Herschel fact sheet

Herschel, ESA's cutting-edge space observatory, will carry the largest, most powerful infrared telescope ever flown in space. A pioneering mission to study the origin and evolution of stars and galaxies, it will help understand how the Universe came to be what it is today.

Status: In operation

Study cool objects across the Universe and in our Solar System, in particular the formation and evolution of stars and galaxies and their interaction with the interstellar medium.

Carrying the largest telescope ever flown in space with a main mirror 3.5 m across, Herschel is studying the cool Universe at infrared to submillimetre wavelengths. It is probing the formation of stars and galaxies across the history of the Universe, and investigating their interaction with the interstellar medium – the dilute matter between stars from which new stars are forming. Herschel is also examining the physical state and chemical composition of asteroids and comets in our own Solar System, seeking out planet formation, and tracing the signature of water from the interstellar matter from which they form all through to the discs around newly forming stars in other stellar systems.

What’s special?
The Herschel Space Observatory has the largest telescope ever flown in space with a main mirror 3.5 m across, more than four times larger than any previous infrared space telescope and almost one and a half times larger than that of the Hubble Space Telescope. It is also the first space observatory to extend the observations from the far-infrared into submillimetre wavelengths and bridge the two, exploring further into the far-infrared than any previous mission has done. By tapping these unexploited wavelengths, Herschel is seeing phenomena beyond the reach of other observatories, and studying others at a level of detail that has not been captured before.

Herschel is sensitive to the heat from the small fraction of cold dust mixed in with the clouds of gas in space where stars and planets form, and to signatures from particular substances like water. By imaging such regions, Herschel can point astronomers to dense gas where new stars are forming, and study the action in detail.

The Herschel Space Observatory is approximately 7.5 m high and 4 m wide, with a launch mass of 3400 kg . The primary mirror is 3.5 m in diameter and is accompanied by three science instruments: two cameras and imaging spectrometers – PACS (Photoconductor Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging REceiver) – and a very high-resolution spectrometer, HIFI (Heterodyne Instrument for the Far Infrared). Together, these instruments cover approximately 55–671 microns. The detectors in these instruments are cooled to temperatures close to absolute zero by a sophisticated cryogenic system. Herschel is operating autonomously, receiving commands and returning acquired data to Earth in a three-hour communications period every day.

Herschel was launched on 14 May 2009 on an Ariane 5 from ESA’s Spaceport in Kourou, French Guiana. Herschel was launched along with Planck, ESA’s microwave observatory, which is studying the Cosmic Microwave Background. Herschel separated from the Ariane 5 upper stage about 26 minutes after launch; Planck followed a few minutes later. Since then the two spacecraft have operated independently.

Herschel operates from a largo halo orbit around the second Lagrangian point of the Sun–Earth system (L2), a virtual point located 1.5 million km from Earth in the direction opposite to the Sun. The satellite’s average distance from L2 is 800 000 km.

Herschel is built on the heritage of previous ESA successes in infrared astronomy, starting with the pioneering Infrared Astronomical Satellite (IRAS) in 1983, a joint venture between the Netherlands, United Kingdom and USA that produced the first maps of the entire sky at four infrared wavelengths. This success paved the way for ESA's Infrared Space Observatory (ISO), which operated from 1995-1998. The Japanese-led Akari mission mapped more than 94% of the sky at infrared wavelengths in greater detail than IRAS during 2006-2007. NASA’s infrared mission the Spitzer Space Telescope is also currently in orbit.

Herschel takes a giant leap forward in infrared technology while bridging the gap between the wavelengths seen by previous infrared satellites and those studied by radio telescopes on ground.

The telescope is named after the German–British astronomer William Herschel.

Most of Herschel’s observing time is available to the worldwide scientific community through a standard competitive proposal-based time allocation process. A fraction of 32% of the observing time is being allotted to the guaranteed time holders, mainly the instrument consortia.

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