Amanda Cook

How surface composition and meteoroid impacts mediate sodium and potassium in the lunar exosphere

The Moons time-variable exosphere Earths Moon does not have a conventional gaseous atmosphere, but instead an “exosphere” of particles ejected from the surface. Colaprete et al. have used NASAs LADEE orbiter to investigate how the exosphere varies over time, by using the glow from sodium and potassium atoms as a probe (see the Perspective by Dukes and Hurley). The exosphere composition varies by a factor of 2 to 3 over the course of a month, as different parts of the Moon are exposed to sunlight. There are also increases shortly after the Moon passes through streams of meteoroids. Science, this issue p. 249; see also p. 230 The Moon’s tenuous atmosphere varies over each month and after meteoroid streams. [Also see Perspective by Dukes and Hurley] Despite being trace constituents of the lunar exosphere, sodium and potassium are the most readily observed species due to their bright line emission. Measurements of these species by the Ultraviolet and Visible Spectrometer (UVS) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) have revealed unambiguous temporal and spatial variations indicative of a strong role for meteoroid bombardment and surface composition in determining the composition and local time dependence of the Moon’s exosphere. Observations show distinct lunar day (monthly) cycles for both species as well as an annual cycle for sodium. The first continuous measurements for potassium show a more repeatable variation across lunations and an enhancement over KREEP (Potassium Rare Earth Elements and Phosphorus) surface regions, revealing a strong dependence on surface composition.

The O/OREOS Mission: First Science Data from the Space Environment Viability of Organics (SEVO) Payload

We report the first science results from the Space Environment Viability of Organics (SEVO) payload aboard the Organism/Organic Exposure to Orbital Stresses (O/OREOS) free-flying nanosatellite, which completed its nominal spaceflight mission in May 2011 but continues to acquire data biweekly. The SEVO payload integrates a compact UV-visible-NIR spectrometer, utilizing the Sun as its light source, with a 24-cell sample carousel that houses four classes of vacuum-deposited organic thin films: polycyclic aromatic hydrocarbon (PAH), amino acid, metalloporphyrin, and quinone. The organic films are enclosed in hermetically sealed sample cells that contain one of four astrobiologically relevant microenvironments. Results are reported in this paper for the first 309 days of the mission, during which the samples were exposed for ∼2210 h to direct solar illumination (∼1080 kJ/cm(2) of solar energy over the 124-2600 nm range). Transmission spectra (200-1000 nm) were recorded for each film, at first daily and subsequently every 15 days, along with a solar spectrum and the dark response of the detector array. Results presented here include eight preflight and 16 in-flight spectra of eight SEVO sample cells. Spectra from the PAH thin film in a water-vapor-containing microenvironment indicate measurable change due to solar irradiation in orbit, while three other nominally water-free microenvironments show no appreciable change. The quinone anthrarufin showed high photostability and no significant spectroscopically measurable change in any of the four microenvironments during the same period. The SEVO experiment provides the first in situ real-time analysis of the photostability of organic compounds and biomarkers in orbit.

SEVO ON THE GROUND: DESIGN OF A LABORATORY SOLAR SIMULATION IN SUPPORT OF THE O/OREOS MISSION

This technical note describes a novel solar simulation experiment designed to mimic the solar radiation experienced by the Organism/Organics Exposure to Orbital Stresses (O/OREOS) nanosatellite in low-Earth orbit. Thin films of organic compounds within hermetically sealed sample cells (identical to the films and cells of the spaceflight mission) were exposed to simulated AM0 solar radiation in the laboratory for a total of 6 months, and monitored for spectral changes at two-week intervals. The laboratory experiment accurately simulated ultraviolet and visible solar irradiance to within 2% from 200‐1000 nm and the Ly! (121.6 nm) emission line radiation to within 8%. Design and calibration parameters for the experiment are discussed in detail for this ground-based laboratory irradiation experiment, which was built as a complement to, and as scientific validation of, the O/OREOS SEVO experiment in space.