Planets share the same orbit?  |  Urania

Cosmic clouds of matter can coalesce to form orbiting pairs of planets. This is what the latest notes indicate.

Astronomers have discovered what are very likely two planets stuck in the process of forming in the same orbit. The theory predicts the existence of such planets, but they do not occur in the solar system and have not yet been observed around other stars. If confirmed, such sister planets could force astronomers to re-examine their models of planet formation.

Why, in principle, can planets not orbit in the same orbit, at a similar distance from their parent star? The answer is not so simple. In the solar system, asteroids orbiting the sun are common with planets, which are called Trojans. For example, we know that there are about 10,000 asteroids orbiting Jupiter, but the actual number may be in the millions. Trojans congregate at Lagrangian points, regions close to their orbits where the gravitational fields of Jupiter and the sun keep them in balance. The main regions where these bodies congregate are 60 degrees in front of Jupiter in its orbit and 60 degrees behind it.

According to the theorists, one of the newly formed Lagrangian points on the planet can also act as a gravitational magnet for the other planet, attracting dust to its surroundings, which then helps it grow faster. Although no orbital pairs of this type have been observed anywhere around the Sun, in 2018 a team of astronomers began looking for such pairs of planets around other stars. It is still difficult for us to detect exoplanets directly, so scientists have used indirect techniques to detect exoplanets – the characteristic “wobbly” motions of a star due to the gravitational pull of their planets, and the transit method, that is, observing the dimming of a certain light. The star, when a planet passes in front of its disk, is eclipsed slightly for some time. The oscillation or dip of two stars in the same time period may indicate the presence of planets orbiting side by side, or planetary pairs. But initially, nothing of the kind was found.

Scientists changed tactics over time and decided to look at the young planetary system to see if they could detect concentrated protoplanet matter in Lagrangian points. And it was the goal BDS 70a young star 370 light-years from Earth Two protoplanets in different orbits. ALMA Network in Chile has imaged the dust disk around PDS 70, revealing some holes in it. Astronomers believe that the largest of these was sculpted by two protoplanets – PDS 70 b and PDS 70 c – accumulating dust as they grew.

Olga Palsaloper-Rosa and her team analyzed archived ALMA data on PDS 70 collected between 2015 and 2018. By changing the way they process the data, the scientists were able to detect a dusty mass in the orbit of PDS 70 b, exactly where one of the Lagrangian points would be, the team reported. reports in Astronomy and astrophysics.

ALMA’s antenna array is sensitive to millimeter-sized dust, not to planets. So, for now, we can only say that there are some small objects out there. However, the team estimates that the dust cloud may have the mass of two moons, and may surround an already formed protoplanet – the orbital companion of PDS 70 b. However, it must be emphasized that the data do not fully confirm the finding, and the authors themselves allow the possibility that the results obtained may have a source in some kind of data disruption. In their opinion, it is small, because the data received from ALMA were processed by them in many different ways, and a dust cloud appeared in them each time. The final test will be to monitor PDS 70 b over the next few years to see if the planet and its dusty companion orbit in a similar way.

If confirmed, this discovery could have important implications for evolutionary models of the solar system. Theorists believe that Jupiter captured Trojan asteroids from the outer reaches of the solar system after it began moving away from the sun. This migration is thought to have disrupted the orbits of small Kuiper belt objects orbiting Neptune, causing them to get close enough to be captured by Jupiter’s gravity. However, if the Trojans did indeed form in place at Lagrangian points in the Sun-Jupiter system, they are likely made of the same primordial material as their larger neighbour, providing valuable information to planetary scientists.

A pictorial representation of the location of the Trojan asteroids (Troy and the Greek camp) in the orbit of Jupiter (Wikipedia).

In 2021, NASA launched a probe called Lucy, which will visit six Trojan planets of Jupiter starting in 2027 and investigate how similar these objects are to Kuiper belt objects. However, if some of them are more similar in structure to Jupiter, the evolution of our system will certainly require a rethink.

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Prepared by: Elisabetta Kolegoska

Illustration: In this radio image of PDS 70, the spot below the central star is a giant protoplanet. To its right is a dust cloud that may be a planet in the process of formation. Another protoplanet can be spotted to the star’s right, inside a bright ring of dust. Source: alma; ESO/NAOJ/NRAO; Palsaloper Rosa et al.

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