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The Complex Exhumation History of Jezero Crater Floor Unit and Its Implication for Mars Sample Return.

Title:	The Complex Exhumation History of Jezero Crater Floor Unit and Its Implication for Mars Sample Return.
Authors:	Quantin‐Nataf, C.¹ (AUTHOR) cathy.quantin@univ-lyon1.fr; Alwmark, S.^2,3 (AUTHOR); Calef, F. J.⁴ (AUTHOR); Lasue, J.⁵ (AUTHOR); Kinch, K.³ (AUTHOR); Stack, K. M.⁴ (AUTHOR); Sun, V.⁴ (AUTHOR); Williams, N. R.⁴ (AUTHOR); Dehouck, E.¹ (AUTHOR); Mandon, L.⁶ (AUTHOR); Mangold, N.⁷ (AUTHOR); Beyssac, O.⁸ (AUTHOR); Clave, E.⁹ (AUTHOR); Walter, S. H. G.¹⁰ (AUTHOR); Simon, J. I.¹¹ (AUTHOR); Annex, A. M.^12,13 (AUTHOR); Horgan, B.¹⁴ (AUTHOR); Rice, James W.¹⁵ (AUTHOR); Shuster, D.¹⁶ (AUTHOR); Cohen, B.¹⁷ (AUTHOR)
Source:	Journal of Geophysical Research. Planets. Jun2023, Vol. 128 Issue 6, p1-16. 16p.
Subject Terms:	*Eolian processes; Impact craters; Martian craters; Martian meteorites; Lunar craters; Exhumation; Mars (Planet); Martian surface
Abstract:	During the first year of NASA's Mars 2020 mission, Perseverance rover has investigated the dark crater floor unit of Jezero crater and four samples of this unit have been collected. The focus of this paper is to assess the potential of these samples to calibrate the crater‐based Martian chronology. We first review the previous estimation of crater‐based model age of this unit. Then, we investigate the impact crater density distribution across the floor unit. It reveals that the crater density is heterogeneous from areas which have been exposed to the bombardment during the last 3 Ga to areas very recently exposed to bombardment. It suggests a complex history of exposure to impact cratering. We also display evidence of several remnants of deposits on the top of the dark floor unit across Jezero below which the dark floor unit may have been buried. We propose the following scenario of burying/exhumation: the dark floor unit would have been initially buried below a unit that was a few tens of meters thick. This unit then gradually eroded away due to Aeolian processes from the northeast to the west, resulting in uneven exposure to impact bombardment over 3 Ga. A cratering model reproducing this scenario confirms the feasibility of this hypothesis. Due to the complexity of its exposure history, the Jezero dark crater floor unit will require additional detailed analysis to understand how the Mars 2020 mission samples of the crater floor can be used to inform the Martian cratering chronology. Plain Language Summary: Perseverance rover landed within Jezero crater (Mars) in 2021 and is collecting rocks that will be returned to Earth. In terrestrial state‐of‐the art labs, these rocks will be dated. It will allow to test the method planetary scientists are using to assess the age of Martian surfaces: their impact crater statistics. As impact craters are forming regularly, their statistics are used as a timeline in planetary sciences. The present paper studies the statistic of impacts craters within Jezero crater to reveal that the floor of Jezero has been protected from bombardment during years. These results imply that the collected rocks of the Jezero crater floor will not be ideal to test the method of using impact crater as chronometer of Martian surfaces. Key Points: The dark floor unit of the Jezero crater displays an unusual inhomogeneous crater density, suggesting a complex exhumation historyThe crater density of the dark crater floor unit corresponds to the exposure time post exhumationThe crater density of this unit will not allow the calibration of the Martian crater chronology from return samples [ABSTRACT FROM AUTHOR]
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