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ESPRESSO spectrograph concept at the Preliminary Design Review.
ESPRESSO spectrograph optical design at the Preliminary Design Review.

ESPRESSO (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations)[1] is a third-generation, fiber fed, cross-dispersed, echelle spectrograph for the European Southern Observatory's Very Large Telescope (VLT) is the successor of a line of echelle spectrometers (CORAVEL, Elodie, Coralie, HARPS). It measures changes in the light spectrum with great sensitivity, and will be used to search for Earth-like planets via the radial velocity method. For example, our Earth induces a radial-velocity variation of 9 cm/s on our Sun; this gravitational "wobble" causes minute variations in the color of sunlight, invisible to the human eye but detectable by the instrument.[2] The telescope light is fed to the instrument via a Coude-Train optical system and fibers. ESPRESSO is located in the VLT Combined-Coude Laboratory (incoherent focus) 70 meters away from the telescopes where a front-end unit can combine the light from up to 4 Unit Telescopes (UT) of the VLT.

ESPRESSO is scheduled to begin scientific operations in 2017. [3]


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 (for example, laser frequency comb technology). The requirement is to reach 10 cm/s,[4] 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),[5] with an effective precision of the order of 30 cm/s,[6] making it one of only two instruments worldwide with such accuracy.[citation needed] The ESPRESSO would greatly exceed this capability making detection of earth-like planets from ground based instruments possible. Installation and commissioning of ESPRESSO at the VLT is foreseen in 2016.[2]

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 reach extremely faint objects.[2][7][8]

For example, (for G2V type stars):

  • Rocky planets around stars as faint as V ~ 9 in (in 1-UT mode)
  • Neptune mass planets around stars as faint as V ~ 12 (in 4-UT mode )
  • Earth-like planets around stars as faint as V ~ 9 (CODEX on the E-ELT) (2025)[9]

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


ESPRESSO will use as calibration a laser frequency comb (LFC), with backup of two ThAr 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.[10]


Engineering rendering of the ESPRESSO instrument[11]

The project is currently in its manufacturing phase. All design work is complete.[1] ESPRESSO first laboratory light occurred on June 3, 2016.[12]

  • Opened to the Scientific Community by 2017
  • Schedule: First light on Telescope: Second Part of 2016. ESPRESSO first light occurred on September, 25 2016. during this they spotted various objects, among then the star 60 Sgr A [13][14]
  • Preliminary Acceptance Europe, October 2015
  • Final Design Review, May 2013
  • Preliminary Design Review, November 2011
  • Kick-off Meeting, January 2011
  • Phase A Study Review Meeting, March 2010

Scientific Objectives[edit]

The main scientific drivers for ESPRESSO are:

  • The measurement of high precision radial velocities of solar type stars for search for rocky planets.
  • The measurement of the variation of the physical constants (search for possible variations of the constants of nature at different times and in different directions through the study of the light from very distant quasars).
  • The analysis of the chemical composition of stars in nearby galaxies.

These science cases require an efficient, high-resolution, extremely stable and accurate spectrograph.[citation needed][original research?][clarification needed]


ESPRESSO is being developed by a consortium consisting of ESO and seven further scientific institutes:

Comparison between ESPRESSO and CODEX[edit]

Telescope VLT (8m) E-ELT (39m)
Scope Rocky planets Earth-like
Sky aperture 1 arcsec 0.80 arcsec
R ~200.000 150000
λ coverage 380 nm-780 nm nm 380–680 nm
λ precision m/s 1 m/s
RV stability < 10 cm/s < 2 cm/s
4-VLT mode (D = 16 m) with RV = 1 m/s

Radial velocity comparison tables[edit]

