Scientists find a solar-powered asteroid (Forwarded)

Academy of Finland
Helsinki, Finland

For more information please contact:

Mikko Kaasalainen, Academy Research Fellow
tel. +358 40 832 9412
www.rni.helsinki.fi/~mjk

Academy of Finland Communications
Communications Specialist Leena Vähäkylä
tel. +358 9 7748 8327

7 March 2007

Scientists find a solar-powered asteroid

An international research team led by Academy Research Fellow Mikko
Kaasalainen has found an asteroid whose rotation receives an extra kick
from solar radiation. The asteroid 1862 Apollo's diameter is about 1.5 km,
it has a small moonlet, and its orbit crosses that of the Earth. The team
reconstructed Apollo's shape and determined its rotational state using
brightness measurements from several years. They found that Apollo's
rotation speed steadily increases, and showed that this is due to the
re-radiation of solar energy from its surface. The study was published in
Nature online on 7 March.

Apollo's rotation period is slightly over three hours, and it decreases
only by four thousandths of a second per year, so the analysis required
accurate mathematical methods. Because of the acceleration, Apollo is
likely to break apart or radically change its figure in the future. It may
already have done so earlier, and its present moonlet may be a remnant of
such a breakup.

The study confirms that non-gravitational forces are important in the
dynamical evolution of asteroids. Re-radiation of solar energy acts as a
propulsion engine on the asteroid's surface. There are two coupled
manifestations of this phenomenon: the one changing the orbit (the
Yarkovsky effect), and the one changing the spin state (the
Yarkovsky-Radzievskii-O'Keefe-Paddack or YORP effect). The study confirmed
the latter, and the former was detected by radar in 2003.
Non-gravitational orbital and spin changes can be significant or even
critical over long time intervals. They affect the motion of asteroids
that may collide with the Earth. The phenomenon can also be used to
estimate the masses of asteroids. Apollo is now the first object larger
than one kilometre across for which the propulsion effect has been
detected.

Academy Research Fellow Mikko Kaasalainen works in the Centre of
Excellence in Inverse Problem Research of the Academy of Finland at the
Department of Mathematics and Statistics of the University of Helsinki.
The CoE develops and applies mathematical methods in data analysis in
various fields from biology to space research. Dr. Kaasalainen coordinates
an international solar system research and observation network with
researchers from Europe, America, Asia, and Australia. The study published
in Nature was carried out by scientists from Finland, Czech Republic, the
United States, and Ukraine.

Nature online DOI:10.1038/nature05614
Mikko Kaasalainen, Josef Durech, Brian Warner, Yurij Krugly, and Ninel
Gaftonyuk: Acceleration of the rotation of asteroid 1862 Apollo by
radiation torques
The paper will appear in print in Nature later this month.


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