Subscribe free to our newsletters via your
. 24/7 Space News .

Rosetta's OSIRIS Cameras Reveal The Nature Of Asteroid Steins
by Staff Writers
Paris, France (ESA) Jan 13, 2010

Images of asteroid Steins taken with the OSIRIS wide angle camera (left) and narrow-angle camera (right) onboard Rosetta. (Click on the image for detailed caption.) Credit: ESA 2008 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA. View video sequence from OSIRIS WAC of asteroid Steins

Close-up images of asteroid (2867) Steins, obtained with the OSIRIS cameras on Rosetta, have provided extensive new measurements of the physical properties of this main-belt asteroid. Steins is revealed to be a loosely-bound 'rubble pile' whose diamond shape has been honed by the YORP effect.

This is the first time this effect has been seen in a main-belt asteroid. The results are reported by H. Uwe Keller and colleagues in the 8 January issue of Science magazine.

Most models of Solar System formation posit that the planets formed from the collision and eventual coalescence of planetesimals. Beyond the orbit of Mars, the gravitational perturbation of the giant planet Jupiter prevented the formation of a planet-sized body by disrupting the orbits of many of these planetesimals.

The remaining bodies, some of them several hundred kilometres in size, have undergone frequent collisions since this time and today mostly occupy the asteroid belt between the orbits of Mars and Jupiter.

Asteroids are of interest for understanding the formation process of our Solar System because they carry information about the nature and composition of the Solar System at an early stage of its formation. Asteroid (2867) Steins, an E-type asteroid, is a rare type of solar system body. Only a few tens of these asteroids have been detected.

In the results published in the 8 January issue of Science, H. Uwe Keller and colleagues report on observations of asteroid Steins obtained during the Rosetta flyby of 5 September 2008.

This is the first time that a close-up view of an E-type asteroid has been obtained. The closest approach to the asteroid was at 18:38:20 UTC at a distance of 803 km. About 60 per cent of the surface was resolved during the flyby providing a unique set of images from which a number of important physical properties can be inferred.

Little was known about asteroid (2867) Steins when it was chosen early in 2004 as one of the targets for a close flyby during the Rosetta mission. At the time, it was classified as an E-type asteroid on the basis of its visual and near-infrared spectrum and its high albedo. Later, ground-based observations estimated a diameter of approximately 4.6 km and determined a rotation period of about 6 hours.

The new OSIRIS images show Steins to be an oblate body, resembling a brilliant cut diamond, with dimensions of 6.67x 5.81 x 4.47 cubic kilometers. Its surface is mostly covered with shallow craters with some of the larger craters being pitted with smaller ones.

Analysis of the impact craters reveals a deficit of small craters (those with diameter less than 0.5 km) which Keller and his colleagues attribute to surface reshaping as a result of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect (see footnote). The effect would have caused landslides which filled-in the smaller craters.

This is the first time that the YORP effect has been seen in a main-belt asteroid.

Two remarkable features are clearly visible in the images obtained near closest approach: a large, 2.1 km diameter crater located at the south pole, and a chain of pits which extend northwards from this crater.

Taken together these features suggest that Steins was subject to a big impact which created the large crater and caused fracturing of the asteroid body resulting in it having a rubble pile structure. This type of loosely-bound structure is also consistent with the YORP effect hypothesis.

Detailed study of the OSIRIS images has also allowed Keller and his colleagues to confirm the nature of Steins as an E-type asteroid - the albedo and spectral characteristics are consistent with this classification - and to demonstrate that there is no measurable surface colour variation, which points to a homogeneous composition.

The view of Steins obtained by OSIRIS during the September 2008 flyby with Rosetta has provided scientists with the first detailed characterisation of this rare type of solar system body.

Footnote: The YORP effect is a phenomenon that occurs when photons from the Sun are absorbed by a body and reradiated as infrared emission which carries off momentum as well as heat. The loss of momentum causes a change in the rotation rate of a small body such as an asteroid. The resulting high spin rate of asteroid Steins could have caused material to migrate towards the equator of the asteroid resulting in the distinctive conical shape.

The results are reported in "E-type asteroid (2867) Steins as Imaged by OSIRIS on board Rosetta" by H. U. Keller, C. Barbieri, D. Koschny, P. Lamy, H. Rickman, R. Rodrigo, H. Sierks, M. F. A'Hearn, F. Angrilli, M. A. Barucci, J.-L. Bertaux, G. Cremonese, V. Da Deppo, B. Davidsson, M. De Cecco, S. Debei, S. Fornasier, M. Fulle, O. Groussin, P. J. Gutierrez, S. F. Hviid, W.-H. Ip, L. Jorda, J. Knollenberg, J. R. Kramm, E. Kuhrt, M. Kuppers, L.-M. Lara, M. Lazzarin, J. Lopez Moreno, F. Marzari, H. Michalik, G. Naletto, L. Sabau, N. Thomas, K.-P. Wenzel, I. Bertini, S. Besse, F. Ferri, M. Kaasalainen, S. Lowry, S. Marchi, S. Mottola, W. Sabolo, S. E. Schroder, S. Spjuth, and P. Vernazza, Science, Vol. 327. no. 5962, pp. 190 - 193, 8 January 2010. DOI: 10.1126/science.1179559


Related Links
Asteroid and Comet Mission News, Science and Technology

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

Rohrabacher Suggests Partnership With Russia On Asteroid Interception Project
Washington DC (SPX) Jan 08, 2010
Rep. Dana Rohrabacher (R-CA) has sent a letter to Anatoly Perminov, head of the Russian Space Agency, praising Russia's decision to set up a mission to alter the path of an asteroid on a potential collision course with Earth. The impetus for such a project stems from the current trajectory of Asteroid Apophis, scheduled to makes its first pass around Earth in the year 2029, close enough to ... read more

Planning Our Phases On The Moon

Space Systems Loral To Supply Lunar Mission Propulsion System

Lava tube could house moon colony

Moon Mission In Running For Next Big Space Venture

Just A Few More Approaches To Try For Extrication

Hints Of Hesperian Lakes

Martian Landform Observations Fill Special Journal Issue

NASA plans for Mars laboratory

Spectacular Years Ahead In Space

Galactic GPS Possible With Pulsars And Gravity Waves

US still has space ambitions: NASA chief

Chairman Gordon Comments On President's Budget Request

US official questions China space intentions

China's Space Pioneers Hit New High

China Building Large Radio Telescope For Space Observation

China To Launch Civil HD Survey Satellite In 2011

How To Live Long And Prosper In Space

Russia Set To Launch Another Space Truck To ISS

Obama budget extends US commitment to space station

Mini-Research Module MRM1 At Cape For Shuttle Processing

Roscosmos Reserves Site For Vostochny Spaceport

USAF Awards ULA WGS-4 Satellite Launch

ISRO Plans Special Launch Pad At Sriharikotta

Arianespace Poised For 2010 Boost

Unprecedented Details Imaged On The Surface Of Betelgeuse

Satellite Could Locate Hundreds Of Earth-Sized Planets

Second Smallest Exoplanet Found To Date Discovered At Keck

Massive Stars Easy Targets For Planet Hunters

Change-2 Satellite's Camera Resolution Reaches One Meter

China places record order for Taiwan flat screens

Lego expands its universe with online game

New sunglasses can also be used for 3-D viewing

The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement