Second interstellar object 2I/Borisov resembles comets from our solar system unlike the curveball that was Oumuamua

The physical properties of Oumuamua turned out to be impossible to reconcile with solar system objects, challenging our view of interstellar minor bodies.


                            Second interstellar object  2I/Borisov resembles comets from our solar system unlike the curveball that was Oumuamua

The second object from another star that is speeding through our solar system - 2I/Borisov - is a never-seen-before 'real' interstellar comet, conclude astronomers from their initial observations. At the same time, say scientists, based on its initial characteristics, the comet is exactly what astronomers had expected. 

According to the findings, the extended coma and the broad tail of 2I/Borisov is what makes it similar to comets native to our solar system.

"We immediately noticed the familiar coma and tail that were not seen around 'Oumuamua. This is really cool because it means that our new visitor is one of these mythical and never-before-seen 'real' interstellar comets," says Michal Drahus from Jagiellonian University, who co-led the study.

"Make of this what you will, but based on these initial characteristics, this object appears indistinguishable from the native solar system comets," says Piotr Guzik, who led the study from Jagiellonian University, in Krakow, Poland.
 
Initially dubbed as C/2019 Q4 (Borisov), the object was first detected on August 30 by Gennady Borisov, an amateur astronomer at the MARGO observatory in Nauchnij, Crimea. The first interstellar object to pass through the solar system - 'Oumuamua - was detected and confirmed in October 2017.

"The dynamical properties and morphology of 2I/Borisov make it clear that the body is the first certain case of an interstellar comet, and the second known interstellar minor body identified in the solar system (after 'Oumuamua). Evidently, the extended coma and the broad tail stand in stark contrast with the purely asteroidal appearance of 'Oumuamua," state the findings published in Nature Astronomy.

According to Guzik, the research work on 2I/Borisov will be "transformative for planetary astronomy" and a milestone for astronomy in general.

The researchers observed that comet Borisov has a dust-dominated morphology, a reddish hue and that its solid nucleus is about 1 km in radius. The estimated nucleus size of 2I/Borisov, says the team, is common among the solar system's comets.

The findings, say scientists are remarkable, especially after ‘Oumuamua, the "multiple peculiarities" of which had prompted them to rethink their entire view of the nature of “interstellar interlopers.”
 
"Interstellar comets penetrating through the solar system had been anticipated for decades. The discovery of asteroidal-looking 'Oumuamua was thus a huge surprise and a puzzle. Furthermore, the physical properties of the 'first scout' turned out to be impossible to reconcile with solar system objects, challenging our view of interstellar minor bodies. Here, we report the identification and early characterization of a new interstellar object, which has an evidently cometary appearance," says the study.

It further says, "Images show an extended coma and a faint, broad tail. The nucleus is probably approximately 1 km in radius, again a common value among solar system comets, and has a negligible chance of experiencing rotational disruption. Based on these early characteristics, and putting its hyperbolic orbit aside, 2I/Borisov appears indistinguishable from the native solar system comets." 

Two-color composite image of comet 2I/Borisov captured by the Gemini North telescope on September 10, 2019. The image was obtained with eight 60-second exposures, four in green and four in red bands. (Gemini Observatory/NSF/AURA)

Prompted by the earlier visit of 'Oumuamua, a research team led by astronomers from the Jagiellonian University created a computer program nicknamed "Interstellar Crusher" that scanned through online data of newly-found comets and asteroids in search of objects from far away. On September 8, 2019, the program issued a red alert and informed the scientists of a possible new hyperbolic object arriving from interstellar space. 

Two days after receiving the alert, the team started scrutinizing the first images of the object obtained at the William Herschel Telescope on La Palma, Spain, even as they were getting ready to receive more data from the larger Gemini North Telescope on Maunakea, Hawaii.

According to Guzik, the code was written specifically for this purpose, and the researchers had "really hoped to receive this message" one day. A closer investigation into the object's orbit confirmed its exosolar origin, making it the second-known "interstellar interloper," says Guzik.

"On September 8, 2019, at 04:15 universal time, we were alerted by our software Interstellar Crusher of a possible new hyperbolic object gb00234. The orbit became reliable enough to trigger the first announcements, and subsequently, the body received an official name 2I/Borisov. As of September 20, 2019, at 12:00 universal time, 447 published astrometric positions are demonstrably incompatible with a parabolic orbit," the findings state.

According to the researchers, they took proper measurements before determining the comet's color and estimating its other properties.

These findings, says the team, are only the beginning of a more thorough investigation. "The comet is still emerging from the sun's morning glare and growing in brightness. It will be observable for several months, which makes us believe that the best is yet to come," says co-author of the study Waclaw Waniak from Jagiellonian University.

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