Home / Science / In 1997 NASA's Pathfinder mission unconsciously landed near the shores of an ancient Martian sea

In 1997 NASA's Pathfinder mission unconsciously landed near the shores of an ancient Martian sea

The Pathfinder spacecraft and the Sojourner rover examining a large rock.
Image: NASA

Nearly 25 years ago, the Pathfinder spacecraft investigated a suspected flood area on Mars. Unknown to NASA back then, the waters that carved the landing pad of Pathfinder from a previously undocumented inland sea long ago prove new research.

A new paper published in Scientific Reports finally confirms the Pathfinder landing site as an overflow at sea. Now dry, this overflow was once covered with water and not lava or debris, as some scientists had suspected. It is important that the new investigations also show that the flood comes from a nearby inland sea, the existence of which was previously unknown. It is further proof that there was once liquid water on the surface of Mars – a possible sign that the Red Planet was once able to promote life. As the new research shows, the Pathfinder Landing was more intriguing than NASA could ever have guessed.

This story begins in the 70s with the launch of NASA's Mariner 9. The soiled surface features of the Mars orbiter are unlike anything seen so far – apparent overflow landscapes known as Mars outflow channels. These vast floodplains formed around 3.4 billion years ago, when abundant rushing water that emanated below the surface has shaped the Martian landscape. These ancient outflow channels are bigger than anything you see on Earth. The channel in Kasei Vallis, for example, is about 3,500 km long and more than 400 km wide. So yes, they are enormous.

Mars drain channels at Aurorae Chaos.
Image: ESA / DLR / FU Berlin / J. Cowart, CC BY-SA 3.0 IGO

The theory is that the drainage channels were formed by water surges from underground aquifers, but scientists could not exclude other possibilities, namely Lava or Debris Flows (How Heavily Porous)

To study these drainage channels at close range, NASA sent the $ 280 million Mars Pathfinder probe into the lower reaches of Tiu and Ares Valles, the probe in 1997 with her companion, the Sojourner Rover. This particular site was chosen for its intriguing surface features recognized by the Mariner Orbiter. Observations made during the Pathfinder mission confirmed the landscape as the site of an earlier flood, but a tide at a much lower level than estimates derived from space-based observations – on the order of 10 times shallower. This surprising result meant that scientists were still unable to exclude other mechanisms for the eroded surface features, namely the alleged lava and debris flows.

Now, 22 years later, new research led by Alexis Rodriguez, senior scientist at the Planetary Science Institute, finally presents the evidence needed to show that the region was actually carved by rushing liquid water. This evidence included data collected by Pathfinder, as well as new geological mapping and numerical modeling.

Charts showing the spillage mechanism (left) and the hypothetical inland sea and the northern ocean. The region marked A corresponds to the diagram on the left. The location of the Pathfinder is also displayed.
Image: JAP Rodriguez et al., 2019 / Scientific Reports

The key to the discovery was the discovery and characterization of the Simud Interior Basin – a large basin about 250 km to the south and upstream of Pathfinder's landing site. This basin is about the size of California and is slightly higher than the presumed northern ocean, a former body of water north and downstream of the Pathfinder Landing. This basin is not connected to other gigantic Martian channels according to the new research results.

"The basin has been dried for about 3,400 million years, so it has been heavily modified due to asteroid impacts and wind." Rodriguez said to Gizmodo. "Its form, which is somewhat hidden in the existing orbital image and in the topographical datasets of Mars, has for years evaded identification."

In simulations, the researchers observed how the floodwaters filled the basin and formed a large inland sea. This created a land barrier between the North Ocean and the New Sea – an area that Pathfinder visited in the 1990s. Finally, inland waters flooded the land barrier and formed the overflow areas observed by Pathfinder.

"The Mars Pathfinder identified numerous geological features that were probably caused by shallow floods. Our article shows that these floods were ocean overflow waters from a previously unknown sea, "Rodriguez said. "When the sea disappeared, it left behind extensive sediment materials. These deposits are particularly interesting as they are probably some of the most accessible marine sediments on Mars. "

An ice sheet finally covered the inland sea and disappeared according to the new one due to the rapid evaporation and sublimation research.

Importantly, the simulations showed that the inland sea acted as a kind of dam that mitigated or limited the amount of effluent water, an observation that reconciles Pathfinder's observations well. The researchers argued that debris or lava flows did not form the characteristics of the Pathfinder site, as these rivers would have completely erased all signs of the basin. As a fluent liquid, lava or fluidized debris flows would have behaved like water and filled the Simud inner basin before entering the land barrier.

"This is simply because the pelvis still exists, indicating that it was only temporarily filled. Lava or debris flows would have buried them permanently. "

Rodriguez and her colleagues are now exploring the astrobiological potential of marine sediments. To this end, it is working with a new initiative led by NASA Ames, which could lead to the evaluation of the remaining marine sediments as a potential landing pad.

"Because the water from which the sea was formed was expelled from the subsurface, its sediments could contain habitability data," she said. Nothing that would not have known if the Mars Pathfinder mission had not been.

"This is a legacy of tremendous importance," said Rodriguez.

[Scientific Reports]

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