Water vapour on Mars as measured by Mars Express
- Paper number
IAC-05-A3.P.07
- Author
Mr. Martin Tschimmel, Max Planck Institute for Solar System Research, Germany
- Coauthor
Dr. Dmitri Titov, Germany
- Coauthor
Dr. Nikolay Ignatiev, Space Research Institute (IKI), RAS, Russia
- Coauthor
Dr. Emmanuel Lellouch, Observatoire de Paris, France
- Year
2005
- Abstract
As the history of water on Mars is of fundamental importance for our understanding of the Red Planet and its possible development of life the first observations of water vapour from a spacecraft were already made by it Mariner 9. But the first global and seasonal coverage of H2O distribution was generated by the it Viking orbiters in the late 1970’s.
Their investigations showed complex behavior of atmospheric water that includes exchange with the polar caps and regolith, transport by the general atmospheric circulation and cloud formation. More recent observations by it Mars Global Surveyor also show strong seasonal, spatial and diurnal variability of atmospheric water which implies a variety of physical processes involved.
Since the successful insertion of the European it Mars Express spacecraft into Mars’ orbit the Planetary Fourier Spectrometer (PFS) has delivered more than 100.000 spectra.
The PFS instrument is an infrared Fourier spectrometer with two channels. The long-wavelength channel (LW) observes the thermal spectrum emitted by Mars both in daytime and nighttime at wavelengths between 5 micrometers and 50 micrometers. The short-wavelength channel (SW) covers the spectrum from 1.2 micrometers to 5 micrometers by utilizing reflected solar light. Therefore it can only operate during daytime and appropriate observational phase angles. During operation about every 8 seconds a spectrum is recorded which spectral resolution lies at 2 cm-1. The spatial resolution is 10 km for SW for a single spectrum and 20 km for LW respectively. One of the main goals of PFS is to study the atmospheric water cylce on Mars. To determine the correct amount of water vapour in the atmosphere over a selected area up to 20 spectra have to be averaged in order to get a reliable signal-to-noise ratio. This in turn decreases the spatial resolution, though. For the retrieval we have chosen the strong H2O band at 2.56 micrometers. In each orbit with PFS observations there are around 200 - 300 spectra taken which yields to approximately 15 datapoints for every orbit.
To this date the calibrated SW spectra of several dozens of orbits have been processed. During the Northern winter the average amount of water vapour in the atmosphere varies around an average of 10 precipitable micrometers with extremes in the low regions like the Hellas basin or the volcanoes such as Olympus Mons.
However, one area is already of special interest: Arabia Terra. In this region of Mars the H2O concentration is clearly higher than elsewhere. Interestingly this feature coincides with a region of increased amount of hydrogen in the upper soil as measured by the HEND instrument on the it Mars Odyssey orbiter.
In the current year it Mars Express will finish to observe the planet over the course of nearly an entire Martian year. Therefore the interesting seasonal and diurnal variations of water vapour will become visible. This knowledge will contribute significantly to the understanding of the atmosphere, its interaction with the soil, and finally the climate history of the Red Planet.
- Abstract document