Oort Cloud news: How many comets from elsewhere?

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Oort Cloud News: Blurry blue light with a blurry plus dimmer gas cone around and behind it.
Comet Borisov, spotted in 2019, was a visitor from another solar system. It is the 2nd known interstellar object and the 1st known interstellar comet. But could there be billions of additional interstellar comets in the Oort Cloud? Image via NASA / ESA / D. Jewitt (UCLA).

News from the Oort Cloud

Astronomers imagine the Oort cloud as a cloud of comets on the far outskirts of our solar system. Dutch astronomer Jan Oort theorized its existence in 1950. He stated that long-period comets are sometimes driven from their distant orbits in the Oort cloud (possibly by the passage of stars). This is how they end up in orbits that bring them closer to our sun. If it exists, Oort thought, this cloud of comets is made of material from the formation of our solar system 4.5 billion years ago. But is it? Scientists now generally agree that billions of comets must reside in the Oort Cloud. But what fraction of these comets could have come from other star systems? This week (August 22, 2021), two scientists said the answer could be … most of them.

The two scientists are Amir Siraj and Avi Loeb, both from Harvard. Loeb is also the author of Extraterrestrial, the First Sign of Intelligent Life Beyond Earth, which proposes that the first known interstellar visitor (1I / ‘Oumuamua), could have been a artificial object, made by an advanced alien civilization. The peer-reviewed journal Monthly notices from the Royal Astronomical Society published the new study of these scientists on the Oort cloud on August 23, 2021.

The study focuses on an area of ​​space that is between 1,000 and 100,000 times the distance from Earth to our sun. In fact, some astronomers estimate that the Oort Cloud can extend up to a light year from our sun. In contrast, the star closest to our sun is about 4 light years away.

Comet Borisov, the first interstellar comet

Astronomers spotted the first known interstellar object, ‘Oumuamua, in 2017. In 2019, they spotted a second object in interstellar space. It looked more like a comet. Astronomers call it 2I / Borisov, or sometimes just comet Borisov. Traveling at 110,000 miles per hour (177,000 km / h), Comet Borisov passed closer to the Sun and Earth in December 2019, displaying a tail 14 times the size of Earth. Then he left for interstellar space.

It was information from Comet Borisov that allowed Siraj and Loeb to speculate that the Oort Cloud is mostly made up of interstellar visitors. Scientists admit that information on Comet Borisov still contains a certain degree of uncertainty. But, even with these uncertainties, the scientists said their calculations show that there are more interstellar objects than solar system objects in the Oort Cloud. Siraj commented in a statement:

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 that there should be fewer visitors than permanent residents. Now we are seeing that there could be a lot more visitors.

Interstellar objects are dark and distant

If the Oort Cloud may contain billions of interstellar objects, why haven’t we seen more? Siraj said it’s because we don’t have the technology to see them yet. First consider how far away the Oort Cloud is. The Earth-Sun distance (93 million miles, or 150 million km) is called the astronomical unit (AU) of the sun. Tiny Pluto is about 40 AU from the sun. Even smaller comets in the Oort cloud are about 1,000 to 100,000 AU. But remember that comets do not shine by their own light. They only reflect the light of our sun. So a comet in the Oort cloud, interstellar or otherwise, is just too far from the sun, too faint, and too small for us to see directly. So we only see comets – and speculate on an Oort cloud – thanks to those comets that are dislodged from the Oort cloud and rush into our part of the solar system.

Solar system diagram with large and far right Oort Cloud.
The Oort Cloud is so far from the Sun that its existence is still hypothetical (although it is logical to believe that it exists). The cloud is visualized as extending from 1,000 times the Earth-Sun distance to about 100,000 times that distance. Image via NASA.

Could there be interstellar objects closer to Earth?

Matthew Holman, former director of the Center for Astrophysics Minor Planet Center, who was not involved in the research, questioned whether the abundance of interstellar visitors to the most remote regions of the solar system could translate into interstellar visitors. closer to the sun. He said:

These results suggest that the abundances of interstellar cloud objects and Oort are comparable closer to the sun than Saturn. This can be tested with current and future solar system surveys. When looking at the data on asteroids in this region, the question is: are there any truly interstellar asteroids that we just didn’t recognize before?

There are asteroids that scientists have detected but not tracked over the years. Holman reflects:

They are thought to be asteroids and then they are lost without doing a detailed examination.

Co-author Loeb added:

Interstellar objects in the planetary region of the solar system are said to be rare, but our results clearly show that they are more common than solar system materials in the dark areas of the Oort Cloud.

Future research

The Vera C. Rubin Observatory, currently under construction in Chile, is expected to help astronomers find more visitors outside of our solar system. Siraj said the new observatory:

… Blow up previous searches for interstellar objects out of the water.

The first light for Vera Rubin’s engineering camera is expected in October 2022 – and full investigative operations are expected perhaps a year later.

Also scheduled for 2022, the Transneptunian Automated Occultation Survey will operate three medium-sized telescopes at the Observatorio Astronomico Nacional in San Pedro Mártir, a mountain range in Baja California, Mexico. This system is specially designed to find small bodies on the outer edges of our solar system. Maybe that will open the door to more interstellar objects. Siraj said:

Our results show that interstellar objects can impose interesting constraints on the formation processes of planetary systems. [A large number of interstellar objects in the Oort Cloud] requires the ejection of a large mass of material [from our solar system] in the form of planetesimals. With observational studies of protoplanetary discs [disks around newly forming stars] and computational approaches to the formation of planets, the study of interstellar objects could help us unlock the secrets of the formation of our planetary system – and others.

Conclusion: Scientists’ calculations show that the majority of comets in the Oort Cloud can be interstellar objects or visitors from beyond our solar system.

Source: Interstellar objects outnumber solar system objects in the Oort cloud

Preprint at arXiv: Interstellar objects outnumber solar system objects in the Oort cloud

Via Harvard and Smithsonian Center for Astrophysics

Kelly kizer whitt

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About the Author:

Kelly Kizer Whitt has been a science writer specializing in astronomy for over two decades. She started her career at Astronomy Magazine and has regularly contributed to AstronomyToday and the Sierra Club, among others. Her children’s picture book, Solar System Forecast, was published in 2012. She also wrote a dystopian young adult novel called A Different Sky. When not reading or writing about astronomy and gazing at the stars, she enjoys traveling in national parks, creating crosswords, running, playing tennis, and paddleboarding. Kelly lives with her family in Wisconsin.

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