume some further human-related constraints, such as:
• The trajectory should allow for a safe way to return rapidly to Earth in case of problems up to half way to the target asteroid.
• The overall mission duration should not be too long in order to keep the journey bearable for astronauts.
As well as some technical constraints such as:
• No new revolutionary propulsion system by 2020 - thus delta V values within the range of current capabilities.
• A maximum hyberbolic excess velocity relative to Earth of 4.5 km/s for the return leg so as to allow for a safe landing of the return capsule.

The technical parameters used for the selection are:
Table 1: Baseline for asteroid selection
 Apparent magnitude (corresponding to roughly 200m) H ≤ 22 Time of flight < 1.5 years Stay time on the asteroid > 5 days Relative velocity at Reentry 4.5 km/s Propulsion Chemical, with 1 deep space manoeuvre per leg Launch V infinity 6 km/s

Table 2 lists those asteroids considered as the prime candidates for such a mission.

Table 2: Preliminary list of best suited asteroids for a human mission

 Id Designation Nominal  deltaV (km/s) Nominal return time of flight (days) Emergency return time of flight (days) Emergency return deltaV (km/s) Asteroid orbit's semi major axis a (AU) Asteroid orbit's eccentricity e 323 2000 EA14 6.590 405 195 6.022 1.11 0.2 1365 207945 (1991 JW) 6.937 414 70 3.167 1.03 0.12 1109 2002 TD60 8.776 365 110 5.107 1.20 0.08 434 998 HG49 7.141 405 80 2.654 1.20 0.11 853 2001 QC34 7.428 379 85 2.349 1.12 0.19 1000 2002 OA22 8.675 389 90 2.803 0.94 0.24 1595 2000 OK8 8.931 500 90 4.043 0.98 0.22 515 2006 YF 8.217 448 195 6.677 1.11 0.19 1109 2002 TD60 8.776 365 110 5.107 1.20 0.08 209 65717 (1993 BX3) 8.505 248 120 1.808 1.39 0.28 1527 2006 HR29 9.187 500 120 3.613 0.98 0.26 173 2006 SU49 7.197 230 170 1.019 1.41 0.31 1491 2006 KL21 8.015 373 170 1.836 1.2 0.12 222 2004 KE1 8.561 320 130 2.256 1.30 0.18 66 25143 Itokawa 7.274 261 140 1.945 1.32 0.28 304 2006 QQ23 8.155 249 145 6.167 0.80 0.29 1685 1999 RA32 7.959 369 175 2.160 1.03 0.09 122 2002 TC70 8.714 405 150 2.839 1.37 0.20 1444 2007 SQ6 7.428 369 180 6.629 1.04 0.14 468 10302 (1989 ML) 7.701 351 165 3.622 1.27 0.14

Link: ACT News Item

### NASA Exploration Enterprise Workshop: NEOs (specifically in ESMD Robotic Scout Precursor Missions)

As NASA reveals more details on their new plans (FY2011 Budget details and plans), there are some interesting NEO aspects of the plan, specifically a human NEO mission in the mid 2020s and then a series of robotic precursors beyond what has been envisioned in NASA's Science Mission Directorate (SMD). Slides from Day 1 (25 May 2010) of the NASA Exploration Enterprise Workshop have been released and there are multiple interesting aspects related to NEOs, specifically a presentation by Jay Jenkins about the Exploration Precursor Robotic Missions (xPRM). These are series of new robotic missions to the moon, Mars, and asteroids (separate from SMD). Generally this could add more funding for actual larger ($500-$800M) and smaller ($100-$200M) mission to NEOs.

There are references to two notional, Point of Departure (POD), mission concepts (thus extremely notional) in 2014 called NEO Exploration Rendezvous Orbiter (NERO) and a 2019 mission (see below for more information).

Some highlights of the ESMD Robotic Precursor Mission from the presentation...

NASA Planning for FY11 calls for a “steady stream of [Exploration] Robotic
Precursor missions” and related activities:
– We define this effort as Exploration Precursor Robotic Missions (xPRM)
– The xPRM effort would consist of two Programs:
• xPRP: set of linked flight missions, instrument developments, and R&D for the purpose of acquiring applied precursor knowledge for human spaceflight (HSF)
– Cost range $500M to$800M (total mission life cycle cost with launch)
• xScout: focused, less-expensive, higher-risk missions, with cost cap of $200M including launch • Science Mission Directorate (SMD) missions are driven almost entirely by science objectives set by the National Academies Decadal Survey process, and therefore do not typically address high-priority Exploration precursor/HSF objectives • xPRM missions will be designed to conduct the precursor measurements/experiments to quantitatively inform and support HSF objectives – These are different objectives that lead to different activities in many cases • xPRM is a budget line “umbrella” encompassing two proposed (NPR 7120.5) Programs • Exploration Precursor Robotic Program (xPRP) managed by MSFC – Flight Missions: • Precursor measurements/experiments to enable safe and effective HSF beyond LEO • Platforms for technology demonstration – Instrument Development (Missions of Opportunity) • Enhance investigation opportunities and promote partnerships • Fly on non-xPRP missions – Research and Analysis for Exploration • Turn data into Strategic Knowledge for Exploration – Engineering Information, Visualization, Dissemination • Exploration Scouts (xScouts) managed by ARC: – Small ($100M -$200M incl access to space), higher-risk XScout Program • Principal Investigator (PI)-led or small, common approach to reduce costs • Higher risk, more focused investigations • Assume 18-24 mo cadence • Co-manifest with xPRP missions where practical • First launch 2014 – Stretch: Goal of 2013 launch readiness (requires dedicated launch) • Budgeting$100-$200 M per mission – Includes approx.$50M for access to space (e.g.: Dual-Payload Attachment Fitting, co-manifest or small Expendable Launch Vehicle)
• Mission content:
– Focused scope in support of HSF objectives:
• Could be threshold measurements or existence-proof experiments
– xScout AOs written to complement xPRP portfolio with the goal of accomplishing common xPRM objectives

NOTIONAL Point of Departure Asteroid Mission Concepts:

2014: NEO Exploration Rendezvous Orbiter (NERO) - NOTIONAL Point of Departure – Subject to Change

Discovery-class, with scope similar to NEAR-Shoemaker (rendezvous and close proximity conops with end-game “touchdown”) but geared toward HSF objectives:
– Hazards, Prox-Ops, Quantify engineering boundary conditions, Resources
• Measurements (potential candidates):
– Sub-meter-per-pixel imaging in multiple colors
– Geodetic imaging lidar altimetry (topography)
– Compositional mapping via multiple approaches,
• Gamma-ray/Neutron Spectrometry (GRNS) best if low altitude orbit can be established for months, or hyperspectral spectroscopy (0.4 to 5 um)
– Small sounding-imaging-radar or long-wavelength sounder
• 2014 launch with results in 2015/16, would be in time to influence engineering concepts for HSF to NEO class missions in 2025
• Launch may permit co-manifest opportunity with first xScout
• Option:
– Investigating feasibility of modifying early xPRM portfolio to investigate several NEO targets early

2019: NEO TBD Mission - NOTIONAL Point of Departure – Subject to Change

Little Definition to date:
– Later mission requires less definition at this time
– Objectives Definition Team (ODT)-process against refined HSF objectives will be used
• Implementation Options in discussion:
– Discovery/New Frontiers-Class observation platform rendezvous
– Pair of ESPA-derived prop systems with a “to be defined” instrumentation package to separate targets
• Separate targets may be attainable with chemical prop by lunar fly-by redirection or by near Earth phasing orbit.
– 3 to 6 spacecraft in single launch “shotgun” with small instrumentation package and solar electric propulsion systems to separate targets
• Investigation Options under discussion
– Proximity remote sensing, beacon placement, small hoppers, touch & go, grappling, sample return (especially relevant to resources)

Link: Explorations Precursor Robotic Missions (xPRM) - Day 1 Presentations - May 25, 2010

Link: NASA Exploration Enterprise Workshop (25 - 26 May 2010) (NASA Site)

Link: NASA Exploration Enterprise Workshop (25 - 26 May 2010) (AIAA Site)

## 24 May 2010

### Video on NEOWISE (Space Rock Census)

Video interview with NEOWISE principal investigator (PI) Amy Mainzer (JPL biography page)

Link: Video Interview (NEOWISE) - JPL

Link: Video Interview (NEOWISE) - NASA

### Article: WISE Makes Progress on its Space Rock Catalog

This animation shows asteroids and comets observed so far by NASA's Wide-field Infrared Survey Explorer, or WISE.

