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| SPHERE (instrument) | |
|---|---|
| Name | SPHERE |
| Mission | Very Large Telescope |
| Operator | European Southern Observatory |
| Type | Adaptive optics coronagraph |
| Wavelength | Visible to near-infrared |
| Resolution | Diffraction-limited |
| Launched | Commissioned 2014 |
SPHERE (instrument) SPHERE is an extreme adaptive optics instrument and coronagraphic imager installed on Unit Telescope 3 of the Very Large Telescope at the Paranal Observatory operated by the European Southern Observatory. Designed for high-contrast imaging of exoplanets and circumstellar environments, SPHERE combines wavefront control, coronagraphs, and differential imaging to suppress starlight and reveal faint companions and disks around nearby stars. SPHERE has been central to programs led by consortia from institutes such as the Max Planck Institute for Astronomy, Observatoire de Paris, INAF, and the European Southern Observatory.
SPHERE was developed as part of the instrumentation program for the Very Large Telescope to address exoplanet characterization pioneered by projects like NACO, NaCo, and successor concepts from the Keck Observatory and Gemini Observatory. The instrument integrates technologies drawn from instruments such as GPI and prototypes tested at facilities including the Laboratoire d'Astrophysique de Marseille and the Institute for Astronomy, University of Hawaii. SPHERE's science cases were defined in the context of missions like Kepler, Gaia, and preparatory work for space observatories such as JWST and future concepts like LUVOIR and HabEx.
The SPHERE architecture comprises three principal science channels: the infrared differential imager and spectrograph (IRDIS), the integral field spectrograph (IFS), and the Zurich Imaging Polarimeter (ZIMPOL). Each channel was developed through collaborations among institutions including the Max Planck Institute for Astronomy, INAF, ETH Zurich, and the European Southern Observatory. The instrument is fed by an extreme adaptive optics system based on a deformable mirror and a high-order Shack–Hartmann wavefront sensor similar in heritage to systems used at Keck Observatory and Subaru Telescope. Optical designs use coronagraphic masks inspired by concepts from NACO and theoretical work by groups linked to LESIA and CEA.
IRDIS provides dual-band imaging for searches and astrometry in the near-infrared with detectors and optics developed alongside teams from IPAG and ONERA. The IFS delivers low-resolution spectroscopy across the YJ or YJH bands enabling spectral characterization tied to libraries like those from SPEX and surveys such as the PALMS and SONG programs. ZIMPOL operates at visible wavelengths with fast modulation polarimetry techniques developed at ETH Zurich and used in studies by groups at MPIA and Observatoire de Genève.
SPHERE's adaptive optics system, SAXO, uses a high-order deformable mirror and a pyramid/Shack–Hartmann hybrid wavefront sensor architecture influenced by techniques from ESO and laboratories such as ONERA. Extreme adaptive optics corrects atmospheric turbulence characterized by the Kolmogorov turbulence model employed in site studies at Paranal Observatory and performance budgets referencing measurements from the Fried parameter at Cerro Paranal. Coronagraph designs implemented include apodized pupil Lyot coronagraphs and pupil-stabilized masks building on work by teams at CEA, LESIA, and Laboratoire d'Astrophysique de Marseille. Differential techniques include angular differential imaging (ADI) used in surveys like NACO Large Program and spectral differential imaging (SDI) developed in parallel at facilities such as VLT.
SPHERE supports several observing modes: IRDIS dual-band imaging, IRDIS long-slit spectroscopy, IFS integral field spectroscopy, and ZIMPOL polarimetric imaging. Performance metrics are benchmarked against instruments such as GPI and earlier VLT instruments including NACO, with achieved contrasts reaching 10^-6–10^-7 at separations of ~0.5–1.0 arcseconds under good seeing conditions recorded by the Paranal Seeing Monitor. Astrometric accuracy and photometric stability enable follow-up programs tied to catalogs from Gaia and target lists from surveys like HARPS and SOPHIE.
SPHERE was conceived to image young, self-luminous exoplanets, resolve protoplanetary and debris disks, and characterize atmospheric properties of substellar companions. Key survey programs include the SHINE (SpHere INfrared survey for Exoplanets) consortium and targeted programs connected to teams from MPIA, IPAG, INAF, and Observatoire de Paris. SPHERE has yielded direct images and spectra of companions such as wide-orbit planets analogous to discoveries by HR 8799 imaging teams and has resolved disk structures comparable to results for systems like Beta Pictoris and TW Hydrae. Polarimetric observations with ZIMPOL provided detailed mapping of scattered light in disks studied alongside observations from ALMA and HST.
Data processing for SPHERE uses the ESOREX framework provided by ESO and specialized pipelines developed by consortium partners at IPAG, MPIA, and LESIA. Reduction steps include bad-pixel correction, flat-fielding, distortion calibration with reference fields such as 47 Tucanae and NGC 3603, PSF subtraction via principal component analysis methods like KLIP developed in laboratories including STScI and teams working on GPI data, and spectral extraction routines validated against standards from SPEX libraries. High-level data products feed archives at the ESO Science Archive Facility and are used by follow-up facilities such as JWST and ALMA.
Commissioned in 2014 on Unit Telescope 3 at the Very Large Telescope, SPHERE has undergone performance optimizations, realignment campaigns, and software upgrades overseen by ESO and consortium institutes including MPIA and INAF. Instrument maintenance and incremental upgrades addressed detector cosmetics, coronagraph mask sets, and control algorithms influenced by developments at ONERA and LESIA. SPHERE continues to contribute to legacy surveys like SHINE and to coordinated programs with facilities including ALMA, HST, and JWST.