Recent advances in interplanetary dust modelling provide much improved estimates of the fluxes of cosmic dust particles into planetary (and lunar) atmospheres throughout the solar system. Combining ...the dust particle size and velocity distributions with new chemical ablation models enables the injection rates of individual elements to be predicted as a function of location and time. This information is essential for understanding a variety of atmospheric impacts, including: the formation of layers of metal atoms and ions; meteoric smoke particles and ice cloud nucleation; perturbations to atmospheric gas-phase chemistry; and the effects of the surface deposition of micrometeorites and cosmic spherules. There is discussion of impacts on all the planets, as well as on Pluto, Triton and Titan.
ABSTRACT
Transit searches have uncovered Earth-size planets orbiting so close to their host star that their surface should be molten, so-called lava planets. We present idealized simulations of the ...atmosphere of lava planet K2-141b and calculate the return flow of material via circulation in the magma ocean. We then compare how pure Na, SiO, or SiO2 atmospheres would impact future observations. The more volatile Na atmosphere is thickest followed by SiO and SiO2, as expected. Despite its low vapour pressure, we find that a SiO2 atmosphere is easier to observe via transit spectroscopy due to its greater scale height near the day–night terminator and the planetary radial velocity and acceleration are very high, facilitating high dispersion spectroscopy. The special geometry that arises from very small orbits allows for a wide range of limb observations for K2-141b. After determining the magma ocean depth, we infer that the ocean circulation required for SiO steady-state flow is only 10−4 m s−1, while the equivalent return flow for Na is several orders of magnitude greater. This suggests that a steady-state Na atmosphere cannot be sustained and that the surface will evolve over time.
Mars methane detection and variability at Gale crater Webster, Christopher R.; Mahaffy, Paul R.; Atreya, Sushil K. ...
Science (American Association for the Advancement of Science),
01/2015, Volume:
347, Issue:
6220
Journal Article
Peer reviewed
Open access
Reports of plumes or patches of methane in the martian atmosphere that vary over monthly time scales have defied explanation to date. From in situ measurements made over a 20-month period by the ...tunable laser spectrometer of the Sample Analysis at Mars instrument suite on Curiosity at Gale crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 parts per billion by volume (ppbv) at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period (where 1 sol is a martian day), we observed elevated levels of methane of 7.2 ± 2.1 ppbv (95% CI), implying that Mars is episodically producing methane from an additional unknown source.
Reanalysis of the Viking Lander results on Mars has suggested a surface reservoir of organic carbon at the ppm level. The size of this putative reservoir could be explained if the source of carbon on ...Mars is meteoritic in origin and is destroyed primarily by UV irradiation, yielding methane. By combining a numerical UV model for the surface of Mars with published laboratory measurements of organic UV photolysis, the times required to completely convert the carbon within individual particles to methane may be calculated. For interplanetary dust particles (IDPs) initially containing 10 wt% carbon, lifetimes of organics range from 3.9 years for a 0.2 μm diameter particle at equatorial latitudes to 4900 years for a 200 μm diameter particle at polar latitudes, and implies a median time for IDP organics by UV photolysis of 320 years at equatorial latitudes and 1500 years at polar latitudes. Assuming no redistribution of organics over the surface, the IDP organic reservoir at the surface would range from 1.1 × 10−6 kg m−2 at equatorial latitudes to 6.6 × 10−6 kg m−2 at polar latitudes. If accreted carbon is evenly mixed with the soil, up to 3.4 ppm of organic carbon at the VL1 landing site can be explained from a meteoritic origin and up to 4.9 ppm at the VL2 landing site. Derived from the IDP organic reservoir, small fluctuations in methane would exist due to variations in UV irradiation with latitude and LS. Production of methane is expected to range up to 0.35 pptv sol−1.
Key Points
IDP organic carbon can persist on the surface for longer than one Martian year
Carbon inferred at Viking landing sites is consistent with IDP organics
Methane produced from IDPs cannot explain observed variations in the atmosphere
We report new measurements of atmospheric methane by the Curiosity rover’s Tunable Laser Spectrometer that is part of the Sample Analysis at Mars suite (TLS-SAM), finding nondetections during two ...daytime measurements of average value 0.05 ± 0.22 ppbv (95% confidence interval CI). These are in marked contrast with nighttime background levels of 0.52 ± 0.10 (95% CI) from four measurements taken during the same season of northern summer. This large day-night difference suggests that methane accumulates while contained near the surface at night, but drops below TLS-SAM detection limits during the day, consistent with the daytime nondetection by instruments on board the ExoMars Trace Gas Orbiter. With no evidence for methane production by the rover itself, we propose that the source is one of planetary micro-seepage. Dynamical modeling indicates that such methane release is contained within the collapsed planetary boundary layer (PBL) at night due to a combination of nocturnal inversion and convergent downslope flow winds that confine the methane inside the crater close to the point where it is released. The methane abundance is then diluted during the day through increased vertical mixing associated with a higher altitude PBL and divergent upslope flow that advects methane out of the crater region. We also report detection of a large spike of methane in June 2019 with a mean
in situ
value over a two-hour ingest of 20.5 ± 4 ppbv (95% CI). If near-surface production is occurring widely across Mars, it must be accompanied by a fast methane destruction or sequestration mechanism, or both.
