Using the Hubble Space Telescope, astronomers have detected a multi-tailed main-belt comet the likes of which has never been seen before.
A main-belt comet is a special class of celestial objects that orbit inside our asteroid belt and exhibit comet-like activity at some point during their orbits (like shedding some of its mass and having tails). NASA defines it as an object with a distance of more than 2 AU but less than 3.2 AU from the Sun (1 AU being the average distance of the Earth to the Sun). The first MBC was discovered in 1979, and it was initially thought to be an asteroid. But astronomers Eric Elst and Guido Pizarro noticed it had a tail in 1996. There are currently 11 known main-belt comets in our solar system, including PANSTARRS.
Scientists think that main-belt comets, sometimes referred to as active asteroids, may have been the source of the Earth's water. Typical comets lack the right substances to have provided enough water to fill the oceans. But this recently discovered comet, named P/2013 P5, exhibits strange characteristics that would — at least in this case — contradict that assumption.
A team of astronomers led by David Jewitt from the Department of Earth and Space Sciences at the University of California at Los Angeles recently surveyed the comet over a two week period (between September 10 and 23 of this year). What they saw was completely unheard of: a main-belt comet spewing out no less than six tails.
The configuration of these tails changed dramatically during the course of the observations. At the same time, however, the astronomers also noticed that the comet's core was not degrading at a noticeable rate. The angle of each tail could be traced back to a different time of cometary ejection over a five month span (dating back to April). This is a good sign that there's continuing activity at the nucleus.
The scientists theorize that the unique multi-tailed comet is experiencing a gradual loss of mass due to highly unstable rotational disruption — it's a comet that's spinning wildly and shedding mass, likely on account of the torque imposed by solar radiation.
Observations also showed that P/2013 P5 is unlikely to contain ice. The astronomers don't think it came from the Kuiper belt or the Oort cloud. Its orbit is located near the inner edge of the asteroid belt, in the neighborhood of the Flora family of S-type asteroids. These bodies are primarily made from stone, containing lots of iron. So the six-tailed comet isn't likely to contain water ice.
Read the entire study at the preprint archive arXiv: "The Extraordinary Multi-Tailed Main-Belt Comet P/2013 P5."