5,000 exoplanets have been discovered!

The science post of the weekend with Mathilde Fontez, editor-in-chief of the scientific magazine Epsiloon, look to the sky today, because NASA astronomers have just announced that a milestone has been reached: 5,000 exoplanets have been discovered.

franceinfo: 5,000 planets that revolve around stars other than ours, Mathilde?

Mathilde Fontez: Yes, it’s a milestone. It was crossed this week: 65 of these planets were added to the list at once – their existence was validated by telescope observations. There are therefore today – precisely – 5,005 exoplanets. 5,005 worlds, which revolve around other stars.

The first exoplanet was discovered in 1995, it is called Pegasi 51-b: its discoverers received the Nobel Prize for that, in 2019. And today, we see that there are exoplanets everywhere.

5,000 expoplanets is a lot?

That’s a lot, because the statistics we draw from these detections are dizzying: in fact, all the stars, or almost, would have planets. There would be hundreds of billions of exoplanets in our galaxy.

Before observing them, before 1995, astronomers suspected that other worlds existed. Why would the other stars, the other suns, be different from ours? But in almost 30 years of observations, they have been blown away by their profusion – they are everywhere, of all kinds: gas giants, planets the size of Earth.

And even new types of planets, which do not exist in our Solar System. For example super-Earths: these are planets twice as big as ours, probably made up largely of water: 30% of the exoplanets detected are of this type. And there would be some in half of the planetary systems. Whereas in ours, there is none.

Is this diversity the great discovery?

Clearly yes. Astronomers talk a lot today about this surprise: before these observations, it was obvious to them: they were going to discover systems that resemble ours. Eight neat planets: rockies on one side, like Earth or Mars, and gas giants farther away, like Jupiter and Saturn.

While in fact not at all: all systems are very different: there are super-Earths everywhere, but also superheated planets, giants very close to their star, planets whose orbit is very inclined.

What exactly do we know about these exoplanets?

In fact, not much. Quite simply because we do not see them, for the most part. We detect their orbit, their size or their mass. But that’s all. And from that, we draw pretty artist’s views, which we don’t know at all if they are realistic. This is the challenge now: to really observe exoplanets, to know if they have an atmosphere, if they have oceans. And of course, if they could harbor a life.

For this, astronomers target the systems that are closest to Earth, the only ones we can hope to see. There is one in particular that draws attention: Trappist-1, a system discovered in 2015 by a Belgian telescope – yes, that’s why the name. It contains seven planets. It orbits 40 light-years from Earth, and the James Webb Space Telescope, which was put into orbit earlier this year, should be able to see it. This is one of his first targets…