SKY_September2014.pdf

(Axel Boer) #1
14 September 2014 sky & telescope

News Notes

14 September 201 4 sky & telescope

The Planck polarization map is at 353
gigahertz (GHz), where the dust emission
is strong. But BICEP2 observed at 150 GHz.
So cosmologists must (1) know how much
of the galactic dust emission is polarized
at 353 GHz; (2) correctly deduce what the
signal looks like at 150 GHz, where the dust
emission is weaker; and (3) correctly split
that polarization signal into its two types,
E-modes and B-modes.
The BICEP2 team extrapolated to 150
GHz using a 353-GHz, CIB-tainted map of
the section of sky that it observed. The two
other teams extrapolated using a 353-GHz
map that’s clean of the CIB but doesn’t
include the BICEP2 fi eld of view. The
Planck team has yet to release its data for
regions near the north and south galactic
poles because those sectors are incredibly
diffi cult to analyze. And BICEP2 observed
near the south galactic pole.
The Planck analysis is diffi cult because
the mission’s team is working on a cosmic
scale. The satellite observed the CMB to
high precision in order to measure the
parameters that characterize the universe
(S&T: June 2013, p. 10). The team has
to correlate all its calculations with one

another to make sure the resulting cos-
mology is self-consistent — they can’t have
one result that doesn’t jibe with another.
Until that’s done, they’re not done.
The fi nal Planck data will obviate the
need to extrapolate. Planck measured
polarization at 30, 44, 70, 100, 143, 217, and
353 GHz. In the units that the cosmolo-
gists use to make their maps, the CMB
signal’s strength doesn’t change as you
look in diff erent frequencies. But the dust
signal does. So if researchers can see how
the signal changes as they move between
frequencies, they can eff ectively wipe the
dust off their cosmic windshield.
The Planck team will release the tem-
perature and polarization data from the full
mission in late 2014 (no later than the fi rst
week of December, and maybe sooner). The
previous release in 2013 included only the
fi rst half of the temperature data. It’s too
soon to say whether the upcoming release
will include Planck’s version of direct
B-mode measurements.
■ CAMILLE M. CARLISLE

NASA’s 35-year-old International Sun-
Earth Explorer 3 spacecraft is back in
action. In late May, about 20 space buff s
banded together to revive ISEE 3.
Launched in 1978, the craft studied
the solar wind and completed two suc-
cessful comet fl ybys. It’s been silently
cruising around the Sun since 1999. But
ground controllers neglected to turn off
its carrier signal.
Realizing that ISEE 3 would pass
close to Earth in August 2014, volunteers
banded together to reestablish communi-
cation. NASA no longer had radio dishes
rigged to transmit and receive at the right
frequency, nor the programs needed to
command the craft — nor the time or
money to hunt it down.
Led by veteran spacewatchers Dennis
Wingo and Keith Cowing and collectively
known as the ISEE-3 Reboot Project, the
group spent months unearthing the old
code, scavenging equipment, and fi nding
two suitable radio dishes. A crowdfund-
ing eff ort yielded more than 2,200 donors
and nearly $160,000.
First contact came on May 29th, hours
after NASA managers gave the go-ahead
for the attempt. Using a makeshift
receiver and transmitter installed at the
Arecibo radio observatory in Puerto Rico,
the team successfully established a two-
way radio link at a transmission rate of
512 bits per second.
Normally, ISEE 3’s 355-day-long orbit
around the Sun would have taken it sail-
ing by Earth in August. But with the craft
back under human control, project mem-
bers plan to fi re its rocket to direct it into a
holding pattern near the fi rst Lagrangian
point, roughly 1.5 million kilometers (0.
million miles) from Earth’s sunward side.
Although it carries no cameras, ISEE 
has two working radio systems, ample
fuel reserves, and a dozen instruments
for studying charged particles, electro-
magnetic fi elds, and related phenomena.
■ J. KELLY BEATTY

SPACECRAFT


ISEE 3 Phones Home


EXOPLANETS I Ancient Kapteyn’s Worlds


Watch a video of the intended
capture at skypub.com/isee3wakes.

Astronomers have discovered two exo-
planets orbiting Kapteyn’s Star, a nearby, dim
M dwarf in a Milky Way Galaxy halo orbit that
likely formed in another galaxy.
Kapteyn b and c might be super-Earths, with
minimum masses of 4.8 and 7 times Earth’s,
respectively. Kapteyn b goes around its host
star in 48 days, closer than Mercury’s orbit
around the Sun. Because the star is a cool red
dwarf, the planet lies in its habitable zone.
At 8 arcseconds per year, Kapteyn’s Star
moves across the sky at a fast clip, covering
the diameter of a full Moon every 225 years.
Only Barnard’s Star migrates more quickly.
Astronomers explain this speed with a
dwarf-galaxy origin. If the Milky Way tidally
shredded a dwarf galaxy, that interaction
would have fl ung the dwarf’s stars into diff er-
ent orbits. Currently, Kapteyn’s Star is only 12.
light-years away; it could be the remnant of a
tidally stripped galaxy whose surviving core
might be the globular cluster Omega Centauri.

The interaction happened at least 10 bil-
lion years ago, meaning that Kapteyn’s Star
and its planets are roughly twice as old as
the solar system, Guillem Anglada-Escudé
(Queen Mary University of London and
University of Göttingen, Germany) and col-
leagues report in an upcoming Monthly
Notices of the Royal Astronomical Society.
That makes it one of the most ancient plan-
etary systems known.
But because M dwarfs emit harsh radia-
tion in their early years, Kapteyn b might not
actually be habitable, suggests a study by
Ofer Cohen (Harvard-Smithsonian Center
for Astrophysics) and colleagues. Harsh stel-
lar weather would strip the atmosphere of a
rocky planet orbiting in a red dwarf’s habit-
able zone, leaving the planet more Mars-like
than Earth-like, Cohen’s team announced
June 2nd at the American Astronomical Soci-
ety meeting in Boston.
■ SHANNON HALL

Read the teams’ research papers at
skypub.com/dustybmodes.

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