16. December 2019
Surveying exoplanets by size, density and possible atmospheres

CHEOPS space tele­scope to in­ves­ti­gate ex­tra­so­lar plan­ets

Artist's impression of CHEOPS, the characterising exoplanets satellite, with an exoplanet system in the background
Artist's im­pres­sion of CHEOPS, the char­ac­ter­is­ing ex­o­plan­ets satel­lite, with an ex­o­plan­et sys­tem in the back­ground
Image 1/3, Credit: ©ESA/ATG medialab

Artist's impression of CHEOPS, the characterising exoplanets satellite, with an exoplanet system in the background

In re­al­i­ty, the CHar­ac­ter­is­ing Ex­O­Plan­ets Satel­lite (CHEOPS) will be lo­cat­ed in Earth or­bit and will study ex­o­plan­et sys­tems from a dis­tance, ac­cu­rate­ly mea­sur­ing the size of the plan­ets as they pass in front of their host star. These mea­sure­ments, com­bined with in­for­ma­tion about the mass of the plan­et based on sep­a­rate ob­ser­va­tions, will en­able the den­si­ty of the plan­ets to be es­ti­mat­ed. This will place lim­its on the pos­si­ble com­po­si­tion and struc­ture of the plan­ets and show, for ex­am­ple, whether they are pre­dom­i­nant­ly rocky or gaseous, or whether they might be home to sig­nif­i­cant oceans. CHEOPS will fo­cus in par­tic­u­lar on bright stars that host Earth to Nep­tune-sized plan­ets. The char­ac­ter­i­sa­tion of these worlds – many of them with­out equiv­a­lents of the So­lar Sys­tem – is a crit­i­cal part of un­der­stand­ing the for­ma­tion, ori­gin and evo­lu­tion of ex­o­plan­ets in this size range.
An­i­ma­tion show­ing ESA's CHar­ac­ter­is­ing Ex­O­Plan­ets Satel­lite (CHEOPS) in or­bit above Earth
Video 2/3, Credit: ©ESA/ATG medialab

Animation showing ESA's CHaracterising ExOPlanets Satellite (CHEOPS) in orbit above Earth

Credit: ©ESA/ATG medialab
Length: 00:00:22
The CHar­ac­ter­is­ing Ex­O­Plan­ets Satel­lite (CHEOPS) or­bits Earth at an al­ti­tude of ap­prox­i­mate­ly 700 kilo­me­tres in a Sun-syn­chronous or­bit that trav­els above the day-night ter­mi­na­tor; such a con­fig­u­ra­tion is al­so re­ferred to as a dawn/dusk or­bit. This or­bit al­lows CHEOPS to al­ways di­rect its in­stru­ment to­wards the night side of the Earth to lim­it the im­pact on the mea­sure­ments of sun­light and re­flect­ed stray­light light from Earth.
Focal plane module for the data acquisition sensor and the sensor electronics module
Fo­cal plane mod­ule for the da­ta ac­qui­si­tion sen­sor and the sen­sor elec­tron­ics mod­ule
Image 3/3, Credit: ©ESA/C. Carreau

Focal plane module for the data acquisition sensor and the sensor electronics module

The Fo­cal Plane Mod­ule (FPM – tri­an­gu­lar shape) and the Sen­sor Elec­tron­ics Mod­ule (SEM) are shown here, both of which are un­der the re­spon­si­bil­i­ty of DLR Berlin. The FPM hous­es the CHEOPS CCD de­tec­tor ar­ray and the Front End Elec­tron­ics (FEE). The SEM con­tains a pow­er sup­ply unit and a pro­ces­sor which is used to con­trol the FEE and to read out da­ta from the CCD. Con­duc­tive ther­mal straps at the rear of the FPM pro­vide the ther­mal link be­tween the FPM and the ra­di­a­tors that cool the CCD to its op­er­at­ing tem­per­a­ture of mi­nus 40 de­grees Cel­sius. The heat is trans­ferred from the CCD via a heat sink.

+++ Update: CHEOPS was successfully launched on 18 December 2019 at 09:54 CET and injected into a Sun-synchronous orbit. +++

  • Several hundred bright stars and their planets will be observed during the mission.
  • DLR is involved in the scientific evaluation of the data and contributed the focal plane module for the data acquisition sensor and the sensor control module for the front-end electronics.
  • Focus: Space, exploration

On 17 December 2019 at 05:54 local time (09:54 CET), the European Space Agency (ESA) CHaracterising ExOPlanets Satellite (CHEOPS) space telescope is scheduled to lift off from Europe’s spaceport in Kourou, French Guiana, on board a Soyuz launcher. The mission will further extend the search for exoplanets, which was one of the topics of this year's Nobel Prize in physics. Didier Queloz, one of the Nobel Prize winners, is Chair of the CHEOPS Science Team. With the participation of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), CHEOPS will determine the radii and densities of a large number of exoplanets and investigate which of them might have an atmosphere. In addition to providing on-board hardware, DLR will contribute its extensive expertise in data analysis. The space telescope will examine exoplanets from a Sun-synchronous Earth orbit at an altitude of 700 kilometres.

"More than 4000 exoplanets have been discovered in the Milky Way, yet we still know far too little about these distant worlds in our cosmic neighbourhood," says Heike Rauer, Director of the DLR Institute of Planetary Research in Berlin. "We are all eager to see which 'faces' the planets characterised by CHEOPS will show us."

