Comet makes a pit stop near Jupiter’s asteroids

After traveling several billion miles to the sun, a young, comet-like object orbiting the giant planets found a temporary parking space. The object settled near a family of captured ancient asteroids, called Trojans, orbiting the Sun along Jupiter. This is the first time a comet-like object has been spotted near the Trojan population.

The unexpected visitor belongs to a class of icy bodies that occur in the space between Jupiter and Neptune. Called ‘Centaurs’, they become active for the first time when heated as they approach the sun, and dynamically change into more comet-like.

Visible light snapshots through NASA’s Hubble Space Telescope reveal that the orbital object shows signs of comet activity, such as a tail, which radiates in the form of rays and an enveloping coma of dust and gas. Earlier observations by NASA’s Spitzer Space Telescope provided clues to the composition of the comet-like object and the gases that drove its activity.

“Only Hubble has been able to detect active comet-like features so far in these details, and the images clearly show these features, such as a broad tail of about 400,000 miles and high resolution near the core due to a coma and jets,” Hubce said. researcher Bryce Bolin, of Caltech in Pasadena, California, said.

Describing the capture of Centaur as a rare event, Bolin said: “The visitor must have entered the orbit of Jupiter in the right orbit to have this form of configuration that gives the appearance of sharing its orbit with the planet. We “re-examining how it was captured by Jupiter and ended up under the Trojans. But we think it may be related to the fact that it had a somewhat close encounter with Jupiter.”

The team’s minutes appear in the issue of 11 February 2021 The Astronomical Journal.

The research team’s computer simulations show that the icy object, named P / 2019 LD2 (LD2), probably swung near Jupiter about two years ago. The planet then pulled the stray visitor to the Trojan asteroid group’s co-orbital location heavily, leading Jupiter about 437 million miles.

Bucket Brigade

The nomadic object was discovered in early June 2019 by the ATLAS telescopes of the Asteroid Asteroid Terrestrial Impact (ATLAS) on the extinct volcanoes, one on Mauna Kea and one on Haleakala. Japanese amateur astronomer Seiichi Yoshida sent the Hubble team off on possible comet activities. The astronomers then scan archival data from the Zwicky Transient Facility, a wide field survey conducted at the Palomar Observatory in California, realizing that the object was clearly active in images from April 2019.

They followed up with observations from the Apache Point Observatory in New Mexico, which also hinted at activity. The team observed the comet with the help of Spitzer a few days before the observatory’s retirement in January 2020 and identified gas and dust around the comet’s core. These observations convinced the team to use Hubble to take a closer look. Aided by Hubble’s sharp vision, the researchers identified the tail, coma structure and size of the dust particles and their ejection velocity. These images helped them confirm that the features were due to relatively new comet-like activities.

Although the location of LD2 is surprising, Bolin wonders if this pit stop could be a common attraction for some comets bound by the sun. “It could be part of the path of our solar system through the Jupiter Trojans to the inner solar system,” he said.

The unexpected gas will probably not stay between the asteroids for very long. Computer simulations show that it will have a close encounter with Jupiter again in about two years. The solid planet will pick up the comet from the system, and it will continue its journey to the inner solar system.

“The coolest thing is that you actually catch Jupiter to throw this object around and to change its orbital behavior and bring it into the inner system,” said team member Carey Lisse of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, said. . “Jupiter controls what goes on with comets as soon as they end up in the inner system by changing their orbits.”

The icy intermediary is most likely one of the youngest members of the so-called “bucket brigade” of comets kicked out of its icy home in the Kuiper Belt and into the giant planetary region by interactions with another object of the Kuiper Belt. The Kuiper Belt is located outside the orbit of Neptune and is a refuge of icy, residual debris from the construction of our planets, 4.6 billion years ago, containing millions of objects. Sometimes these objects almost miss or collisions that drastically change their orbits from the Kuiper belt inwards. in the giant planetary region.

The bucket brigade of icy remains endures a bumpy ride during their journey to the sun. They bounce gravely from one outer planet to the next in a game of celestial pinball before reaching the inner solar system, and they warm up as they get closer to the sun. According to the researchers, the objects spend as much or even more time around the giant planets and attract their gravitational pull – about 5 million years – than they cross in the inner system where we live.

“In the inner system, ‘short-period’ comets erupt about once a century,” Lisse explained. “To maintain the number of local comets we see today, we think the bucket brigade should deliver a new comet about once every 100 years.”

An early bloom

To see researchers how degassing activities on a comet come 465 million miles from the sun (where the intensity of sunlight is 1 / 25th as strong as on Earth). “We were interested to see that the comet only began to become active for the first time so far from the sun at distances where water ice is barely beginning to sublimate,” Bolin said.

Water remains frozen on a comet until it reaches about 200 million miles from the sun, where heat from sunlight converts water ice into gas escaping from the core in the form of rays. The activity therefore indicates that the tail may not have been made of water. In fact, observations by Spitzer indicated the presence of carbon monoxide and carbon dioxide gas, which may cause the creation of the tail and rays orbiting the Jupiter comet. These volatiles do not need much sunlight to heat their frozen form and convert it into gas.

Once the comet is kicked out of Jupiter’s orbit and continues its journey, it can meet the giant planet again. “Comets as short periods as LD2 meet their fate by throwing into the sun and disintegrating completely, hitting a planet or once again venturing too close to Jupiter and throwing out of the solar system, which is the usual fate,” said Lisse. . “Simulations show that in about 500,000 years there is a 90% probability that this object will become out of the solar system and become an interstellar comet.”