JPL news article on the Wide-field Infrared Survey Explorer (WISE) spacecraft (includes animation of asteroids/comets observed by WISE and a video interview with NEOWISE PI). From the article...

NASA's Wide-field Infrared Survey Explorer, or WISE, is busy surveying the landscape of the infrared sky, building up a catalog of cosmic specimens -- everything from distant galaxies to "failed" stars, called brown dwarfs.

Closer to home, the mission is picking out an impressive collection of asteroids and comets, some known and some never seen before. Most of these hang out in the Main Belt between Mars and Jupiter, but a small number are near-Earth objects -- asteroids and comets with orbits that pass within about 48 million kilometers (30 million miles) of Earth's orbit. By studying a small sample of near-Earth objects, WISE will learn more about the population as a whole. How do their sizes differ, and how many objects are dark versus light?

"We are taking a census of a small sample of near-Earth objects to get a better idea of how they vary," said Amy Mainzer, the principal investigator of NEOWISE, a program to catalog asteroids seen with WISE.

So far, the mission has observed more than 60,000 asteroids, both Main Belt and near-Earth objects. Most were known before, but more than 11,000 are new.

"Our data pipeline is bursting with asteroids," said WISE Principal Investigator Ned Wright of UCLA. "We are discovering about a hundred a day, mostly in the Main Belt."

About 190 near-Earth asteroids have been observed to date, of which more than 50 are new discoveries. All asteroid observations are reported to the NASA-funded International Astronomical Union's Minor Planet Center, a clearinghouse for data on all solar system bodies at the Smithsonian Astrophysical Observatory in Cambridge, Mass.

"It's a really exciting time for asteroid science," said Tim Spahr, who directs the Minor Planet Center. "WISE is another tool to add to our tool belt of instruments to discover and study the asteroid population."
A network of ground-based telescopes follows up and confirms the WISE finds, including the NASA-funded University of Arizona Spacewatch and Catalina Sky Survey projects, both near Tucson, Ariz., and the NASA-funded Magdalena Ridge Observatory near Socorro, N.M.

Some of the near-Earth asteroids detected so far are visibly dark, but it's too early to say what percentage. The team needs time to properly analyze and calibrate the data. When results are ready, they will be published in a peer-reviewed journal. WISE has not found an asteroid yet that would be too dark for detection by visible-light telescopes on the ground.

"We're beginning the process of sorting through all the objects we're finding so we can learn more about their properties," said Mainzer. "How many are big or small, or light versus dark?"

WISE will also study Trojans, asteroids that run along with Jupiter in its orbit around the sun and travel in two packs -- one in front of and one behind the gas giant. It has seen more than 800, and by the end of the mission, should have observed about half of all 4,500 known Trojans. The results will address dueling theories about how the outer planets evolved.

With its infrared vision, WISE is good at many aspects of asteroid watching. First, infrared light gives a better estimate of an asteroid's size. Imagine a light, shiny rock lying next to a bigger, dark one in the sunshine. From far away, the rocks might look about the same size. That's because they reflect about the same amount of visible sunlight. But, if you pointed an infrared camera at them, you could tell the dark one is bigger. Infrared light is related to the heat radiated from the rock itself, which, in turn, is related to its size.
A second benefit of infrared is the ability to see darker asteroids. Some asteroids are blacker than coal and barely reflect any visible light. WISE can see their infrared glow. The mission isn't necessarily hunting down dark asteroids in hiding, but collecting a sample of all different types. Like a geologist collecting everything from pumice to quartz, WISE is capturing the diversity of cosmic rocks in our solar neighborhood.
In the end, WISE will provide rough size and composition profiles for hundreds of near-Earth objects, about 100 to 200 of which will be new.

WISE has also bagged about a dozen new comets to date. The icy cousins to asteroids are easy for the telescope to spot because, as the comets are warmed by the sun, gas and dust particles blow off and glow with infrared light. Many of the comets found by WISE so far are so-called long-period comets, meaning they spend billions of years circling the sun in the frigid hinterlands of our solar system, before they are shuttled into the inner, warmer parts. Others are termed short-period comets -- they spend most of their lives hanging around the space near Jupiter, occasionally veering into the space closer to the terrestrial planets. WISE's measurements of these snowy dirtballs will allow scientists to study their size, composition and density. Measurements of the comets' orbits will help explain what kicks these objects out of their original, more distant orbits and in toward the sun.

WISE will complete one-and-a-half scans of the sky in October of this year. Visit http://wise.astro.ucla.edu to see selected WISE images released so far.

JPL manages WISE for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu .

Link: JPL News Release

Link: NASA News Release

Link: WISE Animation (.mov)

Link: Video: Space Rock Census - JPL

Link: Video: Space Rock Census - NASA

## 23 May 2010

### U.N. COPUOS and NEOs: June 2010 Meeting

The fifty-third session of the Committee on the Peaceful Uses of Outer Space will be held from 9-18 June 2010 at the United Nation Office at Vienna, Vienna International Center, Vienna, Austria (agenda). There may be some NEO related activity here.

The Draft report of the Working Group on Near-Earth Objects includes discussion of some plans for 2010-2011 work. From that report in February 2010 here are some highlights:

Draft report of the Working Group on Near-Earth Objects (Committee on the Peaceful Uses of Outer Space Scientific and Technical Subcommittee, Forty-seventh session, Vienna, 8-19 February 2010)

1. Pursuant to paragraph 9 of General Assembly resolution 64/86, the Scientific and Technical Subcommittee, at its forty-seventh session, reconvened its Working Group on Near-Earth Objects.

2. Sergio Camacho (Mexico) was elected Chair of the Working Group on Near- Earth Objects at the 729th meeting of the Subcommittee, on 15 February 2010. The Working Group expressed its appreciation to the outgoing Chair, Richard Crowther (United Kingdom of Great Britain and Northern Ireland), for the excellent manner in which he had led its work and the work of the Action Team on Near-Earth Objects.

3. In accordance with the multi-year workplan under the item on near-Earth objects (A/AC.105/911, annex III, para. 11), the Working Group did the following:
(a) Considered the reports submitted in response to the annual request for information on near-Earth object (NEO) activities and continued intersessional work;
(b) Continued the work begun during the intersessional period on drafting international procedures for handling the NEO threat and sought agreement on those procedures;
(c) Reviewed progress made on international cooperation and collaboration on NEO observations;
(d) Facilitated, for the purpose of NEO threat detection, a more robust international capability for exchanging, processing, archiving and disseminating data;
(e) Prepared an updated interim report of the Action Team on Near-Earth Objects (2009-2010) (A/AC.105/C.1/L.301).

4. The Working Group noted with satisfaction the work of the Action Team on Near-Earth Objects, as reflected in the draft recommendations for an international response to the threat of NEO impact (A/AC.105/C.1/L.301, annex).

5. The Working Group heard a statement from the representative of Australia on the report entitled “Legal aspects of NEO threat response and related institutional issues”, prepared by the University of Nebraska-Lincoln (United States), in which key legal and institutional issues linked to potential future threats posed by NEOs were examined. The Working Group also heard a statement by the observer for the Secure World Foundation (SWF) on a workshop organized jointly by the Association of Space Explorers and SWF, with support from the Regional Centre for Space Science and Technology Education for Latin America and the Caribbean, on the establishment of a NEO information, analysis and warning network. The workshop was held in Mexico City from 18 to 20 January 2010, under the auspices of the Government of Mexico. The Working Group agreed that the report of the workshop and the report prepared by the University of Nebraska-Lincoln could be considered by the Action Team on Near-Earth Objects between sessions during 2010 and 2011.

