Planetary surfaces

Abstract:

Future missions to measure the mid-infrared spectra of extrasolar planets will obtain spectra spatially integrated over the visible hemisphere of the planet. Interpretation of these spectra will be difficult because they will depend on several imponderable factors; the axial inclination of the planet to the line of sight, the illumination of the planet by its parent star, and the planets' season and climatic state. The spectra will also contain variable components due to changing clouds, planetary rotation and the presence of large satellites. In order to interpret better such spectra, and to constrain the design of missions to measure them, a study is underway of a dedicated mission to take spectra of the spatially-unresolved Earth and to quantify the dependence of the spectrum on these variables.

Abstract:

The standardisation of 210Pb is complicated by the presence of the daughters, 210Bi and 210Po. In addition, the low energies of the beta emissions from 210Pb make it difficult to obtain high detection efficiencies in an atmospheric proportional counter and hence produce the need for large extrapolations with consequential large uncertainties when extrapolating to unit efficiency with the conventional 4pi(PC)-gamma-coincidence technique. In order to produce a reliable standardisation, it is necessary to remove the daughter products. A solution of 210Pb was therefore chemically separated from its daughters and then standardised using the conventional 4pi(LS)-gamma-coincidence technique. The low energy (46 keV) and low emission probability (4%) of the associated photon emissions effectively rules out the possibility of using ionisation chambers as secondary standard transfer instruments for this nuclide. A germanium spectrometer therefore was calibrated for this purpose using 241Am as a normalising agent. The results of this work are presented together with an analysis of the standardisation uncertainties that can be achieved in practice.

Abstract:

The pointwise meteorological observations of the Viking Lander and Mars Pathfinder as well as the orbital mapping and sounding performed by, e.g., Mariner 9, Viking Orbiters and the Mars Global Surveyor have given a good understanding of the basic behaviour of the Martian atmosphere. However, the more detailed characterisation of the Martian circulation patterns, boundary layer phenomena and climatological cycles requires deployment of meteorological surface networks. The European NetLander concept comprising four well-instrumented landers is being studied for launch in 2005 and operations spanning at least a Martian year in 2006-2008. The landers are to be deployed to areas in both Martian hemispheres from equatorial regions to low mid-latitudes. The NetLander atmospheric instrument system (ATMIS) on board each of the landers is designed to measure atmospheric vertical profiles of density, pressure and temperature during the descent onto the surface, as well as pressure, atmospheric and ground temperatures, wind, atmospheric optical thickness and humidity through a full Martian year, possibly beyond. The main operational objective of this meteorological experiment is to provide a regular time series of the meteorological parameters as well as accelerated measurement campaigns. Such a data set would substantially improve our understanding of the atmospheric structure, dynamics, climatological cycles, and the atmosphere-surface interactions. The ATMIS sensor systems and measurement approaches described here are based on solutions and technologies tested for similar observations on Mars-96, Mars Pathfinder, Huygens, and Mars Polar Lander. Although the number of observation sites only permits characterisation of some components of the general circulation, the NetLander ATMIS will more than double the number of in situ vertical profiles (only three profiles - two from Viking Landers and one from Mars Pathfinder - are currently available and as envisioned at the time of writing, none of the 2001 and 2003 landers' payloads include entry phase measurements of pressure or temperature), perform the first in situ meteorological observations in the southern low- and mid-latitudes and provide the first simultaneous in situ multi-site observations of the local and general circulation patterns, in a variety of locations and terrains. As such, NetLander ATMIS will be the precursor of more comprehensive meteorological surface networks for future Mars exploration. © 2000 Elsevier Science Ltd. All rights reserved.