The planet Mars has long been a favorite subject for science fiction writers, who have crafted countless stories around the idea of intelligent life forms from that planet. However, science has always told us that was impossible, partly because the planet didn’t have enough atmosphere to protect from the Sun’s rays. Now, new research suggests that the planet may have an atmosphere, but that the air is trapped in hidden reservoirs on the planet’s surface.

This research, reported in the journal Science, is based on two years’ worth of data from the European Space Agency’s Mars Express spacecraft. This data does not support the long-held theory that Mars’ atmosphere was eroded by billions of years of solar winds. The atmosphere today is very thin--about 0.7 percent of the average surface pressure at sea level on Earth. But scientists found that only a small fraction of the planet’s air is escaping--about 20 grams per second. This does not seem to be enough to account for the missing air, and observations from channels and gullies on the planet’s surface also suggest that the water was at one point quite deep in places. To support this much water, Mars must have had a higher atmospheric temperature, and therefore, a much greater atmospheric pressure. With the new evidence, researchers think the missing air may be hidden just underneath the planet’s surface, in a place they have not yet been able to find.

Mars is believed to be similar to Earth, with polar ice caps, volcanoes, possibly even water. It is believed that about 3.5 billion years ago, Mars experienced the largest known floods in the solar system, with the water possibly forming lakes or shallow oceans. Little of that water remains on the surface, however; certainly not enough to account for the planet’s many flood plains and channels. The planet’s atmosphere is so thin that water can’t exist on the surface for long, but there may be underground reserves of water. If so, this water might support simple life forms like those found in ice in Earth’s Antarctic region, although the possibility is remote.

Its similarity to Earth has fueled years of debate as to whether the planet once supported life, and if it could now. That’s why understanding what happened to the planet’s atmosphere is so important to scientists--not only can it help them unravel the evolution of Mars, it could also help them determine whether life once existed there.