# I know some Martian navigators who can still do that today #MarsWalk

(apologies to Tom Lewis.)

If you start up Google Earth, then go to the View menu and select Explore, then Mars, you get Mars. Very cool. The Layers include satellite images, IAU/USGS place names, guided tours, and the locations of about everything we’ve ever put on Mars, like, oh, for instance, Viking 2 and Curiosity. Curiosity’s landing site and subsequent path are both shown, though the path looks like it’s some weeks or months old.

But if you draw a path from Viking 2 to Curiosity and look at the length of that path, Google says it’s about 3059 km. Boyan’s #MarsWalk posts say it’s 2880 km. Bit of a discrepancy there.

So, first of all, are Google’s positions right?

For Curiosity’s present position see http://curiosityrover.com/rovermap1.html. Using that I made a pin in Google Earth/Mars with Curiosity’s updated position. Viking, of course, has stayed put for 40 years, and we know where it is too. The Google Earth position is accurate.

The distance of 2880 km is also given at NASA’s Mars Mileage Guide which gives a handy table of all the distances between ten landers and three geographical features. That page also states coordinates: For Viking 2, 44° N, 226° W, and for Curiosity, 4.59°S, 222.56°W. But the Viking 2 coordinates are said to be 47.97° N, 225.74° W here. In Google Earth the coordinates are 47.66° N, 134.28° W and 4.40° S, 137.22°W. Obviously a different coordinate system. If it’s just a meridian shift of 88° then Google’s reasonably consistent with the second of those pages but not the first.

Hm. If I put a marker in Google Earth at 44° N, 134° W and measure the distance to Curiosity I get about 2843 km. Close enough to 2880 to make me confident that’s the source of the discrepancy… it’s based on a wrong location for Viking 2!

I have a query in with the NASA contact for that page. Maybe I’m getting something wrong. But it looks to me as though, unfortunately for anyone walking, the actual distance is about 180 km longer than we thought.

MarsWalk spreadsheet

MarsWalk kmz file (for Google Earth — View >> Explore >> Mars)

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