6. The Working Group noted that, in 2011 it should do the following, among other things:
(a) Consider the reports submitted in response to the annual request for information on NEO activities and continue intersessional work;
(b) Finalize the agreement on international procedures for handling the NEO threat and engage international stakeholders;
(c) Review progress on international cooperation and collaboration on NEO observations and on capability for exchanging, processing, archiving and disseminating data for the purpose of detecting NEO threats;
(d) Consider the final report of the Action Team on Near-Earth Objects.

7. The Working Group further noted that its intersessional work for the period 2010-2011 could include workshops involving experts in various subjects related to the draft recommendations made by the Action Team (A/AC.105/C.1/L.301, annex). The Working Group agreed that the reports of those workshops could further assist the Action Team in finalizing recommendations for the international response to the threat posed by NEOs.

8. The Working Group agreed that the Action Team should continue its intersessional work, in accordance with the multi-year workplan, to further review draft recommendations for an international response to the threat of NEO impact, for consideration by the Working Group at the forty-eighth session of the Subcommittee, in 2011. The Working Group agreed that the Action Team would meet on the margins of the fifty-third session of the Committee on the Peaceful Uses of Outer Space, to be held in June 2010, to finalize draft recommendations for the international response to the threat of NEO impact. In that context, the Working Group encouraged Member States to participate in the intersessional work on NEOs and submit their contributions to the Chair of the Action Team.

9. At its […] meeting, on […] February 2010, the Working Group adopted the present report.

Link: Draft report of the Working Group on Near-Earth Objects (Committee on the Peaceful Uses of Outer Space Scientific and Technical Subcommittee, Forty-seventh session, Vienna, 8-19 February 2010)

Link: Provisional agenda and indicative schedule of work for the fifty-third session of the UN COPUOS

## 21 May 2010

### Vast asteroid crater found in Timor Sea

Artist's impression of an asteroid in front of Earth (Image: Getty Images)
From the article...

EVIDENCE OF A MASSIVE crater, at least 50 km across, has been discovered under the Timor Sea and may help scientists explain a rapid cooling of the planet 35 million years ago.

The new findings, announced today and published in the Australian Journal of Earth Sciences, suggest that the impact could have contributed towards the formation of the Antarctic ice sheet.

When Dariuz Jablonski, an oil exploration geologist with Finder Exploration, was conducting seismic surveys in the Timor Sea north of Broome in Western Australia, he found what he suspected to be the remains of large crater site. Dariuz asked Dr Andrew Glikson of the Australian National University in Canberra to help investigate.

Andrew, a specialist in extraterrestrial impacts, conducted tests on rock specimens from the sea floor. He found structural features which suggested great heats and pressures and he concluded that the area was the raised “dome” of a crater produced by an asteroid collision 35 million years ago.

"The identification of microstructural and chemical features in drill fragments taken from the... drill hole revealed evidence of a significant impact," he says.

The minimum size of the dome, which "represents elastic rebound doming of the Earth crust triggered by the impact" is 50 km across, but the full size of the crater could be significantly larger, he told Australian Geographic. "It would be possibly 100 km.”

From the probable diameter of the crater, Andrew estimates that the asteroid which struck the Timor Sea was between 5 and 10 km in size.

Correlation with global cooling

This impact coincided with a time of heavy asteroid bombardment globally. Several other craters have been documented from a similar time, including one off the WA coast measuring 120 km in diameter. Another impact structure in Siberia was created by an asteroid 100 km in size.

Andrew believes that collisions such as this may have played a role in the rapid decline in global temperatures. He says that the onslaught of numerous asteroids shifted the Earth's plates to create a rift between South America and Antarctica known as the Drake Passage, which still exists today.

“It allowed the circum-Antarctic ocean current, a cold current, to be established — this allowed the Antarctic ice sheets to form,” he says. These ice sheets, along with the newly established circular current around Antarctica, forced cooler water into the world’s ocean and may have resulted in a well documented cooling of the planet.

Link: Australian Journal of Earth Sciences An International Geoscience Journal of the Geological Society of Australia

Link: ANU News Release

## 19 May 2010

### Russian Apophis Mission?

From the article...

Russia is developing an unmanned spacecraft designed to explore the asteroid Apophis that, astronomers worry, may several times come dangerously close to the Earth in 2029-2036.

The spacecraft is being built at the Lavochkin plant, Russian academic Lev Zeleny told the Interfax news agency on Tuesday.

If the "space wanderer" hits the Earth, the explosion will be a few times more powerful than that caused by Tunguska blast that shook Siberia in 1908.

The craft that is being built at the Lavochkin plant, located in Khimki just north of Moscow, is not designed to destroy the asteroid or amend its orbit, bur rather, to study the tiny planet "more closely," said Zeleny.

Apophis was discovered in 2004 by the U.S. astronomers. It is expected that the asteroid will approach the Earth at about 30,000 km, that is 12 times as little as the distance between the Earth and the Moon.

In last December the head of Russia's space agency Anatoly Perminov told reporters that Russia was considering sending a spacecraft to the asteroid to knock it off its course and prevent the possible collision.

A last October update on Apophis's orbit by NASA indicated "a significantly reduced likelihood of a hazardous encounter with Earth in 2036."

Scientists have long theorized about asteroid deflection strategies. Some have proposed sending a probe to circle around a dangerous asteroid to gradually change its trajectory. Others have suggested sending a spacecraft to collide with the asteroid and alter its momentum or using nuclear weapons to hit it.

Link: Xinhua Article (Russia to Build Spacecraft to Study Asteroid)

## 18 May 2010

### Paper on 2009 Jupiter Impact Event

A new paper on the 2009 Jupiter Impact Event.

The impact of a large object with Jupiter in July 2009

Authors: A. Sánchez-Lavega, A. Wesley, G. Orton, R. Hueso, S. Perez-Hoyos, L. N. Fletcher, P. Yanamandra-Fisher, J. Legarreta, I. de Pater, H. Hammel, A. Simon-Miller, J. M. Gomez-Forrellad, J. L. Ortiz, E. García-Melendo, R. C. Puetter, P. Chodas
(Submitted on 13 May 2010)

Abstract:

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55^{\circ}S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory opposite and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4,800 km east-west and 2,500 km north-south, with those produced by the SL9 fragments, and dynamical calculations of pre-impact orbit, indicate that the impactor was most probably an icy body with a size of 0.5-1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890-nm and K (2.03-2.36 {\mu}m) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary cloud.

Comments: 15 pages, 5 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: The Astrophysical Journal Letters, 715, 2, L150 (2010)
DOI: 10.1088/2041-8205/715/2/L155
Cite as: arXiv:1005.2312v1 [astro-ph.EP]

Selections from the MIT Technology Review article...

Estimating the likelihood of such impacts is hard for a gas giant like Jupiter because the events leave no long-lasting scars on the surface. Jupiter's bruise has already faded away.

So astronomers have to rely on historical records. Before last year's impact, astronomers knew only of the Shoemaker-Levy impact and a possible impact observed by the Italian astronomer Giovanni Cassini in 1640. Together with other evidence such as crater counts on Jupiter's large moons and various theoretical calculations, astronomers guessed that Jupiter was liable to a strike perhaps as rarely as once in every 350 years.

Sánchez-Lavega and co say that last year's strike significantly changes these numbers. Seeing two strikes in 15 years means that that Jupiter may be liable to be hit as often as once a decade. The reason we haven't seen impacts before is simple: digital cameras and image processing techniques have only become easily available to amateurs in the last ten years. (Before that, even professionals often had to rely on hand drawn pictures of the planets.)

Link: MIT Technology Review Article

## 16 May 2010

### NASA's 2010 Astrophysics Senior Review Committee: Do not Extend WISE Mission

Summary of the recent Report of the 2010 Senior Review of the Astrophysics Division Operating Missions April 6 – 9, 2010 from space.com...

A NASA advisory panel is recommending that the Wide-field Infrared Survey Explorer (WISE) mission end in October as originally planned instead of continuing to search for comets, asteroids and stars during a three month extended phase.

