Comets outside our solar system could visit us often, study finds


In the past four years, astronomers have spotted two visitors to the solar system from elsewhere in the galaxy. Both have provided an abundance of data that will be studied for many years to come – and have left scientists wanting more. A new article argues that one of those guests, Comet Borisov, represents a class of objects that we will see a lot more of in the near future, although it recognizes that the margins for error are huge.

Interstellar visitors could provide great insight into other star systems, but we need to find them first. Amir Siraj of Harvard University and Professor Avi Loeb conclude in the Royal Astronomical Society’s monthly notices that we should have plenty of opportunities.

“Before the detection of the first interstellar comet, we had no idea how many interstellar objects were in our solar system, but the theory about the formation of planetary systems suggests there should be fewer visitors than permanent residents. “Siraj said in a statement. . “Now we are seeing that there could be a lot more visitors. “

We only saw a single interstellar comet and thousands of inhabitants, which makes the idea that visitors outnumber the natives deeply counterintuitive. However, Siraj points out that the Oort Cloud extends 160,000 billion kilometers (100,000 billion miles) from the Sun in all directions. Locals congregate closer, but the vast majority of visitors will pass through its confines with no chance of being detected.

The possibility that chunks of rock and ice frequently pass beyond Neptune’s orbit is intriguing, but of limited relevance. However, the document goes further – suggesting that even in Saturn’s orbit, there may be a similar number of visitors to locals. We now detect many asteroids too far away to pose a threat and never determine their orbits. Some may be long gone by the time someone tries to follow.

Siraj and Loeb’s calculations are based on estimates of the chances of detecting a small enough object that never approaches the Sun. If we found one, there must be plenty more, and they tried to quantify it.

Borisov contained 97 percent oxygen and carbon by mass. If the authors’ estimates are correct, about 1% of these elements in the galaxy could be contained in objects floating in interstellar space, unrelated to a star.

Theoretically, the possibility of finding an interstellar comet dates back to the 18th century, when we started to trace the orbits of comets. However, with only a few not very advanced telescopes observing the sky at the time, only the brightest comets were seen – all of which had trajectories indicating they were coming from within the solar system.

There have been many improvements since then, but it wasn’t until 2017 that Umuamua made his appearance, followed by Borisov two years later. The question was obvious: Did these two findings reflect pure luck, or had there been a lot of objects like this that we didn’t have the instruments to find?

The question is likely to be answered soon, which makes this document either very prescient or very false. Loeb gained a lot of notoriety for his insistence on Oumuamua is an alien spaceship and aggressive behavior towards his colleagues. However, his work on subjects unrelated to extraterrestrial civilizations remains more respected.

The Vera C. Rubin Observatory is expected to start operating in 2022 and should transform our ability to detect moving objects of low origin, regardless of their origin. Within a few years, we should have a statistically useful sample of visitors. Even before that, the automated Transneptunian occultation survey can provide useful data.


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