[iceman (Mike)]

Data accumulated by the ASPERA-3 instrument on board the European Space Agency's Mars Express spacecraft seems to indicate how Mars got so dry. Scientists believe that water used to cover Mars, but over the course of 3.8 billion years, it was stripped away from the planet by the Sun's solar wind. ASPERA-3 tracks the inflow of particles from the solar wind, and then tracks the outflow of particles escaping from the Martian atmosphere. It found that the solar wind penetrates deeply into the atmosphere to an altitude of 270 km, energizes particles, and causes about 1 kg (2.2 pounds) of material to trail away from Mars every second. Over the years it added up to make the planet bone dry.