view of Mars as it might have appeared more than 2 billion years ago,
with an ocean filling the lowland basin that now occupies the north
Since 1991, planetary scientists have floated
the idea that Mars once harbored vast oceans that covered roughly
one-third of the planet. Two long shore-like lips of rock in the
planet's northern hemisphere were thought to be the best evidence, but
experts argued that they were too "hilly" to describe the smooth edges
of ancient oceans.
The view just changed dramatically with a surprisingly simple breakthrough.
once-flat shorelines were disfigured by a massive toppling over of the
planet, scientists announced today. The warping of the Martian rock has
hidden clear evidence of the oceans, which in any case have been gone for at least 2 billion years.
"This really confirms that there was an ocean
on Mars," said Mark Richards, a planetary scientist at the University
of California at Berkeley and co-author of the study, which is detailed
in the June 14 issue of the journal Nature.
major shorelines exist on Mars, each thousands of miles long — one
remaining from the older Arabia Ocean, and another from the younger
Deuteronilus Ocean, said study co-author Taylor Perron of UC Berkeley.
Arabia would have contained two to three times the volume of water than
in the ice that covers Antarctica," Perron told SPACE.com.
Somewhere along the way to toppling over 50 degrees to the north, Mars probably lost some of its water,
leaving the Deuteronilus Ocean's shoreline exposed. "The volume of
water was too large to simply evaporate into space, so we think there
is still some subterranean reservoirs on Mars," Perron said.
The remaining sea would have been located in the same lowland plain as the Arabia Ocean, but almost 40 degrees to the north.
As a planet spins, the heaviest things tend to shift towards the equator, where they are most stable. Earth, too, has a bulge at its equator. The volcanic Tharsis region of Mars, a vast raised area along Mars' equator, is evidence for how this works.
is the reason why this discovery packs extra punch," Perron said. More
than a billion years ago, he explained, something happened in the way
mass was distributed on Mars to cause the imbalanced portion to shift
toward the equator-and allow the vast shores of the Martian oceans to
"We found evidence of the path the shift would
have to have occurred, and it matches with the deformation of the
shorelines," Perron said.
the equator, the surface of a planet stays in a relatively flattened
bulge under the pressure of centripetal forces. But outside of the
equator, the rock behaves elastically and often bunches up, like the
surface of a deflating balloon. Perron and his team reasoned that the
oceanic shorelines were once near the equator, but warped into hilly
up-and-down elevations of rock as they move towards the north with the tilting planet.
planets like Mars and Earth that have an outer shell ... that behaves
elastically, the solid surface will deform," Richards said.
calculating the deformation, which occurs in a predictable way, the
planetary research team found the ridges had to have once been flat,
like ocean shorelines.
"This is a beautiful result that Taylor
[Perron] got," Richards said. "The mere fact that you can explain a
good fraction of the information about the shorelines with such a
simple model is just amazing. It's something I never would have guessed
at the outset."
and his colleagues aren't certain what caused the toppling of the
planet, but they think forces beneath the surface are to blame. "There
could have been a massive change in the distribution of mantle," Perron
said, "which would have caused the planet to shift into its current