Hubble views extraordinary multi-tailed asteroid P/2013 P5
Labelled view of extraordinary multi-tailed asteroid P/2013 P5
Schematic of active asteroid P/2013 P5
Hubble astronomers observe bizarre six-tailed asteroid
Astronomers using the NASA/ESA Hubble
Space Telescope have observed a unique and baffling object in the
asteroid belt that looks like a rotating lawn sprinkler or badminton
shuttlecock. While this object is on an asteroid-like orbit, it looks
like a comet, and is sending out tails of dust into space.
Normal asteroids appear as tiny points of light. But this asteroid,
designated P/2013 P5, has six comet-like tails of dust radiating from it
like the spokes on a wheel. It was first spotted in August of this year
as an unusually fuzzy-looking object by astronomers using the
Pan-STARRS 1 telescope in Hawaii [1].
Because nothing like this has ever been seen before, astronomers are
scratching their heads to find an adequate explanation for its
mysterious appearance.
The multiple tails were discovered in Hubble images taken on 10
September 2013. When Hubble returned to the asteroid on 23 September,
its appearance had totally changed. It looked as if the entire structure
had swung around.
"We were literally dumbfounded when we saw it," said lead investigator David Jewitt of the University of California at Los Angeles, USA. "Even
more amazingly, 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 explanation for the odd appearance is that the asteroid's
rotation rate increased to the point where its surface started flying
apart, ejecting dust in episodic eruptions that started last spring. The
team rules out an asteroid impact because a lot of dust would have been
blasted into space all at once, whereas P5 has ejected dust
intermittently over a period of at least five months [2].
Careful modelling 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 [3]. Radiation pressure from the Sun smears out the dust into streamers. "Given our observations and modelling, we infer that P/2013 P5 might be losing dust as it rotates at high speed," says Agarwal. "The Sun then drags this dust into the distinct tails we're seeing."
The asteroid could possibly have been spun up to a high speed as
pressure from the Sun's light exerted a torque on the body. If the
asteroid's spin rate became fast enough, Jewitt said, the asteroid's
weak gravity would no longer be able to hold it together. Dust might
avalanche down towards the equator, and maybe shatter and fall off,
eventually drifting into space to make a tail. So far, only a small
fraction of the main mass, perhaps 100 to 1000 tonnes of dust, has been
lost. The asteroid is thousands of times more massive, with a radius of
up to 240 metres.
Follow-up observations may show whether the dust leaves the asteroid
in the equatorial plane, which would be quite strong evidence for a
rotational breakup. Astronomers will also try to measure the asteroid's
true spin rate.
Jewitt's interpretation implies that rotational breakup may be a
common phenomenon in the asteroid belt; it may even be the main way in
which small asteroids "die" [4]. "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."
The paper from Jewitt's team appears online in the 7 November issue of The Astrophysical Journal Letters.
Notes
[1] The comet was discovered by Micheli
et al. on 27 August 2013. It was spotted in observations from 18 August
2013. The discovery was announced in a Minor Planet Electronic Circular.
[2] Agarwal calculated that the first ejection event
occurred on 15 April, and the last one on 4 September 2013. Other
eruptions occurred on 18 July, 24 July, 8 August, and 26 August 2013.
[3] A less likely option is that this emission is a
result of water ice sublimating. Water ice can survive within the
asteroid belt, although only at the outskirts or if buried deep enough
within a large enough asteroid to be shielded. However, P5 is likely
made of metamorphic rocks, making it incapable of holding ice in the
same way that comets do. This, coupled with P5's orbit and its very
small size, makes it very unlikely that its mass loss would be due to
ice sublimation.
[4] This is not the first time that Hubble has observed a strange asteroid. In 2010, Hubble spotted a strange X-shaped asteroid (heic1016).
However, unlike P/2013 P5, this was thought to have been formed by a
collision. Later that year astronomers observed asteroid (596) Scheila,
an object with a tail that was surrounded by a C-shaped cloud of dust (opo1113a).
Again, this asteroid was thought to be the result of a collision
between Scheila and a much smaller body — only the second time that such
an event has been spotted.
Notes for editors
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The international team of astronomers in the Hubble study consists of
D. Jewitt (UCLA, USA), J. Agarwal (Max Planck Institute for Solar
System Research, Germany), H. Weaver (The Johns Hopkins University
Applied Physics Laboratory, USA), M. Mutchler (STScI, USA), and S.
Larson (University of Arizona, USA). The paper, entitled “The
Extraordinary Multi-Tailed Main-Belt Comet P/2013 P5”, is published in The Astrophysical Journal Letters.
More information
Image credit: NASA, ESA, D. Jewitt
(University of California, Los Angeles), J. Agarwal (Max Planck
Institute for Solar System Research), H. Weaver (Johns Hopkins
University Applied Physics Laboratory), M. Mutchler (STScI), and S.
Larson (University of Arizona)
Links
Contacts
David JewittUniversity of California at Los Angeles
Los Angeles, USA
Tel: +1-310-825-2521
Email: jewitt@ucla.edu
Nicky Guttridge
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Tel: +49-89-3200-6855
Cell: +44 7512 318322
Email: nguttrid@partner.eso.org
