An alien comet is now passing through our solar system. Here’s what we know
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Diverging Reports Breakdown
An alien comet is now passing through our solar system. Here’s what we know
1I/’Oumuamua (the Hawaiian word for ‘scout’) was discovered in October 2017. It is thought to be an ancient comet that lost nearly all of its ice while journeying through the galaxy. The second object, 2I/Borisov in August 2019, also came from ‘above’ the solar system, although along a different trajectory. This new interstellar object is quite different from the previous two, and is most certainly a comet, like Borisov. However, we still don’t know for sure.
The first interstellar object discovered, 1I/’Oumuamua in October 2017, was only detected after it passed around the Sun and was on its way back out into the galaxy. Analysis of its trajectory showed that it dove into the inner solar system from ‘above’, at a very steep angle, passed within the orbit of Mercury, and then slingshotted around the Sun to depart in a completely different direction.
There is still some debate about exactly what ‘Oumuamua (the Hawaiian word for ‘scout’) actually was. Observations revealed that it was likely dark red in colour, around 100-200 metres wide, and that it was either shaped like a cigar or a skipping stone, as it tumbled end-over-end passing through the solar system. It wasn’t dense enough to be an asteroid, but it didn’t behave like a comet, either. To throw some extra mystery into the event, as it departed, it even exhibited a small acceleration that couldn’t be easily explained! The most likely answer is that ‘Oumuamua was an ancient comet that had lost nearly all of its ice while journeying through the galaxy. However, we still don’t know for sure.
The paths of ‘Oumuamua and Borisov through the inner solar system. (Image courtesy Tony873004/Wikimedia Commons (CC BY-SA 4.0))
The second object, 2I/Borisov in August 2019, also came from ‘above’ the solar system, although along a different trajectory than ‘Oumuamua. Detected on its way in, astronomers watched it pass just outside the orbit of Mars before continuing on its way, only slightly deviating from its original path.
Borisov was far less mysterious, as it exhibited all the characteristics we come to expect from comets. It was on the small side, at only around 500 metres across, but it developed a large coma surrounding the nucleus, and it had a wide, puffy tail as it passed by the orbit of Mars. Borisov’s speed, trajectory, and odd chemical composition were the only aspects of the object that really set it apart from ‘home grown’ comets.
3I/ATLAS is (so far) unique
This new interstellar object is quite different from the previous two.
3I/ATLAS is most certainly a comet, like 2I/Borisov. Currently just within the orbit of Jupiter, it is already being heated enough by the Sun’s rays that a coma of gases has developed around the nucleus, and it has a short tail as well.