In 2017, the interstellar object known as ʻOumuamua – the first ever to pass through the Solar System – took astronomers by surprise, leaving little time for in-depth study and even giving rise to speculation as to its alien origins.
Luckily for science, on 30 August 2019, an amateur astronomer from Crimea named Gennady Borisov spotted another interstellar object, likely a comet – dubbed C/2019 Q4 (Borisov) (or “gb00234”) – now estimated to cross the Solar System’s orbital plane on 26 October.
Update: The object has been officially named 2I/Borisov by the International Astronomical Union.
The object – with a core diameter between 2 and 16 kilometres – is currently travelling at a speed of roughly 150,000 kilometres. Scientists estimate that it will get no closer than 300,000 kilometres to Earth and will eventually leave the Solar System, possibly by way of Mars.
A new image of the object recently snapped by the Gemini Observatory in Hawaii confirms it to be surrounded by a cloud of dust, which provides further evidence of its interstellar origins, and might help researchers find out more about its composition from a distance.
“Both orbital and morphological properties of this body show that this is the first certain case of an interstellar comet,” wrote the authors of a study (currently awaiting peer review, but available on ArXiv) which examined the data provided by Gemini Observatory and a group of Spanish astronomers from La Palma.
Most of the work is currently focused around finding out whether the comet has an orbit that’s elliptical (oval-shaped and around the sun) or hyperbolic (checkmark-shaped and on an open-ended trajectory. In particular, researchers are now trying to determine the object’s eccentricity (i.e., the extremity of its orbit).
“The error indicates it’s still possible that’s within the Solar System,” said Olivier Hainaut, an astronomer from the European Southern Observatory. “But that error is decreasing as we get more and more data, and the eccentricity is looking interstellar.”
According to the team from the Gemini Observatory, their data shows the object’s eccentricity is at least 3, which is strongly suggestive of interstellar origins, considering that objects from within the Solar System typically have eccentricity measurements below 1.
C/2019 Q4 is estimated to reach peak brightness in December of 2019 and become too dim to see by early 2021, giving astronomers more than a full year for extensive research.
“The discovery of this object indicates that interstellar comets might be common and creates a tremendous opportunity to study the first such object in detail,” wrote the authors of the study.