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.

30 April 2011

Asteroid (596) Scheila and Analysis of Collision with Another Asteroid

From the article...

Scientists have captured and studied the collision of two asteroids for only the second time in the history of astronomy. In the May 20 edition of the Astrophysical Journal Letters (currently online), UCLA's David Jewitt and colleagues report on observations from NASA's Hubble Space Telescope of a large asteroid that was hit by a much smaller one.

On Dec. 11, 2010, astronomers noticed that an asteroid known as (596) Scheila had unexpectedly brightened and was sporting short-lived dust plumes. Data from NASA's Swift satellite and Hubble Space Telescope showed that these changes likely occurred after Scheila was struck by a much smaller asteroid, probably in late November or early December. The shape, evolution and content of the plumes enabled the scientists to reconstruct what occurred.

The smaller asteroid crashed into Scheila with the energy of at least a 100 kiloton nuclear bomb. The smallest particles from the collision escaped, and the dust formed plumes. These plumes were barely visible when Hubble observed Scheila two weeks later, and within two months, the plumes were gone completely, along with the evidence that Scheila had suffered a violent collision.

"The Hubble data are most simply explained by the impact, at 11,000 miles per hour, of a previously unknown asteroid about 100 feet in diameter," said Jewitt, the Hubble team leader and a UCLA professor of Earth and space sciences and of physics and astronomy.



D. Bodewits1, M. S. Kelley1, J.-Y. Li1, W. B. Landsman2, S. Besse1 and M. F. A’Hearn1
1 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
2 NASA GSFC, Adnet Systems, Mailstop 667, Greenbelt, MD 20771, USA

The Astrophysical Journal Letters Volume 733 Number 1
D. Bodewits et al. 2011 ApJ 733 L3 doi: 10.1088/2041-8205/733/1/L3

We observed asteroid (596) Scheila and its ejecta cloud using the Swift UV-optical telescope. We obtained photometry of the nucleus and the ejecta, and for the first time measured the asteroid's reflection spectrum between 290 and 500 nm. Our measurements indicate significant reddening at UV wavelengths (13% per 103 Å) and a possible broad, unidentified absorption feature around 380 nm. Our measurements indicate that the outburst has not permanently increased the asteroid's brightness. We did not detect any of the gases that are typically associated with either hypervolatile activity thought responsible for cometary outbursts (CO+, CO2 +), or for any volatiles excavated with the dust (OH, NH, CN, C2, C3). We estimate that 6 × 108 kg of dust was released with a high ejection velocity of 57 m s–1 (assuming 1 μm sized particles). While the asteroid is red in color and the ejecta have the same color as the Sun, we suggest that the dust does not contain any ice. Based on our observations, we conclude that (596) Scheila was most likely impacted by another main belt asteroid less than 100 m in diameter.


David Jewitt1,2,3, Harold Weaver4, Max Mutchler5, Stephen Larson6 and Jessica Agarwal7
1 Department of Earth and Space Sciences, UCLA, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567, USA
2 Institute for Geophysics and Planetary Physics, UCLA, 3845 Slichter Hall, 603 Charles Young Drive East, Los Angeles, CA 90065-1567, USA
3 Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Los Angeles, CA 90095-1547, USA
4 The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
6 Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721-0092, USA
7 Institute for Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany

The Astrophysical Journal Letters Volume 733 Number 1
David Jewitt et al. 2011 ApJ 733 L4 doi: 10.1088/2041-8205/733/1/L4

We present Hubble Space Telescope Observations of (596) Scheila during its recent dust outburst. The nucleus remained point-like with absolute magnitude HV = 8.85 ± 0.02 in our data, equal to the pre-outburst value, with no secondary fragments of diameter ≥100 m (for assumed albedos 0.04). We find a coma having a peak scattering cross section ~2.2×104 km2, corresponding to a mass in micron-sized particles of ~4×107 kg. The particles are deflected by solar radiation pressure on projected spatial scales ~2×104 km, in the sunward direction, and swept from the vicinity of the nucleus on timescales of weeks. The coma fades by ~30% between observations on UT 2010 December 27 and 2011 January 4. The observed mass loss is inconsistent with an origin either by rotational instability of the nucleus or by electrostatic ejection of regolith charged by sunlight. Dust ejection could be caused by the sudden but unexplained exposure of buried ice. However, the data are most simply explained by the impact, at ~5 km s–1, of a previously unknown asteroid ~35 m in diameter.

