Strange interstellar comet discovery hints at a solar system like ours


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the "unexpected discovery" nickel gas around interstellar comet 21 / Borisov aligns with "astonishing" new observations of local comets, say scientists.

Concept art by 21 / Borisov. Image: NRAO / AUI / NSF / S. Dagnello

ABSTRACT breaks down breathtaking scientific research, future technologies, new discoveries and major breakthroughs.

In the summer of 2019, amateur astronomer Gennadiy Borisov spotted a rogue comet that originated in a star system far beyond the Sun. The comet, named 2I / Borisov, was just the second interstellar intruder ever to be identified in our solar system, after sighting the bizarre ‘Oumuamua object in 2017.

While ‘Oumuamua sparked heated controversy over its strange nature and possible origins, 2I / Borisov fascinated scientists for the opposite reason: it looked roughly like local comets orbiting the Sun, suggesting that the visitor may come from a system very similar to our own.

Now, independent findings from two research teams have strengthened this link between our solar system and the mysterious birthplace of 2I / Borisov, while also revealing a surprising new twist on local and interstellar comets.

Piotr Guzi and MichaÅ‚ Drahus, two scientists from Jagiellonian University in Poland, announced the “unexpected discovery” of nickel vapor in the atmosphere of 2I / Borisov, according to a study published Wednesday in Nature. Although it is well known that heavy metals such as iron and nickel exist as solids inside comets, these elements had never been seen except in gaseous form when comets approach stars, causing extreme heating which triggers the sublimation of the metals into vapor.

This is why Guzi and Drahus were caught off guard by clear evidence of gaseous nickel in the coma or the atmosphere of 2I / Borisov, even though the interstellar comet was about twice as far from the Sun as Earth at the time of the team observations in January 2020 At this distance, the comet’s temperature was estimated to be around -93 ° C, well below the conditions of 425 ° C that normally produce gaseous nickel.

Yet the team’s observations, obtained by the sophisticated X-shooter spectrograph at the European Southern Observatory’s Very Large Telescope, showed evidence of nickel gas over several nights, “effectively removing[ing] the possibility of confusion with a background source or instrumental artefacts, ”according to the study.

“Atomic nickel was a truly unexpected discovery, as observation of the gaseous form of any metal was considered to be limited only to warm environments, such as comets grazing the sun passing a few solar rays from the surface of the Sun. “Guzi said in an email.

“The two brightest nickel lines were clearly visible in our combined spectrum, but since we knew of no typical emissions at these wavelengths, we first made sure that they were present in the spectra taken each night. , and not in the background of the sky. and that they are not artefacts, ”he continued. “Yet it took us a long time to discover their true nature. “

To potentially explain the discovery, Guzi and Drahus propose that heavy metal vapor can be released at cold temperatures through a process known as photodissociation, in which photons (light particles) stimulate a nickel-containing molecule on the surface. to sublimate into gas.

The team’s findings would be quite intriguing in themselves, but they also coincide with the publication of a decades-long compositional study of comets in our solar system, led by University of Liège astronomer Jean Manfroid. . Using observations collected since 2002, the Manfroid team discovered that nickel and iron “are ubiquitous in cometary atmospheres, even far from the Sun”, according to a study also published on Wednesday in Nature.

“We learned of the other document while ours was already under review,” Guzi said. “The fact that the presence of nickel was detected both in the coma of the first known interstellar comet and in a collection of comets originating in our planetary system is simply astonishing.”

“This opens up a new perspective for understanding how the formation of planetary systems takes place in the galaxy since comets are seen as the remnants of this process,” he added.

The new research also strengthens the hypothesis that 2I / Borisov could have originated from a star system very similar to ours, as these studies identify yet another property that the interstellar visitor shares with our own local comets. If scientists find more interstellar comets that look like 2I / Borisov, it could hint at the existence of many solar system analogues across the Milky Way.

“We might expect the conditions at the place of their birth, as well as the chemical makeup of the interstellar cloud from which their original planetary system originated, to be similar to the interstellar cloud from which our solar system was born.” , Guzi said.

“It would be interesting to study the composition of other interstellar comets in the future to compare them with 2I / Borisov,” he continued. “Unfortunately, we don’t know when such an object will appear. The other fascinating question is what is the source of the metallic atoms in the gases surrounding the cometary nucleus.

Fortunately, these tantalizing questions could be answered in the years to come, as next-generation observatories will increase the speed at which interstellar visitors are spotted. In particular, the Vera C. Rubin observatory in Chile, which is due to enter service in the coming years, should speed up the detections of these mysterious intruders.

A larger census of interstellar objects will provide vital information about their distant home systems, highlighting how unique our own cosmic neighborhood is as part of the Milky Way.

“This is an important period in the history of planetary science, because we have the opportunity to study objects born in distant planetary systems and which have been ejected from their homes on their way to our cosmic neighborhood,” Guzi concluded.

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Arline J. Mercier

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