Planet Mass Distance
Radial velocity
Jupiter 1 28.4 m/s
Jupiter 5 12.7 m/s
Neptune 0.1 4.8 m/s
Neptune 1 1.5 m/s
Super-Earth (5 M⊕) 0.1 1.4 m/s
Alpha Centauri Bb (1.13 ± 0.09 M⊕) 0.04 0.51 m/s (1[16])
Super-Earth (5 M⊕) 1 0.45 m/s
Earth 0.04109589 0.30 m/s
Earth 1 0.09 m/s
Source: Luca Pasquini, power-point presentation, 2009[9] Notes: (1) Most precise vradial measurements ever recorded. ESO's HARPS spectrograph was used.[16][17]
Planet Planet Type
Semimajor Axis
Orbital Period
Radial velocity
Detectable by:
51 Pegasi b Hot Jupiter 0.05 4.23 days 55.9[18] First-generation spectrograph
55 Cancri d Gas giant 5.77 14.29 years 45.2[19] First-generation spectrograph
Jupiter Gas giant 5.20 11.86 years 12.4[20] First-generation spectrograph
Gliese 581c Super-Earth 0.07 12.92 days 3.18[21] Second-generation spectrograph
Saturn Gas giant 9.58 29.46 years 2.75 Second-generation spectrograph
Alpha Centauri Bb Terrestrial planet 0.04 3.23 days 0.510[22] Second-generation spectrograph
Neptune Ice giant 30.10 164.79 years 0.281 Third-generation spectrograph
Earth Habitable planet 1.00 365.26 days 0.089 Third-generation spectrograph (likely)
Pluto Dwarf planet 39.26 246.04 years 0.00003 Not detectable

MK-type stars with planets in the habitable zone[edit]

Stellar mass
Planetary mass
0.10 1.0 8×104 M8 0.028 168 6
0.21 1.0 7.9×103 M5 0.089 65 21
0.47 1.0 6.3×102 M0 0.25 26 67
0.65 1.0 1.6×101 K5 0.40 18 115
0.78 2.0 4.0×101 K0 0.63 25 209

See also[edit]

External links[edit]


  1. ^ a b "ESO - Espresso". Retrieved 2012-10-24. 
  2. ^ a b c "ESPRESSO - Searching for other Worlds". Centro de Astrofísica da Universidade do Porto. 2010-10-16. Retrieved 2010-10-16. 
  3. ^ ESPRESSO Sees Light at the End of the Tunnel
  4. ^ 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:1401.5918Freely accessible. Bibcode:2014arXiv1401.5918P. doi:10.1002/asna.201312004. 
  5. ^ "32 planets discovered outside solar system -". CNN. 19 October 2009. Retrieved 4 May 2010. 
  6. ^ "ESPRESSO – Searching for other Worlds". Centro de Astrofísica da Universidade do Porto. 16 December 2009. Retrieved 2010-10-16. 
  7. ^ "ESPRESSO: the Echelle spectrograph for rocky exoplanets and stable spectroscopic observations". American Institute of Physics. July 2010. Retrieved 2013-03-12. 
  8. ^ "ESPRESSO: the Echelle spectrograph for rocky exoplanets and stable spectroscopic observations" (PDF). ESO. July 2010. Retrieved 2013-03-12. 
  9. ^ a b c d "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. 
  10. ^ ESPRESSO: The next European exoplanet hunter
  11. ^ "ESO Awards Contracts for Cameras for New Planet Finder". ESO Announcement. Retrieved 8 August 2013. 
  12. ^
  13. ^ ESPRESSO Sees Light at the End of the Tunnel
  14. ^ ESPRESSO vede la luce in fondo al “tunnel”
  15. ^
  16. ^ a b "Planet Found in Nearest Star System to Earth". European Southern Observatory. 16 October 2012. Retrieved 17 October 2012. 
  17. ^ Demory, Brice-Olivier; Ehrenreich, David; Queloz, Didier; Seager, Sara; Gilliland, Ronald; Chaplin, William J.; Proffitt, Charles; Gillon, Michael; Guenther, Maximilian N.; Benneke, Bjoern; Dumusque, Xavier; Lovis, Christophe; Pepe, Francesco; Segransan, Damien; Triaud, Amaury; Udry, Stephane (25 March 2015). "Hubble Space Telescope search for the transit of the Earth-mass exoplanet Alpha Centauri Bb". arXiv:1503.07528v1Freely accessible [astro-ph.EP]. 
  18. ^ "51 Peg b". Exoplanets Data Explorer. 
  19. ^ "55 Cnc d". Exoplanets Data Explorer. 
  20. ^ Endl, Michael. "The Doppler Method, or Radial Velocity Detection of Planets". University of Texas at Austin. Retrieved 26 October 2012. 
  21. ^ "GJ 581 c". Exoplanets Data Explorer. 
  22. ^ "alpha Cen B b". Exoplanets Data Explorer. 
  23. ^ "An NIR laser frequency comb for high precision Doppler planet surveys". Chinese Academy of Sciences. 2010-10-16. Retrieved 2010-10-16. [dead link]