Marineris: The Invisible Valley?

Since this was mentioned to me over lunch nearly six months ago, it’s been coming back to my brain again and again.  The Valles Marineris (or Mariner’s Valley) is a massive rift system cutting a gash 7 km deep into the surface of Mars.  At 4,000 km long, and 200 km wide, this is the largest known canyon in the Solar System.

Credit: NASA (Viking 1)

The rift is extremely visible from space, but is it visible from inside the canyon itself?  In canyons on Earth, it’s reasonably straightforward to confirm that you are in fact in a canyon.  One quick glance at the cliff face on either side of you will ensure you are well informed.  But what about Marineris?

At lunch, a colleague informed me that Marineris is so wide, that if you stood in the centre of the canyon, the curvature of Mars hides the cliff faces on both sides.  In effect, you would think you were standing on a relatively featureless plain, with the canyon walls safely hidden behind the horizon.  A pretty extravagant claim, no?  You can answer this question for sure with some simple geometry, as long as you know the depth (7km) and width (200km) of the canyon, and the radius of Mars (which is 3,396 km).  I could tell you the answer now, but I’m interested in what you think.  So let’s put it to the vote:

I’ll let you know the answer next week!


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