ESPRESSO, echelle spectrograph for ESO's Very Large Telescope, sees first light

For measuring a star's radial velocity changes, the instrument has a precision of a few centimeters per second.

The Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) has achieved first light on ESO's Very Large Telescope (VLT) at the Paranal Observatory in northern Chile. The new third-generation echelle spectrograph is the successor to ESO's hugely successful High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the La Silla Observatory (echelle gratings are optimized for high diffraction orders). HARPS can attain a precision of around one meter per second in velocity measurements, whereas ESPRESSO aims to achieve a precision of just a few centimeters per second due to advances in technology and its placement on a much bigger telescope.

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The lead scientist for ESPRESSO, Francesco Pepe from the University of Geneva in Switzerland, explains its significance. "This success is the result of the work of many people over 10 years," he says. "ESPRESSO isn't just the evolution of our previous instruments like HARPS, but it will be transformational, 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 simulate a 16-meter telescope. ESPRESSO will be unsurpassed for at least a decade; now I am just impatient to find our first rocky planet."

ESPRESSO can detect very small 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 the star 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 observations included observations of stars and known planetary systems. Comparisons with existing HARPS data showed that ESPRESSO can obtain similar-quality data with dramatically less exposure time.


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