P/2013 P5 (S-type Asteroid)

Location:  Inner Main Asteroid Belt
Asteroid Family:  Flora (Ariadne)
Distance from Sun:  2.1 AU (314 Gm)
Radius:  ~240 meters

Mainstream description
Located at the innermost edge of the main Asteroid Belt, the asteroids from this asteroid family are likely made of metamorphic rocks and so are not capable of holding ices as comets do.  However the asteroid was observed with six comet-like tails that rapidly changed over a period of days as the asteroid rotated.

“We were literally dumbfounded when we saw it,” said lead investigator David Jewitt of the University of California at Los Angeles. “Even more amazing, its tail structures change dramatically in just 13 days as it belches out dust. That also caught us by surprise. It’s hard to believe we’re looking at an asteroid.”

One interpretation is that the asteroid’s rotation rate increased to the point where its surface started flying apart, ejecting dust in episodic eruptions. A recent asteroid impact scenario has been ruled out because a lot of dust would be blasted into space all at once, whereas P5 has ejected dust for at least five months.

Alternative description
Asteroids and comets contain little to no water ice and main belt asteroids are too distant from the sun to be spun up and disintegrated by sunlight pressure.  The tails of these objects are the result of electric arc discharges to their surfaces following a charge imbalance between the object and the Sun and the weak but vast electrical field between them.  These discharges excavate material from the surface of the object explosively at supersonic speeds.  This material is then accelerated into space and collimated along the jets’ observed filamentary arcs.

P/2013 P5 (S-type Asteroid)Shannon Sims