High-frequency sensing is exemplified by ultrasonic anemometry. A simple generation mechanism by Martian dust devils is presented, yielding fundamental frequencies between 0.1 and 10 Hz. At low frequencies, emphasis is placed on infrasound. The salient atmospheric characteristics are described in terms of temperature, pressure, and convective stability profiles, followed by wavenumber predictions, and discussions of low- and high-frequency sensing applications. Acoustic sensing is discussed at 50 km above Venus' surface, a level where aerostats (e.g., European Space Agency's EVE) and manned airships (e.g., NASA's HAVOC) may be deployed in the future. The thermophysical and transport parameters were interpolated at the ambient conditions. For the dense atmosphere of Venus, the van der Waals equation of state is used. Strong absorption constrains acoustic sensing within the Martian planetary boundary layer. For Mars, Pathfinder and Mars Express ambient data and averaged thermophysical parameters are used as inputs to a preliminary model based on the continuum approximation for Mars' thin atmosphere-the need for Boltzmann-based treatment is discussed in the context of Knudsen numbers. Geophysical Research Letters 44 (15): 7686-7694 doi: 10.Generic predictions for acoustic dispersion and absorption in the atmospheres of Mars and Venus are presented. Evidence for a low bulk crustal density for Mars from gravity and topography. These maps show the kinds of variations they expect, such as denser crust beneath Mars’ giant volcanoes. The resulting estimate for the density of the lunar crust essentially matched the GRAIL result of 2,550 kg/m 3 (about 159 pounds per cubic foot).įrom the new model, they generated global maps of the crust’s density and thickness. Terence Sabaka.īefore taking on Mars, the scientists tested their approach by applying it to the gravity field that was in use before the GRAIL mission.

“With this approach, we were able to squeeze out more information about the gravity field from the existing data sets,” said co-author Dr. Instead of taking the standard approach, known to those in the field as the Kaula constraint, the authors created a constraint that considers the accurate measurements of Mars’ topography. The team started with the same data used for an existing gravity model but put a new twist on it by coming up with a different constraint and applying it to obtain the new solution.Ī constraint compensates for the fact that even the best data sets can’t capture every last detail. We also need to know how the rocks have been reworked over time,” said co-author Dr. “As this story comes together, we’re coming to the conclusion that it’s not enough just to know the composition of the rocks. As a result, previous estimates relied more heavily on studies of the composition of the Martian soil and rocks. The data sets for Mars don’t have as much resolution, so it’s more difficult to pin down the density of the crust from current gravity maps. Recent studies of the Moon by NASA’s GRAIL mission also yielded a precise gravity map. The gravity field for Earth is extremely detailed, because the data sets have very high resolution. The new value is derived from Mars’ gravity field, a global model that can be extracted from satellite tracking data using sophisticated mathematical tools. Typically, the Martian crust has been considered at least as dense as Earth’s oceanic crust, which is about 2,900 kg/m 3 (about 181 pounds per cubic foot). That’s comparable to the average density of the lunar crust. He and his colleagues from NASA’s Goddard Space Flight Center mapped the density of Mars’ crust, estimating the average density is 2,582 kg/m 3 (about 161 pounds per cubic foot). “The crust is the end-result of everything that happened during a planet’s history, so a lower density could have important implications about Mars’ formation and evolution,” Dr. Image credit: NASA / Goddard / UMBC / MIT / E. The map is based on modeling of Mars’ gravity field by Goossens et al.

This view is centered on Valles Marineris, with the Tharsis Montes near the terminator to its west. A new map of the thickness of the Martian crust shows less variation between thicker regions (red) and thinner regions (blue), compared to earlier mapping.

Mars density