On the Seas of Mars

On the Seas of Mars

by Adam Frank for McGraw-Hill

The wind is strong and constant as you guide your boat out beyond the shallows. Turning south into open water you crank the throttle, pushing your little craft for all she is worth. It's a beautiful day and completely perfect for a ride on the open sea. The blue water is sparkling and extends to the far horizon in an unbroken line of gentle rippling swells. The sun glistens off the water and while it is not providing a lot of warmth today it gives the entire world a crystalline clarity. But it's the sky that really warms your heart. It fills the world, horizon to horizon, with its usual, ever stunning, pale pink of mid-day. It's the red sky of the Red Planet and another perfect day for power boating on Mars.

There are, of course, no oceans on the Mars we know. For those of us living in this era of the solar system, some five billion years after the Sun's formation, Mars is a cold, arid desert world. Mars is so dry that even the Earth's most inhospitable deserts (i.e. the Sahara) have vastly more water than the average site on the red planet. Now Mars has no water but what about in the past? According to recent studies by a team of astronomers and geologists, Mars may once have had more water by weight than the Earth. All that water had to sit somewhere on the planet. It is hard to escape the conclusion that Mars may once have had a world-spanning ocean.

There was an ocean on Mars? Says who and how? When you hear a claim like this it is important to be skeptical. While the idea of sailing blue seas on the red world may seem like the perfect science-fiction day dream, science is not just about grand visions but also about hard evidence. It's important to see that behind any result claimed by scientists there should stand a sound chain of reasoning and well-documented data.

The presence of oceans on a prehistoric Mars is the conclusion of Dr. Vladimir Krasnopolsky of the Catholic University of America, Washington, D.C., and Dr. Paul Feldman of the Johns Hopkins University, Baltimore, MD. Using data from the Hubble Space Telescope and the ultraviolet-seeing FUSE spacecraft, they were able to calculate the quantity of water Mars should have had at the time of its birth. How they got this result is a nice example of the workings of science.

Krasnopolsky and Feldman were not able to travel backwards in time to take a snapshot of ancient Mars. Instead they had to reason backwards by first finding a quantity they could measure that was related to Martian water. They were interested not in how much water exists now but how much used to exist. That meant they needed to understand the speed at which Mars was losing its water. To accomplish this they measured the ultraviolet glow from Hydrogen (H) atoms high in the Martian atmosphere. They then compared the amount of H to the amount of deuterium (D) atoms in the Martian atmosphere. Deuterium is a heavy form of hydrogen with a neutron in its nucleus. Deuterium is important because like hydrogen it can form water. There is an important difference though. The heavier deuterium will be less likely to escape from the Martian atmosphere than hydrogen due to random thermal (heat) motions. Since deuterium is heavier than hydrogen, less deuterium will escape because it takes more energy to get it moving at the necessary speed. By measuring the amounts of deuterium and molecular hydrogen in the Martian atmosphere, Krasnopolsky and Feldman measured how much deuterium gets left behind. Because deuterium is left behind more often, the portion of "heavy" Martian water rises over time. By assuming Mars started with equal amounts of normal and heavy water and knowing how much of an imbalance there is today, the scientists could calculate how fast Mars has been losing the constituents of its water into space. It's a neat piece of scientific logic.

With this chain of reasoning, Krasnopolsky and Feldman calculated that if all water initially on Mars were distributed across the planet it would have been equivalent to a global sea at least three-quarters of a mile deep. That is 1.3 times more water per mass than the Earth. Since the northern hemisphere of Mars is a kind of giant basin it is actually more likely that much of the water would settled there forming a vast deep northern ocean.

If Krasnopolsky and Feldman are right (and that is a big if) then we may never see the most wonderful period of the solar system's history. There would have been a time when at least one other world glistened blue against the stars. Blue Mars, that is an amazing concept. Perhaps Mars was once a beautiful world. Perhaps it was once a paradise. Now it is just a desert. If so, it is a pity that we have missed its glory.

Questions to Ponder

If Mars' ocean once held life would it all have perished as the world became dry?
Are there any lessons we might learn from Mars and its former ocean?
In general there are many steps from a piece of data to a scientific conclusion. Discuss some ways in which scientists have to make assumptions to fill in those steps. What is a key assumption that Krasnopolsky and Feldman made?

Check Out These Websites

Check out this cool image of a Blue Mars from NASA's scientific visualization studio
http://svs.gsfc.nasa.gov/stories/mars_20011129/index.html