Collision Between Planets May have created a new astronomical object. What will it be?

Using data from NEOWISE, a group of astronomers from Leiden in the Netherlands observed two planets colliding for the first time. The collision resulted in a new structure that had not been observed before. Furthermore, understanding this collision can give us an answer to how the Moon formed when the Earth was still young.

Collision between planets was observed by a group of Dutch astronomers
Collision between planets was observed by a group of Dutch astronomers. Credit: DALL-E3/Bing

One of the ideas for the formation of the Moon is that a planet the size of Mars may have collided with Earth in the early days of the Solar System. In addition to having originated the Moon, the collision may also have caused the Earth to be inclined causing the seasons we know today.

It is expected that in the formation of a new planetary system collisions may occur with a greater frequency. This is because the objects are still forming and different objects may end up interfering in the same orbit. Something similar is expected to have happened to Earth and a planet called Theia.

For the first time, a group of astronomers were able to observe the collision between two planets and the result that originates later. They noticed the formation of a structure that can explain why the luminosity of stars seem to weaken out of nowhere.

How does a planetary system arise?

The most accepted hypothesis today is the nebular hypothesis. In this hypothesis, unstable molecular hydrogen clouds end up collapsing into spheres that rotate to form stars. Part of the surrounding gas also collapses forming the planets.

Proplanetary discs observed by ALMA.
Proplanetary discs observed by ALMA. Credit: ALMA/ESO

Recently, ALMA was able to capture images of discs that are in the process of forming planets around a star. This process is complex and still has several open questions to explain the training.

Solar System emerging from a cloud

The Solar System is expected to have emerged from a nebula according to the nebular hypothesis. It is not yet known exactly what caused the collapse of this gas cloud. Some research suggests that the supernova of a nearby star released enough energy for the cloud collapse.

In the region, near the Sun, the rocky planets appeared: Mercury, Venus, Earth and Mars, while in the outermost region the gaseous giants appeared.

Part of the reason is that the intense gravitational effect of the Sun makes the innermost part a little more chaotic and unstable than the outermost part.This is one of the reasons why giant planets only managed to form on the outside.

The chaotic world where the Earth inhabited

In the inner part of the Solar System it is estimated that dozens and even hundreds of protoplanets have formed. With the large amount along with the gravitational interaction of the Sun, it was common for protoplanets to collide forming larger objects.

This probably happened with the protoplanet that would give rise to Earth and a proplanet called Theia. In this collision, it probably gave rise to a cloud of dust, rock and gas that later formed the Moon.

The ASASSN-21qj planetary system

After the ASASSN observatory warned about a change in brightness in the ASASSN-21qj star, the group focused attention on it. The light of the star seemed to have decreased and in addition, they found evidence that the star had increased the brightness in the infrared moments before it began to decrease.

This sudden change in brightness is not common for a star in the main sequence and similar to the Sun. This caught the attention of researchers who began to investigate a hypothesis: two giant planets crashed in front of the star.

The idea was that the collision between the two planets created the infrared peak seen previously and after the shock a structure called synestia was formed. The synestia would be a donut-shaped structure formed by remnants of the collision. The sinestation would pass in front of the star and give the impression that the brightness of the star has decreased.

A possible explanation for what happened on Earth?

Observing the collision between two planets can give us clues to what happened in the history of our own planet. Some suggest that a structure similar to synestia was responsible for the formation of the Moon.

In addition, the discovery may explain the decrease in brightness that happens in different stars. A more recent one was Bethelgeuse which decreased its brightness in 2021 and it was later found that the cause was a gas cloud passing in front of the star.

Next steps

The idea is to keep watching the next moments of the system. The group proposes to use the James Webb telescope to be able to understand the dynamics of the infrared system. Observing what will happen now can tell us what happened to our planet billions of years ago.