Link: Paper (Collisional Excavation of Asteroid (596) Scheila)

Link: Paper (Hubble Space Telescope Observations of Main-belt Comet (596) Scheila)

Link: News Article

Link: YouTube Video (Scheila Asteroid Crash)

2011 International Primitive Body Exploration Working Group Meeting: Poster Abstract Submission

Poster abstract submission for the 2011 International Primitive Body Exploration Working Group Meeting is available at the meeting website:

Dates : August 22-24, 2011
Venue: Pasadena, CA

Abstracts will be accepted until August 1st. Further information about the meeting, agenda details and abstract submission are all available at the meeting website.

The discussions held at this meeting are expected to open new international collaboration opportunities for primitive body space exploration.

Organizing committee contact:
Keith Grogan
IPEWG 2011 LOC Chair

Link: 2011 International Primitive Body Exploration Working Group Meeting

25 April 2011

ACM [Asteroids, Comets, Meteors] 2011 is postponed

The LOC [Local Organizing Committee] decided to postpone of ACM [Asteroids, Comets, Meteors] 2011. (April. 4, 2011). The conference was scheduled for 17-22 July, 2011 in Niigata, Japan

Link: ACM Japan LOC site

Link: ACM 2011 site from IAU

Paper: Near-Earth object interception using nuclear thermal rocket propulsion

Near-Earth object interception using nuclear thermal rocket propulsion

Journal Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, Issue Volume 225, Number 2 / 2011, Pages 181-193, DOI 10.1243/09544100JAERO753

X-L Zhang, E Ball, C Granier, L Kochmanski, S D Howe
1 Centre for Space Nuclear Research, Idaho National Laboratory, Idaho Falls, USA

Planetary defense has drawn wide study: despite the low probability of a large-scale impact, its consequences would be disastrous. The study presented here evaluates available protection strategies to identify bottlenecks limiting the scale of near-Earth object that could be deflected, using cutting-edge and near-future technologies. It discusses the use of a nuclear thermal rocket (NTR) as a propulsion device for delivery of thermonuclear payloads to deflect or destroy a long-period comet on a collision course with Earth. A ‘worst plausible scenario’ for the available warning time (10 months) and comet approach trajectory are determined, and empirical data are used to make an estimate of the payload necessary to deflect such a comet. Optimizing the tradeoff between early interception and large deflection payload establishes the ideal trajectory for an interception mission to follow. The study also examines the potential for multiple rocket launch dates. Comparison of propulsion technologies for this mission shows that NTR outperforms other options substantially. The discussion concludes with an estimate of the comet size (5 km) that could be deflected using NTR propulsion, given current launch capabilities.

Link: Citation

Link: Paper (PDF)

Paper: Dynamics and control of a solar collector system for near Earth object deflection

Dynamics and control of a solar collector system for near Earth object deflection

Shen-Ping Gong, Jun-Feng Li and Yun-Feng Gao
School of Aerospace, Tsinghua University, Beijing 100084, China

A solar collector system is a possible method using solar energy to deflect Earth-threatening near-Earth objects. We investigate the dynamics and control of a solar collector system including a main collector (MC) and secondary collector (SC). The MC is used to collect the sunlight to its focal point, where the SC is placed and directs the collected light to an asteroid. Both the relative position and attitude of the two collectors should be accurately controlled to achieve the desired optical path. First, the dynamical equation of the relative motion of the two collectors in the vicinity of the asteroid is modeled. Secondly, the nonlinear sliding-mode method is employed to design a control law to achieve the desired configuration of the two collectors. Finally, the deflection capability of this solar collector system is compared with those of the gravitational tractor and solar sail gravitational tractor. The results show that the solar collector is much more efficient with respect to deflection capability.

Link: Citation

Paper: Ion Beam Shepherd for Asteroid Deflection

Ion Beam Shepherd for Asteroid Deflection

C. Bombardelli, J. Pelaez

We present a novel concept to impart a continuous thrust to an Earth threatening asteroid from a hovering spacecraft without need for physical attachment nor gravitational interaction with the asteroid. The concept involves an ion thruster placed at a distance of a few asteroid diameters directing a stream of quasi-neutral plasma against the asteroid surface resulting into a net transferred momentum. As the transmitted force is independent of the asteroid mass and size the method allows deflecting subkilometer asteroids with a spacecraft much lighter when compared to a gravity tractor spacecraft of equal deflection capability. The finding could make low-cost asteroid deflection missions possible in the coming years.

