NASA / ESA’s Hubble Space Telescope has provided astronomers with the sharpest vision to date of the disintegration of Comet C/2019 Y4 (ATLAS). The telescope identified approximately 30 fragments of the fragile comet on April 20 and 25 pieces on April 23, some of which are the size of a house. The comet was first discovered in December 2019 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) robotic astronomical prospecting system in Hawaii. It lit up rapidly until mid-March, and some astronomers initially anticipated that it might be visible to the naked eye in May to become one of the most spectacular comets seen in the past two decades.
However, the comet began to darken abruptly, leading astronomers to speculate that the icy core could fragment or even disintegrate. The fragmentation of ATLAS was confirmed by amateur astronomer José de Queiroz, who photographed around three pieces of the comet on April 11, to the disappointment of many amateur astronomers who were eager to catch a glimpse of comet ATLAS in the sky.
New Hubble Space Telescope observations of the comet’s destruction on April 20 and 23 reveal that the broken fragments are shrouded in a comet dust tail swept away by sunlight. These images provide further evidence that fragmentation of comets is likely to be common and may even be the dominant mechanism by which solid, icy nuclei of comets die.
“Their appearance changes substantially between the two days, so much so that it is quite difficult to connect the dots,” David Jewitt of UCLA, leader of one of the two teams that observed the comet with Hubble, said in a statement.
“I don’t know if this is because the individual pieces turn on and off when they reflect sunlight, act like flickering lights on a Christmas tree, or because different shards appear on different days. This is really exciting, both because such events are super cool to watch and because they don’t happen very often. Most comets that have fragments are too faint to watch. Events on such a scale only happen once or twice a decade.” revealed the head of Hubble’s second observation team, Quanzhi Ye of the University of Maryland.
Because the fragmentation of the comet occurs quickly and unpredictably, reliable observations are rare. Therefore, astronomers remain unsure of the cause of the fragmentation. One suggestion is that the original core breaks apart due to the degassing action of the sublimated ices. Since this vent is likely not to be uniformly dispersed by the comet, it improves rupture.
“Further analysis of the Hubble data could show whether or not this mechanism is responsible,” Jewitt said.
“Anyway, it’s pretty special to take a look with Hubble at this dying comet.”
Sharp Hubble images can give new clues to decay. The telescope has distinguished pieces as small as the size of a house. Before the disintegration of the comet, the entire core may not have been more than the length of two football fields. The disintegrating comet ATLAS is currently within the orbit of Mars, at a distance of approximately 145 million km from Earth when the latest Hubble observations were taken. The comet will make its closest approach to Earth on May 23 at a distance of approximately 115 million km, and eight days later it will border 37 million km from the Sun.