Water and methane maps overlap on Mars: a new clue?   This map shows the concentration of water vapour close to the soil around the equatorial region of Mars. The areas of least concentration are in purple, the highest in green.   Arabia Terra is one of the three equatorial regions where the PFS instrument detected both water vapour and methane concentration. The other two areas are Elysium Planum and Arcadia Memnonia.   This 'spectrum' was recorded in the areas where the methane concentration is higher. The black line shows the measured spectrum, compared to the computed methane spectrum (red line) and indicating 35 parts per billion of methane in the atmosphere. In other areas, the measured average of methane at Mars is only 10 parts per billion. Release date: 22 September 2004