Ultraviolet shielding materials are potential ecological niches for biosignatures. Finding such materials on Mars would narrow the search for potentially habitable regions. A mini-goniometer was ...built to collect transmission spectra as a function of scattering angle for Mars analog regoliths (JSC Mars-1, basalt, cheto bentonite, and kieserite) and crystalline rock samples from the Haughton impact structure on Devon Island, Nunavut, in the Canadian High Arctic Archipelago. The transmission through the materials was assessed at ultraviolet and visible wavelengths and at different scattering angles. From the results, it is possible to classify the samples into UV transmitters and UV quenchers. UV transmitters are materials that favor transmittance of UV wavelengths compared to photosynthetically active radiation (PAR), while the UV quenchers are materials that effectively block UV radiation from propagating into the subsurface. Additionally, samples that are effective UV quenchers tend to have more isotropic scattering profiles, whereas UV transmitters tend to favor forward scattering profiles. Samples with greater porosity had greater overall transmission. The depths at which radioresistant microorganisms can exist on present-day Mars are estimated by modeling the transmission for regoliths and crystalline rocks under martian insolation. The depth at which LD
occurs is found to range down to 0.3 mm, while still allowing up to 1000 kJ/m
of PAR at those depths. Due to the exceptionally protective nature of JSC Mars-1, intimate mixtures of organisms and regolith will result in some organisms experiencing orders of magnitude less UV flux than others, even when protected by only a single grain of simulant.
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 $\mu$m 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.
The upper bound of 50 parts per trillion by volume for Mars methane above 5 km established by the ExoMars Trace Gas Orbiter, substantially lower than the 410 parts per trillion by volume average ...measured overnight by the Curiosity Rover, places a strong constraint on the daytime methane flux at the Gale crater. We propose that these measurements may be largely reconciled by the inhibition of mixing near the surface overnight, whereby methane emitted from the subsurface accumulates within meters of the surface before being mixed below detection limits at dawn. A model of this scenario allows the first precise calculation of microseepage fluxes at Gale to be derived, consistent with a constant 1.5 × 10−10 kg·m−2·sol−1 (5.4 × 10−5 tonnes·km−2·year−1) source at depth. Under this scenario, only 2.7 × 104 km2 of Mars's surface may be emitting methane, unless a fast destruction mechanism exists.
Plain Language Summary
The ExoMars Trace Gas Orbiter and the Curiosity Rover have recorded different amounts of methane in the atmosphere on Mars. The Trace Gas Orbiter measured very little methane (<50 parts per trillion by volume) above 5 km in the sunlit atmosphere, while Curiosity measured substantially more (410 parts per trillion by volume) near the surface at night. In this paper we describe a framework which explains both measurements by suggesting that a small amount of methane seeps out of the ground constantly. During the day, this small amount of methane is rapidly mixed and diluted by vigorous convection, leading to low overall levels within the atmosphere. During the night, convection lessens, allowing methane to build up near the surface. At dawn, convection intensifies and the near‐surface methane is mixed and diluted with much more atmosphere. Using this model and methane concentrations from both approaches, we are able—for the first time—to place a single number on the rate of seepage of methane at Gale crater which we find equivalent to 2.8 kg per Martian day. Future spacecraft measuring methane near the surface of Mars could determine how much methane seeps out of the ground in different locations, providing insight into what processes create that methane in the subsurface.
Key Points
Nighttime SAM‐TLS seasonal cycle enrichment measurements and TGO sunset/sunrise measurements are not in opposition
Microseepage fluxes must be local to Gale, range from 0.82 to 4.6 kg/sol, and are consistent with a constant source at depth
Little of Mars experiences microseepage unless a fast destruction mechanism exists or Gale is very unusual
Abstract
Water-ice clouds were frequently detected throughout the 151-sol Phoenix mission by the Phoenix lidar, providing insight into the Martian water cycle. However, the lidar could not be used ...continuously, and as such, the cloud data were temporally constrained to when observations were acquired. Here we reconstruct a record of water-ice clouds at the Phoenix landing site by examining the radiative contribution made by the clouds to the surface energy balance. This is accomplished by modeling the data from the 2 m MET air temperature sensor on board the lander. Clouds radiating from 0 and 30 W m
−2
of energy toward the surface are consistent with the MET record over the course of the mission. The additional longwave flux at the surface induced a warming of the surface and near-surface temperatures, usually between 1–3 K; however, the clouds showed a high degree of sol-to-sol variability. This radiative analysis indicates that clouds were present much earlier in the mission than previously known, and cloud emission reached a maximum near sol 90, consistent with analyses of the annular cloud at the Phoenix landing site. The modeled flux from clouds was compared to the water-ice optical depth retrieved from the Phoenix lidar, showing that optically thicker clouds emitted more radiation toward the surface.
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