In a cosmic whodunit, Costard et al.  have been searching for the crater that may have generated an ancient tsunami on Mars. It has been proposed for some time that an ocean covered the northern plains of Mars about 3 billion years ago, although the evidence for that ocean remains disputed. A few years ago, the unique geology of a region along the shore of that proposed ocean was interpreted as the result of a large tsunami, which would have been triggered by a large meteor impact.
This article argues that the site of the impact is what is now the Lomonosov crater. This crater presents unique topographic features that may represent the effect of the sea rushing back into the still fresh crater in the wake of the tsunami. Beyond strengthening the case for the presence of an ocean at the time of the crater formation, this study also implies that the ocean was somewhat shallow and fairly long lived, as impacts of this size are uncommon, providing new constraint on the ancient environment of Mars, so different from what the planet is like today.
Citation: Costard, F., Séjourné, A., Lagain, A., Ormö, J., Rodriguez, J. A. P., Clifford, S., et al. . The Lomonosov crater impact event: A possible mega‐tsunami source on Mars. Journal of Geophysical Research: Planets, 124. https://doi.org/10.1029/2019JE006008
—Laurent G. J. Montési, Editor in Chief, JGR: Planets