48 research outputs found
Methane release on Early Mars by atmospheric collapse and atmospheric reinflation
A candidate explanation for Early Mars rivers is atmospheric warming due to
surface release of H or CH gas. However, it remains unknown how much
gas could be released in a single event. We model the CH release by one
mechanism for rapid release of CH from clathrate. By modeling how
CH-clathrate release is affected by changes in Mars' obliquity and
atmospheric composition, we find that a large fraction of total outgassing from
CH clathrate occurs following Mars' first prolonged atmospheric collapse.
This atmosphere-collapse-initiated CH-release mechanism has three stages.
(1) Rapid collapse of Early Mars' carbon dioxide atmosphere initiates a slower
shift of water ice from high ground to the poles. (2) Upon subsequent
CO-atmosphere re-inflation and CO-greenhouse warming, low-latitude
clathrate decomposes and releases methane gas. (3) Methane can then perturb
atmospheric chemistry and surface temperature, until photochemical processes
destroy the methane. Within our model, we find that under some circumstances a
Titan-like haze layer would be expected to form, consistent with transient
deposition of abundant complex abiotic organic matter on the Early Mars
surface. We also find that this CH-release mechanism can warm Early Mars,
but special circumstances are required in order to uncork 10 kg of
CH, the minimum needed for strong warming. Specifically, strong warming
only occurs when the fraction of the hydrate stability zone that is initially
occupied by clathrate exceeds 10%, and when Mars' first prolonged atmospheric
collapse occurs for atmospheric pressure > 1 bar.Comment: Accepted by Planetary and Space Scienc
Why are Mountaintops Cold? The Transition of Surface Lapse Rate on Dry Planets
Understanding surface temperature is important for habitability. Recent work
on Mars has found that the dependence of surface temperature on elevation
(surface lapse rate) converges to zero in the limit of a thin CO2 atmosphere.
However, the mechanisms that control the surface lapse rate are still not fully
understood. It remains unclear how the surface lapse rate depends on both
greenhouse effect and surface pressure. Here, we use climate models to study
when and why "mountaintops are cold". We find the tropical surface lapse rate
increases with the greenhouse effect and with surface pressure. The greenhouse
effect dominates the surface lapse rate transition and is robust across
latitudes. The pressure effect is important at low latitudes in moderately
opaque atmospheres. A simple model provides insights into the mechanisms of the
transition. Our results suggest that topographic cold-trapping may be important
for the climate of arid planets.Comment: 14 pages, 4 figures; accepted for publication on Geophysical Research
Letter
The Super-Earth Opportunity - Search for Habitable Exoplanets in the 2020s
The recent discovery of a staggering diversity of planets beyond the Solar
System has brought with it a greatly expanded search space for habitable
worlds. The Kepler exoplanet survey has revealed that most planets in our
interstellar neighborhood are larger than Earth and smaller than Neptune.
Collectively termed super-Earths and mini-Neptunes, some of these planets may
have the conditions to support liquid water oceans, and thus Earth-like
biology, despite differing in many ways from our own planet. In addition to
their quantitative abundance, super-Earths are relatively large and are thus
more easily detected than true Earth twins. As a result, super-Earths represent
a uniquely powerful opportunity to discover and explore a panoply of
fascinating and potentially habitable planets in 2020 - 2030 and beyond.Comment: Science white paper submitted to the 2020 Astronomy and Astrophysics
Decadal Surve
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Pre- and Post-entry, Descent and Landing Assessment of the Martian Atmosphere for the Mars 2020 Rover
This review provides an analysis of activities undertaken by the Mars 2020 Council of Atmospheres (CoA) in support of the entry, descent, and landing (EDL) of the Mars 2020 rover Perseverance in Jezero crater, Mars. The activities of the CoA were designed to evaluate the safety of early-stage landing site candidates and, later, to constrain the range of plausible conditions expected at Jezero crater during the early northern spring season of EDL, following the successful blueprint of similar councils for prior landed Mars missions. The multiyear effort of the CoA involved using a combination of numerical modeling of the local Martian atmosphere with limited-domain mesoscale models and atmospheric reanalysis using data assimilation techniques, along with atmospheric observations from multiple orbiting assets, to generate an atmospheric “forecast” for the day of landing. Here we present an overview of these activities, focusing in greater detail on those elements that depart from prior CoA activities as performed for Mars Phoenix, Mars Science Laboratory, and the InSight lander. Following the successful landing of Perseverance on 2021 February 18, reconstruction and reassessment activities were performed and are presented here, comparing prelanding predictions with actual, as-flown conditions