Sky and Telescope - March 2016 - 14

News Notes

EXOPLANETS I Watching
Young Worlds Grow

The core technology package for ESA's LISA Pathﬁnder
includes two gold-platinum cubes ﬂoating in vacuum
containers, shown here on either side of the instrument
schematic. Separating the cubes is a laser interferometer
with a set of 22 mirrors and beamsplitters. The beams
measure the cubes' locations within trillionths of a meter.

ESA

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MISSIONS I LISA Pathﬁnder Heads to Space
A trailblazing mission took to the skies
on December 3rd as a Vega rocket carrying the LISA Pathﬁnder spacecraft lit up
the night over Kourou, French Guiana.
LISA Pathﬁnder will test key technologies for the upcoming Evolved Laser
Interferometer Space Antenna (eLISA)
project, slated for launch in 2034. eLISA
will use three free-ﬂying spacecraft to
create a laser interferometer a million
kilometers on a side in order to search for
ripples in spacetime called gravitational
waves (S&T: Dec. 2015, p. 26). The spacecraft's lasers will measure the position
of masses suspended in freefall at the
end of each "arm," enabling researchers to look for any jiggling in the cubes'
positions induced by gravitational waves
passing through the solar system.
LISA Pathﬁnder serves as a testbed
for the new technologies required for
the upcoming European Space Agency
mission, by mimicking one arm of the
14

March 2016 sky & telescope

future interferometer. The craft carries
two 46-mm-wide gold-platinum cubes,
each suspended in a vacuum compartment. The compartments are separated by
38 cm, where sits a miniature laser interferometer (see above). Researchers aim
to detect any relative motion between the
two masses to within a few picometers (a
trillionth of a meter or 10-12 m).
The LISA Pathﬁnder mission will
also check propulsion, laser ranging, and
gravitational sensors built for the full-up
eLISA mission, as well as demonstrate
the ﬁrst use of a micronewton propulsion system.
The craft will start its six-month scientiﬁc mission in early March, circling
around the stable L1 Lagrangian point
between Earth and the Sun.
■ DAVID DICKINSON

W
Watch
the recorded LISA Pathﬁnder
llaunch at http://is.gd/lisapathlaunch.

Results from the American Astronomical Society's third Extreme Solar Systems
meeting in Hawai'i highlight that we're
now moving from counting planets to
characterizing their formation.
Paul Kalas (University of California,
Berkeley), Abhijith Rajan (Arizona State
University), and colleagues explored the
super-Jupiter orbiting 650 astronomical
units from the star HD 106906 - more
than 10 times Pluto's farthest point from
the Sun. Using images of the system
from the Hubble Space Telescope and the
Gemini Planet Imager (GPI), the team
found that a disturbed ring encircles the
star and that the faraway planet's orbit is
tilted 21° out of line with this disk. These
facts conﬁrm the planet probably formed
closer to the star and was later "exiled" by
some sort of gravitational encounter.
Another GPI study by Thayne Currie
(Subaru Telescope) and others detected
spiral arms in the disk surrounding the
10 million-year-old star HD 100546. At
least one growing planet sits at an arm's
end. The planet's color doesn't match any
atmospheric models; instead, the team
thinks the emission GPI detects is from
gas that's feeding the planet.
■ MONICA YOUNG

STELLAR I Massive Star
Forms from Disk
Observations from the ALMA and Atacama Pathﬁnder Experiment instruments
in Chile have enabled astronomers to peer
through a cocoon and see a stable disk of
gas feeding the forming O-star at its center.
Katharine Johnston (University of Leeds,
UK) and colleagues published the results in
the November 1st Astrophysical Journal. The
observations reveal gas swirling in a disk
shape around the protostar, dubbed AFGL
4176. The disk spans somewhere between
760 and 980 astronomical units. Outﬂows
also shoot out from both sides of the structure. The result adds to growing evidence
that the universe's most massive stars form
the same way as its smaller ones (S&T: Oct.
2015, p. 24). ✦
■ MONICA YOUNG
http://www.is.gd/lisapathlaunch
Sky and Telescope - March 2016

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