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An asteroid 113 km in diameter, 596 Scheila, and belonging to the main belt 2.92 astronomical units from the Sun, has undergone a cometary type outburst.
The first to notice the outburst was Steve Larson, of the Catalina Sky Survey (CSS), who noticed the unusual coma around the asteroid on some of the images taken on 11th December with the Catalina telescope, a 68 cm Schmidt.
The same day, and the day after, confirmation was received from various amateurs, especially those involved in the Global Rent a Scope (GRAS) initiative, including G. Sostero, E. Guido, M. Nissinen, R. Ligustri and P. Brunato. The last three are behind the images shown, which highlight both the outburst as well as the motion of the asteroid against the background stars.
There are essentially two possible causes for the phenomenon: an impact by a meteorite at least 1 metre in diameter, or the vaporization of a mass of volatile material present in Scheila, caused by solar heating. In this case, Scheila would lengthen the very short list of asteroids that have the orbital characteristics of other minor bodies in the main belt, but the physical properties of a comet.
To better understand what is going on it will be necessary to monitor Scheila over the coming days and weeks, and in this the contribution of amateurs will be key, especially because the asteroid is accessible to small instruments, at magnitude 14.3 (in the constellation of Leo).
Clearly, to detect the coma it will be necessary to stack several exposures.
For those that would like accurate ephemerides to follow the evolution of the coma of Scheila we recommend this web page:
http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr =596. Just click on "Generate Ephemeris" to get positions up to 12th January 2011. |
