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Big Bang’s glow
maps early mass
By Alexandra Witze
In a cosmic feat of observation, astronomers have used the distortions of
ancient light left over from the Big Bang
to explore how clumps of matter were
distributed in the early universe.
The work also independently confirms the existence of dark energy, an
enigmatic force that appears to be pushing the cosmos apart faster and faster.
Researchers using the Atacama Cosmology Telescope in the Chilean Andes
reported the discoveries July 5 in two
papers in Physical Review Letters. The new
work “will be a really powerful probe for
figuring out dark energy and a lot of other
interesting things,” says team member
Blake Sherwin of Princeton University.
Several scientists have won Nobel
Prizes for studying the cosmic microwave
background radiation, the afterglow left
from the fireball that accompanied the
creation of the universe 13. 7 billion years
ago. In the 2000s, a satellite called the
Wilkinson Microwave Anisotropy Probe
mapped how that radiation is spread
across the entire sky. But seeing the distortions now being studied required a
telescope with more precise vision.
Using the 6-meter Atacama telescope,
astronomers analyzed the temperature
of the afterglow in a narrow strip of sky
along the celestial equator. They used
complex statistical analyses to tease out
how temperature fluctuations — essentially, hot and cold spots on the ancient
sky map — had been distorted by intervening matter.
Astronomers regularly see such
“gravitational lensing” with individual
galaxies or galaxy clusters, when another
massive clump of matter gets in the way.
Just as a piece of broken glass distorts
light passing through it, gravity from the
foreground clump distorts the light com-
ing from the more distant one, making it
appear as a smeared-out arc.
Iapetus splattered in orbital dustup
Black layer is from another Saturn moon’s wrong-way motion
By Nadia Drake
Imagine a powdered-sugar doughnut
hole plowing through a cloud of dark-chocolate dust. The resulting two-colored treat would resemble one of
Saturn’s weirder moons, Iapetus — an icy
world with a coal black face and a bright
white backside.
For centuries astronomers have puzzled over the source of this yin-yang
Dust from another Saturn moon blackens
Iapetus, seen in this false-color image
taken by NASA’s Cassini spacecraft.
color pattern. Now a team led by Daniel
Tamayo of Cornell University offers an
explanation: Dust flung from another
of Saturn’s moons is coating one side of
Iapetus. Because Iapetus doesn’t rotate
relative to Saturn, the same face continually catches the dark moon flakes.
In a study posted online July 7 in Icarus,
Tamayo and colleagues mathematically
describe the movement of dust particles
in the outer Saturnian system. The team
focuses on dust coming from Phoebe, a
dark and distant moon that circles Saturn
in the opposite direction as Iapetus.
Collisions between Phoebe and smaller
outer moons produce an enormous, invisible ring of dust lying far beyond Saturn’s
well-known photogenic ones. Nearly
every particle in that ring larger than 10
micrometers across ends up on Iapetus,
the team concludes. Smaller particles
that miss Iapetus land on the Saturn
moons Titan and Hyperion.
“This is a very significant paper,” says
astronomer Bonnie Buratti of the Jet
Propulsion Laboratory in Pasadena,
Calif. “It does the math.”
