Rover images confirm Jezero crater is an ancient Martian lake
The findings include signs of flash flooding that carried huge boulders downstream into the lakebed.

Date:
October 7, 2021
Source:
Massachusetts Institute of Technology
Summary:
Images from the Perseverance rover confirm that Jezero crater is
an ancient Martian lake, MIT researchers report. The team also
detected signs of flash flooding strong enough to carry large
boulders downstream into the ancient delta.



FULL STORY ==========================================================================
The first scientific analysis of images taken by NASA's Perseverance
rover has now confirmed that Mars' Jezero crater -- which today is a dry, wind-eroded depression -- was once a quiet lake, fed steadily by a small
river some 3.7 billion years ago.


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The images also reveal evidence that the crater endured flash floods. This flooding was energetic enough to sweep up large boulders from tens of
miles upstream and deposit them into the lakebed, where the massive
rocks lie today.

The new analysis, published today in the journal Science, is based
on images of the outcropping rocks inside the crater on its western
side. Satellites had previously shown that this outcrop, seen from above, resembled river deltas on Earth, where layers of sediment are deposited
in the shape of a fan as the river feeds into a lake.

Perseverance's new images, taken from inside the crater, confirm that
this outcrop was indeed a river delta. Based on the sedimentary layers
in the outcrop, it appears that the river delta fed into a lake that
was calm for much of its existence, until a dramatic shift in climate
triggered episodic flooding at or toward the end of the lake's history.

"If you look at these images, you're basically staring at this
epic desert landscape. It's the most forlorn place you could ever
visit," says Benjamin Weiss, professor of planetary sciences in MIT's Department of Earth, Atmospheric and Planetary Sciences and a member
of the analysis team. "There's not a drop of water anywhere, and yet,
here we have evidence of a very different past. Something very profound happened in the planet's history." As the rover explores the crater, scientists hope to uncover more clues to its climatic evolution. Now
that they have confirmed the crater was once a lake environment, they
believe its sediments could hold traces of ancient aqueous life. In its
mission going forward, Perseverance will look for locations to collect and preserve sediments. These samples will eventually be returned to Earth,
where scientists can probe them for Martian biosignatures.



==========================================================================
"We now have the opportunity to look for fossils," says team member Tanja Bosak, associate professor of geobiology at MIT. "It will take some time
to get to the rocks that we really hope to sample for signs of life. So,
it's a marathon, with a lot of potential." Tilted beds On Feb. 18,
2021, the Perseverance rover landed on the floor of Jezero crater,
a little more than a mile away from its western fan-shaped outcrop. In
the first three months, the vehicle remained stationary as NASA engineers performed remote checks of the rover's many instruments.

During this time, two of Perseverance's cameras, Mastcam-Z and the
SuperCam Remote Micro-Imager (RMI), captured images of their surroundings, including long-distance photos of the outcrop's edge and a formation known
as Kodiak butte, a smaller outcop that planetary geologists surmise may
have once been connected to the main fan-shaped outcrop but has since
partially eroded.

Once the rover downlinked images to Earth, NASA's Perseverance science
team processed and combined the images, and were able to observe distinct
beds of sediment along Kodiak butte in surprisingly high resolution. The researchers measured each layer's thickness, slope, and lateral extent,
finding that the sediment must have been deposited by flowing water into a lake, rather than by wind, sheet-like floods, or other geologic processes.



==========================================================================
The rover also captured similar tilted sediment beds along the main
outcrop.

These images, together with those of Kodiak, confirm that the fan-shaped formation was indeed an ancient delta and that this delta fed into an
ancient Martian lake.

"Without driving anywhere, the rover was able to solve one of the big
unknowns, which was that this crater was once a lake," Weiss says. "Until
we actually landed there and confirmed it was a lake, it was always
a question." Boulder flow When the researchers took a closer look at
images of the main outcrop, they noticed large boulders and cobbles
embedded in the youngest, topmost layers of the delta. Some boulders
measured as wide as 1 meter across, and were estimated to weigh up to
several tons. These massive rocks, the team concluded, must have come
from outside the crater, and was likely part of bedrock located on the
crater rim or else 40 or more miles upstream.

Judging from their current location and dimensions, the team says the
boulders were carried downstream and into the lakebed by a flash-flood
that flowed up to 9 meters per second and moved up to 3,000 cubic meters
of water per second.

"You need energetic flood conditions to carry rocks that big and
heavy," Weiss says. "It's a special thing that may be indicative of a fundamental change in the local hydrology or perhaps the regional climate
on Mars." Because the huge rocks lie in the upper layers of the delta,
they represent the most recently deposited material. The boulders sit
atop layers of older, much finer sediment. This stratification, the
researchers say, indicates that for much of its existence, the ancient
lake was filled by a gently flowing river.

Fine sediments -- and possibly organic material -- drifted down the river,
and settled into a gradual, sloping delta.

However, the crater later experienced sudden flash floods that deposited
large boulders onto the delta. Once the lake dried up, and over billions
of years wind eroded the landscape, leaving the crater we see today.

The cause of this climate turnaround is unknown, although Weiss says
the delta's boulders may hold some answers.

"The most surprising thing that's come out of these images is the
potential opportunity to catch the time when this crater transitioned
from an Earth-like habitable environment, to this desolate landscape
wasteland we see now," he says. "These boulder beds may be records of
this transition, and we haven't seen this in other places on Mars."
This research was supported, in part, by NASA.

========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Jennifer
Chu. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. N. Mangold S. Gupta O. Gasnault G. Dromart J. D. Tarnas S. F. Sholes
B.

Horgan C. Quantin-Nataf A. J. Brown S. Le Moue'lic R. A. Yingst
J. F.

Bell O. Beyssac T. Bosak F. Calef B. L. Ehlmann K. A. Farley J. P.

Grotzinger K. Hickman-Lewis S. Holm-Alwmark L. C. Kah
J. Martinez-Frias S. M. McLennan S. Maurice J. I. Nun~ez
A. M. Ollila P. Pilleri J. W. Rice M. Rice J. I. Simon D. L. Shuster
K. M. Stack V. Z. Sun A. H. Treiman B.

P. Weiss R. C. Wiens A. J. Williams N. R. Williams K. H. Williford.

Perseverance rover reveals an ancient delta-lake system and flood
deposits at Jezero crater, Mars. Science, 07 Oct 2021 DOI: 10.1126/
science.abl4051 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211007145745.htm

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