You may have read a few stories online noting the discovery of a 'Skull' rock on Mars by NASA's Perseverance rover.
Perseverance has been making its way down lower ‘Witch Hazel Hill’ on the rim of Jezero Crater, an ancient lake that it's been studying since landing on Mars on 18 February 2021.
It stopped at the boundary between light and dark rock outcrop for a closer look, and has discovered, say NASA scientists, a few rocks that don't seem to fit in with the surrounding landscape.
These out-of-place rocks – known as 'float rocks' by planetary scientists – may have come from elsewhere and been somehow transported to the location in which Perseverance found them.
This is interesting enough in itself. What could have brought these rocks to this region of Mars?
One rock that NASA scientists have been calling 'Skull Hill' stood out in particular, and is the subject of a blog post written by Margaret Deahn on NASA's science website.
A quick search online led us to discover all sorts of theories about this rock, from scientific to non-scientific, including one rather bizarre question as to whether or not NASA had actually found a human skull on Mars.
Clearly, the temptation to dwell upon the 'Skull' moniker for this rather ordinary-looking rock (to a non-planetary scientist), was too much for some!
As mentioned in the blog, the image of Skull Hill was captured by the rover’s Mastcam-Z instrument.
It clearly stands out among the lighter-toned rocks surrounding it.
Also visible are some small pits in the rock, and even tiny spherical objects known as 'spherules' in the surrounding regolith.
Spherules were visible on another float rock seen by Perseverance, known as 'St Paul's Bay', and their origin is as yet unknown.
The small pits in Skull Hill may be a result of erosion or of battering by strong Martian winds.
"We’ve found a few of these dark-toned floats in the Port Anson region, and the team is working to better understand where these rocks came from and how they got here," the blog says.
One obvious theory as to why Skull Hill has such a markedly different colour is that it's a meteorite.
The blog does explain how Skull Hill's colour is similar to meteorites found in Gale Crater by Curiosity rover.
However, data captured by Perseverance rover's SuperCam instrument on the composition of nearby similar rocks effectively rules out this possibility.
Could Skull Hill be an igneous rock formed by cooling magma or lava?
Could it have been ejected from an impact crater when a large spacerock hit the Martian surface?
What's clear is that planetary scientists will need more data before they can understand what exactly this rock is made of, and how it got there.
But for now, one thing we can be sure that it definitely isn't, is a skull!
