How do massive stars form? What molecular species hide in the Martian atmosphere? Are there Earth-like exoplanets in habitable zones? These questions can be answered using the Extremely Large Telescope (ELT), which will be built over the next six to seven years. ‘To make these future discoveries possible, we are building METIS – one of ELT’s scientific instruments,’ says Bernhard Brandl.
The detection and characterisation of exoplanets – a planet orbiting a star other than our sun – is one of the scientific motivations for the METIS (Mid-infrared ELT Imager and Spectrograph) instrument. Exoplanet research has taken off in the last decade, with several thousands of planets known today. However, most were indirect observations which did not tell us much about nature of the planets. ‘With METIS, we will be able to take a picture of the exoplanet itself and analyse it,’ says Brandl, who is a principal investigator of METIS.
World’s biggest telescope
The ELT – which will have a 39-metre mirror in diameter – is currently being built in the Chilean dessert at 3,000 metres altitude. It will be the world’s biggest optical and infrared telescope. In addition to METIS, it will house two other scientific instruments. ‘With these instruments, we can use the full power of the telescope to really push astronomy to the next level,’ says Brandl.
METIS will be six metres high and weigh 20 tons. Brandl: ‘It is one of the most complex scientific astronomical instruments ever built.’ It contains a high-contrast imaging camera and a high-resolution spectrograph, which will make it possible to detect exoplanets – even during their formation –, see how other planetary systems are constructed, and investigate properties, like their temperature and the composition of their atmosphere.
‘We use the biggest telescopes to see the faintest exoplanets – and then we struggle with the billions of photons from their host star flooding our image. METIS will help us to see only the photons we’re interested in.’
Flooded with light
Taking such pictures of exoplanets is hard because their light is millions of times fainter than the light of their host star. ‘It is like taking a photograph of the sun,’ says Brandl. ‘You won’t just see one very bright spot in the middle; your whole picture will be flooded with sunlight.’ The challenge is to confine the light to the point it originates from to give you greater sensitivity to the surrounding area where a faint exoplanet could be hiding. This will be possible with the light-gathering power of the ELT, combined with the high-performance optics of METIS. Once an exoplanet has been found, we can follow up with the spectrograph to determine the exoplanet’s physical and chemical properties.
Last year, the METIS consortium reached an important milestone: the preliminary design was approved by the European Southern Observatory (ESO). ‘Developing this instrument is a long, but exciting process,’ says Brandl. ‘There is a lot of creativity needed to balance scientific and technical issues, and build the best instrument with the available funding, within the given time.’
When the design is finalised in 2022, the international consortium (12 partner institutes) can start building and testing the instrument. METIS will be transported to Chile in 2027. ‘Then another exciting chapter of ground-based astronomy will start.’
Like most young people interested in science, Bernhard Brandl was fascinated by the Universe. ‘But I had never imagined myself as an astronomer, until I started working on an astronomical instrument during my PhD.’ His PhD supervisor was Reinhard Genzel, who received the Nobel Prize in Physics last year, for the discovery of a supermassive compact object at the centre of our galaxy. ‘I was working on one telescope at ESO in Chile when at the other telescope the observations that led to the discovery started. The excitement surrounding this discovery defined my career path.’ After his PhD, Brandl continued working on instruments, which keep on getting bigger – in size, cost and complexity.