Euclid project in Helsinki
ESA Cosmic Vision 2015-2025
Euclid is one of the four space missions of the European Science Agency (ESA)
science program for 2015-2025 (Cosmic Vision 2015-2025).
The full Cosmic Vision program is:
M refers to a "medium-sized" mission and L to a "large" (in cost) mission.
- M1: Solar Orbiter (close look at the Sun), launch 2017
- M2: Euclid (cosmology), launch 2020
- L1: JUICE (Jupiter Icy Moon Explorer), launch 2022
- M3: PLATO (PLAnetary Transits and Oscillations of stars), launch 2024
The Dark Energy Problem
The main objective of the Euclid mission is to address the "Dark Energy Problem" - why is
the expansion of the universe accelerating? The acceleration was discovered in 1998 by
observing distant supernovae. For this discovery, the 2011 Physics Nobel Prize was awarded
to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess. According to General Relativity
(at least in the homogenous and isotropic approximation to the universe) accelerated
expansion requires that the energy density of the universe is dominated by a previosly
unknown energy component with negative pressure, "Dark Energy". Another possibility is that
General Relativity needs to be modified at cosmological distance scales. A yet third
possibility is that inhomogeneities in the universe affect the observations or the
expansion of the universe much more than expected.
Euclid will address this question by measuring the expansion history of the universe by two
If the two methods agree, we can solve from the expansion history the equation of state for
the dark energy: how its pressure depends on its energy density. If the two methods
disagree, we have discovered that gravity at cosmological scales deviates from General
Relativity, and we can compare the observations to the various suggested modified gravity
- Measuring the expansion history directly using the baryon acoustic oscillation
(BAO) scale as a standard ruler.
- Measuring the dark matter distribution in the universe using its gravitational
lensing effect. The observed growth depends on the expansion rate, so that, assuming
General Relativity, we can solve the expansion rate from it.
Euclid - the next cosmology mission
Euclid is a 1.2 meter space telescope with a large field of view, 0.5 square degrees.
It carries two instruments:
In six years, Euclid will make images of almost half the sky (the part that is 30 degrees
or more from the plane of the Milky Way). The exposure time for each 0.5 square degree
image is about 1 hour, reaching a sensitivity corresponding to limiting magnitude 24.5.
This way we will obtain images of
about 1.5 billion galaxies, from which we determine their distortion due to gravitational
lensing. For the brighter ones, over 50 million galaxies, NISP will
deliver accurate spectroscopic redshifts. These accurate redshifts are used to determine
the three-dimensional distribution of galaxies, from which we get the BAO scale at
different redshifts. For the rest of the 1.5 billion galaxies we obtain (less accurate)
photometric redshifts, from observations at three different infarend bands with NISP,
supplemented by observations at different visible bands from ground-based surveys.
These redshifts are needed for solving the 3-dimensional distribution of dark matter from
the lensing distortions.
- VIS: Imaging instrument ("camera") for visible wavelengths with 0.1 arcsec pixels
- NISP: Near infrared (1 - 2 micron) instrument for slitless spectroscopy with
spectral resolution of 1/500 and imaging (photometry) with 0.3 arcsec pixels
Euclid will be launched to an orbit around the second Lagrange point (L2) of the Sun-Earth
system. The launch is planned for the last quarter of 2019.
There are currently 16 countries in the Euclid consortium: France, Italy, Britain,
Germany, Spain, Netherlands, Switzerland, Norway, Austria, Denmark, Finland, Romania,
Portugal, Bekgium, USA, and Canada, and about 1400 individual consortium members. Finland joined in 2011. From
Finland, there are @4 consortium members, from the Universities of Helsinki, Turku, and
Jyväskylä, and Aalto University. The Physics Department of the University of Helsinki has the leading
role in Finland.
Euclid at the Department of Physics
The Euclid Consortium members from the Department of Physics, University of Helsinki:
- Hannu Kurki-Suonio, group leader, Finnish representative in the Euclid Consortium Board,
manager of the Finnish Euclid Science Data Center
- Elina Keihänen, deputy manager of the Finnish Euclid Science Data Center
- Peter Johansson
- Alexis Finoguenov
- Kari Enqvist
- Seppo Korpela
- Syksy Räsänen
- Pekko Metsä
- Jussi Väliviita
- Charles Kirkpatrick
- Viola Allevato
- Ghassem Gozaliasl
- Francesco Montanari
- Anna-Stiina Suur-Uski
- Valtteri Lindholm
- Kimmo Kiiveri
ESA Euclid page
Euclid Consortium Home Page