Sky and Telescope - May 2018 - 8

NEWS NOTES
COSMOLOGY

Dark Energy Survey
Releases Three-Year Data
SCIENTISTS PRESENTED the ﬁrst data

Successful Falcon Heavy Launch
AT 3:45 P.M. EST on February 6th,

SpaceX successfully launched its Falcon
Heavy from the Kennedy Space Center
in Florida. Currently the world's most
powerful rocket, it's capable of carrying 141,000 pounds to Earth orbit,
more than twice the capacity of the
next most powerful rocket, United
Launch Alliance's Delta IV Heavy.
About eight minutes after liftoff,
the rocket's side boosters landed in
perfect synchrony on concrete pads
not far from the launch complex.
These boosters had seen space once
before, but they won't be used again, as
SpaceX plans to upgrade the rockets.
The center core, which was supposed to land on a drone ship in the
Atlantic Ocean, ran out of ignition
ﬂuid and hit the water at 100 meters
per second (300 mph) about 100
meters (300 feet) from the ship.
Despite this hitch, the mission
was deemed a success. The payload
that SpaceX CEO Elon Musk chose to
send into space - Musk's own Tesla
Roadster - reached an elliptical orbit
8

M AY 2 0 1 8 * S K Y & T E L E S C O P E

p The Falcon Heavy lifted off from Launch
Complex 39-A at the Kennedy Space Center
in Florida on February 6th.

around the Sun that extends slightly
past the orbit of Mars to an aphelion
of 1.67 astronomical units. (Typically,
a demo ﬂight would carry weighted
ballast such as concrete, but Musk
opted to send his car instead.)
SpaceX unveiled plans for a Falcon
Heavy in 2011 with an initial ﬂight set
for 2014, but it experienced a series of
delays. Now taking customers, SpaceX
says a ride will start at an affordable $90 million, a quarter of what it
costs to launch a Delta IV Heavy. The
Falcon Heavy opens a new class of
payload, Musk said, capable of sending
37,000-pound payloads to Mars and
7,700-pound payloads to Pluto. SpaceX
doesn't plan to have it carry humans,
though. For now, the rocket's next
tasks include launching satellites for
a Saudi Arabian communications company and the U.S. Air Force.
■ PAULINE ACALIN

■ GOVERT SCHILLING

* For more details on the Dark Energy
Survey and its results, visit https://is.gd/
darkenergysurveyDR1.

PAULINE ACA LIN

SPACE

release of the Dark Energy Survey (DES)
at January's American Astronomical
Society meeting in Washington, D.C.,
which contains observations collected
between mid-2013 and early 2016.
Preliminary results include discoveries
around the Milky Way to new constraints on cosmological parameters.
The Dark Energy Camera at the
4-meter Victor Blanco Telescope of the
Cerro Tololo Inter-American Observatory in Chile sports 62 CCDs with a
total of 570 million pixels. The survey's
ﬁrst three years cover about 5,000
square degrees - one-eighth of the sky
- and catalog 310 million galaxies and
80 million stars.
Incredibly sensitive DES data led to
the discovery of 11 new stellar streams,
tidally stretched remains of dwarf
galaxies around the Milky Way (S&T:
April 2017, p. 22). The new streams are
located between 40,000 and 165,000
light-years away.
Cosmologists are also using DES to
map dark matter. The invisible stuff
gravitationally lenses light, systematically distorting the shapes of distant
galaxies. So far, scientists have analyzed the shapes of 26 million galaxies
observed in DES's ﬁrst year of operation.
Combining the DES weak-lensing
results with other data yields an
independently measured value for the
current expansion rate of the universe,
known as the Hubble constant (see page
20). The new value, which lies between
66.2 and 68.4 kilometers per second per
megaparsec, is consistent with the value
derived from the Planck mission's measurements of the cosmic background
radiation, but it's still lower than that
obtained from observations of Cepheid
variable stars and Type Ia supernovae.
https://www.is.gd/darkenergysurveyDR1 https://www.is.gd/darkenergysurveyDR1
Sky and Telescope - May 2018

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