Atmosphere and water loss from early Mars under extreme solar wind and extreme ultraviolet conditions

Weak magnetism of Martian impact basins may reflect cooling in a reversing dynamo

Understanding the longevity of Mars's dynamo is key to interpreting the planet's atmospheric loss history and the properties of its deep interior. Satellite data showing magnetic lows above many large impact basins formed 4.1-3.7 billion years ago (Ga) have been interpreted as evidence that Mars's dynamo terminated before 4.1 Ga-at least 0.4 Gy before intense late Noachian/early Hesperian hydrological activity. However, evidence for a longer-lived, reversing dynamo from young volcanics and the Martian meteorite ALH 84001 supports an alternative interpretation of Mars's apparently demagnetized basins. To understand how a reversing dynamo would affect basin fields, here we model the cooling and magnetization of 200-2200 km diameter impact basins under a range of Earth-like reversal frequencies. We find that magnetic reversals efficiently reduce field strengths above large basins. In particular, if the magnetic properties of the Martian mantle are similar to most Martian meteorites and late remagnetization of the near surface is widespread, >90% of large ( > 800 km diameter) basins would appear demagnetized at spacecraft altitudes. This ultimately implies that Mars's apparently demagnetized basins do not require an early dynamo cessation. A long-lived and reversing dynamo, unlike alternative scenarios, satisfies all available constraints on Mars's magnetic history.

Water Vapor Adsorption Provides Daily, Sustainable Water to Soils of the Hyperarid Atacama Desert

Water is necessary for all life on Earth. Water is so critical that organisms have developed strategies to survive in hyperarid environments. These regions with extremely low water availability are also unique analogs in which to study the physico-chemical conditions of extraterrestrial environments such as Mars. We have identified a daily, sustainable cycle of water vapor adsorption (WVA) and desorption that measurably affects soil water content (SWC) in the hyperarid region of the Atacama Desert in southern Perú. We pair field-based soil temperature and relative humidity soil profiles with laboratory simulations to provide evidence for a daily WVA cycle. Using our WVA model, we estimate that one adsorptive period-one night-increases SWC by 0.2-0.3 mg/g of soil (∼30 μm rainfall). We can plausibly rule out other water inputs during our field campaign that could account for this water input, and we provide evidence that this WVA cycle is driven by solar heating and maintained by atmospheric water vapor. The WVA may also serve to retain water from infrequent rain events in these soils. If the water provided by WVA in these soils is bioavailable, it could have significant implications for the microorganisms that are endemic to hyperarid environments.

Geophysical and atmospheric evolution of habitable planets

The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere.