Marsquakes
Mars is a lifeless barren desert planet, with long extinct volcanos and no evidence of any surface water or life. At least, that was the idea from the moment the canals were dismissed up until the late mid to late 1990s, until we began to discover that it is anything but !
No, Mars wasn't the home to an intelligent life form about to invade Victorian Britain and by default conquer the Earth as HG Wells had imagined in War of the Wolds, nor was it covered in canals as Giovanni Schiaparelli's entry into the encyclopaedia Britannica in the 1890s had suggested.
Then in the mid 60s to early 70s, NASA's Marina craft began the road towards a more rationalised version of Mars, although not without a few spates of Pareidolia on the low resolution images brought up an entirely new mythology about the Cydonia region of Mars and it's pyramids and carved faces.
At greater resolutions, the face turned out to be nothing more than our brains making faces from patterns and shadows, but it was interesting while it lasted.
The first landings came quickly after, in 1975 the VIking I and II landers finally made it to the surface in one piece, and the puzzle of Mars began to open up.
You'd be forgiven for not agreeing that Mars was a lifeless hunk of Rock on the back of this, except the Viking probes carried an experiment to detect life, which actually was triggered, it's just that at the time every scientist bar a few felt it was a false positive.
https://blogs.scientificamerican.com/observations/im-convinced-we-found-evidence-of-life-on-mars-in-the-1970s/
It wasn't for another 20 years in 1995 before ground based observations were made, with the Pathfinder mission, the very first robot to move around on the surface of mars.
Then in 2003 Scientists looking through data from the Global Surveyor orbiter proposed that the Martian core was not solid, but instead like Earth, liquid Iron and still active, and therefore those long dormant volcano's may still have some life in them, even if at a much greater depth than once they had.
On the 6th April 2019, the seismometer onboard the InSight lander on Mars recorded it's very first marsquake, and more recently this March a further two magnitude 3 marsquakes were detected. While Mars doesn't have active plate tectonics as on Earth, we now know it does have some regions that are more active than others.
Add to this the detection of Methane, evidence of past water, rivers, delta's and sedimentary rock on the surface found by the myriad of robotic landers since Pathfinder, our view of Mars as a once wet world, with potential bacterial life underground and even underground water has swept away the assumptions of a few decades ago.
Who knows what we'll find in the coming decades, and how our view of this world will change with it.
