Comet makes a pit stop near the asteroids of Jupiter

After traveling several billion kilometers towards the Sun, a capricious young object resembling a comet orbiting the giant planets has found a temporary parking space along the way. The object settled near a family of ancient captured asteroids, called Trojans, which orbit the Sun alongside Jupiter. This is the first time that a comet-like object has been spotted near the population of Troy.

The Unexpected Visitor belongs to a class of frozen bodies found in the space between Jupiter and Neptune. Called “Centaurs,” they first become active when heated as the Sun approaches and dynamically transform to become more comet-like.

Visible light snapshots from NASA’s Hubble Space Telescope reveal that the wandering object is showing signs of comet activity, such as a tail, outgassing in jets, and an enveloping coma of dust and gas. Previous observations from NASA’s Spitzer Space Telescope have given clues to the composition of the comet-shaped object and the gases that direct its activity.

“Only Hubble could detect active comet-like features this far in such high detail, and the images clearly show such features, such as a tail around 400,000 miles wide and high resolution features near the nucleus due to ‘a coma jets,’ said Bryce Bolin, principal investigator at Hubble, of Caltech in Pasadena, Calif.

Describing the capture of the Centaur as a rare event, Bolin added, “The visitor had to have come into Jupiter’s orbit just on the correct trajectory to have this kind of configuration which makes it appear to share its orbit with the planet. . re investigating how he was captured by Jupiter and landed among the Trojans. But we think it could be related to the fact that he had a fairly close encounter with Jupiter. “

The team’s article appears in the February 11, 2021 issue of The astronomical journal.

The research team’s computer simulations show that the icy object, called P / 2019 LD2 (LD2), likely flipped near Jupiter about two years ago. The planet then gravitated the stray visitor back to the co-orbital position of the Trojan asteroid cluster, leading Jupiter about 437 million miles.

Bucket Brigade

The nomadic object was discovered in early June 2019 by the University of Hawaii’s Asteroid Terrestrial-Impact Last Alert System (ATLAS) telescopes located on extinct volcanoes, one on Mauna Kea and one on Haleakala. Japanese amateur astronomer Seiichi Yoshida informed the Hubble team of possible comet activity. Astronomers then scanned archival data from the Zwicky Transitional Facility, a wide-field investigation conducted at the Palomar Observatory in California, and realized that the object was clearly active in footage from April 2019.

They followed up with sightings from the Apache Point Observatory in New Mexico, which also hinted at activity. The team observed the comet using Spitzer just days before the observatory’s retreat in January 2020 and identified gas and dust around the comet’s nucleus. These observations convinced the team to use Hubble for a closer look. Using Hubble’s sharp vision, the researchers identified the tail, coma structure, and dust particle size and speed of ejection. These images helped them confirm that the features are due to relatively new comet-like activity.

While the location of LD2 is surprising, Bolin wonders if this pit stop could be a common draw for some sun-facing comets. “It could be part of our solar system’s path through Jupiter’s Trojans to the inner solar system,” he said.

The unexpected guest probably won’t stay among the asteroids for very long. Computer simulations show he will have another close encounter with Jupiter in about two years. The large planet will fire the comet from the system and continue its journey into the inner solar system.

“What’s cool is that you actually catch Jupiter throwing this object and changing its orbital behavior and bringing it into the internal system,” said Carey Lisse, a member of the Lab team. of Applied Physics (APL) from Johns Hopkins University in Laurel, Maryland. . “Jupiter controls what happens with comets once they enter the internal system by changing their orbits.”

The Icy Intruder is probably one of the last members of the so-called “bucket brigade” of comets to be kicked out of his icy home in the Kuiper Belt and Giant Planet region through interactions. with another Kuiper Belt object. Located beyond the orbit of Neptune, the Kuiper Belt is a haven of icy and leftover debris from the construction of our planets 4.6 billion years ago, containing millions of objects, and sometimes these objects have near misses or collisions that drastically change their orbits from the Kuiper belt inward. in the region of the giant planet.

The Frozen Relic Bucket Brigade endures a bumpy ride on their journey to the sun. They gravitationally bounce from one outer planet to another in a celestial pinball game before reaching the inner solar system, heating up as they get closer to the Sun. Researchers say objects spend as much time, if not more, around giant planets, gravitationally attracting them – around 5 million years ago – than they pass through the internal system in which we live.

“Internal system, ‘short period’ comets disintegrate about once a century,” Lisse explains. “So in order to maintain the number of local comets that we see today, we think the Bucket Brigade needs to deliver a new short-lived comet about once every 100 years.”

An Early Bloomer

Seeing outgassing activity on a comet 465 million kilometers from the Sun (where the intensity of sunlight is 1 / 25th as strong as on Earth) surprised the researchers. “We were intrigued to see that the comet had just started to become active for the first time so far from the Sun at distances where the water ice is just starting to sublimate,” Bolin said.

Water remains frozen on a comet until it reaches about 200 million kilometers from the Sun, where heat from sunlight converts water ice into gas that escapes from the core in the form of jets. . Thus, activity indicates that the tail may not be made of water. In fact, Spitzer’s observations indicated the presence of carbon monoxide and carbon dioxide, which could be behind the creation of the tail and jets seen on the comet orbiting Jupiter. These birds do not need much sunlight to heat their frozen form and convert them to gas.

Once the comet is expelled from Jupiter’s orbit and continues its journey, it may encounter the giant planet again. “Short-lived comets like LD2 meet their fate by being thrown into the Sun and totally disintegrating, hitting a planet or again venturing too close to Jupiter and being kicked out of the solar system, which is the usual fate, ”Lisse said. . “The simulations show that in about 500,000 years, there is a 90% probability that this object will be ejected from the solar system and become an interstellar comet.”