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Abstract:

Dark spots on Neptune observed by Voyager and the Hubble Space Telescope are thought to be anticyclones with lifetimes of a few years, in contrast with very long-lived anticyclones in Jupiter and Saturn. The full life cycle of any Neptune dark spot has not been captured due to limited temporal coverage, but our Hubble observations of a recent feature, NDS-2018, provide the most complete long-term observational history of any dark vortex on Neptune. Past observations suggest some dark spots meet their demise by fading and dissipating without migrating meridionally. On the other hand, simulations predict a second pathway with equatorward migration and disruption. Our HST observations suggest NDS-2018 is following the second pathway. Some of the HST observations reveal transient dark features with widths of about 4000 to 9000 km, at latitudes between NDS-2018 and the equator. The secondary dark features appeared before changes in the meridional migration of NDS-2018 were seen. These features have somewhat smaller size and much smaller contrast compared to the main dark spot. Discrete secondary dark features of this scale have never been seen near previous dark spots, but global-scale dark bands are associated with several previous dark spots in addition to NDS-2018. The absolute photometric contrast of NDS-2018 (as large as 19%) is greater than previous dark spots, including the Great Dark Spot seen by Voyager. New simulations suggest that vortex internal circulation is weak relative to the background vorticity, presenting a clearly different case from stronger anticyclones observed on Jupiter and Saturn.

Abstract:

Inverse techniques are used to extract information about an exoplanet's atmosphere. These techniques are prone to biased results if the appropriate forward model is not used. One assumption used in a forward model is to assume that the radius of the planet is constant with wavelength; however, a more realistic assumption is that the photospheric radius varies with each wavelength. We explore the bias induced when attempting to extract the molecular abundance from an emission spectrum, which was generated with a variable radius. We find that for low-gravity planets, the retrieval model is not able to fit the data if a constant radius model is used. We find that biased results are obtained when studying a typical hot Jupiter in the MIRI LRS wavelength range. Finally, we show that high-gravity planets do not suffer a bias. We recommend that future spectral retrievals that interpret exoplanet emission spectra should take into account a variable radius.

Abstract:

Lava planets have non-global, condensible atmospheres similar to icy bodies within the Solar system. Because they depend on interior dynamics, studying the atmospheres of lava planets can lead to understanding unique geological processes driven by their extreme environment. Models of lava planet atmospheres have thus far focused on either radiative transfer or hydrodynamics. In this study, we couple the two processes by introducing ultraviolet (UV) and infrared (IR) radiation to a turbulent boundary layer model. We also test the effect of different vertical temperature profiles on atmospheric dynamics. Results from the model show that UV radiation affects the atmosphere much more than IR. UV heating and cooling work together to produce a horizontally isothermal atmosphere away from the substellar point regardless of the vertical temperature profile. We also find that stronger temperature inversions induce stronger winds and hence cool the atmosphere. Our simulated transmission spectra of the bound atmosphere show a strong SiO feature in the UV that would be challenging to observe in the planet’s transit spectrum due to the precision required. Our simulated emission spectra are more promising, with significant SiO spectral features at 4.5 and 9 μm that can be observed with the James Webb Space Telescope. Different vertical temperature profiles produce discernible dayside emission spectra, but not in the way one would expect.