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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| ESPRESSO | 1/2 | https://en.wikipedia.org/wiki/ESPRESSO | reference | science, encyclopedia | 2026-05-05T09:40:41.044146+00:00 | kb-cron |
ESPRESSO (Echelle Spectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations) is a third-generation, fiber-fed, cross-dispersed, echelle spectrograph mounted on the European Southern Observatory's Very Large Telescope (VLT). The unit saw its first light with one VLT in December 2017 and first light with all four VLT units in February 2018. ESPRESSO is the successor of a line of echelle spectrometers that include CORAVEL, Elodie, Coralie, and HARPS. It measures changes in the light spectrum with great sensitivity, and is being used to search for Earth-size rocky exoplanets via the radial velocity method. For example, Earth induces a radial-velocity variation of 9 cm/s on the Sun; this gravitational "wobble" causes minute variations in the color of sunlight, invisible to the human eye but detectable by the instrument. The telescope light is fed to the instrument, located in the VLT Combined-Coude Laboratory 70 meters away from the telescope, where the light from up to four unit telescopes of the VLT can be combined.
== Sensitivity ==
ESPRESSO builds on the foundations laid by the High Accuracy Radial Velocity Planet Searcher (HARPS) instrument at the 3.6-metre telescope at ESO's La Silla Observatory. ESPRESSO benefits not only from the much larger combined light-collecting capacity of the four 8.2-metre VLT Unit Telescopes, but also from improvements in the stability and calibration accuracy that are now possible by laser frequency comb technology. The requirement is to reach 10 cm/s, but the aimed goal is to obtain a precision level of a few cm/s. This would mean a large step forward over current radial-velocity spectrographs such as ESO's HARPS. The HARPS instrument can attain a precision of 97 cm/s (3.5 km/h), with an effective precision of the order of 30 cm/s. The ESPRESSO would greatly exceed this capability making detection of Earth-size planets from ground-based instruments possible. Commissioning of ESPRESSO at the VLT started late 2017. The instrument is capable of operating in 1-UT mode (using one of the telescopes) and in 4-UT mode. In 4-UT mode, in which all the four 8-m telescopes are connected incoherently to form a 16-m equivalent telescope, the spectrograph detects extremely faint objects. For example, for G2V type stars:
Rocky planets around stars as faint as V ≈ 9 (in 1-UT mode) Neptune-mass planets around stars as faint as V ≈ 12 (in 4-UT mode ) Earth-size rocky planets around stars as faint as V ≈ 9 (CODEX on the E-ELT) The best-suited candidate stars for ESPRESSO are non-active, non-rotating, quiet G dwarfs to red dwarfs. It operates at the peak of its efficiency for a spectral type up to M4-type stars.
== Instrument ==
In the singleHR mode ESPRESSO can be fed by any of the four UTs.