Falling Apart
Hubble spots an asteroid disintegrating
Astronomers working with the Hubble Space Telescope have successfully photographed an asteroid breaking into ten pieces because sunlight caused it to spin too fast.
The asteroid, known as P/2013 R3, was originally spotted as a faint blur in September 2013 by the Catalina and Pan-STARRS sky surveys. Follow-up observations by the Keck telescope in Hawaii showed something rather interesting — three small chunks of asteroid inside a ball of dust about the same diameter as the Earth.
“Keck showed us that this thing was worth looking at with Hubble,” said David Jewitt, who led the investigation. They scheduled some time with the space telescope, which showed that the asteroid was comprised not of three chunks, but of ten — the largest about twice the length of a football pitch — drifting away from each other at about 1.5 kilometres per hour. Their results appeared in Astrophysical Journal Letters.
“This is a really bizarre thing to observe — we’ve never seen anything like it before,” said co-author Jessica Agarwal. “The break-up could have many different causes, but the Hubble observations are detailed enough that we can actually pinpoint the process responsible.”
It’s unlikely that the breakup is happening due to a collision with another asteroid — otherwise the process would be considerably more violent, with the pieces travelling much faster. It’s also unlikely that the breakup is due to the forces caused by the ice inside the asteroid warming up and vaporising — it’s too cold for that in the asteroid belt, 480 million kilometres from the Sun.
That just leaves one answer left — the spacerock is breaking apart due to a subtle effect caused by sunlight. When objects in space that aren’t perfectly spherical are hit by sunlight, they start to spin very slowly — an effect known as the Yarkovsky–O’Keefe–Radzievskii–Paddack effect, or ‘YORP effect’ for short.
Over millions of years, this spin-rate increases and increases until its components can’t stand the centrifugal force and pull themselves apart. Such a possibility has been discussed for many years but never actually observed — we’ve seen asteroids spinning faster but never disintegrating.
“This is the latest in a line of weird asteroid discoveries, including the active asteroid P/2013 P5, which we found to be spouting six tails,” said Agarwal. “This indicates that the Sun may play a large role in disintegrating these small Solar System bodies, by putting pressure on them via sunlight.”
The various bits of 200,000 tonne asteroid will probably meet a fiery end — turning into meteoroids that will most likely plunge into the heat of the Sun over the coming millennia.
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