In 2017, astronomers and the world were surprised to learn that an interstellar object (named ‘Oumuamua) passed by Earth on its way to the outer Solar System. After multiple surveys were conducted, scientists were left scratching their heads as to what this object was – which speculation ranging from it being a comet or an asteroid to comet fragment or even an extra-terrestrial solar sail!
But one of the greatest takeaways from that event was the discovery that such objects pass through our Solar System on a regular basis (and some stay). And as it turns out, astronomers with NASA, the ESA, and the International Scientific Optical Network (ISON) announced the detection of what could be a second interstellar object! Could this be ‘Oumuamua 2.0? And if so, what mysteries might it present?
The new object has been designated C/2019 Q4 (Borisov) in honor of Gennady Borisov, an astronomer with the Crimean Astrophysical Observatory who first detected the object on August 30th. NASA’s Scout system, which monitors newly-discovered asteroids and comets as part of the Center for Near-Earth Object Studies (CNEOS), indicated that it had an unusual orbit shortly thereafter.
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A few days later, famed astronomer Marco Micheli – from the ESA’s Near-Earth Object Coordination Center (NEOCC) – managed to obtain images of the object through ISON. Micheli, who is credited with the discovery of multiple NEOs, also conducted several measurements of the object’s position using data provided by the Canada-France-Hawaii Telescope (CHFT) in Manua Kea, Hawaii.
The ESA is now analyzing all available data and planning more observations in order to get a better idea of the object’s path and its origin. But based on its eccentricity, it seems likely this object could be an interstellar visitor, though that remains to be said conclusively. As Micheli explained:
“We are now working on getting more observations of this unusual object. We need to wait a few days to really pin down its origin with observations that will either prove the current thesis that it is interstellar, or perhaps drastically change our understanding.”
At this point, what is known is that C/2019 Q4 is a relatively large and active comet that measures a few km in diameter. It is expected to make its closest approach of the Sun in early December, reaching a distance of about 300 million km (186 million mi) or just over twice the distance between the Earth and the Sun (2 AU). This distance will place it outside of the orbit of Mars, and therefore doesn’t fit the definition of Near-Earth Object (NEO).
Assuming C/2019 Q4 is a comet, it will begin to outgas once it reaches the closest point in its path around our Sun. This will be caused by temperature increases on its surface, causing its frozen volatiles (i.e. water, carbon dioxide, methane, ammonia) to sublimate and be released. Astronomers will be able to confirm that the object actually is a comet based on the halo (or “tail”) that will result.
Since comets are known to remain stable up to a distance of about 3 AU (448.8 million km; mi) from the Sun, it is fair to say that C/2019 Q4 should experience outgassing. This is where ‘Oumuamua began to confound scientists, which experienced no outgassing despite reaching a distance of 38.1 million km (23.7 million mi) from the Sun.
Nevertheless, it managed to accelerate on its way out of the Solar System, which was consistent with the behavior of a comet. This is what led some scientists to consider that ‘Oumuamua might actually be an artificial object, or at the very least, a celestial object that human being had never before encountered. This is what makes interstellar objects such a prize.
It is little wonder then why scientists are so excited that another interstellar object appears to have entered our Solar System. It is also why many are looking for low-cost, rapid-deployment concepts for spacecraft that could rendezvous with and investigate these objects. If only C/2019 Q4 arrived in our Solar System a few years from now, the ESA’s ‘Comet Interceptor’ mission would be able to do just that.
This mission is part of the Cosmic Vision Program, the ESA’s long-term vision for space exploration that includes “fast-class” missions capable of rendezvousing with transient phenomena (like comets). The Comet Interceptor proposal (inspired by ‘Oumuamua) envisions three spacecraft that will be the first to visit a comet or interstellar object as it begins making its way to the inner Solar System.
In any case, should further observations show that C/2019 Q4 is indeed interstellar in origin, it will mean that our Solar System has been visited by at least two such objects in as many years. This would indicate that such bodies are far more common than previously thought, which also means we’ll have plenty of opportunities to study them in the future!
Further Reading: ESA