Effects of high altitude on humans

Quantum mechanics

Atmospheric escape

Martian

Geology

Hydrogen

Physics

Organic chemistry

Oxygen

Mathematics

Mars Exploration Program

Environmental science

Geometry

Atmosphere of Mars

Astrobiology

Atmospheric models

Water vapor

Chemistry

Meteorology

Atmosphere (unit)

Atmospheric sciences

Altitude (triangle)

Nature Geoscience

Atmospheric loss has controlled the history of Martian habitability, removing most of the planet’s initial water through atomic hydrogen and oxygen escape from the upper atmosphere to space. In standard models, H and O escape in a stoichiometric 2:1 ratio because H reaches the upper atmosphere via long-lived molecular hydrogen, whose abundance is regulated by a photochemical feedback sensitive to atmospheric oxygen content. The relatively constant escape rates these models predict are inconsistent with known H escape variations of more than an order of magnitude on seasonal timescales, variation that requires escaping H to have a source other than H2. The best candidate source is high-altitude water, detected by the Mars Express spacecraft in seasonally variable concentrations. Here we use a one-dimensional time-dependent photochemical model to show that the introduction of high-altitude water can produce a large increase in the H escape rate on a timescale of weeks, quantitatively linking these observations. This H escape pathway produces prompt H loss that is not immediately balanced by O escape, influencing the oxidation state of the atmosphere for millions of years. Martian atmospheric water loss may be dominated by escape via this pathway, which may therefore potentially control the planet’s atmospheric chemistry. Our findings highlight the influence that seasonal atmospheric variability can have on planetary&nbsp;evolution. Most of Mars’s initial water has been lost through atmospheric escape, but seasonal imbalances of measured hydrogen loss compared to oxygen are enigmatic. Photochemical models suggest that seasonal water vapour at high altitudes enhances hydrogen loss rates.

Elevated atmospheric escape of atomic hydrogen from Mars induced by high-altitude water