Are Exomoons a Better Place to Look For Life?

Let’s talk about ExoMoons, you know, those moons in orbit around other planets around other stars in our galaxy. Is it possible that they might be better harbors for life?

Published on 9th Aug, 2018

Hello Space Fans and welcome to another edition of Space Fan News. In this episode, let’s talk about ExoMoons, you know, those moons in orbit around other planets around other stars in our galaxy. Is it possible that they might be better harbors for life? Even in our own solar system, the moons Europa and Enceladus look the most promising, even better than Mars. So, what about elsewhere? Could life be better found on an exomoon around and exoplanet around another star? So far in our search for planets around other stars, also called exoplanets, we have discovered , which means confirmed, 2,954 planets. These exoplanets come in a lot of shapes and sizes. Some are gaseous and the size of Jupiter and even bigger. Some are rocky and the size of Earth and even larger. But here’s what I find interesting, of those 2,954 planets, astronomers consider only 55 habitable. Of those, 32 are super-terran, meaning they are 5-10 times more massive than Earth and 1.5 to 2.5 times the radius of the Earth; 22 are terran-sized, which is self-explanatory, and only one, that’s right one possible habitable planet that is sub-terran, or about the size of Mars. And of those 55 possibilities, some are quite attractive. You’ve got Promixa Centaur b which is the closets, Trappist-1 e one of the strongest candidates which astro biologists put posters up above their beds and dream about at night, there’s Kepler-1652 b, Kepler-442b, TRAPPIST-1 f, the list goes on and on. But those planets are all Earth-sized and believed to be rocky, and - wait for it - they are also in the habitable zones of their hosts stars which means they might have liquid water on them if they have water, and an atmosphere, and a bunch of other things. Most of these exoplanets were discovered using data from the Kepler Space Telescope and lately, astronomers going over this data have found what they think are 121 giant exoplanets that might host habitable exomoons. The vast majority of the exoplanets we know of are huge, massive gas giants. And some of those gas giants were found in the habitable zone, and some of them might have exomoons. No actual exomoons were identified in this study, but there’s a good chance these exoplanets, all of which have a radius three times wider than Earth, feature natural satellites. And because these 121 planets reside within their star system’s habitable zone, some of these exomoons might even have the conditions required for life. Remember, in our solar system alone we have over 175 moons, and two of those look really promising for harboring life: Europa and Enceladus, maybe even Titan. So the question we should ask is, “Is it reasonable, or even likely, that life might better be found on a moon around a giant planet orbiting its star in the habitable zone?” I think it’s a good question and so did the researchers of this study led by astronomers from the University of California, Riverside and the University of Southern Queensland which looked at the 121 possibilities it found. Using Kepler data, the researchers estimated the frequency of giant planets (i.e. planets with a radius three times larger than Earth) in habitable zones. Their numbers show that about six to 12 percent of stars in our galaxy have giant planets within their habitable zones. Working with the assumption that each of these exoplanets has at least one moon, they estimate that around 121 giant planets detected by the mission could host a potentially habitable moon. And that’s being conservative—the actual number is likely much higher. I mean think about it, Jupiter has 69 known moons and Saturn hosts 62, saying there might be one isn’t stretching it. And if you think about it even more, you can see the distinct advantages life might have on an exomoon versus being on its own around the star. The exomoon could be sheltered from asteroid collisions, it could snuggle nicely inside the giant’s magnetic field protecting it from harmful radiation, the exomoon could get energy from gravitational tidal forces (that could also be a minus though). There are potentially lots of advantages for life to thrive in close quarters to a gas giant planet. The researchers coined this term ‘super-habitable’ to describe how great it could be in there. The downside? Well, exomoons are small, much smaller than their host planets and maybe too small to hold an atmosphere. Some astronomers estimate that in order to have a big enough moon, a planet needs to have 1000 times the Earth’s mass and be over 10 Earth Radii to have a Mars-sized moon and thus have be big enough to have a dense atmosphere for life. So, making those adjustments, the team estimated that among all exoplanets, not just those from the Kepler database, there might be 40 giant planets in the habitable zone that are large enough to likely hold a Mars-sized or larger moon that could be potentially habitable. Remember neither Europa nor Enceladus has an atmosphere, Titan does have an atmosphere and it’s a little smaller than Mars at 2500 kilometers vs Mars at 3400 km. So we do need large moons to get and hold an atmosphere. All this means though, that it is definitely worth taking a look at the moons around other exoplanets. It will be a while though because we don’t have anything remotely capable of seeing them yet. Exoplanets are hard enough and we’ve only just started with them. To see an exomoon around another planet around another star will require telescope we just don’t have yet. Even JWST won’t cut it, so were years away from those observations. But when we are, I’ll be sure to keep you posted. Well that’s it for this episode Space Fans, thanks to all Patreon Patrons who keep the videos coming and the advertisements turned off. I couldn’t do it without you. Do you like my shirt? I want to thank space Fan Michal from who made this and other cool shirts. If you get one, you’re helping both Michal and Deep Astronomy so check it out, there’s a link in the description box. That’s what I love about our Space Fan community, we always want to help each other out. Thanks Michal. Thanks to all of you for watching and as always, Keep Looking Up! Link to paper talked about in this episode: Consider supporting Space Fan News: to ensure you get current space & astronomy news each week! 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