WWW.ASTRONOMY.COM 23The earliest snapshot of
our universe, dubbed the
cosmic microwave background
(CMB), comes from 380,000
years after the Big Bang. From
2009 to 2013, the European
Space Agency’s Planck mis-
sion, with significant partici-
pation by NASA, returned the
most detailed measurements
of the CMB, charting tiny
fluctuations in its light. These
fluctuations hold a wealth of
information, allowing us to
tease out details about the Big
Bang and the early universe.
But some details are per-
plexing. “At very large scales,
there are strange effects that
leave us a little less than com-
pletely comfortable operating
the standard model [of cos-
mology]” that scientists use to
describe the universe, says
Krzysztof Górski, a senior
research scientist at NASA’s
Jet Propulsion Laboratory in
Pasadena, California. Among
those effects: The temperature
f luctuations of the CMB skyseem divided into two hemi-
spheres: a less “wrinkled”
northern one, and a more
wrinkled southern one, in
which the hot spots are hotter
and the cold spots are colder.
And the southern hemisphere
contains a strangely large cold
spot that spans about 10° on
the sky.
The standard model
describes very well many other
aspects of Planck’s view of the
cosmos. So, the question is:
What do these anomalies tell
us about the early universe?
In a paper published June 6
by the Planck Collaboration in
Astronomy and Astrophysics,
researchers including Górski
analyzed Planck’s newest pub-
licly released data. These
include improved all-sky maps
of CMB polarization, which
records how the CMB photons
that we now observe have
scattered off ionized matter— such as electrons not bound
in atoms — in the universe
since they were first emitted.
Finding places where peculiar
patterns in temperature and
polarization f luctuations over-
lap, they hoped, might offer
insight into what caused the
temperature anomalies.
But while Planck measured
CMB temperature f luctuations
extremely well, it was not orig-
inally designed for polarim-
etry, Górski notes. Although
its all-sky maps of CMB polar-
ization are the best available,
they represent the limit of the
satellite’s capabilities to even
measure tiny fluctuations in
the CMB’s polarization across
the sky, he says. To the best of
Planck’s ability to measure, the
CMB polarization gives no
clues as to why various regions
of the CMB sky appear dis-
cernibly different, and isn’t the
key astronomers were hopingfor. The temperature anoma-
lies could be random fluctua-
tions, rare but not completely
unexpected, or caused by some
as-yet-unknown process. But
astronomers can’t point to a
clear explanation just yet. “The
cut-and-dry statistical state-
ment is you can’t really tell one
way or another,” Górski says.
Understanding the CMB
anisotropy anomalies will
hopefully tell us something
fundamentally important
about the early universe, he
says. But newer, better polar-
ization measurements are
needed to determine their
cause. For now, the cosmic
mystery remains unsolved.that the top layer of lunar soil
reaches lower temperatures
than those measured by Apollo
astronauts on the nearside, pos-
sibly because of differences in
soil composition between theMoon’s two hemispheres. By
early October, the pair had com-
pleted 10 lunar days of work.
China’s next robotic lunar
mission, Chang’e-5, is slated
for launch by the end of 2019.Chang’e-5 is a sample return mis-
sion, aiming to return the first
new samples from the lunar sur-
face since 1976. If all goes well,
the Chang’e name may return to
our list in 2020.9
The
cosmic
cold spot
conundrum
continues
The temperature of the cosmic
microwave background, as measured
by the Planck satellite, shows some
strange anomalies: The universe is
divided into roughly two hemispheres,
based on variations in temperature. A
large cold spot (circled) — bigger than
astronomers expect — also appears
in the sky. ESA AND THE PLANCK COLLABORATION