On the hunt for exomoons, the next frontier of planetary exploration

There is a planet on the outskirts of our Solar System that has 79 moons.

He is named after a god, Jupiter, and he deserves it.

The god of gods in Roman mythology was jealous and vengeful.

In the recycling of his name as a planet, I am not sure if it is possible to speak of toponymy outside the Earth, it is simply that, a planet.

Of course, the largest we have at home, so wearing the name of a god fits like a glove.

Jupiter has so many satellites that some have not yet been officially named, specifically 23 of them.

Among the moons of Jupiter that do have a name, we can find the lesser-known Thyone, Adrastea, Isonoe or Kale and also the famous Europa, Ganymede, the largest in the Solar System, or Io, the one with the volcanoes.

If the mere presence of a moon fascinates us on Earth, we can fantasize what the night sky would be like on the surface of our giant neighbor: a sky crossed by natural satellites of different colors and sizes, and with recurrent alignments.

Imagination is an important part of the multiple abilities of the brain and since in summer the nights are short and invite us to look at the sky, let us dream what it would be like to have a planet with as many moons as Jupiter or as Saturn with its more than 60.

But where do so many moons come from?

From what we know to date, the process of the formation of a satellite around a planet is similar to that of the construction of a planet orbiting a star, both growing in the disk resulting from the process of formation of the larger body.

Although in the case of the moons they can also be created from a giant collision as in the case of ours.

Or they may have been captured.

This seems to be the origin of Triton, a captivating satellite that orbits the planet Neptune.

Triton has an orbit that rotates away from the planet and this, together with its chemical composition, which is similar to that of Pluto, suggests that we are dealing with an object that has possibly been bound by Neptune's gravitational field and that Originates from the so-called Kuiper belt

The fact is that in the Solar System there are hundreds of natural satellites orbiting, above all, the giant planets.

But outside of our system we still do not have any moons, exomoons, confirmed even though they could be around the thousands of exoplanets that we have managed to detect in recent years.

The search for exomoons continues.

The problem is that its detection is complicated.

The most prolific technique for detecting exoplanets is that of transits.

This is how most of the confirmed planets to date have been discovered (see Kepler for example).

The method involves pointing a telescope at the star, either on the ground or in space, and waiting for something to pass by.

Obviously, it is easier to measure something that passes in front of it when it is large with respect to the body it hides and is in the same plane.

In the same way that it is more likely that it was your grandmother, and not a fly, that has spoiled you more than one highlight while watching your favorite show on television.

Although both have always passed the same distance from the television and there are on average many more flies than grandmothers, your grandmother is, hopefully,

or.

The detection of exoplanets by this transit technique works best when the orbit of the large object is also close to the star, that is, when its orbital periods are short.

We have an extreme example in the total occultation that occurs in an eclipse.

A planet like Saturn takes 29.4 Earth years to go around the Sun, that is its period.

Obviously, detecting the signal of transiting Saturn from a distant planet would be much more difficult than doing it if it were placed at the distance that the Earth is from the Sun that has a period of one year (terrestrial, obviously).

Continuing with the example of the grandmother: if you had a huge house like a famous soccer player (here I assume that they are the only ones who make enough money in this country to have a big house) and your grandmother passed away from the television, you would not see her,

The problem with detecting moons in transiting exoplanets is that it is precisely in these long-period planets where the moons are expected to be more abundant, but not due to considerations of similarity with the Solar System but rather due to dynamic effects.

We think that the giant planets form with high probability far from the star, beyond the ice line.

But then you can get closer to the star.

When the planet migrates in the protoplanetary disk until it is in the closest orbit where we detect it by transits, the planet's gravitational sphere of influence decreases, causing it to lose its moons.

The moons become unstable or are either ejected or collide with the planet.

The giant planets that we detect most easily by transits were not born where they are, they had to migrate and the fate of the moons of a giant planet that is close to the star depends on the migration history of the planet.

If moons are detected around a planet with a small orbit around its star, it is very likely that it is not a moon that formed with the planet, but that it has been captured in the migration process.

The first candidate exomoon orbiting the planet Kepler-1625b would be the size of Neptune and was detected using the Hubble telescope, although further analysis of the data seems to rule out its existence.

Another candidate is Kepler-1708 bi, which would be twice the size of Earth.

We continue to search very carefully.

Eva Villaver

Cosmic Void

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