Solar system’s Oort cloud may harbor an astonishing number of objects from other stars


‘Oumuamua, the first interstellar object discovered near Earth, left us with more questions than answers. The visitor was first observed upon exiting the solar system, and the limited data that astronomical observatories were able to collect has proven difficult to explain. What we do know is that Oumuamua was neither a comet nor an asteroid, and none of the exotic theories regarding its origin to date have been able to fully explain its properties.

Two years later, however, the second interstellar visitor was spotted – and he couldn’t be further from the nature of Oumuamua. Borisov bore a strange resemblance to comets from the far reaches of our own solar system, but he was traveling in a clearly hyperbolic orbit. As the first interstellar comet, Borisov’s similarities to known objects in the solar system provide an exciting opportunity never before offered by ‘Oumuamua: a direct comparison between the solar system and its cosmic neighborhood.

In a recent paper in Monthly notices from the Royal Astronomical Society: letters, we report for the first time the not very intuitive reality that the discovery of the first interstellar comet revealed: the Oort cloud, the vast reservoir of comets in our solar system, which extends halfway to the star the closest, is home to more visitors than permanent residents. Near Earth, comets originating from inside the solar system outnumber those outside the solar system – hence the fact that there has been only one definitive intruder since the first comet was detected with a telescope by Gottfried Kirch in 1680. But the observations that have been made are not representative of most places in the solar system, as they are biased by our proximity to the sun.

Due to gravitational focusing, the sun preferentially attracts comets from within the solar system, like a streetlight attracting swarms of moths. On the other hand, interstellar objects, which roam the galaxy at high speed, are almost impervious to the sun’s gravitational pull, and therefore do not cluster near the sun in the same way as objects in the Oort Cloud. Our new work shows that they are so numerous that, despite their speed, there are many more interstellar intruders in the dark areas of the solar system at any given time than there are locally produced comets.

This finding has profound effects on future observations and theories. It motivates further searches for objects in the Oort Cloud, including stellar occultation records like TAOS II which scan the sky for spots in starlight resulting from random alignments of near objects and distant stars. At the same time, the new discovery directly challenges our theoretical understanding of how planets were formed, as it implies that planetary systems must reject orders of magnitude more mass than previously thought. In fact, our new paper shows that stars may have to expel at least as much mass as they retain, a striking new constraint on the formation of the planetary system.

Future discoveries of interstellar objects will continue to inform our understanding of the solar system in its galactic context. The Legacy Survey of Space and Time (LSST) on the Vera C. Rubin Observatory, whose start of operations is scheduled for the end of 2023, should discover at least one interstellar object per month, a pace that will help us locate the origins of interstellar objects, and learn more about the formation of stars and planetary systems. The most exciting scientific revelations regarding interstellar objects, however, will likely come from the direct study of interstellar matter. What are these surprisingly abundant objects made of? Priced at a few hundred million dollars, the European Space Agency project Comet interceptor The mission might be able to sample the gas tail of an object like Borisov in the 2030s, if we approach the sun at the right time, at the right speed and in the right direction.

There is also another way to search for interstellar objects, and even obtain humanity’s first samples of matter from outside the solar system, at a relatively low cost and from the comfort of the Earth’s surface. . Any material that comes into contact with our planet’s atmosphere burns by friction with the air, briefly appearing as a trail of light across the sky: a meteor. As a result, it is much easier to find small objects in the atmosphere than in space, where we should rely on reflected sunlight. And while the atmosphere provides a much smaller search volume than expanses of space, the abundance of smaller interstellar objects should be large enough to make the search for meteors interstellar. a seductive idea.

In fact, when analyzing a publicly available U.S. government meteor dataset in 2019, I found a recorded impact that appeared to have approached far too quickly to have been tied to the solar system. I could hardly believe it, as astronomers have been looking for an interstellar meteor for 1950 or before. This discovery will be later provisionally confirmed as the first larger-than-dust interstellar meteor, and since then Pentagon officials have expressed interest in potentially declassifying error bars associated with detection, given its immense scientific value.

As director of interstellar object studies of the Galileo Project, I’m leading an effort to discover gram-scale interstellar meteorites in our atmosphere, using unclassified and transparent sensor arrays. Along with the interstellar objects the LSST will detect in Earth’s vicinity, such discoveries would revolutionize our understanding of the solar system in the context of its peers. The holy grail of interstellar meteorites is said to be a kilogram-scale or larger object that burned above the earth, as such events could leave easily recoverable meteorites, rocks that could represent the first chunks of interstellar matter ever. obtained by mankind. Such a goal could be achieved in a decade for just a few tens of millions of dollars – a budget ten times less than that of the Comet Interceptor mission – with a thousand passive camera systems all over the world distributed around the world patiently awaiting the release. proverbial needle in the sky. meteoroid from a haystack to beautify our planet.

One of the most beautiful things about the study of interstellar objects is that it connects so many disparate fields in astrophysics, ranging from planetary science to high-energy phenomena and incorporating an equally diverse array of methods to detect them. With other “multi-messenger” branches of astronomy seeking to supplement traditional methods of astronomical investigation, such as gravitational wave and neutrino readings, searches for interstellar objects could help reveal unprecedented information that challenges questioned how we understand our place in the universe.

This is an opinion and analysis article; the opinions expressed by the author or authors are not necessarily those of American scientist.

This is an opinion and analysis article; the opinions expressed by the author or authors are not necessarily those of American scientist.

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