Hubble has a front row seat to a rare celestial event. The space telescope has snapped some strikingly clear shots of a comet in the process of breaking apart as it approaches the Sun.
Comet C/2019 Y4 (ATLAS) was discovered on December 29 last year, by the Asteroid Terrestrial-impact Last Alert System (ATLAS). Over the following months it brightened as it streamed towards the inner solar system, and it was expected that by May it would be bright enough to see with the naked eye from Earth.
But we were robbed of that light show. In early April the comet began to fade instead, and amateur astronomer Jose de Queiroz discovered that it was beginning to disintegrate. So Hubble turned its eye towards the crumbling comet.
The two images were taken on April 20 and 23, when the comet was about 146 million km (91 million mi) from Earth. In the first, the science team spotted around 30 pieces, and 25 in the second. The smallest of these may be about the size of a house, but it’s hard to tell how much overlap there are between those groups of fragments.
“Their appearance changes substantially between the two days, so much so that it’s quite difficult to connect the dots,” says David Jewitt, lead researcher of one of the two teams behind the photos. “I don’t know whether this is because the individual pieces are flashing on and off as they reflect sunlight, acting like twinkling lights on a Christmas tree, or because different fragments appear on different days.”
Comets are known to fall apart on occasion, but astronomers don’t entirely know what causes this to happen to some but not others. It usually occurs as a comet leaves the chilly outskirts of the solar system and gets closer to the Sun, which warms it up. This melts the ice and creates the tail characteristic of all comets. But in some cases the gas escaping from inside could blast it apart.
“Further analysis of the Hubble data might be able to show whether or not this mechanism is responsible,” says Jewitt. “Regardless, it’s quite special to get a look with Hubble at this dying comet.”
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