NASA's first rover mission to Mars, the Pathfinder, may have explored the edges of an early Martian sea in 1997, according to scientists who say that images from the probe could yield evidence of habitability on the Red Planet.
The landing site is on the spillway of an ancient sea that experienced catastrophic floods released from the planet's subsurface and its sediments.
Nearly half a century ago the Mariner 9 spacecraft returned images of some of the largest channels in the Solar System.
Orbital observations of the gigantic channels suggested they were formed approximately 3.4 billion years ago by cataclysmic floods, much larger than any known to have occurred on Earth.
The prospect that abundant flowing water once sculptured the Martian landscape ignited renewed interest in the possibility that life may have once thrived on the planet.
To test the Martian mega-flood hypothesis, NASA deployed its first Martian rover; the Sojourner, on board the 1997 Mars Pathfinder spacecraft that journeyed to the Red Planet.
NASA spent a total of USD 280 million on the mission, including the launch vehicle and mission operations. The terrain within the rover's visual range includes potential fluvial features suggestive of regionally extensive flooding.
However, those features suggest floods that were at least 10 times shallower than those estimated using images obtained from orbit.
Hence, the mission was not able to exclude still disputed alternative views sustaining that debris or lavas flows could have in fact dominated the channels' formational history without significant water discharges.
"Our paper shows a basin, with roughly the surface area of California, that separates most of the gigantic Martian channels from the Pathfinder landing site," said said Alexis Rodriguez, lead author of the study published in the journal Nature Scientific Reports.
"Debris or lava flows would have filled the basin before reaching the Pathfinder landing site. The very existence of the basin requires cataclysmic floods as the channels' primary formational mechanism," he said.
"The basin is covered by sedimentary deposits with a distribution that precisely matches the inferred extent of inundation from potential catastrophic floods, which would have formed an inland sea," Rodriguez said.
"This sea is approximately 250 kilometres upstream from the Pathfinder landing site, an observation that reframes its paleo-geographic setting as part of a marine spillway, which formed a land barrier separating the inland sea and a northern ocean," he said.
"Our simulation shows that the presence of the sea would have attenuated cataclysmic floods, leading to shallow spillovers that reached the Pathfinder landing site and produced the bedforms detected by the spacecraft," Rodriguez said.
The team's results indicate that marine spillover deposits contributed to the landscape that the spacecraft detected nearly 22 years ago, and reconcile the mission's in situ geologic observations and decades of remote-sensing outflow channel investigations.
The sea bears an uncanny resemblance to the Aral Sea on Earth in that in both instances they lack distinct shoreline terraces.
Its rapid regression over shallow submerged slopes resulted in rates of shoreline front retreat too fast for the terraces to form. The same process could partly account for the long-recognised lack of northern plains shorelines