New Estimate of Amount of Water on Surface of Mars


NASA’s rover Curiosity, which landed on the surface of Mars on 6 August 2012, has led to more detailed estimates of the amount of water on the Martian surface. The Finnish Meteorological Institute is part of the NASA research team.

A study published in the magazine Science on 27 September reveals that according to observations made by the NASA rover Curiosity, the surface layer of the Gale crater near the Martian equator has a water content of about 2%, which is at the lower end of previous estimates (citation below). The Finnish Meteorological Institute is also part of the NASA research team. Previous estimates of the amount of water based on orbital observations have varied between 2-12%. This estimate is based mainly on measurements by the Mars Odyssey probe.  It is estimated that the surface layer at higher latitudes contains considerably more water. This is based both on orbital observations and measurements by the Phoenix lander in 2008.

The main observational device in the study of the surface layer of Mars was Curiosity’s ChemCam laser spectrometer, which examines the elemental content of targets by shooting laser pulses at them, and by spectroscopically examining the resulting flashes. ChemCam is capable of studying its environment at a distance of up to about seven metres with the help of laser pulses. Observations of the relative humidity of the Martian atmosphere, which were needed for the study, were conducted using the REMS-H device supplied by the Finnish Meteorological Institute.

The research group also studied the fluctuation of water vapor between the Martian atmosphere and the surface layer. In this process, the relative humidity of the atmosphere plays an important role.

“During this study there were no observations of a water cycle between the atmosphere and the surface layer that would have been linked with the diurnal cycle”, says Ari-Matti Harri, head of research at the Finish Meteorological Institute. During the time of operation of ChemCam, the relative humidity of the atmosphere was low – about 20 percent. “In a longer time-frame, it is likely that water circulation between the surface layer and the atmosphere does occur at higher levels of relative humidity”, Ari-Matti Harri adds.

New Series of Observations

The Finnish Meteorological Institute has supplied the Curiosity rover with the instruments (REMS-P and REMS-H) for measuring pressure and humidity in the Martian atmosphere. The instruments are part of the REMS package of instruments for studying the Martian environment supplied for the rover by the Spanish INTA-CAB institute.

The REMS-H and REMS-P measuring devices have monitored pressure and humidity in the Martian atmosphere for about 400 days so far, which is slightly more than half of a year on Mars. The aim is to compile a time series of pressure and humidity covering an entire Martian year. This would bring another series of measurements after those of the Viking landers (1976 – 82) that would cover an entire year on Mars. With the help of these observations, the behaviour of the Martian atmosphere is being studied on a scale ranging from seconds to the alternation of seasons on Mars. This also allows for a study of changes in the climate of Mars in the past 40 years, by comparing series of observations by the Viking landers and those of Curiosity together with orbital observations.

At present Curiosity is moving toward Mt. Sharp, a mountain located in the middle of the Gale Crater. By studying its surface layers, Curiosity will seek to ascertain the environmental conditions on Mars going back hundreds of millions of years.

Atmosphere on Mars Resembles That of Earth

Composed of carbon dioxide, the atmosphere on Mars is dry, cold, and about 100 times thinner than that on Earth.  The tilt of the axes of both Mars and Earth and the similar lengths of the day on both planets mean that the atmospheres behave in a similar fashion. The similar characteristics of the atmospheres of Mars and Earth give a reason for comparative planetary research. “By investigating Mars we can also learn something new about Earth and its atmosphere, for which reason this is a very important target of research for the Meteorological Institute”, Ari-Matti Harri says. The similarities of the atmospheres has made it possible for the Finnish Meteorological Institute, together with the University of Helsinki to use the HIRLAM weather forecasting model used in the Nordic Countries and other places, to work in research about Mars.

Source: Finnish Meteorological Institute


Meslin PY, et. al. (2013). Soil Diversity and Hydration as Observed by ChemCam at Gale Crater, Mars. Science (New York, N.Y.), 341 (6153) PMID: 24072924

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