Going back over some old posts, I was re-reading what I wrote back in 2011 about the evidence for water on Mars.

More Water Evidence Adds to Intrigue Surrounding Mars

15 years have passed - and I think we need an update...

1. The "Flowing Liquid" Reality Check

Back in 2011 I highlighted the exciting discovery of Recurring Slope Lineae (RSLs) - the dark tendrils making their way down Martian slopes. At the time, the leading theory was briny water. I remember the excitement this created at the time...

However, the scientific consensus has shifted fairly significantly. High-resolution imaging and thermal data gathered in the years since suggest that these RSLs are far more likely to be dry, granular flows - essentially mini sand avalanches - rather than flowing liquid water. While trace amounts of atmospheric water vapour might play a role in triggering them, the idea of active, flowing brine on the surface has largely been ruled out.

2. Curiosity Confirms Habitability

At the time Curiosity was heading to Mars and specifically Gale Crater, it landed successfully in 2012 and completely delivered on its primary mission.

Curiosity found smooth, rounded pebbles indicating ancient, vigorous stream beds, and drilled into mudstones in an area called Yellowknife Bay. The chemical analysis proved that Gale Crater was once a long-lasting, freshwater lake environment with all the basic chemical building blocks for life (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur). It definitively answered the question: Could Mars have supported life? The answer is now widley regarded as a resounding yes!

3. The Great Methane Contradiction

The methane story has become one of the most intriguing mysteries in modern astronomy. Curiosity did detect background levels of methane that rise and fall with the Martian seasons, and it even detected sudden, localized "spikes" of the gas.

However, the European Space Agency’s Trace Gas Orbiter (TGO), which arrived in 2016 with instruments specifically designed to sniff out methane high in the atmosphere, found... absolutely nothing. The current debate is fierce: is the methane seeping from the ground and being rapidly destroyed before it reaches the upper atmosphere, or is there an issue with how we are measuring it?

4. Perseverance and the Hunt for Biosignatures

If Curiosity was sent to find out if Mars was habitable, the Perseverance rover (which landed in Jezero Crater in 2021) was sent to find actual evidence of past life (biosignatures). Jezero is an ancient river delta, one of the best places to preserve organic molecules.

Perseverance has successfully detected diverse, complex organic molecules in the rocks there. It is currently caching these rock samples in specialized titanium tubes for a future Mars Sample Return mission, which remains the holy grail for planetary scientists hoping to study Martian dirt in Earth-based laboratories. Bringing these precious samples home really would be an absolute wonder! I can only wish to see that within my lifetime.

Cover photo by Kevin Gill from Los Angeles, CA, United States - Mars - August 30 2021, CC BY 2.0, Link