While not dedicated planet-hunters, space observatories with completely different mission goals have also contributed to exoplanet studies. It is an all-sky mission with the main goal of detecting small planets with bright host stars. Although it only looked at a small area of the sky, the slew of discoveries gave an indication of the vast number of exoplanets that must exist in our galaxy.The most recent NASA addition to the exoplanet-hunting fleet is the Transiting Exoplanet Survey Satellite, Tess, launched in April 2018. It looked at a fixed patch of sky for over four years, monitoring over 150 000 stars and discovering thousands of exoplanets. NASA’s 2009 Kepler mission was an exoplanet discovery machine, accounting for almost three-quarters of all exoplanet discoveries to date. More may be discovered during the post-mission data analysis. Using the transit method, CoRoT has uncovered 37 exoplanets, including the first confirmed rocky planet (though it was orbiting much too close to its star to be habitable!). The mission’s two objectives were to search for extrasolar planets with short orbital periods (of days or even hours), and to measure oscillations in stars. ESA was part of the mission by providing the optics for the telescope and testing of the payload. One of the first exoplanet-sensitive space telescopes was the CNES-led Convection, Rotation and planetary Transits mission, CoRoT (2006–13). In addition to being free of the disturbances caused by viewing through Earth’s atmosphere, satellites offer a more continuous line-of-sight visibility to the target star and round-the-clock observations. What really opened the floodgates for the discovery of exoplanets was the use of space-based telescopes. By combining the results of targeted observations and broad surveys using different techniques, we are able to build a representative picture of the diversity of exoplanets and planetary systems Astrometry requires very precise data, which is hard to obtain and thus only a handful of planets have been discovered this way.Ī few planets have been found using other techniques, including pulsar timing. We can only use one of the two methods, depending on the orientation of exoplanetary systems towards us. If we look from ‘the side’ we use the radial velocity method as we see the light of the star become redder and bluer. If we look from ‘above’ we see the star wobble around the mass centre and use the astrometry method. The difference between the radial velocity and astrometry methods is how we look at the exoplanetary systems. Using astrometry, exoplanets can be found by measuring tiny changes in the star's position as it wobbles around its centre of mass. Astrometry means tracking the motion of a star using precise measurements.
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