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ESPRESSO spectrograph concept at the Preliminary Design Review.
ESPRESSO spectrograph optical design at the Preliminary Design Review.
ESPRESSO successfully made its first observations in November 2017.

ESPRESSO (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations) [1] 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 on September 25, 2016. [2] [3]


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 will be 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. [4] 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 4 Unit Telescopes of the VLT can be combined. The Principal Investigator is Francesco Pepe.


Data from ESPRESSO First Light. [5]

ESPRESSO will build 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 will benefit 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, [6] 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 like ESO's HARPS. The HARPS instrument can attain a precision of 97 cm/s (3.5 km/h), [7] with an effective precision of the order of 30 cm/s, [8] making it one of only two spectrographs worldwide with such accuracy.[ citation needed ] 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 will detect extremely faint objects. [4] [9]

For example, for G2V type stars:

ESPRESSO will focus the observations on the best-suited candidates: non-active, non-rotating, quiet G dwarfs to red dwarfs. It will operate at the peak of its efficiency for a spectral type up to M4-type stars.


First light of the ESPRESSO instrument with all four Unit Telescopes. [11]

ESPRESSO will use as calibration a laser frequency comb (LFC), with backup of two Th Ar lamps. It will have three instrumental modes: singleHR, singleUHR and multiMR. In the singleHR mode ESPRESSO can be fed by any of the four UTs. [12]


Engineering rendering of the ESPRESSO instrument [13]

All design work was completed and finalised by April 2013, with the manufacturing phase of the project commencing thereafter. [1] ESPRESSO was tested on June 3, 2016,. [14] [15] [16] ESPRESSO first light occurred on September 25, 2016, during which they spotted various objects, among them the star 60 Sgr A. [2] [3] and after being shipped to Chile and installed at the VLT, ESPRESSO saw its first light there on 27 November 2017. [17] [18] ESPRESSO is currently in testing phase, but by December 2018 it will officially begin its mission proper. [19]

Scientific objectives

The main scientific objectives for ESPRESSO are: [20] [21]


ESPRESSO is being developed by a consortium consisting on the European Southern Observatory (ESO) and seven scientific institutes:

ESPRESSO specifications

Telescope VLT (8m)
ScopeRocky planets
Sky aperture 4 arcsec
λ coverage380 nm-686  nm [22]
λ precision5  m/s
RV stability< 10 cm/s
4-VLT mode (D = 16 m) with RV = 1 m/s
Source: [10] [23] [21]

Radial velocity comparison tables

Planet Mass Distance
Radial velocity
Jupiter 128.4 m/s
Jupiter 512.7 m/s
Neptune 0.14.8 m/s
Neptune 11.5 m/s
Super-Earth (5 M⊕)0.11.4 m/s
Alpha Centauri Bb (1.13 ± 0.09 M⊕)0.040.51 m/s(1 [24] )
Super-Earth (5 M⊕)10.45 m/s
Earth 0.090.30 m/s
Earth 10.09 m/s
Source: Luca Pasquini, power-point presentation, 2009 [10] Notes: (1) Most precise vradial measurements ever recorded. ESO's HARPS spectrograph was used. [24] [25]
Planets [10]
PlanetPlanet Type
Semimajor Axis
Orbital Period
Radial velocity
Detectable by:
51 Pegasi b Hot Jupiter 0.054.23 days55.9 [26] First-generation spectrograph
55 Cancri d Gas giant 5.7714.29 years45.2 [27] First-generation spectrograph
Jupiter Gas giant 5.2011.86 years12.4 [28] First-generation spectrograph
Gliese 581c Super-Earth 0.0712.92 days3.18 [29] Second-generation spectrograph
Saturn Gas giant 9.5829.46 years2.75Second-generation spectrograph
Proxima Centauri b Habitable planet (potentially) 0.0511.19 days1.38 [30] Second-generation spectrograph
Alpha Centauri Bb Terrestrial planet 0.043.23 days0.510 [31] Second-generation spectrograph
Neptune Ice giant 30.10164.79 years0.281Third-generation spectrograph
Earth Habitable planet 1.00365.26 days0.089Third-generation spectrograph (likely)
Pluto Dwarf planet 39.26246.04 years0.00003Not detectable

MK-type stars with planets in the habitable zone

Stellar mass
Planetary mass
Source: [32] [33]

