A newly discovered comet has excited the astronomical community this week because it appears to have originated from outside the solar system.
For decades, astronomers have speculated that the space between stars may be populated by solar minor bodies — comets and asteroids. These are thought to have been ejected from their home planetary systems.
Studies have also suggested that these bodies may occasionally pass through our Milky Way Solar System and be identified thanks to their strongly open orbits. The discovery of ‚Oumuamua two years ago brought the long-awaited confirmation, sparking hopes for subsequent detections.
A team of scientists led by astronomers from the Jagiellonian University in Krakow, Poland had done their homework well ahead of time. Prompted by the earlier visit of ‚Oumuamua, they created a computer program nicknamed „Interstellar Crusher” that scanned tirelessly through online data of newly-found comets and asteroids in search of guests from far away.
It’s only the second interstellar comet ever detected in our solar system and the first that looks like a traditional comet. The first one, cigar-shaped ‚Oumuamua, which was discovered in 2017, did not resemble a comet in the usual sense.
The unusual body was spotted in August by a Crimean (Ukraine) amateur astronomer, Gennady Borisov. It was swiftly identified as an outcast from another star system and may have been wandering the Milky Way for millions if not billions of years.
“This is the first comet known to science that arrived from outside the solar system, and it is completely similar to those we see inside the solar system,” said Michal Drahus, an astronomer at Jagiellonian University in Krakow, Poland.
On September 8, 2019 at 04:15 universal time, the program issued a red alert and notified the team of a possible new hyperbolic object arriving from interstellar space. „This code was written specifically for this purpose, and we really hoped to receive this message one day. We only didn’t know when,” said Piotr Guzik of the Jagiellonian University, who led the study. A closer investigation into the object’s orbit confirmed its exosolar origin.
Two days after receiving the alert, the team was already scrutinizing their first images of the object obtained at the William Herschel Telescope on La Palma, Spain, and getting ready to receive more data from the larger Gemini North Telescope on Mauna Kea, Hawaii. With its high elevation, dry environment, and stable airflow, Mauna Kea’s summit is one of the best sites in the world for astronomical observation. Since the creation of an access road in 1964, thirteen telescopes funded by eleven countries have been constructed at the summit. The Mauna Kea Observatories are used for scientific research across the electromagnetic spectrum.
The photographs were obtained in two color bands and provided the first astrophysically significant glimpse of the body.
„We immediately noticed the familiar coma and tail that were not seen around ‚Oumuamua,” said Drahus. „This is really special and it means that our new visitor is one of these mythical and never-before-seen ‚real’ interstellar comets,” continued Drahus.
It took proper measurements before the team could determine the comet’s color and estimate its other properties. They have found that comet Borisov has a dust-dominated morphology, a reddish hue, and that its solid nucleus is about 1 km in radius. „Make of this what you will, but based on these initial characteristics, this object appears indistinguishable from the native Solar System comets,” said Guzik.
The team’s findings are being published in Nature Astronomy on October 14, 2019. However, this is only a prologue to 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,” said Waclaw Waniak of the Jagiellonian University, co-author of the study. The team still has a considerable amount of observing time reserved on the Gemini North Telescope, and they had booked a large slot on the European Southern Observatory’s Very Large Telescope well ahead of Borisov’s discovery.
Guzik added, „We can safely say that research on this body will be transformative for planetary astronomy and a milestone for astronomy in general.”
The study was conducted with significant financial support from the Polish National Science Centre as part of the SONATA BIS program. The project is part of research conducted at the Department of Stellar and Extragalactic Astronomy of the Jagiellonian University’s Astronomical Observatory.
By Raymond Rolak