Surface energy budget and thermal inertia at Gale Crater: Calculations from ground‐based measurements

The analysis of the surface energy budget (SEB) yields insights into soil‐atmosphere interactions and local climates, while the analysis of the thermal inertia ( I ) of shallow subsurfaces provides context for evaluating geological features. Mars orbital data have been used to determine thermal inertias at horizontal scales of ~10 4  m 2 to ~10 7  m 2 . Here we use measurements of ground temperature and atmospheric variables by Curiosity to calculate thermal inertias at Gale Crater at horizontal scales of ~10 2  m 2 . We analyze three sols representing distinct environmental conditions and soil properties, sol 82 at Rocknest (RCK), sol 112 at Point Lake (PL), and sol 139 at Yellowknife Bay (YKB). Our results indicate that the largest thermal inertia I  = 452 J m −2  K −1  s −1/2 (SI units used throughout this article) is found at YKB followed by PL with I  = 306 and RCK with I  = 295. These values are consistent with the expected thermal inertias for the types of terrain imaged by Mastcam and with previous satellite estimations at Gale Crater. We also calculate the SEB using data from measurements by Curiosity's Rover Environmental Monitoring Station and dust opacity values derived from measurements by Mastcam. The knowledge of the SEB and thermal inertia has the potential to enhance our understanding of the climate, the geology, and the habitability of Mars. Key Points We calculate the thermal inertia and surface energy budget at Gale Crater We use MSL REMS measurements for our calculationsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108664/1/jgre20287.pd

Reevaluating the evidence for a Hadean-Eoarchean dynamo.

The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown

Reevaluating the evidence for a Hadean-Eoarchean dynamo

The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown

Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity

Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements

Lifetime of the outer solar system nebula from carbonaceous chondrites

The evolution and lifetime of protoplanetary disks (PPDs) play a central role in the formation and architecture of planetary systems. Astronomical observations suggest that PPDs evolve in two timescales, accreting onto the star for up to several million years (Myr) followed by gas dissipation within ≲1 Myr. Because solar nebula magnetic fields are sustained by the gas of the protoplanetary disk, we can use paleomagnetic measurements to infer the lifetime of the solar nebula. Here, we use paleomagnetic measurements of meteorites to constrain this lifetime and investigate whether the solar nebula had a two-timescale evolution. We report on paleomagnetic measurements of bulk subsamples of two CO carbonaceous chondrites: Allan Hills A77307 and Dominion Range 08006. If magnetite in these meteorites can acquire a crystallization remanent magnetization that recorded the ambient field during aqueous alteration, our measurements suggest that the local magnetic field strength at the CO parent body location was <0.9 μT at some time between 2.7 and 5.1 Myr after the formation of calcium-aluminum-rich inclusions. Coupled with previous paleomagnetic studies, we conclude that the dissipation of the solar nebula in the 3–7 AU region occurred <1.5 Myr after the dissipation of the nebula in the 1–3 AU region, suggesting that protoplanetary disks go through a two-timescale evolution in their lifetime, consistent with dissipation by photoevaporation and/or magnetohydrodynamic winds. We also discuss future directions necessary to obtain robust records of solar nebula fields using bulk chondrites, including obtaining ages from meteorites and experimental work to determine how magnetite acquires magnetization during chondrite parent body alteration

Reevaluating the evidence for a Hadean-Eoarchean dynamo.

The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown.NERC and ER

Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity

Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kV m−1 to 100 kV m−1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m−1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)—MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ electrical measurements

Likely frost events at Gale crater: Analysis from MSL/REMS measurements

International audienceWe provide indirect evidence for the formation of frost at the surface of Gale crater by analyzing the highest confidence data from simultaneous measurements of relative humidity and ground temperature during the first 1000 sols of the Mars Science Laboratory (MSL) mission. We find that except for sol 44, frost events could have occurred only between sols 400 and 710, corresponding to the most humid and coldest time of the year (from early fall to late winter). In particular, measurements at Dingo Gap during sols 529-535, at an unnamed place during sols 554-560, at Kimberley during sols 609-617 and at an unnamed place during sols 673-676 showed the largest likelihood of the occurrence of frost events. At these four locations, the terrain is composed of fine-grained and loosely packed material with thermal inertia values of ∼200 SI units, much lower than the 365 ± 50 SI units value found at the landing ellipse. This is important because terrains with exceptionally low thermal inertia favor the formation of frost by lowering minimum daily ground temperatures. An order-of-magnitude calculation to determine the thickness of the frost layer at these four locations results in values of tenths of μm, while the precipitable water content is a few pr-μm. Therefore, surface frost events can have important implications for the local water cycle at Gale crater. In addition, frost is the most likely type of water that can be temporarily found in bulk amounts on the surface of Mars at low latitudes and therefore can cause weathering, influencing the geology of Gale crater