While the WISE mission is expected to produce significant results, NASA's 2010 Astrophysics Senior Review Committee said there was not adequate scientific justification to continue the mission once the spacecraft depletes its supply of hydrogen used to cool the onboard telescope and detectors.

The WISE spacecraft built by Ball Aerospace & Technologies Corp. of Boulder, Colo., carries an infrared telescope built by the Space Dynamics Laboratory of Logan, Utah, that is designed to detect the faint glow of distant objects with instruments chilled to the point where they produce no detectable infrared light.

The original plan for the 10-month WISE mission, which was launched in December and managed by the Jet Propulsion Laboratory in Pasadena, Calif., includes one month for on-orbit checkout, followed by a six-month survey of the entire sky in four wavelengths of infrared light.

During the last three months of the original mission, the WISE team plans to conduct a second survey covering half the sky in those four infrared wavelengths.

Because the spacecraft and telescope remain in excellent condition, Ned Wright, WISE principal investigator and a professor at the University of California, Los Angeles, proposed a three-month extension of the mission to complete the second half of the second sky survey in two of the four infrared wavelengths because those images could be captured even when the hydrogen supply is exhausted and the instruments can no longer be chilled.

That additional three-month project, known as Warm WISE, would have added $6.5 million to the program's$320 million price tag, according to NASA spokesman J.D. Harrington. WISE mission officials also proposed spending $8 million on an Extended Source Catalog, a detailed database of large objects, such as galaxies and interstellar clouds of gas and dust, revealed in WISE imagery but not of primary concern to astronomers looking at specific stars or comets. Currently, WISE is producing approximately 7,500 images a day in each of four infrared wavelengths. That original mission "should produce a catalog and image atlas of great utility to the entire astronomical community," according to the report of the NASA review panel. "Although it is impressed with the promise of the cryogenic mission, the Senior Review Committee did not find adequate scientific justification in the proposal for the cost of either the Warm Extension or the Enhanced Data Products." Link: Space.com Article From the report of NASA's 2010 Astrophysics Senior Review Committee: Warm WISE The WISE mission will produce a survey of the entire sky at wavelengths 3.4, 4.6, 12, and 22 μm. WISE was launched into a Sun-synchronous orbit on 2009 December 14, and began its prime survey mission on 2010 January 14. WISE has a cryogenic primary mission utilizing a solid hydrogen cryostat, a 40 cm telescope, and four infrared detector arrays. The focal plane has four 1024x1024 infrared detector arrays, HgCdTe for the two shorter wavelengths and Si:As for the two longer wavelengths. The former will remain available after cryogen exhaustion. WISE maps the sky in a highly redundant manner by scanning the sky continuously, taking out the orbital smearing by using synchronized motions of a scanning mirror. WISE produces a complete sky map in 6 months. Data products for the primary mission include an Image Atlas and a point source catalog. Cryogenic WISE will also identify and characterize a number of Near Earth Objects(NEO) using the 12 and 22 μm windows. These bands will not be available after exhaustion of the cryogen, thus no NEO work is anticipated in the warm mission phase. The proposal to the SRC included two main elements: a three-month extension of WISE flight operations after cryogen depletion to complete the second-pass sky coverage in the 3.4 and 4.6 μm bands, and enhanced data products and enhanced data analysis tools. Spacecraft/instrument health & status: WISE is currently conducting its prime cryogenic mission. All systems on the instrument payload and spacecraft are performing well. The first pass on the sky should be complete in July 2010, and the solid hydrogen cryogens are expected to last until October 2010. The 9-month cryogen lifetime should be sufficient to cover half the sky for a second pass. After the depletion of the cryogens, the focal planes and optics are predicted to radiatively equilibrate at 72 ± 4 K. This temperature should be low enough to continue operation of the two shorter wavelength channels with little change in performance. Science strengths: The WISE cryogenic survey will be orders of magnitude more sensitive than previous all sky surveys at these wavelengths. The WISE survey is expected be an important astronomical database for decades to come. The team is highly experienced and includes experts in both the instrumentation and the processing of very large astronomical data sets. Relevance to NASA priorities: WISE is relevant to NASA priorities since the WISE catalog will contain positions and infrared photometry for all types of astronomical objects ranging from solar system objects to sources in the distant universe. In particular, Warm WISE would contribute to the NASA strategic goal of understanding the formation of low mass stars and the properties of massive exoplanets by increasing the sample of known objects. Data accessibility: The final release of the Warm WISE data is scheduled for the fourth quarter of CY2012. Synergy with other missions and ground-based work: It is expected that the WISE data will be important as a general source of infrared information for other missions as well as for ground-based work. In particular, WISE will provide targets for Spitzer verification and further characterization. Proposal weaknesses: The proposal did not convincingly demonstrate to the SRC the need for the three-month extension for the warm mission. The primary science example, the detection of ultra-cool brown dwarfs, would certainly benefit from the warm mission, but the transformational benefit of increasing the sample size from, for example, 85 to 170 objects, was not shown. Most of the other examples were statistical in nature and could reasonably be performed over the half of the sky covered twice in the cryogenic mission. In terms of the general survey sensitivity, only the 4.6 μm band is expected to show a significant improvement in sensitivity from the extension. While the enhanced reliability in the repeated regions is desirable, the requested funding seems high for the anticipated improvement. The science return for the investment in the Absolute Brightness Calibrated Atlas was not well demonstrated. For many studies of extended structures, manual background corrections of the individual 1.56ºx1.56º images should be sufficient. The WISE Variability and Proper Motion Database will likely have limited utility given the several-year delay between the observations and the availability of the tool. Moreover, the cadence of the WISE observations is far from optimal for synoptic studies. The requested funding for the WISE Extended Source Catalog appears to be very high for the perceived effort required to produce the catalog. The SRC was unconvinced about the need for the Custom Image Co-adder Tool and the Custom Source Extractor given their costs. Overall assessment and recommendations: The WISE prime mission should produce a catalog and image atlas of great utility to the entire astronomical community. Although it is impressed with the promise of the cryogenic mission, the SRC did not find adequate scientific justification in the proposalfor the cost of either the Warm Extension or the Enhanced Data Products. The SRC recommends no funding for the extended Warm WISE mission nor for theenhanced tool development. Link: Report of the 2010 Senior Review of the Astrophysics Division Operating Missions April 6-9, 2010 ## 15 May 2010 ### WISE Spacecraft Observation: Asteroid Passing in Image of Nebula Image Credit: NASA/JPL-Caltech/WISE Team From the news release... A new infrared image from NASA's Wide-field Infrared Survey Explorer, or WISE, showcases the Tadpole nebula, a star-forming hub in the constellation Auriga about 12,000 light-years from Earth. As WISE scanned the sky, capturing this mosaic of stitched-together frames, it happened to catch an asteroid in our Solar System passing by. The asteroid, called 1719 Jens, left tracks across the image, seen as a line of yellow-green dots in the boxes near center. A second asteroid, designated 1992 UZ5, was also observed cruising by, as highlighted in the boxes near the upper left Link: Wise Article Link: Space.com Article ## 14 May 2010 ### NEO News (05/15/10) NASA shifts course toward NEAs From Dave Morrison... NEO News (05/15/10) NASA shifts course toward NEAs NASA's future course for human space exploration has been subject to extensive and often passionate debate ever since the Augustine Commission recommended a "flexible path" with "multiple destinations." The new approach was implemented in the President's proposed NASA budget for FY11, which would (if approved by Congress) terminate the Constellation program aimed at human landings on the Moon by 2020. In its place the NASA budget would strengthen science and technology research and study options for human flights to asteroids and the moons of Mars. The new direction was made official on April 15 when President Obama spoke about his vision for space exploration, calling specifically for a human visit to a NEA by 2025. Additional perspective on this new asteroid focus can be found in an address on April 26 by NASA Deputy Administrator Lori Garver, and in a background interview with Wes Huntress, former NASA Associate Administrator for Science and President of the Planetary Society. David Morrison ============================= REMARKS OF PRESIDENT BARACK OBAMA ON SPACE EXPLORATION IN THE 21ST CENTURY Kennedy Space Center, April 15, 2010 Š.. We are setting a course with specific and achievable milestones. Early in the next decade, a set of crewed flights will test and prove the systems required for exploration beyond low Earth orbit. And by 2025, we expect new spacecraft designed for long journeys to allow us to begin the first-ever crewed missions beyond the Moon into deep space. We'll start by sending astronauts to an asteroid for the first time in history. By the mid-2030s, I believe we can send humans to orbit Mars and return them safely to Earth. And a landing on Mars will follow. Now, critical to deep space exploration will be the development of breakthrough propulsion systems and other advanced technologies. So I'm challenging NASA to break through these barriers. And I know you will - as always - with ingenuity and intensity. Š.. I understand that some believe that we should attempt a return to the surface of the Moon