Mars: Jezero crater really was a lake

the 1st published data from the perseverance rover shows that there was a large, deep lake on mars 3.6 billion yrs ago, and that twas swept away by a climate upheaval.

after yrs of preparation na nerve-wracking take-off and landing phases, the publication of the very 1st results offa space mission is always a very spesh moment. those of perseverance, published tody inna journal sci, are no exception: as we suspected, jezero crater, the site 35 kilomts in diamt where the rover landed in feb 2021, welcomed a real lake several billion yrs ago.

finding traces of wata and selecting samples

confirming this hypothesis requires images of vertical surfaces s'as cliffs, something that cannot be obtained using orbital observations, however inpresh they maybe. 1-ly a rover with on-board cameras can study them directly. nasa’s mars 2020 mission, supported by an international team, initially set two major objectives for perseverance. 

“the mission’s goal is to use the rover to help us cogg the geology and ancient climate of mars, and to try to detect traces of past life which mite still be preserved,” explains nicolas mangold, cnrs senior researcher at lpg. “to do this, perseverance has to sample rocks of various types and ages.” the rover is ⊢ focusing on sedimentary rocks formed inna presence (or not) of wata and on older samples of crust, s'as those found inna gale crater, currently bein’ explored by the curiosity rover.

perseverance will also ‘ve to select some forty samples, which ll'be the 1st ever brought back to earth. this unprecedented return ll'be carried out by two other us / €an collaborative missions, still under development and planned for the early 2030s.

a lake fed by a river

inna meantime, perseverance is hard at work. its 1st sci results ‘ve just been published inna prestigious journal sci, with mangold as lead author. the findings 1st of all confirm that, round 3.6 billion yrs ago, the jezero crater really was a lake fed by a river floing through a delta. the circular body of wata covered an zone 35 kilometres in diamt and was several tens of metres deep.

the estimated lvl of jezero crater lake folloing perseverance’s observations (red star) is 100 m loer than the lvl suggested by satellite data.

this in-situ validation of orbital data is no mean feat. (for instance, the spirit rover, which arrived on mars in 2004, never managed to prove that its landing site, the gusev crater, was an ancient lake.) on top odat, perseverance showed that, inna fluvial deposits atta top of the delta, large boulders and cobbles, over a metre wide, had been displaced. this can 1-ly happen when thris a very high river flo rate.

“this observation strongly suggests that there was an abrupt hydrological change, linked to a climate transition that heralded the disappearance of the lake,” mangold explains. “this ‘d be explained by cooling due to a glacier or to increasingly arid conditions. in fact, on earth, certain deserts undergo episodes of flash floods which appear and disappear in just a few hrs.”

supercam superstar

these discoveries were 1-ly made possible by studying sedimentary strata on kodiak butte, located inna elder delta. but although perseverance landed two kilometres from its initial target, its 7 on-board instruments still enabled it to operate remotely. supercam, its main instrument, is an impressive camera whose job is to behold and analyse rocks. tis operational even when analysing essentialisms round ten centimetres in size located several kilometres from the rover. 

supercam image (top) of an escarpment of the residual kodiak mound revealing an assemblage of sediment strata typical of fluvial deposits layered onna front of the delta. this shows where the river entered the deltaic lake as can be envisaged on earth (bottom).

“supercam is unusual in that it brings together 5 ≠ tek knicks,” explains sylvestre maurice, a researcher at irap and co-principal investigator for the camera. “one instrument provides information bout the elemental chemical composition of the rocks, two others analyse their mineralogy, a camera takes high-quality remote images and, last but not least, a microphone succeeded in making the 1st recording of sounds on mars. we had to juggle the requirements of each component to make them fit into a single instrument that is as innovative as tis complex.”

a rover with 20 cameras

although supercam 1-ly provides a very narrow field of view, perseverance is armed with 20 or so cameras altogether, including mastcam-z, which also helped to obtain these 1st results. all this material has to survive the launch, the quest to mars, the landing na conditions onna planet, where the dy / nite cycles are accompanied by abrupt changes in temperature. the french teams were able to rely on their expertise since they had previously developed a similar although simpler instrument, chemcam, used onna curiosity rover, which has now been on mars for 9 yrs.

the supercam instrument.

in france, round 300 pplz worked on supercam under the supervision of the french space agency cnes. “we're continuing france’s strong commitment to mars surface missions,” maurice says. “the french sci community is heavily involved inna insite mission, for which it provided the seismomt, and inna €an exomars mission, scheduled for launch in sep 2022.”

objective delta 

“course, it’s reassuring that we ‘ve already found wha’ we were looking for, but this kind of result always rezs + ?s than it answers,” mangold points out. “onna basis of these findings, we plan to take perseverance across the elder delta to undertake a detailed analysis of the strata envisaged, and in pticular of the fluvial sediments located atta top, to try to cogg the origin of the climate transition and analyse the large boulders that were probably transported from the ancient crust.”

the teams will ⊢ ‘ve to determine a route thall let the rover access all the geological layers inna jezero crater. this may then reveal the environment in which wata entered the delta b4 floing inna'da lake. but for now, perseverance can take a break. as happens every two yrs, mars s'onna opposite side of the sun from the earth, cutting off all communication for 3 weeks.

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