Present-day Mars is cold and dry, but this has not always been the case, as findings from Mars rover confirm.
In February 2021, NASA landed the Perseverance rover on the surface of Mars and rapidly started to collect data. The landing site – a crater named Jezero – was chosen because pictures taken from the orbit of Mars showed features that resembled a network of rivers and an ancient lake bed. But satellite images are taken a few hundred kilometers away, so many uncertainties about Jezero crater remained. Imagine being in Chicago and trying to see what the rocks look like on the North side of Lake Michigan!
Scientists knew there had been water at some time in the past, but they didn’t know exactly when there was water, or how the amount of water evolved over time. That’s where Perseverance comes in. The rover drove up to the foot of a rocky outcrop called Kodiak butte. From there, it took images of the different layers that make up the butte. With the cameras on top of its mast (the left and right Mastcam-Z cameras, as well as the Remote Micro Imager included in the SuperCam), Perseverance can see details as small as 10 centimeters.
Perseverance observed layers of sedimentary rocks of the Kodiak butte, and noticed tilted layers of sediments in between other horizontal layers. On Earth, this kind of geological formation is typically found in deltas and can be used to know how deep the water was when the sediments formed at the bottom of the lake. The observations made by Perseverance show that there was water in Jezero crater 3.6 billion years ago, and the lake was 35 kilometers wide. But the lake wasn’t quite as deep as what was suggested by satellite imagery.
Perseverance also noticed something interesting on top of these layers of sedimentary rocks: large pebbles and boulders more than 1 meter wide. On Earth, rocks like these pile up in one place during flash-floods, when there are strong currents. These piles of rock might be the signature of sudden hydrological change, possible caused by larger scale changes in climate.
These first findings pave the way for future exploration. Samples from the sedimentary rocks could be cached for a future sample return mission to try to find traces of past life. Samples from the large boulders could be cached to learn more about Mars’ crust. Another rover will pick up the caches prepared by Perseverance and bring them back to Earth in 2030.
Based on the article Perseverance rover reveals an ancient delta-lake system and flood deposits at Jezero crater, Mars. N. Mangold, S. Gupta, O. Gasnault, G. Dromart, J. D. Tarnas, S. F. Sholes, B. Horgan, C. Quantin-Nataf, A. J. Brown, S. Le Mouélic, R. A. Yingst, J. F. Bell, O. Beyssac, T. Bosak, F. Calef III, 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. Nuñez, A. M. Ollila, P. Pilleri, J. W. Rice Jr, 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 et K. H. Williford. Science, October 7, 2021.