First gas molecules from an interstellar comet detected
Astronomers from Europe, the United States, and Chile have identified the first gas molecules from a comet originating from outside the solar system. Using ground-based telescopes trained on the interstellar comet 2I/Borisov as it passes through the inner solar system, the scientists have detected traces of cyanogen in the comet's coma or atmosphere.
First seen by by Gennady Borisov at the MARGO observatory in Nauchnij, Crimea on August 30, 2019, 2I/Borisov is the second interstellar object detected passing through the solar system, but unlike its predecessor, 'Oumuamua, it's been identified as a comet because telescopic images show it to be a small, icy object with a coma of gas that gets larger and denser as it approaches the Sun.
Like 'Oumumua, 2I/Borisov was confirmed within 12 days of discovery as coming from outside the solar system because its trajectory is hyperbolic with a velocity of 93,000 mph (150,000 km/h), as well as being at a very high angle relative to the ecliptic. However, 2I/Borisov is different in that it was detected far enough away on its inboard journey for astronomers to mount a campaign to study it properly.
According to Professor Alan Fitzsimmons of the Astrophysics Research Centre, Queen’s University Belfast, this provides an opportunity to learn about the interstellar comet's composition. Using the William Herschel Telescope on La Palma in the Canary Islands, Fitzsimmons and his colleagues began observations on September 13, but it wasn't until September 20 that the comet was high enough in the morning sky to capture spectrographs of the light coming from it.
The discovery of cyanogen is interesting because it's relatively common in comets in our solar system and is quite famous for causing panic in 1910 when the gas was detected in the tail of Halley's comet, which the Earth was set to pass through. A rather irresponsible claim by the astronomer Camille Flammarion that this would kill all life on Earth sparked mass buying of gas masks and "comet pills" – all pointless because the amount of cyanogen in a comet's tail is so tenuous as to be indistinguishable from a vacuum.
However, by comparing the spectrographs taken at La Palma with filtered images from the TRAPPIST-North telescope in Morocco, the team was able to estimate the amount of dust in the coma, as well as the upper limit of 2I/Borisov's size.
According to the astronomers, 2I/Borisov is unusually active, which is to be expected from a comet that hasn't been close to a star very often, and that it seems to be about 4.6 billion years old. This makes it as old as the comets in our solar system, which is interesting for a stranger to these parts that had a different origin.
"The next year is going to be extremely exciting, as we will be able to follow 2I's evolution as it zooms through our solar system," says Dr Oliver Hainaut from the European Southern Observatory. "In comparison, we had only a few weeks to study 'Oumumua before it became too faint."
The research was published in The Astrophysical Journal Letters.
Source: Queen's University Belfast