“Now that Cheops has observed its first target, we are one step closer to the start of the mission science,” says physicist Kate Isaak, ESA Cheops project scientist, about the mission to observe bright stars that are already known to host alien worlds that are larger than Earth and smaller than Neptune, by measuring minuscule brightness changes due to the planet’s transit across the star’s disc. “This beautifully blurred image carries the promise of a new, deeper understanding of worlds beyond our Solar System.”
“After two decades of planet discoveries, with CHEOPS we enter the era of exoplanetology, delving into the physical and chemical properties of planetary systems beyond our own,” says Didier Queloz, chair of the CHEOPS science team, from University of Geneva, Switzerland.
“By targeting known systems, we know exactly where to look in the sky and when in order to capture exoplanet transits very efficiently,” says Willy Benz, CHEOPS principal investigator at the University of Bern, Switzerland. “This makes it possible for CHEOPS to return to each star on multiple occasions around the time of transit and record numerous transits, thus increasing the precision of our measurements and enabling us to perform a first-step characterization of small planets – in the Earth-to-Neptune size range.”
“The first images that were about to appear on the screen were crucial for us to be able to determine if the telescope’s optics had survived the rocket launch in good shape,” explains Benz. “When the first images of a field of stars appeared on the screen, it was immediately clear to everyone that we did indeed have a working telescope.
One of the first images taken by CHEOPS of its target star above, taken after its cover was opened. This star is 150 light-years from Earth. (ESA/Airbus/CHEOPS Mission Consortium)
The Cheops telescope deliberately delivers defocused images of a target star onto the detector – a charge-coupled device, or CCD – in order to distribute the light from each star over many pixels. This makes the measurements of starlight more precise, as they are much less sensitive to small differences in the response of individual pixels in the CCD and to variations in the telescope pointing.
Having a precise measurement of the stars’ brightness and its variation is of critical importance to the scientists striving to learn as much as possible about the planets known to orbit those stars. A planet transiting in front of a star in Cheops’ view causes the star to dim – a barely detectable dip that can reveal key information about the planet’s properties, most importantly its size.
Over coming weeks, teams at the Mission Operations Center in Torrejón, near Madrid, Spain, together with colleagues from the Universities of Bern and Geneva, Switzerland, will conduct an extensive series of tests on Cheops’ instrument and detector to characterize their in-orbit performance. The same tests will be used to confirm that the scientific data taken by Cheops is processed appropriately.
Launched on 18 December 2019, Cheops is ESA’s first mission dedicated to the study of exoplanets. Rather than search for new planets, the mission will follow up on hundreds of known planets in orbit around bright stars, with sizes smaller than Saturn’s, that have been discovered by other methods.
Cheops will observe individual stars as a planet transits in front of them and blocks a fraction of the starlight, using the dip in the light level to measure the planet’s size with exquisite precision. By combining these very accurate and precise sizes with existing measurements of planet masses, it will be possible to determine the bulk densities of large numbers of planets in the size range between Earth and Neptune, which provide vital clues to the planets’ composition and structure. This first-step characterization is a critical step towards understanding how these small extrasolar worlds form and evolve.
Routine science operations, during which Cheops will observe many hundreds of exoplanet transits, are foreseen to start at the beginning of April.
Cheops is an ESA mission implemented in partnership with Switzerland, with important contributions from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden, and the United Kingdom.
The Daily Galaxy, Sam Cabot, via ESA