Our solar system has most likely had many interstellar visitors over the eons, but we’ve only managed to spot a few. The first was ‘Oumuamua in 2017, but amateur astronomer Gennady Borisov spotted the object now known as 2I/Borisov late last year. Scientists have been able to take a closer look at this object as it nears the sun, even managing to analyze its composition. And it’s pretty, well… alien.
Astronomers all over the world turned their telescopes toward 2I/Borisov in the months following the discovery, and among them was a team from NASA using the Atacama Large Millimeter/submillimeter Array (ALMA). While scientists now believe ‘Oumuamua is technically a comet, it’s very old and has lost most of the volatile materials that normally form the coma around a comet. 2I/Borisov, however, formed a bright, robust coma as it passed the sun a few months ago.
The NASA team, operating out of Goddard Space Flight Center, turned ALMA toward the comet as it made its closest approach to the sun in late 2019. Radio telescopes are ideal for probing cold, low-energy gas like the outgassing from a comet. Peering inside the coma allowed the team to gather data on the objects chemical composition — these are quite possibly the first data points from an alien solar system.
First, the team went looking for the most easily detectable gas in comets: hydrogen cyanide. Like the comets from our solar system, 2I/Borisov has plenty of that gas. The researchers were in for a surprise when they turned their attention to carbon monoxide, which is present at low levels in native comets. However, 2I/Borisov had many times more carbon monoxide than other comets.
The table above shows the distribution of carbon monoxide levels in comets. 2I/Borisov is far out in front of most objects (keep in mind this is a logarithmic scale). The object to the far right is C/2016 R2, an anomalous object spotted by the PanSTARRS observatory in 2016. Carbon monoxide is the most volatile of compounds found in comets. This suggests that 2I/Borisov formed far away from its host star, but we don’t know why it has so much carbon monoxide. That might be indicative of all comets in 2I/Borisov’s home system. It could also be a fragment of a dwarf planet that was high in carbon monoxide.
Sadly, we won’t be able to examine 2I/Borisov in greater detail to unravel the mystery. It’s moving too fast to remain in orbit of the sun — it’s already heading out into deep space again, never to be seen in our solar system again.
- Was Interstellar Visitor ‘Oumuamua Torn Apart by a Star?
- Hubble Gets Its Closest Look Yet at Approaching Interstellar Comet
- Astronomers Capture Image of Second Known Interstellar Object