The European Space Agency's Gaia
spacecraft is poised to begin its
mission to map a billion stars in our
galaxy to an unprecedented level of
detail, with its scheduled launch on
Thursday.
"It's going to be the most
accurate and the most detailed 3D
map of stars there has ever been,"
said Dr Ralph Cordey, head of science
at Astrium UK, a company involved
in the building of the spacecraft.
More than a decade in gestation,
and costing €740m (£625m), Gaia is
set to spend five years orbiting
around the Sun at a distance of 1.5m
km from the Earth at the so-called L2
Lagrangian point, capturing
information relating to stars
distributed across the Milky Way.
The starry "census" will record
many parameters including stars'
distances from the Earth accurate to
around 1%. "It's a revolution in
accuracy," said Albert Zijlstra,
Director of the Jodrell Bank Centre
for Astrophysics and Professor in
Astrophysics at the University of
Manchester. "In astronomy 1% is
marvellous."
Gaia will also measure stars'
velocities and movements as well as
their type, age and spectra – which
reveal details of their temperature
and chemical makeup. "It's enabling
us to understand the dynamical
evolution of our galaxy," said
Cordey.
Gaia will record data for around
1% of the 100bn stars in our galaxy,
taking around 70 measurements for
each star over the mission's lifetime.
It is hoped that the data gathered by
Gaia will help to develop a better
'yardstick' for measuring distances in
the universe.
The spacecraft will also provide
indirect clues as to the existence of
planets. "[Gaia] will see the motion of
the star but as a big planet moves
around a star, the star itself should
move a little bit because of the
gravity of the planet," said Zijlstra.
"It is a minute effect but Gaia should
see it – but only for nearby stars and
only for large planets."
Gaia could also help scientists to
understand the mysterious nature of
dark matter, which we cannot see but
is thought to exert strong
gravitational effects. "The motion of
stars in our galaxy is very important
to understanding the distribution and
the behaviour of this stuff that we call
dark matter," says Cordey. The
spacecraft's has two telescopes that
will look at stars in two directions
simultaneously. The telescopes will
focus the light from the stars on to a
billion pixel camera built by
Chelmsford company E2V
Technologies.
A vast amount of data will be
collected, meaning that is must be
'filtered' by an onboard computer
before being beamed down. "What
this video processing unit does is it
captures the important interesting
parts [of the data], the tracks of the
stars for example as they go across
the camera, and it sends those back to
earth," Cordey reveals.
Gaia is not the first mission to
map the Milky Way's stars. Its
predecessor, the ESA's Hipparcos
mission, ran between 1989 and 1993
and resulted in the creation of the
Hipparcos catalogue containing
118,218 stars. Gaia's observing
technique also stems from the
Hipparcos mission.
"Hipparcos was a big, big step
forward," says Cordey. Zijlstra
agrees. "That had an enormous
impact on astronomy but it only did
things out to a couple of hundred light
years, maybe a thousand light years
for accurate distances" he says. "Gaia
will go very much further than that.
Gaia spacecraft set for launch on mission to map a billion stars
