argued that such a process might have contributed far more water to the Martian surface than once thought.
| Mars Epochs |
| The geologic history of Mars is divided into three epochs, defined by the number of impact craters (older surfaces have more craters, from back when the solar system was a more chaotic place). The timing of the epochs is not known precisely. |
Noachian Epoch: Runs from the birth of Mars to between 3.8 and 3.5 billion years ago.
Hesperian Epoch: A time of extensive lava plains, ended sometime around 1.8 billion years ago. |
Amazonian Epoch: Extends to the present day. Ground surfaces of Amazonian age have few meteorite impact craters, but the period is thought to have included the formation of the huge volcano Olympus Mons, landslides in Valles Marineris, and the formation of the broad plains and sand dunes near Mars" poles. |
Phillips said the new computer modeling shows that enough carbon dioxide could have accumulated to create a greenhouse effect, trapping heat and raising the surface temperature above freezing. And while the Martian atmosphere would always have been less dense than the present-day Earth atmosphere, Phillips said enough water might have been pumped to the surface to saturate the atmosphere, possibly leading to precipitation.
All this, if true, could explain large-scale features that resemble riverbeds and flood plains, thought to have been created around the same time. Mars Global Surveyor has returned a growing number of
that are difficult to explain by means other than running and standing water -- rivers, lakes and oceans.
And scientists have suspected that Mars was warm and wet during the epoch of Martian history called the Noachian, which runs from the birth of Mars, nearly 4.5 billion years ago, to between 3.8 and 3.5 billion years ago.
"What our study shows is that this [volcanic] period may have been confined to just the late Noachian, and the clement conditions may have been directly related to Tharsis outgassing," Phillips said. "Interestingly, this clement period came to an end fairly quickly at the end of the Noachian, and this may be because Tharsis was done."
The timing of Tharsis volcanism, as seen by the researchers, is at odds with many previous scenarios, which had Tharsis forming by volcanic processes throughout most of Mars' history.
"We are saying that most of Tharsis was in place by the end of the Noachian," Phillips said. He added that the amount of time it took to build the Tharsis rise could not be pinned down exactly, but likely took several hundred million years.
More to learn
But why was so much volcanic energy concentrated in one area?
"This is a question that has been plaguing us for 30 years," Phillips said, "and there is still not a clear answer."
He speculated that perhaps the Tharsis rise developed from a huge thermal plume that welled up from deep inside the planet, where much of the material is thought to be hot and molten. This upwelling might have left the region near the surface hot and weak, so that the normal flow of material inside the planet might have been drawn to the area under what is now the Tharsis rise.
Phillips worked with scientists from NASA, the Carnegie Institution, MIT and the University of Colorado at Boulder. Further findings regarding the network of valleys created by this process will be published in the May issue of the journal Geology.
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