Cite as: arXiv:1102.1276v1 []

Link: Citation

Link: Paper

Paper: Deflecting APOPHIS with a flotilla of solar shields

Deflecting APOPHIS with a flotilla of solar shields

Jean-Yves Prado (a), , , , Alain Perret (b), and Olivier Boisard (b),
a CNES, Toulouse 31401, 18 Avenue Edouard Belin, Toulouse cedex 9, France
b Union pour la Promotion de la Propulsion Photonique, 37530 Nazelles-Négron, France

The possibility to use the photonic pressure from the Sun for acting upon the orbit of a man-made object is well known. What is presented in this paper is the capacity to use a solar sail like vehicle to change the orbit of a small body of the solar system by hovering over its sunlit surface. One of the forces that affect the orbit of small bodies is a tiny but permanent thrust of thermal origin, the intensity and direction of which are directly related to the nature of the soil, the characteristics of the rotation and the physical properties of the body. This effect is known as the Yarkovsky Effect. It concerns mainly hundred meter class asteroids. There are hundred thousands of small bodies of this type. About 10% of them are classified as Near Earth Object and one of them, APOPHIS, is of special interest. APOPHIS has been discovered in 2004. Its diameter is estimated to be 270 m. Its rotation period is around 30 h so the Yarkovsky Effect on its orbit should not be negligible. These parameters and possibly others should be refined in 2012 when this asteroid can be observed again. APOPHIS will make a very close (40,000 km) approach to the Earth in April 2029. Depending on the geometry of its swing-by, it can be placed on an impact orbit to the Earth and present a danger for the future decades. The areas that correspond to such trajectories are called Resonant Orbit Keyholes and are only a few hundred meter wide. From the observation in 2012, it will be possible to determine the magnitude of the Yarkovsky Effect on APOPHIS and to greatly improve the prevision of its 2029 swing-by. If the Yarkovsky Effect is found to be important, cancelling it will be sufficient to avoid any keyhole and prevent any future collision with the Earth. We call Yarkovsky Effect Suppression (YES) this deflection method. This effect can be cancelled by shadowing and cooling down the asteroid with a flotilla of solar shields. This new type of solar sails will have to counter the photonic pressure in order to maintain their hovering position. In this paper, we propose a preliminary mission design and the main system requirements, especially as regards station keeping. This mission is named SHADOW. Finally we discuss the pros and cons of this strategy and compare its effectiveness to already identified mitigation methods.

Link: ScienceDirect (Advances in Space Research)

The "Future of Planetary Defense" outreach event (Sunday, 8 May, 2011, Bucharest, Romania) in conjunction 2011 IAA Planetary Defense Conference

The Space Generation Advisory Council (SGAC) is organizing a "Future of Planetary Defense" outreach event that will be held Sunday, 8 May, 2011 in Bucharest, Romania in conjunction with the 2011 IAA Planetary Defense Conference.

Link: Event information

Link: SGAC News Release

2011 IAA Planetary Defense Conference Agenda

The agenda is near complete for the 2011 IAA Planetary Defense Conference: From Threat to Action (9-12 May 2011, Bucharest, Romania).

Link: PDC 2011 agenda

Link: PDC 2011 website

Target NEO Workshop - Draft Final Report Available for Comment

From the TargetNEO workshop organizers:

The session chairs have now completed a draft of a final report summarizing the key points of the workshop, posted on the workshop website ( We’d like to solicit your comments to truly make this a document endorsed by the community. To facilitate this, we’ve created a web-based discussion group that can be accessed via the website. Or if you prefer, you can send any comments directly to . We’d like to finalize the document in about a month, so we request that any comments be submitted before May 16.

Link: Public Draft of the Target NEO Workshop Report

Link: TargetNEO website

Move An Asteroid 2011: International Student and Young Professional Technical Paper Competition

From the Space Generation Advisory Council (SGAC):

Move An Asteroid 2011

An outreach project designed to raise awareness by offering students and young professionals the chance to come up with original ideas about NEO deflection and warning. Three successful competitions have been held starting in 2008. The prize is always a full-scholarship to the International Astronautical Congress and the Space Generation Congress. This year's deadline is 1 July, 2011.

Link: Move An Asteroid Competition

Link: SGAC Move An Asteroid Competition News Annoucement
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