A team led by the Massachusetts Institute of Technology has discovered evidence of a giant impact in the nearby star system HD 17255, where an Earth-sized planet likely collided with Earth and a smaller collider at least 200,000 years ago, ripping off part of the planet’s atmosphere. Credit: Mark A. Garlick
Such planetary fractures are likely common in young solar systems, but have not been directly observed.
Young planetary systems usually experience severe growing pains as children’s bodies collide and merge to form increasingly larger planets. In our solar system, the Earth and Moon are thought to be the product of this type of giant collision. Astronomers hypothesize that such refractions should have been common in early systems, but they were difficult to observe around other stars.
Now astronomers WithAnd the National University of Ireland in Galway, Cambridge University and elsewhere have revealed evidence of a giant collision in a nearby star system, only 95 light-years from Earth. The star, called HD 172555, is about 23 million years old, and scientists suspect that its dust bears traces of a recent impact.
The team led by the Massachusetts Institute of Technology noticed new evidence of a giant effect around the star. They conclude that the collision most likely occurred between a planet roughly the size of Earth and a smaller collider at least 200,000 years ago, at 10 kilometers per second, or more. 22,000 miles per hour.
Importantly, they detected gas that suggests such a rapid impact would likely sweep away part of the larger planet’s atmosphere — an exciting event that would explain the observed gas and dust around the star. Results published today in nature, represents the first such discovery.
“This is the first time we’ve detected this phenomenon, the atmospheric phenomenon of bare protoplanets during a giant collision,” says lead author Tajana Schneiderman, a graduate student in the Department of Earth, Atmospheric and Planetary Sciences from MIT. “Everyone is interested in seeing a massive impact because we expect it to be popular, but we don’t have evidence in a lot of systems for that. We now have additional insight into these dynamics.
The star HD 172555 has been the subject of intrigue among astronomers due to the unusual composition of its dust. Observations in recent years have shown that stardust contains large amounts of unusual minerals, in grains much finer than astronomers might expect from a typical stellar debris disk.
“Because of these two factors, HD 172555 was considered this peculiar system,” Schneiderman explains.
She and her colleagues wondered what the gas might reveal about the system’s impact history. They reviewed the data collected by Alma, Atacama Large Millimeter Array in Chile, which includes 66 radio telescopes whose spacing can be adjusted to increase or decrease the resolution of their images. The team examined data in the ALMA public archives, looking for signs of carbon monoxide around nearby stars.
“When people want to study the gas in debris disks, carbon monoxide is usually the brightest, and therefore easier to find,” Schneiderman explains. “So we looked at the carbon monoxide data for HD 172555 again because it was an interesting system. “
Through careful reanalysis, the team was able to detect carbon monoxide around the star. When they measured the abundance of the gas, they found that the gas made up 20% of the carbon monoxide in it Venus‘Atmosphere. They also observed that the gas orbits in large quantities, surprisingly close to the star, at about 10 AU, or 10 times the distance between the Earth and the Sun.
“The presence of carbon monoxide in this close proximity requires some explanation,” Schneiderman explains.
This is because carbon monoxide is generally prone to photodissociation, a process in which photons from the star disintegrate and destroy the molecule. At close range, there is usually very little carbon monoxide near the star. The group thus tested different scenarios to explain the abundant and near appearance of the gas.
They quickly ruled out a scenario in which the gas comes from the debris of a newly formed star, as well as a scenario in which the gas is produced by a nearby belt of icy asteroids. They also envisioned a scenario in which gas from many icy comets is emitted from the distant asteroid belt, similar to our Kuiper belt. But the data didn’t quite fit that scenario either. The final scenario the team considered was that the gas was part of a giant effect.
“Of all the scenarios, this is the only one that can explain all the properties of the data,” Schneiderman explains. “In systems at this age, we would expect giant impacts to occur, and we would expect giant impacts to be really very common. Time scales are arranged, age is arranged, and morphological and compositional constraints are arranged. The only plausible process that could produce carbon monoxide in this system in this context is massive effect. “
The team estimates that the gas was released from a giant collision that occurred at least 200,000 years ago, which is recent enough that the star hasn’t had time to completely destroy the gas. Depending on the abundance of the gas, the impact is likely to be enormous, involving two protoplanets, likely comparable in size to Earth. The impact was so great that it likely exploded part of the planet’s atmosphere, in the form of gas the team observed today.
“There is now an opportunity to work in the future outside of this system,” Schneiderman says. “We show that if you find carbon monoxide in a location and morphology compatible with a giant impact, it provides a new way to search for giant impacts and understand how debris then behaves.”
“What is particularly exciting about this work, in my opinion, is that it demonstrates the importance of atmospheric loss due to giant impacts,” says Helk Schleichting, professor of Earth, planetary and space sciences at the University of California, Los Angeles. Do not participate in the search. “It also opens up the possibility to study the atmospheric composition of extrasolar planets that are subject to gigantic impacts, which could eventually help shed light on the atmospheric conditions of terrestrial planets during their gigantic impact phase.”
Reference: “Carbon monoxide from a giant impact in the interior of a young system” by Tajana Schneiderman, Luca Matra, Alan B. Jackson, Grant M. Kennedy, Quentin Krall, Sebastian Marino, Karen I. Oberg, and Kate Yell. Su, David J. Wellner and Mark C. White, 20 Oct. 2021, Available here. nature.
DOI: 10.1038 / s41586-021-03872-x
This research was supported in part by the ALMA Observatory and the Simons Foundation.
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