Sky & Telescope - September 2021 - 10

NEWS NOTES
COSMOLOGY
Dark Energy Survey Catalogs Millions of Galaxies
Using this technique, astronomers can
discern the evolution of galaxy clustering
and reveal the actions of dark
matter and dark energy over cosmic
time. Estimates of cosmic shear - distortions
due to weak gravitational lensing
- provide additional information about
the distribution of dark matter.
The results support the dark matter-dark
energy scenario, in which dark
energy and slow-moving dark matter
particles vastly overshadow the remaining
5% of " normal " matter that exists
in galaxies, stars, planets, and people.
There's one nagging discrepancy:
ASTRONOMERS HAVE CAPTURED
226 million galaxies up to 7 billion
light-years away in an area covering
about one-eighth of the entire sky.
This treasure trove of data provides the
best-ever probe of cosmic evolution and
illuminates the role of dark matter and
dark energy in shaping the large-scale
structure of the universe.
The Dark Energy Survey (DES)
started back in August 2013. On May
27th, the international collaboration
behind the survey posted 30 scientific
studies covering the first three years of
observations. These papers will appear
SOLAR SYSTEM
Three Missions to Head for Venus in Next Decade
NASA ANNOUNCED on June 2nd that
it had selected two missions to launch
for Venus in the 2028-2030 timeframe
as part of the agency's Discovery
Program: the Deep Atmosphere Venus
Investigation of Noble gases, Chemistry
and Imaging (DAVINCI+) and Venus
Emissivity, Radio Science, InSAR, Topography,
and Spectroscopy
(VERITAS). These spacecraft
mark NASA's first
return to our sister planet
since the Magellan mission,
which ended in 1994.
A week later, the European
Space Agency announced
10 SEPTEMBER 2021 * SKY & TELESCOPE
it will also send its EnVision orbiter to
Venus in the early 2030s.
All three missions will look at
Venus's present conditions for clues to
its past, to see if the planet might once
have hosted a more habitable environment.
DAVINCI+ will deploy a descent
sphere that will sample gases and
weather conditions during
a 63-minute drop through
the Venusian atmosphere.
An orbiter will relay these
data to Earth while also
An artist's concept shows
DAVINCI+ approaching the
surface of Venus.
pDistant galaxies teem in this deep image
taken by the Dark Energy Camera.
in the Monthly Notices of the Royal
Astronomical Society. (Although the
Dark Energy Survey was completed in
early 2019, the collaboration is still processing
the last three years of data.)
To map out large-scale structure,
DES scientists start with individual
galaxies. Based on a galaxy's brightness
at several visible and near-infrared
wavelength bands, the team determines
its photometric redshift, which yields a
rough but reliable distance estimate.
Like previous surveys, DES has found
that the current universe is a few percent
less " clumpy " than the standard
cosmological model would predict.
Nobody knows why.
Another galaxy survey officially took
off a few weeks ago at the Nicholas U.
Mayall 4-meter Telescope at Kitt Peak
National Observatory in Arizona. The
similarly named Dark Energy Spectroscopic
Instrument aims to capture
spectra (rather than images) of tens
of millions of galaxies and quasars
over the next five years. The European
Space Agency's Euclid mission, slated
for launch in 2022, will carry out an
even more sensitive survey with similar
cosmological goals.
¢GOVERT SCHILLING
sticking around to obtain high-resolution
ultraviolet and near-infrared measurements.
These images will zero in on
tesserae, Venus's most ancient terrain,
while also shedding light on the planet's
mysterious " ultraviolet absorber " that
swallows up to half of the incoming
solar energy Venus receives.
VERITAS will construct a complete
topographical map of the planet's surface
in an effort to trace the history of
the planet's plate tectonics. Meanwhile,
EnVision will map Venus's gravitational
field to probe its internal structure.
Both VERITAS and EnVision will also be
looking for signs in the atmosphere and
on the surface to determine whether
Venus is still volcanically active.
¢DAVID DICKINSON
DARK ENERGY SURVEY / DOE / FNAL / DECAM / CTIO / NOIRLAB / NSF / AURA;
ACKNOWLEDGMENTS: T.A. RECTOR / M. ZAMANI / D. DE MARTIN; DAVINCI+: NASA / GSFC
Sky & Telescope - September 2021

Table of Contents for the Digital Edition of Sky & Telescope - September 2021
