Ancient Mars was warm and wet, not cold and icy

This is important because it means these rocks were less likely to have experienced a change in hydrothermal environment, where melting ice temporarily releases hot water due to a volcano or meteorite impact.

Instead, they appear to have changed under moderate temperatures and frequent heavy rainfall. The authors found clear similarities between the chemical composition of these clay pebbles and similar soils found on Earth from a period in our planet’s history when the climate was much warmer and wetter.

The paper concludes that these kaolinite pebbles were altered under high precipitation conditions equivalent to “past greenhouse climates on Earth” and that they “likely represent some of the wettest intervals in Mars’ history and possibly the most habitable parts”.

Furthermore, the paper concludes that these conditions may persist over time periods ranging from thousands to millions of years. Perseverance also recently made headlines for the discovery of potential biosignatures in samples collected last year from within Jezero Crater.

These valuable samples are now stored in special sealed containers on the rover for collection by a future Mars sample return mission. Unfortunately, the mission has recently been canceled by NASA and so what important evidence they may or may not contain will likely not be examined in an Earth-based laboratory for many years.

Critical to this future analysis is the so-called “Knoll criterion” – a concept coined by astrophysicist Andrew Knoll, which states that for something to be evidence of life, an observation must not be explained by biology alone; Without this it would be incomprehensible. Whether these samples ever meet the Knoll criteria will be known only when they can be brought to Earth.

Either way, it’s quite amazing to imagine a time on Mars, billions of years before the first humans arrived on Earth, with a tropical climate and – possibly – a living ecosystem once existed in the now desolate and windswept landscape of Jezero Crater.

Gareth Dorrian is Postdoctoral Research Fellow in Space Science at the University of Birmingham

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