Comet Vales: A spiraling comet

• comets
• observing

15 days post-outburst

Richard Miles, BAA

Richard Miles from British Astronomical Association has been
coordinating UK schools to make observations of a comet that is
behaving strangely. Comet P/2010 H2 (VALES) underwent a major outburst
around 2010 April 15 brightening by more than 1000 times (possibly even
more than this) in a matter of a few hours.  Before this date, the
object  was not known.  After this date it had taken on the appearance
of a 12th magnitude star.  The comet sooon began to exhibit an
expanding coma.

Observations using the Faulkes Telescope North some 15 days following
the initial outburst have now revealed the presence of two extended
jets of material spiraling out from the nucleus of the comet, as shown
in the attached image.  The locus of the most pronounced jet describes
a constant rate of motion radially outwards from the nucleus equal to
0.54+/-0.03 arcsec/degree of rotation as shown in the associated plot. 
It is not clear whether the curvature of the jets is due to an external
influence such as radiation pressure or the solar wind, or whether it
is indicative of a very slow rotation rate of the nucleus.  If the
latter, then the rotation period of the nucleus would be exceptionally
slow for this comet at around 90 days. Most comets have rotation
periods of the order of 0.3-5 days.  Slow rotation rates would lead to
enhanced thermal stress owing to prolonged solar heating of the comet’s
surface and may be the underlying reason why this comet underwent a
major outburst.  Future observations are encouraged especially to
folllow the development of the spiral structures within the coma.