upper atmosphere of Uranus, these results
not only confirm that the planet is a poison-
ous, frozen environment utterly hostile to life
as we know it, but that its prevailing aroma
is also downright offensive. More upliftingly,
the study also highlights the importance of
our far-flung seventh planet for understand-
ing the early history of our Solar System, as
well as the likely conditions on similarly large,
icy worlds beyond the Solar System.
Gemini Speckle Imaging of
Binaries among K2 Planet Hosts
The vast majority of the known exoplanets
have been discovered by the Kepler mission
via the transit method. The 4-arcsecond pixel
size of Kepler means that light from any near-
by companion or background object will be
blended with that of the planetary host. The
blending reduces the observed depths of
planetary transits, making it harder to de-
tect the planets and potentially biasing their
inferred sizes. Thus, knowing the fraction of
exoplanet hosts that are in binary systems is
important for determining the distribution
of planetary sizes as well as establishing any
possible relationship between stellar mul-
tiplicity and planet formation. While there
January 2019 / 2018 Year in Review
are theoretical reasons for expecting that a
stellar companion may inhibit planet forma-
tion, apart from limiting the range of stable
orbits, the influence of stellar multiplicity on
the frequency and properties of planets is
not yet fully understood.
Follow-up imaging studies of the host stars
of transiting planets detected by the Kepler
mission have found little or no difference
in the frequency of stellar multiplicity of
exoplanet hosts compared to nearby field
stars, although there is some evidence that
exoplanet hosts are less likely to have stellar
companions within about 100 astronomical
units (AU). Now, a team of astronomers have
used high-resolution speckle imaging data
from the visiting Differential Speckle Survey
Instrument (DSSI) at both the Gemini North
and South telescopes, as well as at the WIYN
telescope at Kitt Peak National Observatory
in Arizona, to target a sample of planetary
hosts found in Kepler’s K2 mission. The K2
mission has observed a series of fields along
the ecliptic plane, each one for 80 days, and
has detected more than 500 exoplanet can-
didates. The different observing strategy
results in differences in the distributions of
mass and orbital properties as compared to
the original Kepler sample.
GeminiFocus
Figure 8.
Gemini/NIFS observations
of Uranus. Panel A: the
appearance of Uranus at
1.55 μm (low methane
absorption, showing
reflection for cloud/haze
at all vertical levels),
showing the position
of the seven test areas
used for analysis. Panel
B: the appearance of
Uranus at 1.62 μm (high
methane absorption,
showing reflection from
upper atmospheric haze
only). Panel C: reference
spectrum of Uranus
averaged over area “1” (in
Panel A) near the center
of the planet’s disk, just
north of the equator.
Panel D: strength of
the model absorption
coefficients derived over
the Gemini/NIFS spectral
range for conditions
found at the tops of
Uranus’s main visible
clouds.
[Figure reproduced
from Irwin et al., Nature
Astronomy, 2018.]
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