Hunting for exomoons, the next frontier of planetary exploration | cosmic void

Hunting for exomoons, the next frontier of planetary exploration |  cosmic void


There is a planet on the outskirts of our solar system which 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 its name as a planet, I do not know if it is possible to speak of toponymy outside the Earth, it is simply that, a planet. Of course, the biggest one we have at home, so wearing the name of a god fits him like a glove.

Jupiter has so many satellites that some have yet to be officially named, in particular 23 of them. Among the moons of Jupiter that have a name, we can find the lesser known Thyone, Adrastea, Isonoe or Kale but also the famous Europe, Ganymede, the largest in the Solar System, or even Io, the one with volcanoes. If the mere presence of a moon fascinates us on Earth, we can imagine what the night sky would be like on the surface of our giant neighbour: a sky crossed by natural satellites of different colors and sizes, and with recurring alignments. Imagination is an important part of the multiple capacities of the brain and since in summer the nights are short and invite us to look at the sky, let’s dream what it would be like to have a planet with as many moons as Jupiter or as Saturn with its over 60.

But where do so many moons come from? From what we know so far, the process of forming a satellite around a planet is similar to building a planet orbiting a star, with both growing in the resulting disc of the process of forming the larger body. Although in the case of moons, they can also be created from a giant collision as in the case of ours. Or they may have been captured. This appears 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 may have been bound by the gravitational field of Neptune and which originates from the so-called Kuiper belt, a concentration of minor bodies beyond the Neptunian orbit.

The fact is that in the solar system there are hundreds of natural satellites in orbit, especially around the giant planets. But outside our system we still don’t have any confirmed moons, exomoons, 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 planets confirmed 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. Obviously, it is easier to measure something passing in front of it when it is large compared to the body it hides and it is in the same plane. In the same way that it is more likely that your grandmother, and not a fly, spoiled you more than one highlight while watching your favorite TV show. Although both of them have always passed the same distance from the television and there are on average many more flies than grandmas, your grandmother is hopefully taller and if not, you have a pest problem at home jurassic parkThat is.

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 during an eclipse. A planet like Saturn takes 29.4 Earth years to go around the Sun, this is its period. Obviously, detecting Saturn’s transit signal from a distant planet would be much more difficult than doing so if it were placed at the distance between Earth and the Sun which has a period of one year (terrestrial, obviously). Let’s continue with the grandmother’s example: if you had a huge house like a famous footballer (here I’m guessing they’re the only ones making enough money in this country to have a big house) and your big -mother died of television, you wouldn’t see her, let’s remember that she must also be far from you and on the same plane, that we be, let’s not lose the thread, speaking of exoplanets that are at great distances from us.

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

We believe that giant planets form with a high probability far from the star, beyond the ice line. But then you can get closer to the star. As the planet migrates through 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 ejected or collide with the planet.

The giant planets we most easily detect by transits weren’t born where they are, they had to migrate, and the fate of the moons of a giant planet near the star depends on the planet’s migration history. . If moons are detected around a planet with a small orbit around its star, it is very likely that it was not a moon that formed with the planet, but was captured during the migration process .

The first candidate exomoon orbiting the planet Kepler-1625b is believed to be the size of Neptune and was detected using the Hubble Telescope, although further analysis of the data appears to rule out its existence. Another candidate is Kepler-1708 bi, which is said to be twice the size of Earth. We continue to search very carefully.

Eve Villaver She is a researcher at the Center for Astrobiology, dependent on the Higher Council for Scientific Research and the National Institute of Aerospace Technologies (CAB/CSIC-INTA).

cosmic void it is a section in which our knowledge of the universe is presented qualitatively and quantitatively. It aims to explain the importance of understanding the cosmos not only from a scientific point of view but also from a philosophical, social and economic point of view. The term “cosmic vacuum” refers to the fact that the universe is and is, for the most part, empty, with less than one atom per cubic meter, while in our environment, paradoxically, there are quintillion atoms per cubic meter, which invites us to reflect on our existence and the presence of life in the universe. The section is made up Pablo G. Perez Gonzalezresearcher at the Center for Astrobiology; Patricia Sanchez Blazquez, full professor at the Complutense University of Madrid (UCM); Yes Eve Villaverresearcher at the Center for Astrobiology.

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