first, as previously planned. But the simple fact is, we have been there before. There is a lot more space to explore, and a lot more to learn when we do. I believe it is more important to ramp up our capabilities to reach - and operate at - a series of increasingly demanding targets, while advancing our technological capabilities with each step outward. That is what this strategy does. And that is how we will ensure that our leadership in space is even stronger in this new century than it was in the last. ================================= ADDRESS BY LORI GARVER, NASA DEPUTY ADMINISTRATOR Center for Strategic and International Studies April 26, 2010 Before we reach the surface of Mars with humans, we'll explore an asteroid, by 2025. The President announced that unprecedented goal in Florida. NASA engineers have been looking at candidates for a NEO mission that could launch in 2025. Because of orbital dynamics, launch date drives the specific destination. We are discovering new NEOs all the time, so our list of targets will certainly expand over the coming years. One intriguing candidate is asteroid 1999AO10, which we could reach with a 2025 launch on a 150 day round trip mission, spending about 2 weeks at the asteroid. But why would we want to visit an asteroid in the first place? Why are these space rocks such compelling destinations for humans? First, they provide an intermediate destination for human exploration, with round trip times significantly longer than the Moon but shorter than Mars. They also don't require a high gravity landing, perhaps making them even more accessible than the Moon from a hardware development standpoint. Next, asteroids are fascinating scientifically, as evidenced by the National Academy's endorsement of their exploration in Decadal Surveys and other reports. They are remnants of the birth of our solar system - they preserve the primitive materials from which our earth, and possibly even life, formed. Some asteroids are very rich in valuable metals, and may be important space resources. And finally, we know NEOs are important for life on Earth because they have affected our evolution through mass extinctions they have caused. The bottom line is, NEOs represent one of only a handful of threats that could wipe out humanity. It is not a question of WHETHER we will be hit by an extinction-scale NEO in the future, but merely WHEN this will happen. Only by gaining experience operating at these objects might it be possible to someday prevent one from changing the course of humanity's future. One issue with exploring NEOs with humans is that the U.S. has only operated around the largest NEO, with the robotic mission NEAR. The Japanese have visited another. But most of these objects are still very mysterious to us. We know very little about 1999AO10, potentially our most promising target. This is where our Exploration Precursor Robotic missions come into play. With these missions, we can explore potential candidates, and provide ground truth for our Earth-based telescopic observations of NEOs. These are truly tangible reasons for making a NEO, one of our first destinations for humans in deep space. And I have to add, it is incredible how well Hollywood taps in to the psyche and true desires of the public, so having something appear in a movie is not necessarily a bad thing. The public is fascinated by NEOs, and I am sure they are also a little afraid, to be honest. A recent poll just completed by the Everett Group found that sixty-three percent of those who said exploring space was at least somewhat important cited protecting the Earth from collisions with comets and asteroids as a major reason for continuing that exploration. NASA has been working, and in the new budget ramps up, the activity of cataloging and characterizing NEOS. If one is going to pose a danger to Earth, we need to know about it, and by visiting one, we'll have that much better of an understanding of what it might take to mitigate potential future collisions. A mission to a NEO will also test our deep space propulsion systems, since we're talking about 5 million miles of travel as opposed to around 239,000 to reach the Moon. They'll test our ability to orient ourselves and explore on an alien world. They'll test the habitat, radiation protection and life support systems we'll be developing for human beings in deep space. All in all, they're a tough destination. And Mars will be even tougher. ==================================== POTENTIAL CANDIDATE NEAS FOR HUMAN VISITS From Rob Landis, NASA ARC / JSC: Here are the so-called 'Big 6' NEAs that have been identified as potential targets for human visits, together with nominal diameters. None of these has been characterized beyond determining its brightness and orbit. - 1998 HG49 [143 m] - 2001 BB16 [104 m] - 2003 SM84 [100 m] - 2000 AE205 [ 90 m] - 2001 QJ142 [ 72 m] - 2009 OS5 [ 70 m] - 1999 AO10 [ 60 m] ================================= INTERVIEW WITH WESLEY T. HUNTRESS ON NASA'S NEW STRATEGY by James Oberg for IEEE Spectrum, April 2010 http://spectrum.ieee.org/aerospace/space-flight/wesley-t-huntress-author-of-nasas-new-strategy On 15 April, NASA got its long-awaited marching orders from President Obama. The agency is to send people to Mars using a series of "stepping-stone" destinations that are themselves of interest: Lagrange points, near-Earth asteroids, and martian moons. The plan is pretty much exactly what Planetary Society president Wesley T. Huntress Jr. proposed in 2004. James Oberg corresponded with Huntress following President Obama's introduction of the plan. IEEE Spectrum: How do you feel about the new NASA space plan? Wesley T. Huntress: I am absolutely delighted with the new direction NASA has received. And the president demonstrated with his visit [to NASA's Kennedy Space Center on 15 April] that he is fully engaged. Spectrum: How is the president's attention important? WTH: This is the first time NASA has enjoyed full administration support since Apollo, and it is crucial for sustainability of the program. I like what he said: "[By undertaking this strategy,] we will no longer rely on our past achievements and instead embrace a new and bold course of innovation and discovery." It is exactly the kind of inspiration the space program can bring the entire country. Spectrum: Why did Constellation-the program to return to the Moon-have to die? WTH: The old Constellation plan was to go back where we had once been, to do only marginally better than we did 40 years ago. It was neither inspirational nor sufficiently challenging for a space program as storied as America's. Spectrum: Does this mean the end of dreams for human exploration of the Moon? WTH: Others may go there and follow in our footsteps of long ago. Best of luck to them. Spectrum: What do you see as the main theme of American spaceflight strategy? WTH: We want to be in the lead. We want to be out there, farther out than others dare go, clearing a path beyond the moon and onward to Mars. Mars is where the American public really wants us to go, and we can give them a good game, just like we did with getting to the moon in the 1960s. Spectrum: How does the new plan accomplish this? WTH: The new plan is to proceed to Mars step-by-step, making ever farther excursions in space as we develop our technological abilities. [We aim to] proceed to intermediate destinations along the way, beginning with trips to lunar orbit, to the Sun-Earth Lagrange points, to near-Earth asteroids, and finally to the Martian moons before that first trip down to the Martian surface. Spectrum: What role did you play in developing this strategy? WTH: This is an approach to human exploration that my team proposed in a four-year study by the International Academy of Astronautics (IAA) called "The Next Steps in Exploring Deep Space," which was published in early 2004. This same strategy was reemphasized in late 2008 by the Planetary Society's "Beyond the Moon: A New Roadmap for Human Space Exploration in the 21st Century." Spectrum: And when you heard the policy explained from the White House, how did you feel? WTH: Those of us who advocated this plan are gratified. We really felt this plan was an affordable, sustainable, commonsense approach to what should come after Apollo and the space station. Spectrum: Were you surprised by how much it resembled your plan or were you made aware of ongoing policy discussions within NASA? WTH: I was not aware of any ongoing policy discussions within NASA. After the Augustine report [the "Review of U.S. Human Spaceflight Plans Committee," October 2009] showed that Constellation was unaffordable and unsustainable and that there were some bolder and more expansive possibilities to be considered, I was hopeful that the "flexible approach" option would appeal to the new administration. Spectrum: Why did you think the administration might go in that direction? WTH: It just seemed to be the most sensible option even if clearly not the easiest option politically, given Constellation's entrenchment. But politics is not always sensible. I think the right decision has been made, and I am happy to see the administration put some muscle behind its new plan. Spectrum: What do you think are the chief strengths of the policy? WTH: The biggest strengths are first that it proposes a more lofty, challenging, and appealing goal to the American public. Second, it proposes a step-by-step, go-as-you-pay, sustainable plan that can proceed as the technology is developed, not a crash program to "get here by this date." Third, it has intermediate and interesting milestones that can be achieved in reasonable timeframes relative to public expectations and political cycles. Fourth, it restores NASA to the agency that it was meant to be-an exploration agency, not a transportation agency, and [an agency that develops] new technologies in a quest that can fire the economic engine of our country. And fifth, it will inspire many more American youngsters to go into science, engineering, and math and to do what has never been done before. Spectrum: What recommendations from your group were rejected in the new plan? WTH: In general, pretty much all that we recommended is in the new plan. My key worry was that we had no specific directive to build a heavy launch vehicle, without which we are going nowhere. Now we have a specific plan, and I hope we can have a design well in advance of five years. Spectrum: How about the president's plan for commercial human transport into orbit? WTH: I am less interested in who -- government or commercial - builds the transportation system for crew and cargo to low Earth orbit as long as we have one. For crew, perhaps we need a government option as well as a commercial one to reduce risk and have backup options, but for cargo, NASA should no longer be in the trucking