Exoplanets: the quest for other worlds beyond our solar system

On 20 October 2022 RSC Belgium launched into deepest space with an entertaining and informative talk on 'Exoplanets or the quest for other worlds beyond our solar system' from Prof Michaël Gillon of the University of Liege. Michaël led the team that stunned the world with the discovery of seven potentially inhabitable planets orbiting the Trappist-1 star, some 40 light years from Earth.

In the talk he described some of the experiments and missions that have discovered new worlds far, far away – some with potentially Earth like characteristics. In 2017 Prof Gillon led the TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) project that was the first to detect an extrasolar multi-planetary system and this work continues in the SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) project.

Since the dawn of the Copernican revolution, the existence of exoplanets, i.e., planets in orbit around other stars than our Sun, has remained suspected but unconfirmed until very recently. It is only in the last decade of the 20th century that the first of these extrasolar worlds were found. These seminal discoveries initiated the development of more and more ambitious projects that led eventually to the detection of thousands of exoplanets, including a few dozen potentially habitable ones, i.e., Earth-like exoplanets that could harbour large amounts of liquid water -and maybe life- on their surfaces. Our most powerful telescopes will soon be able to probe the atmospheric compositions of some of these extrasolar worlds, performing maybe in the process the historical detection of the chemical signs of life many light-years away. Such a discovery would change our view of the Cosmos forever.

Gillon described our own solar system and Earth's unique place in it: in the 'habitable zone' where liquid water can exist on the planet's surface. He mentioned that the search for exoplanets has existed almost since the start of modern astronomy with Huygens making computations on the possibility to see planets orbiting other stars.

However it was not until the early 80s that the first imaging of circumstellar protoplanetary disks using the Hubble Space Telescope (HST) was possible (see above).

The first exoplanet detection was in 1992 with the first detection of a planet around a Sun-like system in 1995. This was of a Jupiter-like planet orbiting very close to its 'Sun'. These pioneering observations led to a burst of research and now over 5000 exoplanets have been catalogued.

It is probable that planets are everywhere with nearly all stars in our galaxy surrounded by a system of planets. In fact it is likely that planets are a natural byproduct of the formation of all solar systems but there is huge diversity of systems (see above). Our system format seems to be very rare and in addition to planets in solar systems a few hundred ‘free floating’ planets have been discovered; presumably ejected from their 'mother' system at some point in the distant past.

Despite the rarity of Sun-like solar systems plenty of habitable zone planets have been found (see above) and imaging is possible, which also means that spectroscopy of these exoplanets is possible (see below). Life on a planet will alter the composition of the atmosphere on a planet and therefore its spectroscopic signal.

The new James Webb Space Telescope has an infrared detector and so could detect this potential signal of life on distant exoplanets. Gillon is involved with two networks of ground-based robotic telescopes - TOSS (Transient Optical Sky Survey) and SPECULOOS - that are looking for best targets for Webb to further investigate. The TRAPPIST experiment was the prototype for the SPECULOOS robotic telescopes.

Further giant telescopes are planned to aid the search for exoplanets. After James Webb, an Extremely Large Telescope (ELT) should be operational from 2030 equipped with a 40 metre mirror that adapts to compensate for varying atmospheric conditions should be capable of directly imaging exoplanets. And then further, larger and smarter space-based systems.

Gillon believes that an answer to our search for life beyond our solar system could be close! 

Watch again

You can re-watch the webinar on our YouTube Channel or via the video embedded below.