Annual Report 2011 Max Planck Institute for Astronomy

IV.4 The eucLid Dark Energy mission
eucLid is a cosmology satellite mission in the framework
of eSa's Cosmic Vision programme. It will characterize
the nature of Dark Matter and Dark Energy by measuring
the clustering of matter and the expansion history
of the Universe since redshift 2. The task of designing
and building the Euclid instruments is coordinated by a
consortium of 13 European countries, bringing together
scientists and engineers from more than 100 individual
institutions. eucLid will launch in 2020 to the Earth-Sun
L2 point from where 15 000 square degrees of extragalactic
sky will be observed over a six year mission
duration.
Eighty years ago we seemed to know a lot about the
Universe. Galaxies were identified as “island universes”
similar to our own Milky Way, made up of stars and
gas and dust. All constituents of mass seemed to have
been found – until in the 1930s the outer rotation curves
of galaxies proved to be incompatible with the mass of
visible matter given the laws of gravitation. With the
addition of similar discrepancies in galaxy clusters it
became clear that a heretofore unrecognized and invisible
component – coined “Dark Matter” – must contain
5 times more mass than the visible “Baryonic”
matter that makes up stars and galaxies.
70 years later, by the end of the 1990s, another discrepancy
was noticed. The expansion history of the
Universe did not obey the law of gravitation yet again.
Contrary to expectations, the expansion of the Universe
was observed to be accelerating, requiring an additional
ingredient, termed "Dark Energy", in the massenergy
content of the universe. This discovery was
awarded with the Nobel-Prize in physics in 2011. Dark
Energy must provide a mass density, to accommodate a
near-euclidian flat space as identified by the cobe and
WMAP missions, but at the same time deliver a repulsive
effect.
eucLid: a quest for bringing light into darkness
esa’s eucLid mission is designed to investigate the nature
of Dark Energy, and Dark Matter, with the aim to
pin down its equation of state parameters. These differ
between various proposals for the nature of Dark
Energy and can at the same time test predictions made
by modified models of gravitation. eucLid will utilize
Weak Gravitational Lensing measurements to map the
Dark Matter density in 3D-space and at the same time
measure the expansion history of the Universe from
z 2 to today. This combination will allow scientists to
determine the equation of state parameters by a factor
of 30 better than any current or planned measurements
for the next two decades.
eucLid's diagnostic require mapping of 15 000 square
degrees of extragalactic sky with (1) high resolution
imaging, (2) near-infrared spectroscopy, and (3) near-
infrared photometry. While the former will be implemented
in the VIS visual imager, MPIA’s involvement
lies mainly with the latter two, realized in the NISP (Near
Infrared Spectro-Photometer) instrument. We are directly
responsible for two hardware contributions, the NIR
filters as well as a calibration light source to support the
instrumental calibrations in flight. MPIA also fills the
position of instrument scientist and image simulator for
the photometry channel and is hence centrally involved
in the planning and definition aspects of the mission.
The mission was officially selected for the 2 nd M-class
launch slot in esa’s Cosmic Vision Programme in late
Fig. IV.4.1: An early concept of the Euclid telescope. A 1.2 mdiameter
off-axis mirror will feed the two instruments VIS
and NISP, mounted to the lower side of the optical bench.
The light-path will be deliberately simple to allow a very high
image quality for the VIS imager (from the eucLid Red Book,
esa, 2011).
Secondary
Mirror
Structure
Ultra Stable
Support
Truss
Optical
Bench
Secondary Mirror
and Focus System
Primary
Mirror
Credit: A. Anselmi, Thales Alenia Space Italia
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