Interstellar gatecrasher 2I/Borisov is no ordinary comet

星际星gatecrasher 2i/borisov不是普通的彗星

2020/04/20 23:00  Reuters

By Will Dunham

WASHINGTON, April 20 (Reuters) - Scientists have discovered that a comet called 2I/Borisov - only the second interstellar object ever detected passing through the solar system - is surprisingly different in its composition from comets hailing from our celestial neighborhood.

Gas coming off 2I/Borisov contained high amounts of carbon monoxide - far more than comets formed in our solar system - indicating the object had large concentrations of carbon monoxide ice, researchers said on Monday.

Carbon monoxide, poisonous to humans, is common as a gas in space and forms as ice only in the most frigid locations. The presence of so much carbon monoxide, the researchers said, suggests 2I/Borisov formed in a different manner than comets in our solar system - in a very cold outer region of its home star system or around a star cooler than the sun.

Comets essentially are dirty snowballs composed of frozen gases, rock and dust that orbit stars.

"We like to refer to 2I/Borisov as a snowman from a dark and cold place," said planetary scientist Dennis Bodewits of Auburn University in Alabama, lead author of one of two 2I/Borisov studies published in the journal Nature Astronomy.

"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," Bodewits added.

The comet, detected in August 2019 by amateur astronomer Gennady Borisov and estimated to be about six-tenths of a mile (1-km) wide, has zoomed through interstellar space after being ejected from its original star system.

It was born long ago in a rotating disc of gas and dust surrounding a newly formed star in a place that must have been rich in carbon monoxide, Bodewits said. That star may have been what is called an M-dwarf, far smaller and cooler than the sun and the smallest type of star that is known, Bodewits said.

Scientists initially concluded last year that 2I/Borisov was similar to comets from our solar system, but data from the Hubble Space Telescope and an observatory in Chile revealed its differences.

The researchers also found an abundance of hydrogen cyanide at levels similar to comets from our solar system.

"This shows that 2I/Borisov is not a completely alien object, and confirms some similarity with our &aposnormal&apos comets, so the processes that shaped it are comparable to the way our own comets formed," said Martin Cordiner, an astrobiologist working at NASA&aposs Goddard Space Flight Center in Maryland and lead author of the other study.

The only other interstellar visitor discovered in our solar system was a cigar-shaped rocky object called &aposOumuamua spotted in 2017.

威尔·邓纳姆

路透华盛顿4月20日电-科学家们发现,一颗名为2i/Borisov的彗星-这是有史以来第二颗穿越太阳系的星际天体--的组成与来自我们天体附近的彗星有着惊人的不同。

研究人员周一表示,来自2I/Borisov的气体中含有大量的一氧化碳--远远超过太阳系形成的彗星--这表明该天体含有大量的一氧化碳冰。

一氧化碳对人类有毒,在太空中是常见的气体,只有在最寒冷的地方才形成冰。研究人员说,大量一氧化碳的存在表明,2i/Borisov的形成方式与太阳系中的彗星不同--在太阳系外非常冷的区域,或者在比太阳更冷的恒星周围。

彗星本质上是由冰冻气体、岩石和尘埃组成的肮脏雪球,它们围绕着恒星运行。

阿拉巴马奥本大学的行星科学家丹尼斯·博德维茨说:“我们喜欢把2i/Borisov称为来自黑暗和寒冷地区的雪人。”他是发表在“自然天文学”杂志上的两项2I/Borisov研究的主要作者之一。

博德维茨补充说:“彗星是行星形成时遗留下来的积木。我们第一次能够从另一个行星系统中测量出这种积木的化学成分,而它却在我们自己的太阳系中飞行。”

这颗彗星是由业余天文学家Gennady Borisov于2019年8月发现的,估计宽度约为六分之一英里(1公里),在从其原始恒星系统中被逐出后,它已经在星际空间中飞驰而过。

博德维茨说,很久以前,它是在一颗新形成的恒星周围旋转的气体和尘埃盘中诞生的,这个地方一定富含一氧化碳。博德维茨说,这颗恒星可能就是所谓的M矮星,比太阳小得多,比太阳还冷,也是已知最小的恒星。

科学家们最初在去年得出结论,2i/Borisov与太阳系的彗星相似,但来自哈勃太空望远镜和智利一个天文台的数据显示了它的不同之处。

研究人员还发现了大量的氰化氢,其含量与我们太阳系的彗星相似。

马里兰州NASA&aposs Goddard航天飞行中心(NASA&aposs Goddard Space Air Center)的天体生物学家马丁·科维尔(Martin Corder)说,“这表明2i/Borisov并不是一个完全陌生的物体,并证实了它与我们的彗星形成过程有一些相似之处,因此形成它的过程可以与我们自己的彗星形成方式相媲美。”

在我们的太阳系中发现的唯一的星际访客是一个雪茄状的岩石物体,名为&aposoumuamua,于2017年被发现。

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