"We've never seen such a dramatic change like this over such a short period of time," says co-author DeMeo. Since Marsset's team has found 6478 Gault is a dry, rocky body, this means it likely is generating dust tails by some other active mechanism.Īs the team observed the asteroid, they discovered, to their surprise, that the rock was changing color in the near-infrared, from red to blue. When they approach the sun, any surface ice instantly sublimates, or vaporizes into gas, creating the comet's characteristic tail. Over two nights, they observed the asteroid and used a high-precision spectrograph to divide the asteroid's incoming light into various frequencies, or colors, the relative intensities of which can give scientists an idea of an object's composition.įrom their analysis, the team determined that the asteroid's surface is composed mainly of silicate, a dry, rocky material, similar to most other asteroids, and, more importantly, not at all like most comets.Ĭomets typically come from the far colder edges of the solar system. He and his colleagues joined the search for answers to Gault's activity in March, when they secured observation time at NASA's Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. "We know of about a million bodies between Mars and Jupiter, and maybe about 20 that are active in the asteroid belt," Marsset says. But how? The question reignited interest in Gault, and studies since then have unearthed past instances of similar activity by the asteroid. The tails, they concluded, must consist of tens of millions of kilograms of dust, actively ejected by the asteroid, into space. Astronomers estimate that the longer tail stretches half a million miles out, while the shorter tail is about a quarter as long. In January, images from various observatories, including NASA's Hubble Space Telescope, captured two narrow, comet-like tails trailing the asteroid. Until recently, the space rock was seen as relatively average, measuring about 2.5 miles wide and orbiting along with millions of other bits of rock and dust within the inner region of the asteroid belt, 214 million miles from the sun. Marsset and his colleagues, including EAPS Research Scientist Francesca DeMeo and Professor Richard Binzel, have published their results today in the journal Astrophysical Journal Letters.Īstronomers first discovered 6478 Gault in 1988 and named the asteroid after planetary geologist Donald Gault. "It means that probably some mechanism responsible for dust emission is different from comets, and different from most other active main-belt asteroids." "It's the first time to my knowledge that we see a rocky body emitting dust, a little bit like a comet," Marsset says. Marsset and his colleagues have also confirmed that the asteroid is rocky-proof that the asteroid's tail, though seemingly comet-like, is caused by an entirely different mechanism, as comets are not rocky but more like loose snowballs of ice and dust. "We think we have witnessed the asteroid losing its reddish dust to space, and we are seeing the asteroid's underlying, fresh blue layers." ![]() "That was a very big surprise," says Michael Marsset, a postdoc in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS). ![]() It is the first time scientists have observed a color-shifting asteroid, in real-time. While astronomers are still puzzling over the cause of Gault's comet-like activity, an MIT-led team now reports that it has caught the asteroid in the act of changing color, in the near-infrared spectrum, from red to blue.
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