Written by Dr. Tony Phillips
Science at NASA
Washington, D.C. – Astronomers viewing our solar system’s asteroid belt with NASA’s Hubble Space Telescope have seen for the first time an asteroid with six comet-like tails of dust. Designated P/2013 P5, the asteroid resembles a rotating lawn sprinkler.
“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.”
P/2013 P5 has been ejecting dust periodically for at least five months. Astronomers believe it is possible the asteroid’s rotation rate increased to the point where its surface started flying apart. They do not believe the tails are the result of an impact with another asteroid because they have not seen a large quantity of dust blasted into space all at once.
Scientists using the Pan-STARRS survey telescope in Hawaii announced their discovery of the asteroid August 27th. P/2013 P5 appeared as an unusually fuzzy-looking object. The multiple tails were discovered when Hubble was used to take a more detailed image September 10th.
When Hubble looked at the asteroid again September 23rd, its appearance had totally changed. It looked as if the entire structure had swung around.
“We were completely knocked out,” Jewitt said.
Careful modeling by team member Jessica Agarwal of the Max Planck Institute for Solar System Research in Lindau, Germany, showed that the tails could have been formed by a series of impulsive dust-ejection events. She calculated that dust-ejection events occurred April 15th, July 18th, July 24th, August 8th, August 26th and September 4th. Radiation pressure from the sun stretched the dust into streamers.
Radiation pressure could have spun P/2013 P5 up. Jewitt said the spin rate could have increased enough that the asteroid’s weak gravity no longer could hold it together. If that happened, dust could slide toward the asteroid’s equator, shatter and fall off, and drift into space to make a tail. So far, only about 100 to 1,000 tons of dust, a small fraction of the P/2013 P5’s main mass, has been lost. The asteroid’s nucleus, which measures 1,400 feet wide, is thousands of times more massive than the observed amount of ejected dust.
“In astronomy, where you find one, you eventually find a whole bunch more,” Jewitt said. “This is just an amazing object to us, and almost certainly the first of many more to come.”
Additional Information
Jewitt said it appears P/2013 P5 is a fragment of a larger asteroid that broke apart in a collision roughly 200 million years ago. There are many collision fragments in orbits similar to P/2013 P5’s.
Meteorites from these bodies show evidence of having been heated to as much as 1,500 degrees Fahrenheit. This means the asteroid likely is composed of metamorphic rocks and does not hold any ice as a comet does.
