CHEOPS takes its first image of the Universe

Robert Lea
Feb 7 · 4 min read

The European Space Agency’s exoplanet-hunting CHEOPS telescope has taken its first images of the Universe and they are better than expected.

The European Space Agency’s (ESA) first exoplanet-hunting telescope CHaracterising ExOPlanet Satellite (CHEOPS) has made the next leap in its operations. The satellite, placed into a low-Earth orbit by the Soyuz rocket on December 18th 2019, has taken its first image of the Universe.

CHEOPS primary mission is to act as a bridge between the exoplanet-hunting missions of the past and the next generation of exoplanet investigation undertaken by the James Webb space-telescope — set to launch in 2021 — and the Earth-based Extremely Large Telescope — currently under construction in the Acatma Desert, Chile. It will not discover new exoplanets, but rather refine current targets and turn them into ‘golden targets’ prime for further detailed investigations.

The first image of the star chosen as a target for CHEOPS after cover opening. The star, at the centre of the image, is located at a distance of 150 light-years from us, in the constellation of Cancer. The image is about 1000x1000 pixels in size, with each pixel representing a tiny angle of about 0.0003 degrees (1 arcsecond) on the sky. The other, fainter stars in the image are in the background of the target. The inset in the lower right corner shows a region of about 100-pixels in width, centred on the target star. The peculiar shape of the star in the image is due to the deliberate defocusing of CHEOPS optics. CHEOPS measures the star’s brightness by adding up the light received in all pixels within a region centred on the star as illustrated by the circle in the picture. The defocusing spreads the light onto many pixels, which allows CHEOPS to reach best possible photometric precision. (© ESA/Airbus/CHEOPS Mission Consortium)

As well as providing a happy moment for space and astronomy enthusiasts across the globe, receiving the image acted as a significant relief to the Consortium of ESA researchers and scientists from the Universities of Bern and Geneva which operates the telescope.

“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 Willy Benz, Professor of Astrophysics at the University of Bern and Principal Investigator of the CHEOPS mission. “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.”

Cheops in the cleanroom at Airbus, Madrid (© ESA — S. Corvaja)

The team now need to determine just how well the telescope is working. The next two months will consist of the team running a battery of tests to determine CHEOPS’ effectiveness. Fortunately, the initial signs are good. “We will analyze many more images in detail to determine the exact level of accuracy that can be achieved by CHEOPS in the different aspects of the science program,” says David Ehrenreich, CHEOPS project scientist at the University of Geneva.

“The results so far bode well.”


For CHEOPS ‘better’ means blurrier

The first images gathered by CHEOPS are better than the team had expected, but ironically, in the case of CHEOPS, a ‘better’ image does not mean a ‘sharper’ image. The CHEOPS telescope has been deliberately defocused so that the light can be spread over many pixels. This is to ensure that any jostling that affects the satellite is distributed pixel-to-pixel across an image. This is what gives CHEOPS its high photometric precision.

“The good news is that the actual blurred images received are smoother and more symmetrical than what we expected from measurements performed in the laboratory,” says Benz.

An illustration of the photometry technique which relies on a planet crossing its parent star, blocking some of the light it emits (NASA)

CHEOPS need such high-precision so that it can observe the tiny changes in the brightness of a star as an orbiting exoplanet passes in front of it. This is known as the photometry or transit method of exoplanet observation and it requires incredible sensitivity due to the massive size disparity that exists between stars and the exoplanets which orbit them.

A great example of this comes from observing the transit of Mercury across the Sun (seen below).

This speck, highlighted below, is Mercury — thus we can see the tiny fraction of light its transit has obscured. Consider too, that CHEOPS is viewing this scene from hundreds to thousands of light-years away.

The transit technique measures the dip in brightness of a star caused as a planet crosses in front of it, thus allowing astronomers to not just infer the presence of an exoplanet, but also collect details about its characteristics. CHEOPS will particularly focus on exoplanets’ size — something which is proportional to the dip in brightness that results from its transit.

“These initial promising analyses are a great relief and also a boost for the team,” concludes Benz.


Original source: Press release from the University of Bern


Rob is freelance science journalist from the UK, specialising in physics, astronomy, cosmology, quantum mechanics and obscure comic books.

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The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

Robert Lea

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Freelance science journalist. BSc Physics. Space. Astronomy. Astrophysics. Quantum Physics. SciComm. ABSW member. WCSJ Fellow 2019. IOP Fellow.

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

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