business. Spectrum: Has the stepping-stone strategy evolved on its own in the past two years, and if so, in what ways? WTH: I don't know that it has evolved much from our IAA plan other than that the idea seems to have taken this long to gestate and bloom. The intermediate destinations are essentially the same. The sequence is always flexible. Spectrum: How challenged do you think the U.S. space industry -- NASA, contractors, Department of Defense, universities -- will be by the proposed strategy? Do you see any chance of slipping into mediocrity? WTH: Yes, there is a chance of slipping back into mediocrity. The challenge here for Congress, the NASA human exploration centers, and the contractor base entrenched in Constellation is to be flexible and nimble, to turn toward a fundamentally new program-and in the long term, one that is more exciting and sustainable than we have now. If that challenge is not met well in the congressional season this year, we could easily find ourselves back on the old road. Spectrum: What role do you speculate might be played by partners from the International Space Station (ISS) alliance? WTH: The ISS alliance is remarkable and unique. It took a great deal of diplomacy to create, and it is now the model for lessons learned on how to proceed farther into space internationally. I would like to think that we can enlarge the ISS partnership to include all the major players and then have that same alliance repeat this same miracle: to devise how not just the United States but an international consortium can proceed beyond low Earth orbit. Spectrum: Although the moon is not in the critical path your team laid out, do you envision any side branch programs that would expand robot and eventually human activity there? WTH: Yes. The Moon is actually on the path; it is lunar surface ops that are not necessarily critical. Lunar surface excursions should be considered when the resources are available. They should not just be diversionary from the main goal of getting to Mars. Spectrum: What is important about activities on the Moon? WTH: The moon could be a practice Mars for astronaut operations, and there is a lot of interesting science and exploration development that can be done on the lunar surface. It is a major step for space-faring nations that have never been there, and it seems to me a real opportunity for the United States to partner with and assist those nations that want to go there. Spectrum: How does preserving the Orion command module development support the infrastructure requirements of the stepping-stones approach? WTH: No matter what the deep-space destination, a crew habitat will be required. Preserving Orion gets the technology development out to an early start even if it is used only as a return vehicle. We will eventually need a deep-space version of Orion with a long-term habitat. If Earth orbit is used as the "assembly and stepping-off" point for deep-space missions, astronauts returning to Earth will require a version of Orion whether by rendezvous in Earth orbit or by direct return. Spectrum: What role does the extended life of the ISS play in developing infrastructure for the stepping-stones? WTH: It is the research laboratory for finding out how to deal with long-term human spaceflight. It is also the exercise room for deep-space astronaut operational training. And it's a platform for testing technologies and flight systems that will be required for deep-space missions. Spectrum: What do you see as the greatest conceptual breakthrough of this endorsement? WTH: The idea of Mars as the ultimate destination, and the step-by-step approach as the way to get there, have now found their way into policy. Spectrum: What else would you like engineers and future engineers to know about the selection of this strategy? WTH: Simply that it provides for a much more exciting and challenging future. +++++++++++++++++++++++++++++++++++++++++++ NEO News (now in its fifteenth year of distribution) is an informal compilation of news and opinion dealing with Near Earth Objects (NEOs) and their impacts. These opinions are the responsibility of the individual authors and do not represent the positions of NASA, Ames Research Center, the International Astronomical Union, or any other organization. To subscribe (or unsubscribe) contact dmorrison@arc.nasa.gov. For additional information, please see the website http://impact.arc.nasa.gov. If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer. ## 10 May 2010 ### NEO News (05/10/10) Academy Report on NEO Surveys & Hazard Mitigation From Dave Morrison... NEO News (05/10/10) Academy Report on NEO Surveys & Hazard Mitigation Welcome back to NEO News. It has been almost a year since my last email message. Many things relating to NEOs have happened, but I have been delinquent in reporting. I will begin a return to publishing with reports on two major initiatives. The first, discussed in this message, is the completion of a National Research Council report on Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies. This study was carried out at the joint request of NASA and the U.S. Congress, focusing on several issues that have been raised by the House of Representatives in recent years. A major topic was the expanded George E. Brown NEA Survey proposed in the 2005 NASA Authorization Act. The panel also provided for the first time National Academy recommendations on Planetary Defense (also known as Planetary Protection or Impact Hazard Mitigation). A tangential note on Planetary Defense is the emphasis placed on this topic by the NASA Administrator, Charles Bolden. At a review of NASA programs presented to the senior managers of the agency in October 2009, Bolden described his personal interest in the protection of the planet from asteroid and comet impacts. He devoted more time to this topic than to some other NASA activates with much higher budgets and press visibility, such as Mars exploration. The full NRC report is available free as a pdf at [http://www.nap.edu/catalog/12842.html]. Following is just the Charge and Summary of the report. If any of you can't download this full report yourselves, I will be glad to send you a copy (4.3 MB) David Morrison ================================== Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies: Final Report Committee to Review Near-Earth Object Surveys and Hazard Mitigation Strategies of the Space Studies Board; National Research Council ISBN: 0-309-14969-X, 136 pages, 8 1/2 x 11, (2010) This free PDF was downloaded from: http://www.nap.edu/catalog/12842.html PREPUBLICATION COPY-SUBJECT TO FURTHER EDITORIAL CORRECTION ------------------------- Review Committee IRWIN I. SHAPIRO, Harvard-Smithsonian Center for Astrophysics, Chair FAITH VILAS, MMT Observatory at Mt. Hopkins, Arizona, Vice Chair MICHAEL A'HEARN, University of Maryland, College Park, Vice Chair ANDREW F. CHENG, Johns Hopkins University Applied Physics Laboratory FRANK CULBERTSON, JR., Orbital Sciences Corporation DAVID C. JEWITT, University of California, Los Angeles STEPHEN MACKWELL, Lunar and Planetary Institute H. JAY MELOSH, Purdue University JOSEPH H. ROTHENBERG, Universal Space Network -------------------------- Preface The Consolidated Appropriations Act, 2008,1 required NASA to ask the National Research Council (NRC) to conduct a study of near-Earth object (NEO) surveys and hazard mitigation strategies. Task 1: NEO Surveys What is the optimal approach to completing the NEO census called for in the George E. Brown, Jr. Near-Earth Object Survey section of the 2005 NASA Authorization Act[2] to detect, track,[3] catalogue, and characterize the physical characteristics of at least 90 percent of potentially hazardous NEOs larger than 140 meters in diameter by the end of year 2020? Specific issues to be considered include, but are not limited to, the following: o What observational, data-reduction, and data-analysis resources are necessary to achieve the Congressional mandate of detecting, tracking, and cataloguing the NEO population of interest? o What physical characteristics of individual objects above and beyond the determination of accurate orbits should be obtained during the survey to support mitigation efforts? o What role could be played by the National Science Foundation's Arecibo Observatory in characterizing these objects? o What are possible roles of other ground- and space-based facilities in addressing survey goals, e.g., potential contributions of the Large Synoptic Survey Telescope (LSST) and the Panoramic Survey Telescope and Rapid Response System (Pan STARRS)? 1 Consolidated Appropriations Act, 2008 (H.R. 2764; P.L. 110-161), Division B-Commerce, Justice, Science, and Related Agencies Appropriations Act, 2008. December 26, 2007. 2 National Aeronautics and Space Administration Authorization Act of 2005 (P.L. 109-155), S. 1281, January 4, 2005, Section 321, George E. Brown, Jr. Near-Earth Object Survey Act. 3 The committee notes that the statement of task includes the term "detect," which includes spotting asteroids that have previously been discovered. The committee therefore uses the more appropriate term "discover" to refer to the locating of previously unknown objects. Task 2: NEO Hazard Mitigation What is the optimal approach to developing a deflection[4] capability, including options with a significant international component? Issues to be considered include, but are not limited to, the following: o What mitigation strategy should be followed if a potentially hazardous NEO is identified? o What are the relative merits and costs of various deflection scenarios that have been proposed? NASA and NSF requested an initial report for the first task no later than September 30, 2009. The committee delivered its interim report, containing only findings, but no recommendations, in early August. Congress has charged the committee to recommend ways to discover and (partially) characterize 90 percent of NEOs exceeding 140 meters in diameter by the year 2020 (smaller objects are not discarded, once found). However, during its first meeting, the committee was explicitly asked by congressional staff to consider whether or not the congressionally established discovery goals should be modified. 4 The committee interprets "deflection" to mean "orbit change." -------------------------------- Summary The United States spends about four million dollars annually searching for near-Earth objects (NEOs). The goal is to detect those that may collide with Earth. This funding helps to operate several observatories that scan the sky searching for NEOs, but is insufficient to detect the majority of NEOs that may present a tangible threat to humanity. A smaller amount of funding (significantly less than$1 million per year) supports study of ways to protect Earth from such a potential collision ("mitigation").

