ESA’s plans for a home amongst the stars

“There are nine planets, right?” “Wait a second, I’m pretty sure it’s eight now, RIP Pluto.” You’d be forgiven for thinking this, however, in the past 25 years, astronomers have discovered evidence of planets outside of our solar system. Many, many more in fact, than the eight sang about in nursery rhymes. We call them “exoplanets”, “exo” from the ancient Greek meaning “outside”. The European Space Agency (ESA) will launch a mission to discover such planets in the late 2020s.

It’s no surprise that these exoplanets took so long to discover. Stars have been known about for millennia, mostly for two reasons: they’re big and they’re bright. Planets, on the other hand, are usually relatively small compared to the star they orbit and also don’t emit any light for us to detect, they merely reflect light from nearby stars.

So, how do we detect them? The light reaching us from distant stars is usually pretty constant over time. Nonetheless, in 1998, scientists looked at the graph of intensity against time from a distant star and noticed it ‘dipped’. At rather regular intervals as well. It didn’t take very long for the team to deduce that what must be causing this dip in intensity, was a planet moving in front of the star, obscuring some of its light.

In 1998, scientists looked at the graph of intensity against time from a distant star and noticed it ‘dipped’

Since then, this “transit” technique has been used to detect approximately 3,800 planets outside of our solar system. Transit isn’t the only tool astronomers have for detection, however, a technique called “radial velocity” allows us to accurately describe an exoplanet’s orbit and when combined with transit, can give us an exoplanet’s mass and density.

What these techniques don’t tell us, however, is anything about what makes up the planet or its atmospheric composition. Enter ARIEL, a mission to analyse the atmospheres of planets light-years away. A €500 million ESA project with the aim of analysing how the chemical composition of a planet is related to the environment it formed in and how its birth and evolution are affected by its parent star.

Enter ARIEL, a mission to analyse the atmospheres of planets light-years away

ESA will be sending up a satellite, Plato, whose team features University of Warwick’s very own Dr Don Pollaco, in 2026 to search for “true Earths”. These are exoplanets, roughly the same size as our Earth, in the habitable zone of their star. The peaks and troughs in intensity associated with analysing an atmosphere from an exoplanet are tiny, tinier in fact than most systematic errors in satellites. As systematic errors are usually due to the moving parts in a satellite, Plato will have no moving parts whatsoever!

Could ESA and their mission enable us to find planets just like our own to blast off to when this political climate becomes just too much? I sure hope so, it really is getting rather frightening down here. Until then, however, it’ll be nice to know there’s somewhere out there in the universe, perhaps millions of light-years away, just like home.