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Comet 2I/Borisov. Credit: NASA/ESA/J. DePasquale (STScI)

We might be getting interstellar visitors more often than we thought

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Aug 31, 2021, 9:20 PM EDT

When will the next ‘Oumuamua or Borisov fly by? Maybe sooner than you think.

‘Oumuamua is something of an anomaly because we don’t know where it came from, and it whizzed by too fast for close observations. However, strange comets like 2I/Borisov — and other weird things from beyond — are actually interstellar trespassers. They formed in other star systems and ended up in the Oort cloud at the edge of the solar system. These might seem rare, but are more likely to visit the inner solar system than we previously thought.

Harvard astronomer Amir Siraj, a simultaneous undergrad and graduate student who recently led a study published in Monthly Notices of the Royal Astronomical Society Letters, believes Oort cloud objects are everywhere. We just haven’t seen them yet.

“Interstellar asteroids in the inner solar system should be rare,” he tells SYFY WIRE. “However, they are discernible from solar system asteroids by their high speeds relative to the Sun. If the orbital eccentricity is greater than one, the object is from outside of the solar system.”

The Oort cloud is a cosmic junkyard of leftover wreckage from the formation of the solar system and other parts of the universe, and is thought to have accumulated more interstellar than domestic debris over the eons. There’s just one problem: It is so far away that even ‘70s relic Voyager 1, which left the solar system forever in 2013, would take 300 years to reach it. Humans obviously don’t have that kind of time. What can make up for that are calculations that can tell us around how many Oort cloud oddities may end up visiting us in the future.

To figure that out, Siraj and co-author Avi Loeb came up with an estimate of how many interstellar comets take a vacation to the inner solar system. It was similar to how astronomers got an idea of how many ‘Oumuamua objects are flying around. Their calculations were based on the distance that Borisov was observed at, which was within around 200 million miles of the Sun, and the probability for a single detection of any interstellar object. Analysis of gravitational focusing effects (a boost in the chances two objects will collide) was also involved.

Seeing how gravitational focusing could possibly affect objects coming in from the Oort cloud could affect how many actually make it, since two hunks of ice or rock could smash into and destroy each other. Siraj and Loeb looked at the chances of such an event between interstellar objects or Oort cloud comets depending on their distance from the Sun.

“We concluded that, in the outer reaches of the solar system, and even considering the large uncertainties associated with the abundance of Borisov-like objects, transitory interstellar comets should outnumber Oort cloud objects,” Siraj says.

So much space garbage in the Oort cloud is an indication that planetary systems don’t exactly have the most efficient ways of forming. Though systems like our own somehow end up with planets and moons in steady orbits around one or more stars, they have to trash tons and tons of material to get there. That trash could be a scientist’s treasure. Though we can’t exactly launch anything that far and expect to still be alive when it reaches the Oort cloud, identifying and studying objects that do make the journey could tell us about the dawn of time.

Take Borisov as an example. Observations of the comet from NASA’s Hubble Space Telescope and the Atacama Large Mllimeter/submillimeter Array (ALMA) revealed that its composition was rather weird. Because it had higher levels of carbon monoxide than any comet previously seen at the distance it was spotted at, that was taken to mean that it either broke off a planetoid rich in carbon monoxide or formed around a red dwarf star. Red dwarves are smaller and cooler than the Sun, which makes many planets that orbit them ideal for alien hunting.

In the near future, Siraj looks forward to the Transneptunian Automated Occultation Survey (TAOS II), which could actually go online this year. Its vision will extend to the no-man’s land at the outer extreme of the solar system. That and the Vera C. Rubin Observatory could identify distant Oort cloud objects that would otherwise be nearly impossible to see in the darkness.

“TAOS II will hopefully allow us to detect distant objects that might be interstellar,” Siraj says. “The Vera C. Rubin Observatory will vastly increase the discovery rate of interstellar objects near the Earth, which will revolutionize our understanding of their nature and their origins.”

Could that eventually lead to an understanding of the origin of life? Anything might be lurking out there.