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MASCARA stations hunt for exoplanets orbiting bright stars

For a number of years, two ‘boxes’ in the Canary Islands and Chile have been scouring the skies for exoplanets that orbit bright stars. PhD candidate Geert Jan Talens helped develop these ‘MASCARA’ telescopes and has made the first discoveries with them. Together with him, we answer the main questions about Leiden University’s research stations.

What is MASCARA?

MASCARA stands for Multi-site All-Sky CAmeRA. The name says it all: it is a series of cameras that photograph the entire night sky in multiple places simultaneously. The cameras are packaged in aluminium ‘boxes’ of about a square metre in size. One such MASCARA station containing five cameras has been set up at an observatory on La Palma, and another on a mountain top in Chile. This places them far away from the light pollution of big cities. MASCARA is the initiative of Ignas Snellen, Professor of Observational Astrophysics at Leiden University and Geert Jan Talens’s PhD supervisor. Talens hopes to be awarded his PhD on 19 December.

How does MASCARA work?

With MASCARA, astronomers can hunt down exoplanets that orbit bright stars. Exoplanets are planets that orbit stars other than our own Sun. Many are as yet undiscovered, but this is gradually changing. The ten MASCARA cameras take between about 4,000 and 6,000 photos of the sky each night. Each photo is about 20 megabytes in size, so each night the two stations take about a terabyte of photos. That's a bit too much to just send  to Leiden by WeTransfer. The stations therefore also have computers that can immediately analyse the images and convert them to measurements of the brightness of the stars. Astronomers can use these images to discover exoplanets because a tiny bit of starlight is blocked when a planet moves in front of the star. That tiny dip in brightness is often a clue that you have spotted a planet.

Inside a MASCARA station

Why do we want to discover these exoplanets?

The exoplanets that orbit bright stars are very suited to research into the atmospheres around them. When a planet is in front of its star, the starlight shines straight through its atmosphere. We can collect this starlight on Earth, and its wavelengths help us determine the composition of the planet’s atmosphere. In the long term, astronomers hope to discover planets that are somewhat similar to Earth, for instance because their atmosphere protects them from cosmic rays and contains oxygen. This won’t be possible with MASCARA, says Talens, because the stations can only observe larger planets. ‘But if we can test our observation methods and models for atmospheres on these planets, we are a step closer to the planets that are similar to Earth.’

What is there to say abou the first dscoveries?

With MASCARA, Talens discovered two new exoplanets that orbit bright stars. The planets MASCARA 1 and 2 are a distance of about 500 to 600 light years from Earth. Talens studied the mass and radius of these planets, but what proved much more interesting is their orientation to the star. Recent observations have shown that with hotter stars, a planet’s orbital axis tends not to be equal to the star’s rotational axis. The reason for this has not yet been found. The orbital axis of one of the newly discovered planets isn’t equal to the rotational axis of its star but of the other planet it is. ‘This may say something about which explanation is right,’ says Talens, ‘but with only one anomalous observation, it is too soon to make any categorical statements.’ To make his observations, Talens  first nhas to calibrate the MASCARA telescopes. This is because the star’s brightness on the image is strongly affected by influences such as the Earth’s atmosphere, and Talens has to filter these out before he can measure the true brightness of the stars.

Text: Merijn van Nuland
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