December 9, 2021

Beyond Going Long

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Evidence of a massive impact on a nearby star system that separates the atmosphere from the planet

Such planetary collisions are common in young solar systems, but have not been directly observed.

Small planetary systems usually experience severe pain during development as children’s bodies collide and gradually form larger planets. In our solar system, the Earth and the Moon are presumed to be the products of this type of massive influence. Astronomers speculate that such collisions should have been common in early systems, but they were difficult to observe around other stars.

Now astronomers sThe National University of Ireland in Galway, the University of Cambridge and elsewhere have found evidence of a massive impact in the 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 contains traces of a recent impact.

The MIT-led team saw further evidence of a massive impact around the star. They found that the collision may have occurred at least 200,000 years ago between an Earth-sized planet and a small impactor at speeds of more than 10 kilometers per second, or 22,000 miles per hour.

Importantly, they detected gas, suggesting that such a high-speed collision blew up part of the larger planet’s atmosphere — an exciting event that would explain the observed gas and dust around the star. Today’s conclusions temper natureIt is the first identity of its kind.

“This is the first time we’ve seen the atmospheric phenomenon of short protoplanets with a massive impact,” said lead author Tajana Schneiderman, a graduate student in the Department of Earth, Atmospheric and Planetary Sciences at MIT. “Everyone is interested in looking at the massive effect, because we expect it to be common, but we don’t have evidence of that in many systems. We now have another look at this dynamic.”

clear sign

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 stellar dust contains large amounts of unusual minerals in grains that are much finer than astronomers would expect from a typical stellar waste disk.

“For these two factors, HD 172555 was considered this special system,” Schneiderman says.

She and her colleagues were curious to see what the gas might reveal about the system’s impact history. They looked at the data they received AlmaThe Atacama Large Millimeter Array in Chile consists of 66 radio telescopes, the distances of which can be adjusted to increase or decrease the resolution of their images. The team looked at data from the ALMA public archives for signs of carbon monoxide around nearby stars.

“When people want to study the gas in debris disks, carbon monoxide is the brightest, so it’s easy to find,” Schneiderman says. “So we re-evaluated the carbon monoxide data for HD 172555 because it was an interesting system.”

in the aftermath

Through careful reanalysis, the team was able to detect carbon monoxide around the star. When they measured the amount, they found that the gas had 20 percent carbon monoxide in it Venus‘climate. They also note that the gas orbits in large quantities, surprisingly close to the star, about 10 AU or more than 10 times the distance between the Earth and the Sun.

“A closer look requires an explanation for the presence of carbon monoxide,” Schneiderman says.

This is because carbon monoxide is usually subject to photodissociation, a process in which photons from stars break down and damage the molecule. There is usually very little carbon monoxide near the star. Thus, the group tested different scenarios to explain the abundant presence of the closely related gas.

They quickly ruled out a scenario in which the gas came from the debris of a newly formed star, as well as a scenario in which the gas was produced by a belt close to ice asteroids. They also studied a scenario in which gas was emitted from several icy comets from a distant belt of asteroids similar to our Kuiper Belt. But even the data didn’t quite match that scenario. The final scenario considered by the team was that the gas was a huge impact residue.

“Of all the scenarios, this is the only one that can explain all the properties of the data,” Schneiderman says. “In systems of this age, we expect massive effects to occur, and we expect massive effects to be very general indeed. Timescales, age, morphological and compositional constraints are at work. In this context, the only potential process that produces carbon monoxide in this system has a massive impact” .

The team estimates that the gas was released in a massive impact that occurred at least 200,000 years ago — recently that the star would not be able to completely disperse the gas. Depending on the amount of gas, the effect was probably enormous and involved two protoplanets, perhaps comparable in size to Earth. The effect was so great that it may have caused part of the planet’s atmosphere to explode into the gas the team was observing today.

“There is now potential for future work outside of this system,” Schneiderman says. “We show that if you find carbon monoxide immediately and the morphology is consistent with a massive impact, it provides a new opportunity to look for massive shocks and understand how debris behaves afterward.”

said Helk Schleiching, professor of Earth, planetary and space sciences at the University of California, Los Angeles, who was not involved in the research. “It also opens up the possibility of studying the composition of the atmospheres of planets outside the solar system, which are subject to enormous influences, which may eventually help to clarify the atmospheric conditions of terrestrial planets during their massive impact stages.”

Reference: “Colossal Impact Carbon Monoxide Within Young System” Tzana Schneiderman, Luca Matri, Alan B. Jackson, Grant M. Kennedy, Quentin Krall, Sebastian Marino, Karen I. Su, David J. Berg, Kate YL. Wellner and Mark C. White, Oct 20, 2021 Available here. temper 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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