Searching the stars for habitable planets
Funded by the EU’s European Research Council (ERC), the WAVELENGTH STANDARDS project enabled Professor Ansgar Reiners from the Georg-August-Universität Göttingen in Germany to carry out high precision experiments with local and international telescopes and couple them with state-of-the art frequency calibration methods (called laser frequency combs). Before completion in December 2016, this contributed towards some spectacular discoveries such as Proxima b, our nearest exoplanet some 4.2 light years away which orbits a sun within what is known as the habitable zone. Careful calibration To detect “habitable” planets outside our solar system, extremely sensitive equipment is required. Minute, periodic changes in starlight must be identified, which indicate that the star is being orbited by a planet. ‘A small, Earth-like planet is detectable as a change in wavelength observed from a star; in other words, the star very slightly changes colour,’ explains Reiners. ‘Therefore we need new wavelength standards that tell us at what particular wavelengths we are receiving from the starlight at any given time, and this is where our project promises to make a difference. Our group is now one of the few worldwide that can provide calibration strategies and facilities for the next generation of radial velocity spectrometers.’ The last couple of months of the project proved to be extremely exciting, with several other discoveries of transiting nearby exoplanets. Most importantly of all, the project has provided an excellent platform from which further space exploration can be conducted. New age of discovery ‘One aspect of the project that I am very proud of has been the operation of the first high-stability near-infrared spectrograph (CARMENES), which was used in the search for exoplanets,’ says Reiners. The CARMENES project built two spectrographs (instruments to measure wavelengths) to search for Earth-like planets around low-mass stars. Reiners’ team was responsible for calibration, data reduction and analysis. ‘We are currently using an enormous amount of telescope time here to search for extrasolar planets,’ says Reiners. ‘We are gathering lots of exciting data, and we are opening a new path towards a deeper understanding of exoplanets that orbit low-mass stars.’ The WAVELENGTH STANDARDS project has also facilitated a detailed investigation of the velocity fields of moving plasma on the solar surface. ‘For this we are combining several facilities in our institute, and have certainly been motivated by our work in WAVELENGTH STANDARDS,’ says Reiners. ‘Our aim is to collect unique data that will help us understand the Sun, and which will also further improve our methods to search for planets in other stars.’ During WAVELENGTH STANDARDS, Reiners and his team were also responsible for calibrating the CRIRES+ project at the ESO (European Southern Observatory)'s Very Large Telescope facility. Currently undergoing an upgrade, the VLT will be the most sensitive infrared high-resolution spectrograph available, ready to search for molecular signatures in the atmospheres of extrasolar planets. The team is also in charge of calibrating the planned high-resolution spectrograph for ESO's flagship project, the 39m E-ELT (European Extremely Large Telescope), foreseen to be finished in the mid-2020s. ‘This instrument will allow for detailed studies of exoplanets and many other science cases including fundamental physics and the understanding of extremely faint objects,’ says Reiners. Through careful calibration of cutting edge equipment and cooperation with astronomers, the key legacy of the WAVELENGTH STANDARDS project is that it will ensure European exoplanet research remains at the cutting edge well into the future.
Keywords
WAVELENGTH STANDARDS, extraterrestrial, proxima B, exoplanets, stars, ERC, CARMENES, VLT, ELT