Hubble Watches Comet ATLAS Disintegrate Into More Than Two Dozen Pieces

April 28, 2020

April 28, 2020 1:00PM (EDT) Release ID: 2020-28 Hubble Watches Comet ATLAS Disintegrate Into More Than Two Dozen Pieces

Comets are one of the most legendary and opulent denizens of deep space. Their long tails are so mysterious looking, their sudden appearance so unpredictable, and their journey across the sky so ephemeral that they were once feared as omens of evil, pestilence, and war.

These latest images from NASA’s Hubble Space Telescope of the doomed comet C/2019 Y4 (ATLAS), taken on April 20 and 23, 2020, provide the sharpest views yet that the comet’s solid icy nucleus is breaking apart into as many as 30 pieces that are each roughly the size of a house. So, despite the name, ATLAS doesn’t look like anything to be afraid of.

The comet was discovered on December 29, 2019 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) robotic astronomical survey system based in Hawaii. ATLAS’ fragmentation was confirmed by amateur astronomer Jose de Queiroz, who was able to photograph around three pieces of the comet on April 11. Hubble has a front row seat, with its crisp resolution, to go looking for more pieces. And, astronomers weren’t disappointed.

Planetary experts know that the solid comet nucleus – the fountainhead of the glamourous tail – is a fragile agglomeration of ices and dust. However, astronomers don’t know why some comets break apart like exploding aerial fireworks shells. Could it be due to the warming influence of the Sun as a comet enters the inner solar system, causing it to become unglued? Or could the icy nucleus spin up as it shoots out jets of warming gasses? This could cause it to fly apart.

Though classified as “minor bodies” in our solar system family, comets and Earth’s fate go back billions of years. A shower of comets may have irrigated the dry newborn Earth, contributing some of the water in the oceans. They may have seeded Earth with organic compounds, the precursors to life as we know it. A wayward comet may have struck the Earth 65 million years ago, creating such an environmental disaster that the dinosaurs became extinct. This was good news for small mammals, our earliest ancestors, to take over the blue planet.

This pair of Hubble Space Telescope images of comet C/2019 Y4 (ATLAS), taken on April 20 and 23, 2020, provide the sharpest views yet of the breakup of the fragile comet.

Hubble identified about 30 fragments on April 20, and 25 pieces on April 23. They are all enveloped in a sunlight-swept tail of cometary dust. “Their appearance changes substantially between the two days, so much so that it’s quite difficult to connect the dots,” said David Jewitt, professor of planetary science and astronomy at UCLA, Los Angeles, California, leader of one of two teams who photographed the doomed comet with Hubble. “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.”

“This is really exciting — both because such events are super cool to watch and because they do not happen very often. Most comets that fragment are too dim to see. Events at such scale only happen once or twice a decade,” said the leader of a second Hubble observing team, Quanzhi Ye, of the University of Maryland, College Park, Maryland.

The results are evidence that comet fragmentation is actually fairly common, say researchers. It might even be the dominant mechanism by which the solid, icy nuclei of comets die. Because this happens quickly and unpredictably, astronomers remain largely uncertain about the cause of fragmentation. Hubble’s crisp images may yield new clues to the breakup. Hubble distinguishes pieces as small as the size of a house. Before the breakup, the entire nucleus may have been no more than the length of two football fields.

One idea is that the original nucleus spun itself into pieces because of the jet action of outgassing from sublimating ices. Because such venting is probably not evenly dispersed across the comet, it enhances the breakup. “Further analysis of the Hubble data might be able to show whether or not this mechanism is responsible,” said Jewitt. “Regardless, it’s quite special to get a look with Hubble at this dying comet.”

The comet was discovered on December 29, 2019 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) robotic astronomical survey system based in Hawaii. This NASA-supported survey project for Planetary Defense operates two autonomous telescopes that look for Earth approaching comets and asteroids.

The comet brightened quickly until mid-March, and some astronomers anticipated that it might be visible to the naked eye in May to become one of the most spectacular comets seen in the last 20 years.

However, the comet abruptly started to get dimmer instead of brighter. Astronomers speculated that the icy core may be fragmenting, or even disintegrating. ATLAS’ fragmentation was confirmed by amateur astronomer Jose de Queiroz, who was able to photograph around three pieces of the comet on April 11.

The disintegrating comet was approximately 91 million miles (146 million kilometers) from Earth when the latest Hubble observations were taken. If any of it survives, the comet will make its closest approach to Earth on May 23 at a distance of about 72 million miles (116 million kilometers), and eight days later it will skirt past the Sun at 25 million miles (40 million kilometers).

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.