Hello, friends!  Right now, I’m going through some big changes in my life, which leaves me very little time for writing.  And yet, because I am the person I am, I must write something!  So during this time, I’ve been writing these quick and easy posts sharing my #1 favorite facts about each planet of the Solar System.  Today, it’s time for my #1 favorite fact about Mars.

This one’s tough.  Mars is the most thoroughly explored planet in the Solar System (besides Earth, of course), which means there are tons of Mars facts to choose from.  And brand new Mars facts keep coming in all the time, thanks to the fleet of robotic spacecraft that have been continuously exploring the Red Planet for decades now.  But if I must pick just one Mars fact to share today, it would be this: Mars’s beautiful orangey-red color is only skin deep.

A little over a decade ago, the Curiosity Rover did something that had never been done before.  It drilled a tiny hole into the surface of Mars.  This hole was only two inches deep, but that was enough.  Just beneath Mars’s very red surface, the rock changed to a dull grey color.

You’ve probably heard that Mars’s red color is associated with iron oxide (a.k.a., rust).  So it may be that the grey stuff is some other iron-rich mineral, something that didn’t get oxidized (rusted) like the stuff on top of it.  Since drilling that first tiny hole, Curiosity has drilled over forty similar holes in different locations on Mars.  Sometimes, Curiosity finds grey rock, sometimes not.  That probably just means the red top layer is thin in some places and thicker in others.

What does all this tell us about the history of Mars or the modern geology of Mars?  I’m not sure.  But I do think this is a super fun fact to share at parties: beneath a relatively thin layer of red, Mars—the famously red planet—is mostly grey.

Thanks for reading, friends!  Next time I’ll be sharing my #1 favorite fact about Jupiter, which also involves the color red.