Andrew Yee[_1_]
March 7th 07, 08:33 PM
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 Vyl
el. +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.
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 Vyl
el. +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.