Unlike comets, asteroids don't have a trail - with some exceptions.
Spanish researchers observed using the Gran Telescopio Canarias and
discovered that something happened around July 1st, 2011 that caused a
trail to appear on P/2012 F5 (Gibbs) - perhaps an internal rupture or a
collision with another asteroid.
To-date, 10 asteroids have been discovered to at least briefly
display a trail like a comet. They are named main-belt comets (MBC) as
they have a typical asteroidal orbit but display a trail at the same
time. This means that their dust (and possibly gas) emission activity is
like comets. P/2012 F5 (Gibbs) is one of those 10 and was discovered in
March of 2012 at the Mount Lemmon Observatory in Arizona.