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Week 1/2008: Twinkling reveals an asteroid's shape

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A giant asteroid hitting the Earth is one of the most common horror scenarios in science fiction.  Thanks to Johanna Torppa’s doctoral dissertation, the chances of rerouting the orbit of a heavenly body threatening our planet are much improved.
Torppa’s study is based on changes in the brightness of asteroids. Lightcurves based on observations indicate the shape of an asteroid. In turn, knowing the shape of an asteroid will help model its orbit, and reveals whether or not it is approaching the Earth.

But can’t variations in the amount of light reflected by an asteroid be dependent on, for example, different surface materials? “Yes, it can,” says Torppa,“but research has shown that, in practice, variation in brightness tells more about the asteroid’s shape and spin.

In addition to determining the orbits of individual asteroids, the measurements can also be used for producing statistical studies on the previous collisions of asteroids.
The larger the asteroid, the more likely it is a regular round shape. On the other hand, an irregular shape means that the asteroid has probably hit something. Large craters are also evident in light curves.

“If there is a group of irregular asteroids on a particular orbit, it can, to a certain extent, be assumed that they come from one mother asteroid which has fractured in a collision.”

Johanna Torppa’s doctoral dissertation, entitled Lightcurve inversion for asteroid spin and shape in the field of astronomy, was publicly examined at the University of Helsinki on 14 December 2007.

Another doctoral dissertation in astronomy defended at the University of Helsinki in December was  Mikael Granvik’s dissertation on the methods of identifying asteroids.

Text: Juha Merimaa
Picture: European Space Agency ESA
www.helsinki.fi/digitalcommunications

Translation: Valtasana Oy