'Mini eclipse' reveals details

The new space telescope will study several hundred bright stars where orbiting planets have already been discovered by other surveys and missions. These include the Next-Generation Transit Survey (NGTS) telescope system in Chile and NASA’s Transiting Exoplanet Survey Satellite (TESS) all-sky survey mission. CHEOPS will measure the very small dips in apparent brightness that occur when a planet crosses its host star's disc, referred to as a 'transit'. "We could describe this fluctuation in brightness as a 'mini stellar eclipse', as the transiting exoplanet reduces the intensity of the light from the star for a short time," explains Juan Cabrera Perez, Head of the Extrasolar Planets and Atmospheres Department at the DLR Institute of Planetary Research. “This fluctuation can be measured and analysed – an area in which we can contribute suitable tools and many years of experience.”

The mission will focus on stars orbited by planets with sizes ranging between those of Earth and Neptune – in other words, planets with diameters of approximately 10,000 to 50,000 kilometres. The scientists can use their measurements of the transit light curve to determine the size of the planet passing in front of the star. These data, together with information about the masses of the planets already obtained using other observation techniques, will allow scientists to determine their density – one of the most important criteria for characterising an unknown planet. For the first time, it will be possible to understand these extrasolar worlds more precisely. A planet’s density provides important clues about its composition and structure – whether it primarily consists of rock, with a metal inner core, for instance, or whether the planet might even be home to vast oceans, or if it mainly gaseous.

In addition, CHEOPS will observe the planets both during transit and in orbit to the side of the star and illuminated by it, very similar to the situation when Earth's inner neighbouring planet Venus can be observed to the side of the Sun. The measured light curves will enable the scientists to reach conclusions about the existence of an atmosphere and, if possible, even find out whether the planet has clouds.

CHEOPS space tele­scope
CHEOPS space tele­scope.
Credit: DLR (CC-BY 3.0)

High sensitivity and stability with DLR technology

DLR is involved in the scientific analysis of the data, while its institutes of Optical Sensor Systems and Planetary Research in Berlin contributed the focal plane module for the data acquisition sensor and the sensor control module for the front-end electronics. One of the telescope’s outstanding features is its ability to maintain an extremely high pointing accuracy of ideally one arcsecond (1/3600 of a degree) over long periods of time. By way of comparison, when viewed from Earth, the Moon has a diameter of 1800 arc seconds or 30 arc minutes, and Venus, the brightest planet in the sky that can be seen with the naked eye, a diameter of a maximum of 60 arc seconds.

"The focal plane module ensures the high sensitivity and stability of the CHEOPS telescope," emphasises Gisbert Peter from the DLR Institute of Optical Sensor Systems. “The CHEOPS sensor is able to detect differences in brightness of 20 parts per million." The 1.2-metre-long telescope has a 30-centimetre aperture and a mass of almost 60 kilograms. Together with its platform, it weighs just 300 kilograms. For this reason, the space telescope does not require its own launcher for the journey into space, but rather will 'piggyback' with another payload being sent into orbit.

CHEOPS was developed as part of a partnership between ESA and Switzerland. A consortium of more than 100 scientists and engineers from eleven European countries, including DLR in Germany, is involved, led by the University of Bern and ESA. The mission is initially scheduled to last for three-and-a-half years. In addition to the measurements and observations to be carried out by the CHEOPS science team, 20 percent of the observation time is reserved for external scientists from all over the world.

Earth-like planets – extensive tour of discovery planned with PLATO

CHEOPS is the first of three European missions that will explore exoplanets. Together with CHEOPS, DLR is also extensively involved with the ESA 'Planetary Transits and Oscillations of stars' (PLATO) space telescope. PLATO is set to launch in 2026 and will represent a big step forward in the search for Earth-like planets. This much more elaborate space telescope, with its 26 individual optical systems and cameras, will be the first instrument to detect Earth-sized planets in the 'habitable' (that is, life-friendly) zone around Sun-like stars, where it is possible for liquid water to exist on the surface. PLATO is looking for a 'second Earth' and will also be able to pinpoint the age of planetary systems with greater precision than before. The scientific instrument is being developed by an international consortium led by Heike Rauer from the DLR Institute of Planetary Research. The entire mission includes not only discoveries from space using the transit method, but also follow-up measurements with other telescopes.

Finally, in 2028 ESA will launch the 'Atmospheric Remote-sensing Infrared Exoplanet Large-survey' (ARIEL) mission, another space telescope, which will focus on investigating the atmospheres of exoplanets. This will allow a comprehensive catalogue to be produced with precise details of the orbit, radius, mass, density and age of the planets, as well as information about the atmospheric composition of gas planets. In operation from 2007 to 2012 the French 'Convection, Rotation and planetary Transits' (CoRoT) space telescope discovered a total of 32 planets, with significant involvement from the DLR Institute of Planetary Research. As a result, DLR has many years of expertise in this dynamic field of research, which is set to permanently change our view of the cosmos.

  • Falk Dambowsky
    Ger­man Aerospace Cen­ter (DLR)
    Me­dia Re­la­tions
    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-3959
    Fax: +49 2203 601-3249
    Linder Höhe
    51147 Cologne
  • Prof. Heike Rauer
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
  • Juan Perez Cabrera
    Head of the De­part­ment
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Ex­tra­so­lar Plan­ets and At­mo­spheres
    Telephone: +49 30 67055-439
    Rutherfordstraße 2
    12489 Berlin
  • Gisbert Peter
    MER­TIS Project Man­ag­er
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Op­ti­cal Sen­sor Sys­tems
    Rutherfordstraße 2
    12489 Berlin-Adlershof

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