CN gas detected in the interstellar object 2I/Borisov

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An international team including researchers from the STAR Research Insitute of ULiège has just detected CN molecules in the atmosphere of the second interstellar object, 2I/Borisov. This gas, frequently observed in the comets of our Solar System, is now detected for the first time in a body from another system than ours. This important discovery is published in the Astrophysical Journal Letters (1).

Recently named 2I/Borisov by the International Astronomical Union, this celestial body, discovered by the Russian amateur astronomer Gennady Borisov on August 30, is the focus of many astronomers. This object, which looks like a weak comet, surrounded by an atmosphere and a short tail, has indeed a very special orbit. It undoubtedly indicates that it comes from an extrasolar planetary system, and is currently passing through our system at high speed without being gravitationally linked to our Sun. It is only the second interstellar object discovered. The first, 1I/Oumuamua, found at the end of 2017, could only be followed for a few weeks and no gaseous emissions could be observed, limiting the study of this enigmatic object. "Here, we are in a much more favorable situation, explains Emmanuël Jehin, researcher at the ORCA (Cosmological and Astrophysical Origins) laboratory of the University of Liège: we will be able to observe Borisov for many more months because it was discovered at a large distance from Earth and it is now approaching to us. And the first data are already coming in! »

Borisov TN

Animation showing in the center the displacement of the interstellar comet 2I/Borisov on the starry background.
Its speed is very important and testifies that it is not linked to the Sun but is just passing through the Solar System.
credit : Emmanuël Jehin and the TRAPPIST Team

The team of astronomers has just detected CN molecules (made up of a carbon atom and a nitrogen atom linked together) in its atmosphere using the William Herschel telescope in La Palma, Canary Islands. "For the first time we can measure the composition of an "interstellar visitor" and compare it to what we have in our own solar system," says Alan Fitzsimmmons, a researcher at Queen's University in Belfast (Dublin), who leads the research group. And what surprises that scientists is that this first chemical signature is very similar to what is found in the comets of our Solar System. "We could have expected to observe a very different composition," explains Emmanuël Jehin,"since we don't know the origin and history of this object, which probably wandered for millions of years between the stars before reaching us. This would indicate that the physical and chemical processes of formation of these small bodies, which are the building blocks of planets and perhaps the source of water and organic material on Earth, would be very common in the Galaxy. »

The best is yet to come

However, scientists remain cautious and wait to be able to observe it even more accurately. Borisov will be visible from the Southern Hemisphere and will pass at its closest distance to Sun on December 8, at twice the Earth-Sun distance. As the comet approaches the Sun, it should become more active and brighter, releasing more gas and dust, and be more visible to astronomers. "It could even fragment and produce a major outburst of brightness that would be a godsend for us because it would allow us to constrain the composition of the comet much better, for example via its isotopic composition, to better understand its origin, the conditions in which it was formed and around which type of star," concludes Emmanuël Jehin.

Spectre Borisov 

The spectrum of interstellar comet 2I/Borisov obtained by the team a week ago, shows how the amount of light from the comet depends on the wavelength of the light, or color. The light emitted by the molecules of the CN gas is clearly identified. Credit : Alan Fitzimmons

From the University of Liège, Emmanuël Jehin and Youssef Moulane, a PhD student in the lab, monitor the comet using the TRAPPIST-North robotic telescope located at the Oukaimeden Observatory of Cadi Ayyad University in the Moroccan Atlas. ULiège researchers provided crucial data to measure the quantity of particles emitted by Borisov and estimate the size of its nucleus between 0.7 and 3 km. "We are used to seeing images of comets," explains the young doctoral student, "but this one is really special! Looking at it almost every morning for the past two weeks now, I am fascinated by the fact that this object, despite a similar appearance, actually has such a different origin from the others and comes from so far away." The ULiège team, which has about twenty years' expertise in studying the composition of comets, will continue to monitor Borisov closely to try to detect other molecules and determine their abundance ratios in order to compare them to what we observe in the solar system. After TRAPPIST-North, it is TRAPPIST-South located at the observatory of La Silla in Chile, which will take over next December as well as the Very Large Telescopes (VLT) of the European Southern Observatory (ESO) on which researchers have just obtained observation time.

This discovery is an important step forward, as it will allow scientists to begin to decipher what these objects are made of, which will provide new information to better understand the formation and evolution of other planetary systems in our galaxy and make comparisons with our own solar system.

The research team is composed of Alan Fitzsimmons (Queen's University of Belfast), Olivier Hainaut, Cyrielle Opitom, Bin Yang (European Southern Observatory), Karen Meech, Jacqueline V. Keane and Jan T. Kleyna (University of Hawaii), Emmanuël Jehin (University of Liège), Youssef Moulane (ESO, University of Liège and Marrakech), Marco Micheli (European Space Agency) and Colin Snodgrass (Edinburgh University).

Scientific reference

Alan Fitzsimmons, Olivier Hainaut, Karen Meech, Emmanuël Jehin, Youssef Moulane, Cyrielle Opitom, Bin Yang, Jacqueline V. Keane, Jan T. Kleyna, Marco Micheli, Colin Snodgrass, Detection of CN gas in Interstellar Object 2I/Borisov, Astrophysical Journal Letters, 2019.

Contact Information

JEHIN Emmanuël I ORCA Laboratory I STAR Research Institute

GSM 0495/23.72.98 I

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