Ancient Mars was warm and wet, not cold and icy

This is important because it means these rocks were less likely to have been weathered in a hydrothermal environment, where boiling water was temporarily released by melting ice caused by volcanism or meteorite impact.

Instead, they appear to have been weathered by modest temperatures and persistent heavy rains. The authors found distinct similarities between the chemical composition of these clay pebbles with similar clays found on Earth dating from periods in our planet’s history when the climate was much warmer and humid.

The paper concludes that these kaolinite pebbles were weathered under conditions of heavy precipitation comparable to “past greenhouse climates on Earth” and that they “probably represent some of the wettest periods and perhaps most habitable parts of Mars’ history.”

Furthermore, the paper concludes that these conditions may have persisted over periods of thousands to millions of years. Perseverance recently made headlines for discovering possible biosignatures in samples collected last year, also from Jezero Crater.

These valuable samples have now been cached in special sealed containers on the rover for collection by a future sample return mission to Mars. Unfortunately, the mission was recently canceled by NASA and the vital evidence they may or may not contain will likely not be examined in an Earth laboratory for many years.

Crucial to this future analysis is the “Knoll criterion” – a concept formulated by astrobiologist Andrew Knoll, which states that for something to be evidence of life, an observation must not only be explainable by biology; it must be inexplicable without it. Whether these samples will ever meet Knoll’s criterion will only be known if they can be returned to Earth.

Regardless, it’s quite striking to imagine that at one time on Mars, billions of years before the first humans walked the Earth, a tropical climate with – perhaps – a living ecosystem once existed in the now desolate, windswept landscape of Jezero Crater.

Gareth Dorrian is a postdoctoral researcher in space sciences at the University of Birmingham.

This article is republished from The Conversation under a Creative Commons license. Read the original article.