ESA’s CHEOPS exoplanet hunting mission

Later this year the European Space Agency (ESA) is planing to launch the Characterising Exoplanet Satellite (CHEOPS). The aim of this instrument is to measure more detailed characteristics of exoplanets than ever before. This mission comes hot on the heels of NASA’s TESS mission, which is surveying the sky for exoplanets. CHEOPS is a true multinational effort with design, building and assembly across many different countries in Europe. ESA has been busy lately with Mercury-bound BepiColombo heading off to Kourou for it’s launch later in the year. CHEOPS is going to add a wealth of data to what we know about exoplanets. We know a lot about where there are exoplanets, we think, but we don’t know a lot about the size, density and composition of those planets. The aim of this mission is to study the places that we know harbour exoplanets so we can find out more about them.

CHEOPS, like TESS, will look at transiting exoplanets by looking at stars through it’s main instrument to look for dips in the light curve and then infer the characteristics of the potential exoplanets. The important thing to remember with this mission is that it is not searching for new exoplanets, that’s been done by other missions, but is looking at the ones we know about so we can learn a bit more. It will focus on stars with a visual magnitude of less than 12 with known exoplanets. To do this the instrument on CHEOPS needs to be highly sensitive and pointing very accurately. The satellite is essentially a 320mm f8 Ritchey-Chrétien telescope with a 1024 x 1024 pixel charged couple device (CCD) attached to it. Because the telescope is in space it can be cooled passively, by which the designers are planning to keep the CCD at less than 233K. The instrument has to be sensitive to pick up very subtle changes in the brightness of stars, so for an Earth sized planet transmitting a G5 star, just a bit smaller than our Sun, then the instrument has to be able to detect a change of less than 10-20 parts per million to get useful data. The requirement for larger Neptune sized planets is a bit easier at around 85 ppm difference.

The data collected will be used to help understanding just how big exoplanets ar in the range of super-earths through to Neptune sized planets. The objectives of the mission are to measure the radii and densities for xoplanets where there’s currently not a lot of data and at a precision which has not been done before. The mission will also help understand the formation process of gas giants and a bit about their evolution. The information the CHEOPS will obtain will also be useful for directing the next generation of space telescopes such as the James Webb Space Telescope (JWST) and large ground based telescope being planned. Another objective of CHEOPS is to look at the hot Jupiter type planets and try o understand the processes of heat transfer from the day to night sides of the planets.

The satellite is relatively small at around 250kg, which includes the instrument, baffling, controls and power. It will be launched on Soyuz rocket later this year or in early 2019. On of the interesting things that ESA did with CHEOPS was to invite the public to design the logo for the rocket through a competition. Over 300 designs were submitted with the winning design coming from Denis Vrenko from Celje in Slovenia. The design will go on the fairing of the rocket, basically the bit that protects the spacecraft and covers it during the launch.

Another aspects of community involvement is that CHEOPS will have 20% of it’s time open for re-tasking from the public to help wth research and other endeavours. CHEOPS will help a great deal in building our understanding of exoplanets.