Ultra-hot giant exoplanets receive thousands of times Earth’s
insolation
1
,
2
. Their high-temperature
atmospheres (>2,000 K) are ideal laboratories for studying extreme
planetary climates and ...chemistry
3
–
5
. Daysides
are predicted to be cloud-free, dominated by atomic species
6
and substantially hotter than
nightsides
5
,
7
,
8
. Atoms are expected to recombine into molecules over the
nightside
9
, resulting
in different day-night chemistry. While metallic elements and a large
temperature contrast have been observed
10
–
14
, no
chemical gradient has been measured across the surface of such an exoplanet.
Different atmospheric chemistry between the day-to-night
(“evening”) and night-to-day (“morning”) terminators
could, however, be revealed as an asymmetric absorption signature during
transit
4
,
7
,
15
. Here, we report the detection of an asymmetric
atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and
temporally resolve this signature thanks to the combination of high-dispersion
spectroscopy with a large photon-collecting area. The absorption signal,
attributed to neutral iron, is blueshifted by −11±0.7 km
s
-1
on the trailing limb, which can be explained by a combination
of planetary rotation and wind blowing from the hot dayside
16
. In contrast, no signal arises
from the nightside close to the morning terminator, showing that atomic iron is
not absorbing starlight there. Iron must thus condense during its journey across
the nightside.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We present a near-infrared transmission spectrum of the long period (P=542 days), temperate (\(T_{eq}\)=294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 (WFC3) instrument aboard ...the Hubble Space Telescope (HST). With a measured mass of 12 \(\pm\) 3 \(M_{\oplus}\) and a radius of 9.2 \(\pm\) 0.1 \(R_{\oplus}\), HIP 41378 f has an extremely low bulk density (0.09 \(\pm\) 0.02 g/cm\(^{3}\)). We measure the transit depth with a median precision of 84 ppm in 30 spectrophotometric channels with uniformly-sized widths of 0.018 microns. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1-1.7 microns. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for this planet further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with JWST. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap between the Solar System giants, directly imaged planets, and the highly-irradiated hot Jupiters traditionally studied via transit spectroscopy.
We present the bright (V\(_{mag} = 9.12\)), multi-planet system TOI-431, characterised with photometry and radial velocities. We estimate the stellar rotation period to be \(30.5 \pm 0.7\) days using ...archival photometry and radial velocities. TOI-431b is a super-Earth with a period of 0.49 days, a radius of 1.28 \(\pm\) 0.04 R\(_{\oplus}\), a mass of \(3.07 \pm 0.35\) M\(_{\oplus}\), and a density of \(8.0 \pm 1.0\) g cm\(^{-3}\); TOI-431d is a sub-Neptune with a period of 12.46 days, a radius of \(3.29 \pm 0.09\) R\(_{\oplus}\), a mass of \(9.90^{+1.53}_{-1.49}\) M\(_{\oplus}\), and a density of \(1.36 \pm 0.25\) g cm\(^{-3}\). We find a third planet, TOI-431c, in the HARPS radial velocity data, but it is not seen to transit in the TESS light curves. It has an \(M \sin i\) of \(2.83^{+0.41}_{-0.34}\) M\(_{\oplus}\), and a period of 4.85 days. TOI-431d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterisation, while the super-Earth TOI-431b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431b is a prime TESS discovery for the study of rocky planet phase curves.
Ultra-hot giant exoplanets receive thousands of times Earth's insolation. Their high-temperature atmospheres (>2,000 K) are ideal laboratories for studying extreme planetary climates and chemistry. ...Daysides are predicted to be cloud-free, dominated by atomic species and substantially hotter than nightsides. Atoms are expected to recombine into molecules over the nightside, resulting in different day-night chemistry. While metallic elements and a large temperature contrast have been observed, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ("evening") and night-to-day ("morning") terminators could, however, be revealed as an asymmetric absorption signature during transit. Here, we report the detection of an asymmetric atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this signature thanks to the combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. Iron must thus condense during its journey across the nightside.
The Maunakea Spectroscopic Explorer (MSE) is a planned 11.25-m aperture facility with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. A rebirth of the ...3.6m Canada-France-Hawaii Telescope on Maunakea, MSE will use 4332 fibers operating at three different resolving powers (R ~ 2500, 6000, 40000) across a wavelength range of 0.36-1.8mum, with dynamical fiber positioning that allows fibers to match the exposure times of individual objects. MSE will enable spectroscopic surveys with unprecedented scale and sensitivity by collecting millions of spectra per year down to limiting magnitudes of g ~ 20-24 mag, with a nominal velocity precision of ~100 m/s in high-resolution mode. This white paper describes science cases for stellar astrophysics and exoplanet science using MSE, including the discovery and atmospheric characterization of exoplanets and substellar objects, stellar physics with star clusters, asteroseismology of solar-like oscillators and opacity-driven pulsators, studies of stellar rotation, activity, and multiplicity, as well as the chemical characterization of AGB and extremely metal-poor stars.
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