June 20, 2017 | ESA PLATO mission reaches next milestone in the search for exoplanets
Green light for European space telescope PLATO
PLATO adds a new chapter to the search for exoplanets
Since 1995, more than 3500 exoplanets have been discovered. Most of these planets are gas giants, similar to the gas and ice giants in the Solar System, namely Jupiter, Saturn, Uranus and Neptune. Exoplanets that are similar in size to Earth, have a solid surface and may have water are still an exception. This is mainly due to the limited possibilities for observation until now. The ESA PLATO space telescope will allow the detection and characterisation of significantly more exoplanets in the Milky Way. The image is an artist’s impression of extrasolar planets with different characteristics.
In 2009, the French space telescope CoRoT, in which DLR was also involved, discovered the CoRoT-7b exoplanet at a distance of 500 light years from Earth. It orbits its star (seen in the background) at the relatively small distance of two-and-a-half million kilometres. For comparison, Mercury, the Solar System’s innermost planet, orbits the Sun at around 55 million kilometres. CoRot-7b only needs about 20 hours to circumnavigate its host star, which places it into the ultra-short-period exoplanet category. The exoplanet has about eight times the mass of Earth and its ‘day’ side can reach temperatures of up to 2000 degrees Celsius. The planet therefore cannot have any oceans and is unlikely to support life. The PLATO mission will be searching in particular for Earth-like exoplanets.
ESA confirms PLATO mission to search for exoplanets.
DLR is leading the international consortium for the construction and scientific operation of the European space telescope.
Focus: astronomy, exoplanets, space
On 20 June 2017, the European Space Agency (ESA) gave the go-ahead for the further development of the PLATO space telescope. The German Aerospace Center (Deutsches Zentrum für Luft-und Raumfahrt; DLR) is leading the international consortium responsible for the construction and scientific operation of the space telescope. ESA's Science Programme Committee (SPC) assessed the status of the project positively and formally adopted the mission. This means that work can begin on the implementation of the spacecraft and its ground segment. Launch of the telescope is scheduled for 2026.
PLATO is Europe's next large-scale space mission; it will search for and characterise exoplanets. The primary goal of the mission is to look for Earth-like planets that show signs of having liquid water – in other words, planets that have the potential to support life. The aim is to determine the radius, mass and age of exoplanets with unprecedented accuracy.
Hansjörg Dittus, DLR Executive Board member responsible for Space Research and Technology, enthusiastically stated that "PLATO will bring us closer to answering the fundamental question of whether life exists outside the Solar System."
ESA is responsible for the construction and launch of the spacecraft, as well as for its operation. A consortium of several European research institutions will provide the payload – a scientific instrument comprised of 26 telescopes, the on-board computer, the data centre and the scientific data analysis. The To the Institute's website in Berlin will head the consortium, and will also take on joint responsibility with the DLR Institute of Optical Sensor Systems for the readout electronics of the fast telescopes, as well as for the computer on board the spacecraft. France, Italy, Great Britain, Spain and Belgium are all making important contributions to the instrument. Part of the payload development, the data centre and payload operations from 2025 are being supported by the DLR Space Administration with funds from the German Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie; BMWi). Over the past three years, the instrument consortium led by DLR has worked with ESA to develop the PLATO concept, which has now received a positive assessment. If everything goes according to plan, PLATO will be launched in 2026 on board a Soyuz 2-1b rocket from the European spaceport in French Guiana.
PLATO will observe hundreds of thousands of stars for a minimum of two years, and in doing so, will search for rocky planets orbiting Sun-like stars. According to DLR researcher and head of the PLATO instrument consortium Heike Rauer: "This scientific data will not only enable us to significantly expand our knowledge about exoplanets, but we will also learn a great deal about stars and how they evolve, and in turn, the development of our galaxy."
The PLATO mission will allow us to study the myriad of stars and planetary systems in our galactic neighbourhood. "By observing stellar oscillations, PLATO will be able to fully characterise these stars and their planets in terms of their mass, diameter and age," says Laurent Gizon, Director of the Max Planck Institute for Solar System Research and Head of the PLATO data centre. "This will revolutionise our knowledge about the development of exoplanets and their host stars."
26 telescopes on the hunt for exoplanets
The PLATO mission will be the first of its kind to house multiple telescopes on one spacecraft. The instrument consists of 26 individual telescopes, two of which have a particularly fast response time and will be used for bright stars, colour requirements, and fine guidance and navigation. Each telescope has an aperture of 12 centimetres and directs the incoming light onto its focal plane, which consists of four large-format CCD sensors. Rauer explained: "This concept and the high sensitivity of the instruments will enable us to search for and accurately characterise rocky planets that are orbiting Sun-like stars."
The spacecraft will be located at a Lagrange point; these are positions in space where the gravitational effects of two celestial bodies cancel each other out. Named after the Italian mathematician Joseph-Louis Lagrange (1736-1813), these points are locations where a gravitational equilibrium exists, giving the impression that a spacecraft is 'stationary'. The second Lagrange point of the Sun-Earth system (L2), some 1.5 million kilometres from Earth, is one location that is of particular interest for space-based astronomy. From the point of view of the telescope, the Sun is always positioned behind Earth, and Earth is always in the same direction. Looking towards the telescope from Earth, the same face of the spacecraft will always be observed, as is the case for the Moon, which reveals an almost unchanging portion of its surface to terrestrial observers.
DLR continues successful history of search for exoplanets
When we hear the name PLATO, we think of the important ancient Greek philosopher Plato (428/427 BC to 348/347 BC), a pupil of Socrates. Here, however, PLATO also stands for PLAnetary Transits and Oscillations of Stars. Using the transit method, the space telescope will be able to detect planets orbiting other stars within the Milky Way galaxy, and it will record their light curves over a prolonged period of time. This alone, however, is not enough to be able to characterise a planet sufficiently. For that, it is necessary to have full details on the stars around which these planets orbit. Asteroseismological measurements, that is the recording and analysis of the extent to which stars oscillate – similar to how seismology is used for earthquake research on Earth – will allow PLATO to also characterise those stars and more accurately determine the properties of their orbiting planets.
The first exoplanet was discovered in 1995 by two astronomers from Geneva using the telescope at the Observatoire de Haute-Provence, north of Marseille. The PLATO space telescope mission is following in the footsteps of the CoRoT and Kepler missions. In 2007, the French CoRoT mission, in which DLR was also involved, was the first mission to search for exoplanets from space. One of the exciting discoveries it made was that of the first rocky planet, CoRoT-7b, which has approximately seven times the mass of Earth and a radius 1.7 times that of Earth. NASA's Kepler mission began in 2009 and discovered around 3000 planets and thousands of planet candidates. From 2014 it has continued its search as the 'K2 mission'.
Prior to PLATO there will be two other missions – CHEOPS (CHaracterising ExOPlanet Satellite), the first small satellite mission to be undertaken by ESA, and the US mission TESS (Transiting Exoplanet Survey Satellite). CHEOPS will systematically investigate stars that are already known to be orbited by planets to determine planetary radii more accurately. TESS will search for planets orbiting around bright stars that typically have an orbital period of less than one month.
