Planetary surfaces

Abstract:

The density of the upper thermosphere of Venus was measured in situ using the attitude control system of Venus Express during twelve low-pericentre campaigns between 2008 and 2014. The spacecraft's counteraction to aerodynamic drag torque was used to derive total neutral densities for 91 orbits in the altitude range 160–200 km. The results agree with predictions from the widely used VTS3 model based on Pioneer Venus Orbiter data on the dayside, but shows a much more rapid decrease than expected in density beyond the terminator. Superimposed on the mean density, oscillations consistent with gravity wave activity are observed. The measured wavelengths vary from orbit to orbit, spanning 50–250 km along the spacecraft trajectory, and are present across all sampled latitudes (70°–90°N), solar zenith angles (70°–100°), local times (morning and evening), and altitudes (160–200 km). These results demonstrate that gravity waves are a persistent feature of the Venusian high-latitude thermosphere, providing a pathway for coupling between the lower atmosphere and the upper thermosphere.

Abstract:

Abstract The Lunar Thermal Mapper (LTM) instrument is a UK Space Agency funded infrared radiometer designed and built for the National Aeronautics and Space Administration Lunar Trailblazer mission launched in February 2025. LTM is a pushbroom imaging filter radiometer with 15 channels that cover the wavelength range from 6.25 to 100 μm with a 40–70 m/pixel ground sampling. Lunar Trailblazer's mission is to understand the form, abundance and distribution of water across the lunar surface. LTM provides an independent measure of temperature to investigate thermal effects on water's mapped distribution as well as an independent measure of surface mineralogy. The LTM instrument's 15 infrared channels include four broadband temperature sensing channels (6.25–12.5, 12.5–25, 25–50 and 50–100 μm) plus 11 additional narrow band (∼40 cm −1 ) filters from ∼7–10 μm to map and discriminate silicate composition. We review the LTM design and calibration campaign at the University of Oxford's Space Instrumentation facility and show that the instrument has sensitivity from 400 K with a Noise Equivalent Temperature Difference of <0.1 K to <1 K at 110 K for typical integration times (e.g., 30 Hz readout) from a nominal 70–130 km lunar orbit design altitude. Plain Language Summary This paper describes the Lunar Thermal Mapper instrument for NASA's Lunar Trailblazer mission. Lunar Thermal Mapper is a thermal imaging system designed to sense the temperature and composition of the lunar surface using the thermal infrared. By sensing the temperature environment of the Moon, Lunar Thermal Mapper supports the Trailblazer's mission to map water on the lunar surface. Key Points The Lunar Thermal Mapper (LTM) instrument will measure thermal infrared radiation from the Moon across from 400 K to <110 K The LTM instrument completed assembly, testing, calibration and integration on the Lunar Trailblazer spacecraft The LTM instrument demonstrated sensitives of <0.1 K at 400 K and <1 K at 110 K during ground testing and calibration

Abstract:

Characterizing terrain surface properties is an essential step in assessing the feasibility of landing successfully at a location on a planetary surface. Slopes and terrain ruggedness index (TRI) values derived from high-resolution (2 m pixel−1) digital terrain models provided important constraints in selecting the landing site for the upcoming Payloads and Research Investigations on the Surface of the Moon program as part of the Commercial Lunar Payload Services task order CP-21 mission. The selected landing site needed to balance safety requirements with the ability to achieve the science and exploration goals of the Lunar Vulkan Imaging and Spectroscopy Explorer payload. In this study, we compare several morphometric parameters in the context of the CP-21 landing site on Mons Gruithuisen Gamma, or the Gamma dome, and quantify the information they convey about lunar surface properties to assess their utility for future landing site evaluation. TRI was found to be a useful metric for assessing landing site safety. Metrics that better decouple slope and surface roughness, the vector ruggedness measure and the standard deviation of slope, provided additional information about surface characteristics and textures such as the degree to which roughness is isotropic.