Get ready for more interstellar objects, say astronomers

Gregory Laughlin and Malena Rice were not really surprised a few weeks ago when they learned that a second interstellar object had entered our solar system.

The astronomers of Yale University had just put the finishing touches to a new study suggesting that these strange icy visitors from other planets would continue to come. One can expect a few big objects to appear each year, they say; smaller objects entering the solar system could reach hundreds each year.

The study was accepted for publication in The Letters from the Astrophysical Journal.

"There should be a lot of this material floating around," said Rice, a graduate student at Yale and first author of the study. "A lot more data will be available soon, thanks to the new telescopes put online, we will not have to speculate."

The first interstellar object known to cross our solar system was Oumuamua, first seen in October 2017. Its arrival generated an intense debate about its origins and how to classify it. Laughlin, a professor of astronomy at Yale, said: "Oumuamua probably has comet-like properties, although it does not have a telltale tail called coma.

The new object, recently dubbed 2I / Borisov, came into play this summer. Amateur astronomer Gennady Borisov noticed for the first time 2I / Borisov in August and researchers will have about a year to observe the object at the telescope, a considerably longer time than the few weeks where they had to observe "Oumuamua. The new object is also bigger than Oumuamua and has a pronounced coma.

Of course, for scientists, one of the big issues arising from the appearance of interstellar objects is: "Where do they come from?" A simple answer would be that they are planetary building blocks ejected – planetesimals – from other solar systems. According to the researchers, this theory poses a problem at first glance: a thorough study of some 4,000 confirmed planets located outside our solar system shows that most of them are located too close to their parent stars. to be able to easily eject a planetsimale. The planetesimals raised by most known planets to date would remain locked in orbit in the systems where they would have formed.

So where do the interstellar objects come from?

The work of Rice and Laughlin suggests for the first time that interstellar objects could be materials ejected from large new planets, orbiting farther from their sun, which have dug deep gaps in the cosmic plateaux of gas and dust that astronomers call "protoplanetary disks".

When a star is newly formed, it is surrounded by a thin "protoplanetary" disk and rotating consisting of dense gas and dust. The disc is a volatile environment in which the young star warms the gases and dust, as well as its gravitational energy, resulting in movements, collisions and possibly the formation of planets.

Although most known planets form near their sun, there are some that develop much further and create large gaps in the protoplanetary disk. According to Rice and Laughlin, these more distant planets are capable of projecting materials likely to leave their domestic solar system. However, they are also much more difficult to observe than their closer counterparts, which is why few of these planets have been confirmed, the researchers said.

To test their theory, the researchers examined three protoplanetary disks from the DSHARP (High Angle Resolution Disk Substructures) project, made by a large consortium of astronomers. DSHARP focuses on the images of 20 large, bright protoplanetary disks taken by the Atacama Large Millimeter / submillimeter Array telescope in Chile.

"We were looking for records in which it was clear that a planet was there," Rice said. "If a disk contains empty spaces, such as multiple DSHARP disks, it is possible to extrapolate the type of planet that would be there, and then we can simulate the systems to see how much material has to be ejected over time. . "

"This idea well explains the high density of these drifting objects in interstellar space, and shows that we should find up to hundreds with future surveys online next year," he said. said Laughlin.

Beyond the simple novelty of noticing interstellar objects traversing our solar system, the idea of ​​observing such objects offers major opportunities to advance our knowledge of the cosmos, the researchers added.

Unlike many astronomical discoveries, in which data is observed and interpreted at enormous distances, interstellar objects provide a glimpse of a nearer part of the galaxy, they said.

"You do not look at a distant star through a telescope," Rice said. "It is a concrete material that composes the planets of other solar systems and is thrown to us. This is a totally unprecedented way to study extrasolar systems – and this field will begin to explode very soon with data. "