Is it a comet? Is it an asteroid? Well, it’s a bit of both, according to a team of astronomers who captured the rare sight of a lump of space rock radiating with an impressive six comet-like tails using NASA/ESA’s long-serving Hubble Space Telescope.
From Earth, we usually see moving debris as points of light but this object, designated P/2013 P5 and of which has rocked up from our Solar System’s asteroid belt, is really something else. “We were literally dumbfounded when we saw it,” says David Jewitt at the University of California who is the lead investigator of the asteroid that resembles a rotating lawn sprinkler.
However, it wasn’t always this way. Astronomers first clapped eyes on the asteroid back in August where it appeared as a fuzzy point of light in a survey conjured up by the Pan-STARRS 1 telescopes located in Hawaii. It wasn’t until September that P/2013 P5 began showing its true colours as it morphed into its freakish six-tailed glory.
“Even more amazing, its tail structures change dramatically in just 13 days as it belches out dust,” Jewitt adds. These spokes, according to his team, are made of fine-grained dust, ranging from anywhere between 10 to 100 micrometres. “That also caught us by surprise. It’s hard to believe we’re looking at an asteroid.”
So what is the likely explanation? Jessica Agarwal of the Max Planck Institute in Lindau, Germany, isn’t too sure but is, alongside Jewitt, working on it to find out. “We keep observing the asteroid to see how it changes over the next months and we keep refining our models to better understand what is going on,” she tells All About Space. “One thing we would really like to know is if the dust was ejected in a plane, which would strongly support the picture of a fast-spinning asteroid.”
Agarwal is the first to admit that getting to the bottom of why P/2013 P5, which will remain on its near-circular orbit around the Sun currently some 220 million kilometres from Earth, is acting so strangely is a difficult task. “The different tails we see in the Hubble images are not related to active areas on the surface, as in a classical comet,” she says. “Our data do not allow us to say anything on where on the nucleus the material came from.”
But that doesn’t mean that, while they wait, they haven’t been speculating about the 480-metre diameter asteroid’s plumes of dust. “We hypothesise that [the dust] came from the equatorial region, where the centrifugal force is strongest,” Agarwal says. “But once the particles have left the immediate vicinity of the asteroid, their motion is driven by solar radiation pressure and gravity only.” As for the many tails, she suggests that the ejections didn’t occur steadily but rather as six separate outbursts at differing times. “The precise reason why these outbursts occurred at the times we measured still need to be investigated,” she says.
As for the future of this asteroid, Agarwal believes that its outbursts could be a sign of things to come – namely its death: “The jets will not cause the asteroid to fly apart, but they could be signs it is breaking up as a consequence of fast rotation.”
“The asteroid is possibly a member of the so-called Flora-family,” says Agarwal when asked where this asteroid is likely to have come from. “This is an ensemble of asteroids that likely are the remnants of a much larger asteroid that broke apart in a collision 200 million years ago.”
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Images courtesy of NASA/ESA/D. Jewitt (UCLA) (top) and ESA (bottom).