The rise spans about 2,800 miles (4,500 kilometers) of Mars' western hemisphere and includes seven partly buried shield volcanoes, lava plains with clusters fissure vents, and other features that intrigue geologists.
The same region contains the giant Olympus Mons volcano, the largest volcano in the solar system. At about 373 miles (600 kilometers) in diameter—about the size of the state of Arizona—Olympus Mons is twice the size of each of the Tharsis Montes volcanoes.
So far no volcanic activity has been observed at Tharsis Montes.
But the Mars Express, Mars Global Surveyer, and Mars Odyssey spacecraft have recently sent back high-resolution images of the region, providing insights into each volcano's explosive past.
Hawaii and Mars
Bleacher and his team compared the new images with information on Hawaii's volcanoes.
On the Big Island, the youngest volcanoes are on the southeastern end, directly over a magma hot spot.
As the Pacific crustal plate slowly moves to the northwest, the volcanoes are carried away from the hot spot. Over time the movement has created Hawaii's chain of volcanic islands.
Volcanoes over the hot spot have the hottest lava. As the mountains move away, though, only isolated pockets of rising magma remain.
The researchers found the Martian volcanoes had similar surface features and seemed to evolve in a similar way as the Hawaiian volcanoes.
But there is no evidence for such plate movement on Mars. So the researchers suggest that the mountain-creating plume instead moved beneath the stationary Martian crust.
Sleeping Giants?
The findings have some bizarre implications for the evolution of the red planet.
On Earth, cooling magma releases trapped gas, which creates short, explosive eruptions of cinders. Earlier flows become covered with piles of cinders, called cinder cones, which form around these eruptions.
The Tharsis Montes chain show no evidence of cinder cone eruptions—the final stage of hot spot volcanoes—suggesting the mountains might only be dormant, not extinct.
The mountains also erupted relatively recently in Martian history, judging from the lack of large impact craters near the chain.
Volcanic eruptions release large amounts of greenhouse gases, such as carbon dioxide, into the atmosphere.
If eruptions begin again on Mars—and the future eruptions are large enough—they could contribute significant amounts of water and carbon dioxide to the atmosphere.
That's unlikely to make the planet hospitable, though, scientists warn.
"The Martian environment becoming habitable in the future due to a volcanic eruption is extremely improbable," Bleacher told National Geographic News.
Mars once had a magnetic field, but currently lacks one strong enough to protect the atmosphere from solar wind, he pointed out.
"The current Martian surface environment is very hostile towards life as we know it to exist," he added.
"From a planet-wide perspective, a single volcanic eruption—if one was to occur on Mars—would not create an environment suitable for life to survive. Any erupted gases would quickly be stripped away by the solar wind."
Randy Kirk, a geophysicist at the U.S. Geological Survey in Flagstaff, Arizona, said the paper represents an interesting hypothesis that could explain why the three Tharsis volcanoes are equally spaced in a straight line, "which is something people have wondered about for a long time.
"At some level this explanation seems like it just resolves a matter of minor curiosity, why these three volcanoes happen to be in the places they are," he said.
But the work could have farther-reaching implications toward our understanding of magma circulation inside planets, he added—for "Mars definitely, and maybe this will also say something about Earth, eventually."
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