Congress established two mandates for NASA's search for NEOs. The first, in 1998 and now referred to as the Spaceguard Survey, called for the agency to discover 90 percent of NEOs with a diameter of 1 kilometer or greater within 10 years. An object of this limiting size is considered by many experts to be the minimum that could produce global devastation if it struck Earth. NASA is close to achieving this goal, and should achieve it within a few years. However, as the recent (2009) discovery of an approximately 2- to 3-kilometer-diameter NEO demonstrates, there are still large objects to be detected.

The second mandate, established in 2005, known as the George E. Brown, Jr. Near-Earth Object Survey Act, called for NASA to detect 90 percent of NEOs with diameters of 140 meters or greater by 2020. As the committee noted in its August 2009 interim report:

Finding: Congress has mandated that NASA discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020. The administration has not requested and Congress has not appropriated new funds to meet this objective. Only limited facilities are currently involved in this survey/discovery effort, funded by NASA's existing budget.

Finding: The current near-Earth object surveys cannot meet the goals of the 2005 George E. Brown, Jr. Near-Earth Object Survey Act directing NASA to discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020.

The Survey and Detection of NEOs

The charge from Congress to the committee was stated as two tasks. The first asked for the optimal approach to completing the George E. Brown, Jr. Near-Earth Object Survey. The second asked for the optimal approach to developing a capability to avert a NEO-Earth collision, and for options that included a significant international component.

The committee concluded that there was no way to define "optimal" in a universally acceptable manner: there are too many variables involved that can be both chosen and weighted in too many plausible ways. Recognizing this fact, the committee first took a broad look at all aspects of the hazards to Earth posed by NEOs and then decided on responses to the charge.

Regarding the first task of the charge, the committee concluded that it was infeasible to complete the NEO census mandated in 2005 on the required time scale (2020), in part because for the past 5 years the administration requested no funds, and the Congress appropriated none, for this purpose. The committee concluded that there are two primary options for completing the survey:

Finding: The selected approach to completing the George E. Brown, Jr. Near-Earth Object Survey will depend on nonscientific factors:

If completion of the survey as close to the original 2020 deadline as possible is considered most important, a space mission conducted in concert with observations using a suitable ground-based telescope and selected by peer-reviewed competition is the best approach. This combination could complete the survey well before 2030, perhaps as early as 2022 if funding were appropriated quickly.

If cost conservation is deemed most important, the use of a large ground-based telescope is the best approach. Under this option, the survey could not be completed by the original 2020 deadline, but could be completed before 2030. To achieve the intended cost-effectiveness, the funding to construct the telescope must come largely on the basis of non-NEO programs.

Multiple factors will drive the decision on how to approach completion of this survey. These include, but are not limited to, the perceived urgency for completing the survey as close to the original 2020 deadline as possible, the availability of funds to complete the survey, and the acceptability of the risk associated with the construction and operation of various ground- and space-based options.

Of the ground-based options mentioned in the statement of task and the additional ones submitted to the committee in its public request for suggestions, the most capable appears to be the Large Synoptic Survey Telescope (LSST). The LSST is to be constructed in Chile and has several science missions, as well as the capability of observing NEOs. Although the primary mirror for the LSST has been cast and is being polished, the telescope has not been fully funded and is pending prioritization in the astronomy and astrophysics decadal survey currently underway.

Unless unexpected technical problems interfere, a space-based option should provide the fastest means to complete the survey. However, unlike ground-based telescopes, space options carry a modest launch risk and a more limited lifetime: ground-based telescopes have far longer useful lifetimes and could be employed for continued NEO surveys and for new science projects. (Ground-based telescopes generally have an annual operating cost that is approximately 10 percent of their design and construction costs.)

The committee notes that objects smaller than 140 meters in diameter are also capable of causing significant damage to Earth. The most well-known case from recent history is the 1908 impact of an object at Tunguska in the Siberian wilderness that devastated more than 2,000 square kilometers of forest. Previous estimates of the size of this object were on the order of approximately 70 meters in diameter.
Recent research indicates that the object could have been substantially smaller (30 to 50 meters in diameter), with much of the damage it caused due to shock waves from the explosion of the object in Earth's atmosphere. The committee strongly stresses that this new conclusion is preliminary and must be independently validated. Since smaller objects are more numerous than larger ones, however, this new result, if correct, implies an increase in the frequency of such events to approximately once per 3 centuries.

All told the committee was struck by the many uncertainties that suffuse the NEO subject. One other related example: do airbursts from impactors in this size range over an ocean cause tsunamis that can severely damage a coastline? This uncertainty and others have led the committee to a recommendation:

Recommendation: Because recent studies of meteor airbursts have suggested that near-Earth objects as small as 30 to 50 meters in diameter could be highly destructive, surveys should attempt to detect as many 30- to 50-meter objects as possible. This search for smaller-diameter objects should not be allowed to interfere with the survey for objects 140-meters in diameter or greater.

In all cases, the data-reduction and data-analysis needs mentioned in the charge would be covered by the projects themselves and by continuation of the current funding of the Minor Planet Center, as discussed in the report.

Characterization and the Arecibo and Goldstone Observatories

Obtaining the orbits and the physical properties of NEOs is known as characterization and is primarily needed to inform planning for any active defense of Earth. Such defense would be carried out through a suitable attack on any cosmic object predicted with near certainty to otherwise collide with Earth and cause significant damage. The apparently huge variation in the physical properties of NEOs seems to render infeasible development of a comprehensive inventory via in situ investigations by suitably instrumented spacecraft: the costs would be truly astronomical. A spacecraft reconnaissance mission might make good sense to conduct on an object that, without our intervention, would hit Earth with near certainty. Such a mission would be feasible provided that there were sufficient warning time for the results to suitably inform the development of an attack mission to cause the object to miss colliding with Earth.

