Sky and Telescope - November 2015 - 14

News Notes

EXOPLANETS I Microlensing World Conﬁrmed
Astronomers have conﬁrmed the
existence of an exoplanet originally found
via microlensing - the ﬁrst time they've
been able to successfully follow up on this
investigative method.
In a microlensing event, one star passes
in front of another from our perspective,
and this alignment - within a fraction of
a milliarcsecond ( 1/3,600,000°) - boosts the
light of the background star like a magnifying glass would. If the closer, magnifying star has a planet around it, this planet
can add an extra blip to the light curve of
the boosted signal.

Observers have found about three
dozen exoplanet candidates via microlensing. But to conﬁrm these one-shot events,
astronomers generally must wait several
years until the stars move far enough
apart to see them separately. Only then
can they determine each star's physical
characteristics, which they need in order
to conﬁrm the blip's nature.
Virginie Batista (Astrophysics Institute of Paris) and colleagues used images
from the Hubble Space Telescope and the
Keck II telescope on Mauna Kea to study
the stars involved in the microlensing

event OGLE-2005-BLG-169. Collaborating
amateur and professional astronomers
discovered this system in 2005. Since
then, the stars have moved farther apart
in the sky, ﬁnally separating enough for
astronomers to split them.
The analysis, reported in two papers in
the August 1st Astrophysical Journal, shows
that the host star is a K5 main-sequence
star (still fusing hydrogen in its core, as
the Sun does), with a mass about twothirds that of our star. It also conﬁrms that
the planet is 12 to 15 Earth masses (about
equal to Uranus) and orbits its star roughly
4 astronomical units out.
■ CAMILLE M. CARLISLE

EXOPLANETS I Earth Cousin Really Earth-like?

COSMOCHEMISTRY

On July 23rd, the Kepler team
announced the discovery of Kepler-452b.
This exoplanet has a radius 1.6 times that
of our home world and orbits its G-type
star every 385 days. That puts it well
within the star's habitable zone, the (fuzzily deﬁned) region where liquid water
could exist on a planet's surface.
Kepler-452b is the ﬁrst planet to meet
the three criteria of being an Earth-size
planet in the habitable zone around a
truly Sun-like star. But whether it's really
Earth-like remains unknown. The planet
is too small and faint for ground-based
observers to determine its mass and therefore its density and likely composition. (It
was conﬁrmed using statistical methods
rather than additional observations.)
Given the masses of other, comparably sized exoplanets, Jon Jenkins (NASA

Buckyballs Help Solve
Interstellar Mystery

Ames Research Center) and colleagues
estimate Kepler-452b has 3 to 7 Earth
masses. The size measurement and mass
estimate put the planet on the dividing
line between super-Earths, which have
rocky surfaces, and sub-Neptunes, which
have a signiﬁcant gaseous envelope. As
Jenkins put it, "This planet has a somewhat better than even chance of being
rocky." The team reports the discovery in
the August Astronomical Journal.
The announcement comes as part of
Kepler's seventh data release, which netted 521 new planet candidates, including
12 that are less than twice Earth's diameter and in their stars' habitable zones.
The tally of conﬁrmed planets has risen
to 1,030, with about two dozen of those in
their stars' habitable zones.
■ MONICA YOUNG

IN BRIEF
Closest Rocky Exoplanet Discovered.
Using the ESO's 3.6-m telescope in the Canary
Islands and NASA's Spitzer Space Telescope,
Fatemeh Motalebi (University of Geneva, Switzerland) and colleagues discovered a transiting
rocky planet in the constellation Cassiopeia.
The planet orbits HD 219134, a 5th-magnitude
orange dwarf 21 light-years from Earth. The
team also found hints of two additional superEarths and a giant planet, via the gravitational

tugs they exert on their parent star. The
conﬁrmed planet, b, is the innermost. It's a
super-Earth 4 to 5 times more massive and
about 1.6 times larger than Earth, whipping
around its star every 3 days. Its density is
thus somewhere between 4.7 and 7.0 g/cm3,
similar to Earth's density of 5.5 g/cm3, conﬁrming the planet is likely rocky, the team
reports in Astronomy & Astrophysics.
■ MONICA YOUNG

Soccer-ball-shaped molecules
lurking in the dusty corners of the
Milky Way explain part of a spectral
mystery, Ewen Campbell (University
of Basel, Switzerland) and colleagues
report in the July 16th Nature.
Diﬀ use interstellar bands (DIBs)
have haunted astronomers for almost a
century. First discovered in 1922, these
absorption lines (more than 400 of
them) are seen any time astronomers
look toward dust-reddened stars. But
no ions or molecules tested in the lab
have provided a good spectral match.
Campbell's team decided to test
ionized buckminsterfullerene molecules (a.k.a. "buckyballs") to see if
they might explain some of the bands.
Buckyballs link 60 carbon atoms
into a stable, quasi-spherical cage.
Astronomers have already detected
them in space in gaseous and solid
forms, but neutral buckyballs don't
absorb light at the right wavelengths
to explain DIBs.
When cooled to interstellar temperatures, however, the ionized buckyballs'
spectra provide an exact match to two
diﬀ use interstellar bands, the team
found. Other carbon-bearing molecules may explain the remaining lines.
■ MONICA YOUNG

November 2015 sky & telescope

Sky and Telescope - November 2015

Table of Contents for the Digital Edition of Sky and Telescope - November 2015