See also


  1. 1 2 "ESO - Espresso" . Retrieved 2012-10-24.
  2. 1 2 ESPRESSO Sees Light at the End of the Tunnel
  3. 1 2 ESPRESSO vede la luce in fondo al “tunnel”
  4. 1 2 "ESPRESSO - Searching for other Worlds". Centro de Astrofísica da Universidade do Porto. 2010-10-16. Retrieved 2010-10-16.
  5. "First Light for ESPRESSO — the Next Generation Planet Hunter". Retrieved 7 December 2017.
  6. Pepe, F.; Molaro, P.; Cristiani, S.; Rebolo, R.; Santos, N. C.; Dekker, H.; Mégevand, D.; Zerbi, F. M.; Cabral, A.; et al. (January 2014). "ESPRESSO: The next European exoplanet hunter". Astronomische Nachrichten . 335 (1): 8–20. arXiv: 1401.5918 . Bibcode:2014arXiv1401.5918P. doi:10.1002/asna.201312004.
  7. "32 planets discovered outside solar system". CNN. 19 October 2009. Retrieved 4 May 2010.
  8. "ESPRESSO – Searching for other Worlds". Centro de Astrofísica da Universidade do Porto. 16 December 2009. Retrieved 2010-10-16.
  9. Pepe, Francesco A; Cristiani, Stefano; Rebolo Lopez, Rafael; Santos, Nuno C; et al. (July 2010). "ESPRESSO: the Echelle spectrograph for rocky exoplanets and stable spectroscopic observations" (PDF). Ground-based and Airborne Instrumentation for Astronomy III. 7735. American Institute of Physics. p. 77350F. Bibcode:2010SPIE.7735E..0FP. doi:10.1117/12.857122 . Retrieved 2013-03-12.
  10. 1 2 3 4 "ESPRESSO and CODEX the next generation of RV planet hunters at ESO". Chinese Academy of Sciences. 2010-10-16. Archived from the original on July 4, 2011. Retrieved 2010-10-16.
  11. "ESO's VLT Working as 16-metre Telescope for First Time - ESPRESSO instrument achieves first light with all four Unit Telescopes". Retrieved 13 February 2018.
  12. ESPRESSO: The next European exoplanet hunter
  13. "ESO Awards Contracts for Cameras for New Planet Finder". ESO Announcement. Retrieved 8 August 2013.
  15. ESPRESSO Planet Hunter Heads for Chile. European Southern Observatory. 22 August 2017. Accessed on 12 October 2017
  16. Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, ESO
  17. ESPRESSO Planet Hunter Heads for Chile
  19. The black box set to revolutionise the search for life beyond Earth, archived from the original on 2018-02-09, retrieved 2018-08-20
  20. ESPRESSO - A VLT Project. Accessed 12 October 2017.
  21. 1 2 ESPRESSO Baseline Specification. European Southern Observatory (ESO). Accessed: 12 October 2017
  23. Pepe, F; Molaro, P; Cristiani, S; Rebolo, R; et al. (2014). "ESPRESSO: The next European exoplanet hunter". arXiv: 1401.5918v1 [astro-ph.IM].
  24. 1 2 "Planet Found in Nearest Star System to Earth". European Southern Observatory. 16 October 2012. Retrieved 17 October 2012.
  25. Demory, Brice-Olivier; Ehrenreich, David; Queloz, Didier; Seager, Sara; et al. (25 March 2015). "Hubble Space Telescope search for the transit of the Earth-mass exoplanet Alpha Centauri Bb". Monthly Notices of the Royal Astronomical Society. 450 (2): 2043–2051. arXiv: 1503.07528 . Bibcode:2015MNRAS.450.2043D. doi:10.1093/mnras/stv673.
  26. "51 Peg b". Exoplanets Data Explorer.
  27. "55 Cnc d". Exoplanets Data Explorer.
  28. Endl, Michael. "The Doppler Method, or Radial Velocity Detection of Planets". University of Texas at Austin. Retrieved 26 October 2012.[ permanent dead link ]
  29. "GJ 581 c". Exoplanets Data Explorer.
  30. "Proxima Cen b". The Extrasolar Planets Encyclopaedia.
  31. "alpha Cen B b". Exoplanets Data Explorer.
  32. "An NIR laser frequency comb for high precision Doppler planet surveys". Chinese Academy of Sciences. 2010-10-16. Retrieved 2010-10-16.[ dead link ]
  33. Osterman, S; Diddams, S; Quinlan, F; Bally, J; Ge, J; Ycas, G (2010). "A near infrared laser frequency comb for high precision Doppler planet surveys". EPJ Web of Conferences. 16: 02002. arXiv: 1003.0136 . Bibcode:2011EPJWC..1602002O. doi:10.1051/epjconf/20111602002.