The discovery of the first exoplanet almost 25 years ago changed our perception of the origin and evolution of the Universe and challenged the uniqueness of our own Solar System. Today, scientists from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and other organisations are using new techniques and instruments on ESA missions such as CHEOPS and PLATO to set their sights even higher – the hunt for a second Earth.
This year's Nobel Prize in Physics 2019 will be awarded with one half to James Peebles for his work on structure formation in the early Universe, and the other half to the two Geneva-based astronomers Michel Mayor and Didier Queloz, for their discovery of the first exoplanet orbiting a Sun-like star. Their 1995 publication, 'A Jupiter-mass companion to a solar-type star' (Nature, volume 378), confirmed the discovery of a planet orbiting a Sun-like star. Their findings sparked a new and rapidly-expanding area of astronomy – the search for extrasolar planets, or exoplanets. DLR has been active in this field since the beginning, specifically using space telescopes. DLR researchers extend sincere congratulations to their colleagues Michel Mayor and Didier Queloz. They will receive the famous Nobel diploma – each a unique work of art – from the King of Sweden Carl XVI Gustaf in Stockholm on 10 December 2019, the anniversary of the death of Nobel Prize founder Alfred Nobel.
The discovery by the two Swiss astronomers was based on measurements using the ELODIE spectrograph at the Haute-Provence Observatory, located approximately 90 kilometres east of Avignon, France. Since then, the number of discovered exoplanets has risen rapidly, leading to increasing calls from the scientific community for a systematic search for exoplanets using space telescopes, whose observations are not impaired by the Earth's atmosphere. The first space mission dedicated to exoplanetary research, CoRoT, was given green in the year 2000. At that time, only some 50 exoplanets had been confirmed. CoRoT was a French satellite mission with contributions from ESA and DLR. The mission led to the discovery of the first rocky exoplanet, CoRoT-7b. Prior to this, scientists had only identified 'hot Jupiters' – planets with diameters exceeding 100,000 kilometres. These planets are similar to the gas giant Jupiter – the largest planet in the Solar System – but have very short orbital periods that expose them to extremely high temperatures. DLR scientists were named alongside Mayor and Queloz in the list of authors credited with the discovery of CoRoT-7b.
The discovery of 51 Pegasi b revolutionised the field of astronomy
The detection of a planet orbiting a star located approximately 50 light years away in the Pegasus constellation – and hence named 51 Pegasi b – confirmed the beliefs of both philosophers and natural scientists throughout history that other worlds may have formed outside the Solar System. With their discovery, the two Nobel Prize confirmed this belief. But the increasingly frequent discoveries of exoplanets have raised new and exciting questions. The 4000 exoplanets discovered to date are extremely diverse. They have exotic characteristics, such as extremely short orbital periods that defy the general theories of planetary formation and evolution. One of the most fundamental questions addresses the uniqueness of the Solar System and planet Earth – the only celestial body known to harbour life.
Searching for Earth-like exoplanets with CHEOPS and PLATO
Two upcoming ESA missions, both with DLR involvement, will intensify research in this field. CHEOPS (CHaracterising ExOPlanet Satellite) – a small satellite mission under Swiss leadership – is scheduled for launch later this year on 17 December 2019. CHEOPS will characterise previously identified exoplanets (such as those discovered using the NGTS telescope system in Chile or the NASA/ESA space telescope Kepler) in more detail and search for new planets in known exoplanetary systems.
The PLATO (PLAnetary Transits and Oscillations of stars) mission is scheduled for 2026. The consortium responsible for its scientific instrument is led by Heike Rauer of the DLR Institute of Planetary Research. Equipped with 26 individual telescopes and cameras, the PLATO space telescope will be the first instrument able to identify Earth-sized planets in the 'habitable', life-friendly zone around Sun-like stars, in which water can exist in liquid form. The mission will include the detection of planets using the transit method from space as well as subsequent measurements with other telescopes. These findings will help compile a detailed catalogue of the radius, mass, age and host star of each exoplanet.
These future discoveries may include rocky planets with atmospheres, the structure and composition of which will be determined by spectroscopic transit measurements (observing the changes to the light of the star as it passes through the planet’s atmosphere). This will be the primary role of the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL), the ESA exoplanetary mission scheduled for launch in 2028.
The Nobel Prize for Physics awarded to Mayor and Queloz demonstrates that the discovery of the first exoplanet orbiting a Sun-like star 25 years ago changed our understanding of the Universe and our place in it. In the near future, scientific and technological advances and opportunities, such as the PLATO mission, will enable us to obtain further insights into the origin and evolution of our own planet. This research hopes to find out whether exoplanets in the Milky Way, or even beyond, possess the conditions required for the emergence of life and, ultimately, answer the fundamental question of whether they once harboured life or continue to do so.