Possibly the first truly pristine comet ever observed

2I/Borisov passed near the Sun. The colors in these streaks give the image some disco flair and are the result of combining observations in different wavelength bands, highlighted by the various colors in this composite image. Credit:ESO/O. Hainaut
This image was taken with the FORS2 instrument on ESO’s Very Large Telescope in late 2019, when comet 2I/Borisov passed near the Sun. Since the comet was traveling at breakneck speed, around 175 000 kilometers per hour, the background stars appeared as streaks of light as the telescope followed the comet’s trajectory. The colors in these streaks give the image some disco flair and are the result of combining observations in different wavelength bands, highlighted by the various colors in this composite image. Credit:ESO/O. Hainaut

MARCH 30 — New observations with the European Southern Observatory’s Very Large Telescope (ESO’s VLT) indicate that the rogue comet 2I/Borisov, which is only the second and most recently detected interstellar visitor to our Solar System, is one of the most pristine ever observed. Astronomers suspect that the comet most likely never passed close to a star, making it an undisturbed relic of the cloud of gas and dust it formed from.

Comet 2I/Borisov was discovered by amateur astronomer Gennady Borisov in August 2019 and was confirmed to have come from beyond the Solar System a few weeks later. “2I/Borisov could represent the first truly pristine comet ever observed,” says Stefano Bagnulo of the Armagh Observatory and Planetarium, Northern Ireland, UK, who led the new study published today in Nature Communications. The team believes that the comet had never passed close to any star before it flew by the Sun in 2019.

Bagnulo and his colleagues used the FORS2 instrument on ESO’s VLT, located in northern Chile, to study 2I/Borisov in detail using a technique called polarimetry. Since this technique is regularly used to study comets and other small bodies of our Solar System, this allowed the team to compare the interstellar visitor with our local comets.

The team found that 2I/Borisov has polarimetric properties distinct from those of Solar System comets, with the exception of Hale–Bopp. Comet Hale–Bopp received much public interest in the late 1990s as a result of being easily visible to the naked eye, and also because it was one of the most pristine comets astronomers had ever seen. Prior to its most recent passage, Hale–Bopp is thought to have passed by our Sun only once and had therefore barely been affected by solar wind and radiation. This means it was pristine, having a composition very similar to that of the cloud of gas and dust it — and the rest of the Solar System — formed from some 4.5 billion years ago.

By analyzing the polarization together with the color of the comet to gather clues on its composition, the team concluded that 2I/Borisov is in fact even more pristine than Hale–Bopp. This means it carries untarnished signatures of the cloud of gas and dust it formed from.

“The fact that the two comets are remarkably similar suggests that the environment in which 2I/Borisov originated is not so different in composition from the environment in the early Solar System,” says Alberto Cellino, a co-author of the study, from the Astrophysical Observatory of Torino, National Institute for Astrophysics (INAF), Italy.

Olivier Hainaut, an astronomer at ESO in Germany who studies comets and other near-Earth objects but was not involved in this new study, agrees. “The main result — that 2I/Borisov is not like any other comet except Hale–Bopp — is very strong,” he says, adding that “it is very plausible they formed in very similar conditions.”

“The arrival of 2I/Borisov from interstellar space represented the first opportunity to study the composition of a comet from another planetary system and check if the material that comes from this comet is somehow different from our native variety,” explains Ludmilla Kolokolova, of the University of Maryland in the US, who was involved in the Nature Communications research. 

Bagnulo hopes astronomers will have another, even better, opportunity to study a rogue comet in detail before the end of the decade. “ESA is planning to launch Comet Interceptor in 2029, which will have the capability of reaching another visiting interstellar object, if one on a suitable trajectory is discovered,” he says, referring to an upcoming mission by the European Space Agency.

June 12 Meeting: “Telescope Show and Tell”

Photo: Broadhurst, Clarkson & Company Refractor from England. Photo by James Guilford.
Broadhurst, Clarkson & Company Refractor from England

The monthly general meeting of the Cuyahoga Astronomical Association will take place June 12 at 7:30 PM, at the Cleveland Metroparks’ Rocky River Nature Center. The meeting will begin with the annual “Telescope Show and Tell. Several CAA members will bring telescopes of various types and explain the benefits of each. Sometimes the scopes are antique or unusual! The program will be ideal for beginners and those who might like to own a telescope but are not sure what type would best suit them. Questions from the audience will be taken and non-member visitors are welcome. The program is free and open to all interested.

The CAA’s monthly meetings take place at the Rocky River Nature Center; 24000 Valley Parkway; North Olmsted, Ohio, in the Cleveland Metroparks. Meetings begin with a brief business meeting followed by a refreshment and social break to discuss astronomical issues with other members; a business meeting follows.

Major observatory donated to RASC

Photo: David Dunlap Observatory
David Dunlap Observatory

Richmond Hill, ON – In what astronomers might describe as “stellar news,” Corsica Development Inc. is donating the David Dunlap Observatory (DDO) to the facility’s long-time stewards – the Royal Astronomical Society of Canada, Toronto Centre. The observatory is 80 years old this year. It houses what is still the largest optical telescope in the country with a mirror measuring 74 inches (1.9meters) across.

The decision was made in 2012 by Corsica to transfer the Administration Building and Dome to an agency that would honor the spirit of the Observatory and ensure its long-term viability. Members of the RASC Toronto Centre have been managing and operating the David Dunlap Observatory for the last six years and are the resident experts.

Corsica, which purchased the 190 acre Observatory property from the University of Toronto in 2008, is also donating nearly 100 acres of the land to the Town of Richmond Hill.

RASC Toronto Centre has been involved in public outreach programs at the Dunlap Observatory since it first opened in 1935. The registered charity took on full responsibility for the Observatory and Administration building in 2009, including maintaining and operating the largest optical telescope in Canada. “We’re honored by this incredibly generous gift,” says Paul Mortfield, President of RASC Toronto Centre. “Fred DeGasperis was very supportive of our work at the DDO and our commitment as stewards of the Observatory and telescope. We will always be grateful for the confidence he showed in us.”

The historic buildings will continue to be a centre for education and science literacy for the community.

For the last six years RASC Toronto Centre member volunteers have managed the facility and provided hundreds of award-winning educational and outreach programs to York Region families and students. They’ve done so without the use of local tax dollars.

Centre members say they’re looking forward to working collaboratively with the town on new programs and projects that will continue to benefit town residents.

Please see the announcement on www.theDDO.ca for more information.