Euclid is an ambitious ESA mission to investigate the expansion history of the Universe and the growth of cosmic structures over the last 10 billion years of cosmic history. It is a space telescope with instruments that can detect visible and near-infrared radiation.
Euclid's targets are the many and various galaxies that stretch across the Universe, and which are moving away from us because of the expansion of the universe.
The expansion of the universe and the growth of cosmic structures is influenced by the 'dark' universe, which is composed of dark energy and dark matter. These mysterious components combine with gravity to influence the evolution of the cosmos.
Dark energy accelerates the expansion of the universe, while dark matter accelerates the growth of cosmic structure. But scientists do not know what dark energy and dark matter actually are.
There are many hypotheses. For example, particle physicists have proposed plenty of candidates for the dark matter, and there have been hints of dark energy in our theories before, most notably in Einstein's General Theory of Relativity.
By measuring how fast the universe's expansion has been accelerating, and how fast cosmic structure has been growing, astronomers can infer the behaviour of dark energy, dark matter and gravity. This should give us a better clue as to their precise nature.
Euclid was selected for implementation in June 2012 by ESA's Science Programme Committee. It's main scientific objectives are:
- To investigate whether Dark Energy is real, or whether the apparent acceleration of the Universe is caused by a breakdown of General Relativity on the largest scales, or a failure of our assumption that the universe is more or less uniform in density.
- If dark energy is real, to investigate whether it is a constant energy spread across space, which would make it the Cosmological Constant found in Einstein's General Relativity, or a new force of nature that evolves with the expansion of the Universe.
- To investigate the nature of Dark Matter, the mass of neutrino particles and whether there are other, so-far undetected fast moving particle species in the Universe.
- To investigate the conditions in the Universe after the Big Bang that seeded the large-scale structure of the universe that we observe today.
In order to accomplish this, Euclid must survey more than a third of the sky, and image more than a billion galaxies out to a distance from where light has taken up to 10 billion years to reach us.
Euclid is named after the Greek mathematician Euclid of Alexandria, who lived around 300 BC. He founded the subject of geometry in his book Elements. As the density of matter and energy determine the geometry of the universe, the mission was named in his honour.
The Euclid spacecraft is about 4.5 metres tall and 3.1 metres in diameter. It is a space telescope that consists of two major components: the service module and the payload module.
The payload consists of a 1.2 metre three-mirror Korsch type telescope, a thermal control system, the Fine Guidance Sensor (FGS), and two instruments: the visible imager (VIS) instrument and the Near Infrared Spectro-Photometer (NISP) spectrometer.
- The ultra stable silicon-carbide (SiC) is used for the telescope's mirrors and support structure
- The VIS instrument uses 36 CCDs (4k×4k pixels each) in a 6×6 grid
- The NISP instrument uses 16 mercury cadmium telluride (HgCdTe) near infrared detectors (2k×2k pixels each) in a 4×4 grid
- Euclid will deliver an unprecedented large volume of data for an astronomical space mission: more than 1 peta-bits of data every year, or about 4 times more data than Gaia.
Following a cruise of 30 days, Euclid will operate in a large halo orbit around the L2 point of the Sun-Earth system, which is located 1.5 million km from the Earth in the anti-Sun direction. The orbit will not suffer from any Earth eclipses and will have a radius of 1 million kilometres. An operational lifetime of 6 years is planned.
The Euclid spacecraft will be controlled from the European Space Operations Centre (ESOC, Darmstadt, Germany) using the Cebreros (Spain), and Malargüe (Argentina) ground stations. During launch and early operations, the New Norcia (Australia), and Kourou (French Guiana) ground station will also be used.
Science operations will be conducted from the European Space Astronomy Centre (ESAC, Villanueva de la Cañada, Madrid province, Spain).