On the other hand, the committee concluded that vigorous, ground-based characterization at modest cost is important for the NEO task. Modest funding could support optical observations of already-known and newly discovered asteroids and comets to obtain some types of information on this broad range of objects, such as their reflectivity as a function of color, to help infer their surface properties and mineralogy, and their rotation properties. In addition, the complementary radar systems at Arecibo and Goldstone are powerful facilities for characterization within their reach in the solar system, a maximum of about one-tenth of the Earth-Sun distance. Arecibo, which has a maximum sensitivity about 20-fold higher than Goldstone's, but does not have nearly so good sky coverage as Goldstone, can for example, model the three-dimensional shapes of (generally very odd-shaped) asteroids, and estimate their surface characteristics, as well as determine whether the asteroid has a (smaller) satellite or satellites around it, all important to know for planning active defense. Radar can also accurately determine orbits of NEOs, from a few relatively closely spaced (in time) observations, which has the advantage of being able to quickly calm public fears (or possibly, in some cases, show that they are warranted).

Finding: The Arecibo and Goldstone radar systems play a unique role in the characterization of NEOs, providing unmatched accuracy in orbit determination, and insight into size, shape, surface structure, and other properties for objects within their latitude coverage and detection range.

Recommendation: Immediate action is required to ensure the continued operation of the Arecibo Observatory at a level sufficient to maintain and staff the radar facility. Additionally, NASA and NSF should support a vigorous program of radar observations of NEOs at Arecibo and NASA should support such a program at Goldstone for orbit determination and characterization of physical properties.

For both Arecibo and Goldstone continued funding is far from assured, not only for the radar systems, but for the entire facilities. The incremental annual funding required to maintain and operate the radar systems even at their present relatively low levels of operation, is about $1 million at each facility (see Chapter 4). The annual funding for Arecibo is approximately$12 million. Goldstone is part of the
Deep Space Network and its overall funding includes additional equipment for space communications.

Mitigation

Mitigation refers to all means of defending Earth and its inhabitants from effects of an impending impact by a NEO. Four main types of defense are discussed in this report. The choice of which one(s) to use depends primarily on the warning time available and on the mass and speed of the impactor. The types of mitigation are:

1. Civil defense. This option may be the only one feasible for warning times shorter than perhaps a year or two. Depending on the state of readiness to apply an active defense, civil defense may be the only choice for even longer times.

2. "Slow push" or "slow pull" methods. For these options the orbit of the target object would be changed so that it avoided collision with Earth. The most effective way to change the orbit, given a constraint on the energy that would be available, is to change the velocity of the object, either in or opposite to the direction in which it is moving (direct deflection-moving the object "sideways"-is much less efficient). These options take considerable time to be effective, of the order of decades, and even then would be useful only for objects whose diameters are no larger than 100 meters or so.

3. Kinetic impactors. In these scenarios the target's orbit would be changed by sending one or more spacecraft with very massive payload(s) to impact directly on the target at high speed in its direction, or opposite to its direction, of motion. The effectiveness of this option depends not only on the mass of the target, but on any net enhancement due to material being thrown out of the target, in the direction opposite to that of the payload upon impact.

4. Nuclear explosions. For non-technical reasons, this would likely be a last resort, but it is also the most powerful technique and could take several different forms, as discussed in the report. The nuclear option would be usable for objects up to a few kilometers in diameter. For larger NEOs (more than a few kilometers in diameter), which would be on the scale that would inflict serious global damage and, perhaps, mass extinctions, there is at present no feasible defense. Luckily such events are exceedingly rare, the last known being about 65 million years ago.

Of these options, only kinetic impact has been demonstrated (via the very successful Deep Impact spacecraft that collided with comet Tempel-1 in July 2006). The other options have not advanced past the conceptual stage. Even Deep Impact was on a scale far lower than would be required for Earth defense for an NEO on the order of 100 meters in diameter, and impacted on a relatively large-and therefore easier to hit-object.
,
Although the committee was charged with determining the "optimal approach to developing a deflection capability," it concluded that work in this area is relatively new and immature. The committee therefore concluded that the "optimal approach" starts with a research program.

Further Research

The committee was struck by the significant unknowns in many aspects of NEO hazards that could yield to Earth-based research and was led to:

Recommendation: The United States should initiate a peer-reviewed, targeted research program in the area of impact hazard and mitigation of NEOs. Because this is a policy driven, applied program, it should not be in competition with basic scientific research programs or funded from them. This research program should encompass three principal task areas: surveys, characterization, and mitigation. The scope should include analysis, simulation, and laboratory experiments. This research program does not include mitigation space experiments or tests which are treated elsewhere in this report.

National and International Cooperation

Responding effectively to hazards posed by NEOs requires the joint efforts of diverse institutions and individuals. Thus organization plays a key role. Because NEOs are a global threat, efforts to deal with them could involve international cooperation from the outset. (However, this is one area where one nation, acting alone, could address such a global threat.) The report discusses possible means to organize, both nationally and internationally, responses to those hazards. Arrangements at present are largely ad hoc and informal here and abroad, and involve both government and private entities.

The committee discussed ways to organize the national community to deal with the hazards of NEOs and also recommends an approach to international cooperation.

Recommendation: The United States should take the lead in organizing and empowering a suitable international entity to participate in developing a detailed plan for dealing with the NEO hazard.

One major concern with such an organization, especially in the disaster-preparation area, is the maintenance of attention and morale given the expected exceptionally long intervals between harmful events. Countering the tendency to complacency will be a continuing challenge. This problem would be mitigated if, for example, the civil defense aspects were combined in the National Response Framework with those for other natural hazards.

Recent NEO-Related Events

The U.S. Department of Defense, which operates sensors in Earth orbit capable of detecting the high-altitude explosion of small NEOs, has in the past shared this information with the NEO science community. The committee concluded that this data-sharing was important for understanding issues such as the population size of small NEOs and the hazard that smaller NEOs pose. This sharing is also
important to validate airburst simulations, characterize the physical properties of small NEOs (such as their strength), and to assist in the recovery of meteorites.

Recommendation: Data from NEO airburst events observed by the U.S. Department of Defense satellites should be made available to the scientific community to allow it to improve understanding of the NEO hazards to Earth.

In 2008, Congress passed a NASA appropriations act that called for the Office of Science and Technology Policy to determine by October 2010 which agency should be responsible for conducting the NEO survey and detection and mitigation program. Several agencies are possible candidates for such a role.

During its deliberations the committee learned of several efforts outside the United States to develop spacecraft to search for categories of NEOs. In particular, Canada's NEOSSat and Germany's AsteroidFinder are interesting and capable small scale missions that will detect a small percentage of specific types of NEOs, those primarily inside Earth's orbit. These spacecraft will not accomplish the goals of the George E. Brown, Jr. Near-Earth Object Survey Act. However, they highlight the fact that other countries are beginning to seriously consider the NEO issue. Such efforts also represent an opportunity for future international cooperation and coordination in the search for potentially hazardous NEOs. In addition, the committee was impressed with the European Space Agency's early development of the Don Quijote spacecraft mission that would consist of an observing spacecraft and a kinetic impactor. This mission, though not funded, would have value for testing a mitigation technique and could still be an opportunity for international cooperation in this area.

Finally, the committee points out a current estimate of the long-term average annual human fatality rate from impactors: slightly under 100. At first blush, one is inclined to dismiss this rate as trivial in the general scheme of things. However, one must also consider the extreme damage that could be inflicted by a single impact; this presents the classic problem of the conflict between extremely important and extremely rare. The committee considers work on this problem as insurance, with the premiums devoted wholly towards preventing the tragedy. The question then is: What is a reasonable expenditure on annual premiums? The committee offered a few possibilities for what could possibly be accomplished at three different levels of funding (see Chapter 8); it is, however, the political leadership of the country that determines the amount to be spent on scanning the skies for potential hazards and preparing our defenses.
--
+++++++++++++++++++++++++++++++++++++++++++
David Morrison, NASA Ames Research Center N-17
Tel 650 604 5094
david.morrison@nasa.gov
website: http://impact.arc.nasa.gov
Note: Any opinions expressed on the blog are solely those of the author. The site is not sponsored by, nor does it represent the opinions of, any organization, corporation, or other entity.