by How do you tell the difference between a spaceship and a space rock?
For astronomers like me, this question became complicated — so trivial that it was only a matter of time before we had the first recorded, named interstellar object. ‘Oumuamuaseen passing through the inner solar system in 2017.
Astronomers once thought that anything moving at its own speed, with no apparent means of propulsion, must be artificial technology. We knew how ‘Oumuamua should behave if it was an interstellar space rock, or so we thought, but in every way it behaved quite the opposite.
Related: ‘Oumuamua: Solar system’s 1st interstellar visitor explained in photos
As ‘Oumuamua went through the Solar system, we only had a few weeks where we could monitor it with our telescopes around the world. These observations showed that the object came from outside the solar system, and that it was extremely elongated and tumbling. ‘Oumuamua did not show any comet-like tail though moved under his own drive.
Comets they also move under their own propulsion, but show beautiful tails caused by dust and ice blown from their surfaces, which also cause rockets to recoil. ‘Oumuamua was different. Its mysterious flight through our solar system prompted whispers of an artificial base. Some astrologers even He is called Rama.
The real explanation, which we determined from its motion and the amount of energy it received from the sun, is just as strange: an entirely new kind of object. We call them “dark comets”. Since we saw ‘Oumuamua, a population of seven dark comets has been hidden among our solar system. asteroids. They get their name because they move like a comet, but show no dust tail.
Visitors from outside the solar system – interstellar travelers – have long been predicted by science fiction writers as Arthur C. Clarke, but in reality, it is not so easy to identify what we are seeing – or just how many interstellar space rocks, or spacecraft, are in the vicinity of Earth at a given time. This difficulty arose as we rushed to make sense of ‘Oumuamua, but with new telescopes such as the James Webb Space Telescope (JWST) and the upcoming Space and Time Legacy Survey from the Rubin Observatory (LSST) in Chile’s Atacama Desert, we will have the tools we need to make sense of future interstellar travelers — and expand our understanding of the cosmos.
If only JWST had been with us when Oumuamua was discovered, we would have been able to take more detailed images of the object and get information about what it looked like in different wavelengths of light. By doing this, we could better understand what was being driven through space. We would have seen molecules like water or carbon dioxide that only show up at certain wavelengths and don’t reflect sunlight. We often see ordinary solar system comets drifting by as their surfaces heat up as water and carbon dioxide ice turn into gas. We immediately recognized it as a dark comet-like object. The good news is that if we spot another ‘Oumuamua, we already have a JWST approved program to monitor it.
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In the future, the JWST will not be the only powerful tool in our toolkit. The LSST, due to come online in a year or so, should detect many other interstellar objects and be able to identify dark comets in our own solar system. Located in the Atacama Desert, a great place to observe the Skies, the LSST will begin scanning the entire Southern Hemisphere sky almost every night. The LSST will be able to see much fainter objects than any of our surveys that currently monitor the whole sky for fast-moving objects. It will be able to detect mysterious objects like ‘Oumuamua which are dimmer, because they are smaller or further away from the World. The LSST will also be able to find many more smaller asteroids, and will be able to see if they are dark comets as they move under their own propulsion.
It is possible that when the LSST gives first light, we will begin to detect interstellar objects on a monthly – or even weekly – basis. Some of these may be dark like ‘Oumuamua, and some may be brighter with beautiful tails, like the second interstellar comet, 2I/Borisov.
It could happen that the sky close to Earth is full of interstellar objects even smaller than ‘Oumuamua, all of which have been invisible until now. These little interstellar visitors may be whirring continuously through Earth’s neighborhood within the solar system. If that eventually happens, the LSST could see an interstellar target close enough for a dedicated space mission.
Close contact with an interstellar visitor will no longer be a subject reserved for science fiction writers.
With the LSST and JWST, we have the tools to distinguish the difference between the smart visitor and a dark interstellar comet. Let’s get fooled.
Darryl Seligman is a research associate in the Department of Astronomy at Cornell University. His research focuses mainly on planetary science and theoretical and computational astrophysics.
