Spectro-Polarimetric High-Contrast Exoplanet Research

For other uses, see Sphere (disambiguation).
SPHERE (black container and silver cylinder) attached to the telescope from the adjunct platform

Spectro-Polarimetric High-contrast Exoplanet REsearch (VLT-SPHERE) is an adaptive optics system and coronagraphic facility at the Very Large Telescope (VLT). It provides direct imaging as well as spectroscopic and polarimetric characterization of exoplanet systems. The instrument operates in the visible and near infrared, achieving, albeit over a limited field of view, superior image quality and contrast for bright targets.[1]

Results from SPHERE complement those from other planet finder projects which include HARPS, CoRoT, and the Kepler Mission.[2] The instrument was installed on Unit Telescope "Melipal" (UT3) and achieved first light in June, 2014. At the time of installation, it was the latest of a series of second generation VLT-instruments such as X-shooter, KMOS and MUSE.[3]

Science goals

The star HR 7581 (Iota Sgr) was observed in SPHERE survey mode. A very low mass star, more than 4000 times fainter that its parent star, was discovered orbiting Iota Sgr at a tiny separation of 0.24". The bright star itself has been suppressed almost completely by SPHERE, to allow the faint companion to appear as a clear bright spot to the upper right of the centre.

Direct imaging of exoplanets is extremely challenging:

  1. The brightness contrast between the planet and its host star typically ranges from 10−6 for hot young giant planets emitting significant amounts of near-infrared light, to 10−9 for rocky planets seen exclusively through reflected light.
  2. The angular separation between the planet and its host star is very small. For a planet ∼10 AU from its host and tens of parsec away, the separation would be only a few tenths of an arcsec.[4]

SPHERE is representative of a second generation of instruments devoted towards direct high-contrast imaging of exoplanets. These combine advanced adaptive optics with high-efficiency coronagraphs to attenuate glare from the host star. In addition, SPHERE employs differential imaging to exploit differences between planetary and stellar light in terms of its color or polarization.[5] Other high-contrast imaging systems that are operational include Project 1640 at the Palomar Observatory and the Gemini Planet Imager at the Gemini South Telescope.[4] The Large Binocular Telescope, equipped with a less advanced adaptive optics system, has successfully imaged a variety of extrasolar planets.[6]

SPHERE is targeted towards direct detection of Jupiter-sized and larger planets separated from their host stars by 1 to 100 AU. Detecting and characterizing a large number of such planets should offer insight into planetary migration, the hypothetical process whereby hot Jupiters, which theory indicates cannot have formed as close to their host stars as they are found, migrate inwards from where they were formed in the protoplanetary disk.[7] It is also hypothesized that massive distant planets should be numerous; the results from SPHERE should clarify the extent to which the current observed preponderance of closely orbiting hot Jupiters represents observational bias. SPHERE observations will focus on the following types of targets:

Results from SPHERE complement those of detection projects that use other detection methods such as radial velocity measurements and photometric transits. These projects include HARPS, CoRoT, and the Kepler Mission.[2]

Instrument description

The SPHERE instrument and diagram of its subsystems

SPHERE is installed on ESO’s VLT Unit Telescope 3 at the Nasmyth focus. It comprises the following subsystems:

Science results

This infrared image shows the dust ring around the nearby star HR 4796A in the southern constellation of Centaurus. It was one of the first produced by the SPHERE instrument soon after it was installed on ESO's Very Large Telescope in May 2014. It shows not only the ring itself with great clarity, but also reveals the power of SPHERE to reduce the glare from the very bright star — the key to finding and studying exoplanets in future.

Early results have validated the power of the SPHERE instrument, as well as presenting results that challenge existing theory.


  1. "SPHERE Overview". European Southern Observatory. Retrieved 23 May 2015.
  2. 1 2 3 Beuzit, Jean-Luc; et al. "SPHERE: a 'Planet Finder' Instrument for the VLT" (PDF). European Southern Observatory. Retrieved 24 May 2015.
  3. "First Light for SPHERE Exoplanet Imager". ESO. 4 June 2014.
  4. 1 2 Mesa, D.; Gratton, R.; Zurlo, A.; Vigan, A.; Claudi, R. U.; Alberi, M.; Antichi, J.; Baruffolo, A.; Beuzit, J. -L.; Boccaletti, A.; Bonnefoy, M.; Costille, A.; Desidera, S.; Dohlen, K.; Fantinel, D.; Feldt, M.; Fusco, T.; Giro, E.; Henning, T.; Kasper, M.; Langlois, M.; Maire, A. -L.; Martinez, P.; Moeller-Nilsson, O.; Mouillet, D.; Moutou, C.; Pavlov, A.; Puget, P.; Salasnich, B.; et al. (2015). "Performance of the VLT Planet Finder SPHERE". Astronomy & Astrophysics. 576: A121. arXiv:1503.02486Freely accessible. Bibcode:2015A&A...576A.121M. doi:10.1051/0004-6361/201423910.
  5. "First Light for SPHERE Exoplanet Imager". European Southern Observatory. Retrieved 24 May 2015.
  6. Esposito, S.; Mesa, D.; Skemer, A.; Arcidiacono, C.; Claudi, R. U.; Desidera, S.; Gratton, R.; Mannucci, F.; Marzari, F.; Masciadri, E.; Close, L.; Hinz, P.; Kulesa, C.; McCarthy, D.; Males, J.; Agapito, G.; Argomedo, J.; Boutsia, K.; Briguglio, R.; Brusa, G.; Busoni, L.; Cresci, G.; Fini, L.; Fontana, A.; Guerra, J. C.; Hill, J. M.; Miller, D.; Paris, D.; Pinna, E.; et al. (2012). "LBT observations of the HR 8799 planetary system". Astronomy & Astrophysics. 549: A52. arXiv:1203.2735Freely accessible. Bibcode:2013A&A...549A..52E. doi:10.1051/0004-6361/201219212.
  7. D'Angelo, G.; Lubow, S. H. (2008). "Evolution of Migrating Planets Undergoing Gas Accretion". The Astrophysical Journal. 685 (1): 560–583. arXiv:0806.1771Freely accessible. Bibcode:2008ApJ...685..560D. doi:10.1086/590904.
  8. "SPHERE - Instrument Description". European Southern Observatory. Retrieved 24 May 2015.
  9. "The Strange Case of the Missing Dwarf". European Southern Observatory. Retrieved 24 May 2015.
  10. Hardy, A.; Schreiber, M. R.; Parsons, S. G.; Caceres, C.; Retamales, G.; Wahhaj, Z.; Mawet, D.; Canovas, H.; Cieza, L. (2015-02-01). "The First Science Results from Sphere: Disproving the Predicted Brown Dwarf Around V471 Tau". The Astrophysical Journal Letters. 800: L24. arXiv:1502.05116Freely accessible. Bibcode:2015ApJ...800L..24H. doi:10.1088/2041-8205/800/2/L24. ISSN 0004-637X.
  11. Wagner, K.; Apai, D.; Kasper, M.; Robberto, M. (2015-10-22). "Discovery of a Two-armed Spiral Structure in the Gapped Disk around Herbig Ae Star HD 100453". The Astrophysical Journal Letters. 813: L2. arXiv:1510.02212Freely accessible. Bibcode:2015ApJ...813L...2W. doi:10.1088/2041-8205/813/1/L2.

Coordinates: 24°37′39″S 70°24′16″W / 24.6274°S 70.4044°W / -24.6274; -70.4044

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