Free Astronomy Magazine January-February 2018

23 JANUARY-FEBRUARY 2018 SPACE CHRONICLES HARPS can attain a precision of around one metre per second in velocity measurements, whereas ESPRESSO aims to achieve a precision of just a few centimetres per second, due to advances in technology and its placement on a much bigger telescope. The lead scientist for ES- PRESSO, Francesco Pepe from the University of Geneva in Switzerland, explains its sig- nificance: “This success is the result of the work of many people over 10 years. ESPRES- SO isn’t just the evolution of our previous instruments like HARPS, but it will be transfor- mational, with its higher resolution and higher precision. And unlike earlier instruments it can exploit the VLT’s full collecting power — it can be used with all four of the VLT Unit Telescopes at the same time to sim- ulate a 16-metre telescope. ES- PRESSO will be unsurpassed for at least a decade — now I am just im- patient to find our first rocky planet!” ESPRESSO can detect tiny T his colourful image shows spectral data from the First Light of the ESPRESSO instru- ment on ESO’s Very Large Tele- scope in Chile. The light from a star has been dispersed into its component colours. This view has been colourised to indicate how the wavelengths change across the image, but these are not exactly the colours that would be seen visually. Close in- spection shows many dark spec- tral lines in the stellar spectra and also the regular double spots from a calibration light source. The dark gaps are features of how the data is taken, and are not real. [ESO/ESPRESSO team] changes in the spectra of stars as a planet orbits. This radial velocity method works because a planet’s gravitational pull influences its host star, causing it to “wobble” slightly. The less massive the planet, the smaller the wobble, and so for rocky and possibly life-bearing exoplanets to be detected, an instrument with very high precision is required. With this method, ESPRESSO will be able to detect some of the lightest planets ever found. The test observa- tions included ob- servations of stars and known plane- tary systems. Com- parisons with exist- ing HARPS data showed that ES- PRESSO can obtain similar quality data with dramatically less exposure time. Instrument scien- tist Gaspare Lo Curto (ESO) is de- lighted: “Bringing ESPRESSO this far has been a great accomplishment, E SPRESSO successfully made its first observations in November 2017. Installed on ESO’s Very Large Telescope (VLT) in Chile, ESPRESSO will search for exoplanets with un- precedented precision by looking at the minuscule changes in the properties of light coming from their host stars. For the first time ever, an instrument will be able to sum up the light from all four VLT telescopes and achieve the light col- lecting power of a 16-metre telescope. [ESO/P. Horálek] with contributions from an interna- tional consortium as well as many different groups within ESO: engi- neers, astronomers and administra- tion. They had to not just install the spectrograph itself, but also the very complex optics that bring the light together from the four VLT Unit Telescopes.” Although the main goal of ES- PRESSO is to push planet hunting to the next level, finding and charac- terising less massive planets and their atmospheres, it also has many other applications. ESPRESSO will also be the world’s most powerful tool to test whether the physical constants of nature have changed since the Universe was young. Such tiny changes are predicted by some theories of fundamental phys- ics, but have never been convinc- ingly observed. When ESO’s Ex- tremely Large Telescope comes on line, the instrument HIRES, which is currently under conceptual design, will enable the detection and char- acterisation of even smaller and lighter exoplanets, down to Earth- like planets, as well as the study of exoplanet atmospheres with the prospect of the detection of signa- tures of life on rocky planets. !