25 April 2020
Scientists recently reported new details about the second interstellar object ever seen passing through our solar system. It is a comet called 2I/Borisov.
Comets are made up of frozen gases, rock and dust that orbit stars. The Reuters news agency likens them to dirty snowballs. Comets leave behind a mix of gas and dust in space as they move.
2I/Borisov is different from other comets, scientists have observed.
The interstellar comet 2I/Borisov travels through our solar system in an artist's impression obtained by Reuters April 20, 2020. (NRAO/AUI/NSF, S. Dagnello/Handout via REUTERS)
Researchers reported on Monday that gas coming off 2I/Borisov had high levels of carbon monoxide - far more than comets formed in our solar system.
Carbon monoxide is poisonous to human beings. It forms as ice only in the coldest places. The presence of so much carbon monoxide, the researchers said, suggests 2I/Borisov was formed differently than comets from our solar system. It could have formed in a very cold part of its home star system or around a star cooler than the sun.
Dennis Bodewits is a planetary scientist at Auburn University in the United States. He was the lead author of one of two 2I/Borisov studies. Both appear in the publication Nature Astronomy.
"We like to refer to 2I/Borisov as a snowman from a dark and cold place," Bodewits said. He noted that, "comets are left-over building blocks from the time of planet formation. For the first time, we have been able to measure the chemical composition of such a building block from another planetary system while it flew through our own solar system."
Amateur astronomer Gennady Borisov was the first person to identify the comet in August of 2019. The comet is thought to be about 1 kilometer wide. It has flown through interstellar space after being forced out from its original star system.
Bodewits said the comet was born long ago in a mix of gas and dust circling around a newly formed star. He said it came from a place that must have been rich in carbon monoxide.
That star may have been what is called an M-dwarf, far smaller and cooler than our sun. M-dwarf stars are the smallest kind of star known to scientists, Bodewits said.
At first, researchers believed that 2I/Borisov was like comets made in our solar system. However, information gathered by the Hubble Space Telescope and an observatory in Chile showed differences.
The researchers also found a large amount of hydrogen cyanide at levels similar to comets from our solar system.
Martin Cordiner was the lead author of the second study. He said, "This shows that 2I/Borisov is not a completely alien object, and confirms some similarity with our ‘normal' comets, so the processes that shaped it are comparable to the way our own comets formed."
Cordiner is an astrobiologist working for NASA, the U.S. space agency. He is with the Goddard Space Flight Center in Maryland.
The only other interstellar visitor discovered in our solar system was a rocky object called ‘Oumuamua.' It was found in 2017.
I'm John Russell.
Will Dunham reported on this story for Reuters. John Russell adapted it for VOA Learning English. George Grow was the editor.
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Words in This Story
interstellar – adj. existing or occurring between stars
solar – adj. of or related to the sun
author – n. a writer of a book or report
refer – v. to note or suggest
composition – n. the way in which something is put together or arranged
amateur – n. a person who does something (such as a sport or hobby) for pleasure and not as a job