Sky and Telescope - May 2015 - 16

News Notes

IN BRIEF

EXOPLANETS I Spin-up to Habitability? . . .

Ancient Five-Planet System Found.
Astronomers have conﬁrmed a ﬁveplanet system around the 11 billionyear-old star Kepler-444 (HIP 94931, in
the constellation Lyra). With estimated
sizes ranging from 0.4 to 0.7 times
Earth, all ﬁve should be rocky, but not
one is in the star's habitable zone:
they all orbit the red dwarf within 0.08
astronomical unit, or less than oneﬁfth the size of Mercury's orbit. An
optimistic habitable zone would start
at 0.47 a.u., nearly six times farther
out, Tiago Campante (University of Birmingham, UK, and Aarhus University,
Denmark) and colleagues report in
the February 1st Astrophysical Journal.
Kepler-444 is not the ﬁrst star of this
age with planetary children: astronomers have also found two planets
around Kepler-10 (10 billion years old)
and two planets around Kapteyn's Star
(11 billion years old, S&T: Sept. 2014, p.
14). But those planets are super-Earthsize or larger.

Exoplanets tightly circling their stars
might have a better chance of being habitable than previously thought.
Red dwarfs are the most abundant type
of star in the galaxy. They're also roughly
one-quarter the Sun's mass, bringing
their habitable zones closer in and making it easier to spot Goldilocks planets.
But a planet that orbits close enough to
a red dwarf to be in the star's habitable
zone could become tidally locked. Having a perpetual night side could in turn
destabilize chemical exchanges between
the atmosphere and surface or even cause
the atmosphere to collapse.
New research, however, suggests that
the eﬀect of the planet's atmosphere might
be strong enough to break any tidal locking, allowing the planet to rotate freely.
Jérémy Leconte (University of Toronto
and Pierre Simon Laplace Institute,
France) and colleagues created a 3D
climate model to predict the eﬀect of a
planet's atmosphere on the speed of its
rotation. It all goes back to the amount
of starlight able to penetrate the planet's
atmosphere and reach its surface. Temperature diﬀerences at the surface drive
winds. Those winds constantly push
against the planet by running into mountains or creating waves on the ocean.
Such friction then inﬂuences the rotation

■ CAMILLE M. CARLISLE

Citizen Scientists Find Disks. Volunteers with Disk Detective have found
37 planet-forming disk candidates for
follow-up study. Led by Marc Kuchner
(NASA Goddard) and the Zooniverse
team, Disk Detective uses data from
the Wide-ﬁeld Infrared Survey Explorer
(WISE) satellite, which found hundreds
of thousands of infrared sources that
could be disks around nearby stars
- or far-oﬀ galaxies, interstellar dust
clouds, or other extended infrared
sources. Volunteers can classify each
of the 278,000 infrared sources after
a brief tutorial at www.diskdetective.
org. Thus far they've turned up 478
"objects of interest" (possible disks)
and 37 strong candidates. The strong
candidates range in distance from 80
to 3,300 light-years. By 2018 the project
should net more than 1,000 disks.
■ MONICA YOUNG

May 2015 sky & telescope

rate of the planet, helping to speed it up
or slow it down.
Astronomers have long seen this eﬀect
on the planet Venus, where the atmosphere's inﬂuence is so powerful that
it forces the planet out of synchronous
rotation into a slow retrograde rotation.
But planetary scientists didn't think thinner atmospheres like Earth's could throw
their weight around as eﬀectively.
Leconte's simulations show that thinner atmospheres actually have a larger
rotational eﬀect on their planets. With
less scattered sunlight, extra heat reaches
the deepest atmospheric layer and creates
stronger winds. If Venus had an atmosphere like Earth's, it would spin 10 times
faster, the team reports January 15th in
Science. This is radically diﬀerent from
previous research, which suggested that it
would spin 50 times slower. An unlocked
planet should therefore have strong atmospheric mixing and stable temperatures.
Although a large number of known
terrestrial exoplanets should thus have a
day-night cycle, the duration of their days
could last between a few weeks and a few
months. So these planets would still be
far from Earth-like, with only a few days
per year, cautions René Heller (McMaster
University, Canada).
■ SHANNON HALL

. . . and New Exoplanet Hunters Rising
Several near-future exoplanet hunters
are in development. Here's a non-exhaustive list of projects to keep an eye on:
* Searching for transiting planets around
bright (i.e. nearby) stars are the European
Southern Observatory's Next-Generation
Transit Survey, which recently achieved
ﬁrst light, and the Transiting Exoplanet
Survey Satellite (TESS), slated for launch
in August 2017. By targeting nearby stars,
these two projects both hope to ﬁnd exoplanets that will be easier to follow up on.
* The transit hunter Evryscope is in the
construction phase. Led by Nicholas Law
(University of North Carolina at Chapel
Hill), the prototype array places 27 individual 61-mm telescopes into a common

mount; an attached 780 million-pixel
detector records a continuous movie of
the entire night sky in 2-minute exposures. First light will be later this year.
* Direct imaging is really coming into
its own. In its ﬁrst-light observations,
the Gemini Planet Imager (GPI) found
that planets c and d around HR 8799
appear to be unexpectedly diﬀerent in
composition, maybe due to diﬀerences in
cloud cover. The instruments SPHERE
(Spectro-Polarimetric High-contrast
Exoplanet Research, installed at the VLT)
and SCEXAO (Subaru Coronagraphic
Extreme Adaptive Optics) are also on the
direct-imaging hunt.
■ MONICA YOUNG

http://www.diskdetective.org http://www.diskdetective.org

Sky and Telescope - May 2015

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