Geocache on Mars

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Geocaching is a fun activity here on Earth. Now you can geocache on Mars. And the International Space Station.

On February 18, 2021 the Perseverance rover landing on Mars with a parachute was breathtaking and scary to follow. Safely on Mars, the rover began a series of tests before it started to explore the planet. In one test, the SHERLOC-WATSON instrument focused on a panel on the front of the rover to calibrate features. SHERLOC is a scientific instrument that includes a camera called WATSON.

In addition to calibration results, the WATSON camera also sent a special photo back to Earth: the code for a trackable geocachers can add to their list and follow. While not the first off-Earth geocache or trackable — there’s a geocache on the International Space Station, the Perseverance trackable is the first on Mars.

What’s Geocaching?

If you don’t know, geocaching is a game played mostly outdoors that involves finding objects often hidden in plain sight. Geocachers use tools like a smart phone app, GPS, an online search engine, and a geocaching site to record their finds. A geocache is an item that can include other items, for example, a notepad where finders can add their name and date. Geocaches are hidden with GPS coordinates recorded on a geocaching site for others to find. A trackable is usually a game piece found in a geocache whose movements from one geocache to another can be recorded on a geocaching site.

The code on the front of the Perseverance rover makes the rover a trackable you can add to your collection online!

How Did a Trackable Get to Mars?

NASA scientists Dr. Francis McCubbin and Dr. Marc Freis and Freis son Wyatt are responsible for the idea of including a trackable on the Perseverance rover. McCubbin was struck by the way the rover is geocaching with Mars samples instead of typical Earth geocaches and trackables. The Perseverance is the first of three rovers collecting samples in tubes to be retrieved by a future NASA Mars Sample Return mission. Freis father and son, like McCubbin, are avid geocachers.

With permission from NASA, McCubbin and others included a trackable code as part of the panel used to calibrate the SHERLOC-WATSON assembly. The trackable code is part of a polycarbonate disc used as an optical target for the WATSON camera and a spectroscopic standard for the SHERLOC instrument. The disc material also is a sample of astronaut helmet visor material which is being tested to see how it survives on Mars.

Smart readers like you probably have noticed one problem with a trackable on Mars: it’s on Mars, another planet. There aren’t daily flights to Mars. And trackables are meant to be moved from geocache to geocache.

The solution is to use the website to add the Perseverance rover trackable to your list of items found while geocaching.

How Do You Get the Trackable Code?

Well, there’s an easy way and a harder way.

The easy way is to search online for the Perseverance rover trackable code, with a search engine or the website. But that feels like cheating.

The harder but infinitely more fun way is to go through the SHERLOC-WATSON photos on the NASA Mars Perseverance website to find the photo sent back to Earth. Then visit the website page for trackables, type in the code to display the rover trackable page, and then follow the trackable.

Photos can be found at and be sure to select the SHERLOC-WATSON filter check box on the right side of the page. You’re looking for this photo of the calibration panel from Sol 26 or March 26, 2021 here on Earth. The photo looks like the photo on the bottom, with dust all over it.

Figure A
Figure B

The circle at the top left (B) of the panel already has attracted a lot of Mars dust which is magnetic and sticks to metal surfaces. It’s hard to see the trackable. Here’s what is in the circular geocoin trackable:

Figure C

What Does the Trackable Look Like?

The trackable (C) is a round image with lots of interesting artwork in addition to the trackable ID number you can use on the website to add it to your geocaching collection.

For example, see the dancing stick figures at the bottom of the trackable? The profile drawing of Sherlock Holmes near the top? Apparently the stick figures are from a code Holmes cracked in one of his detective stories. The code on the Mars rover spells out, “Cache me if you can,” a fun shout out to geocachers looking for this trackable. The 221BBAKER code also is a reference to Baker Street where Holmes lived.

Add the Mars Trackable to Your Collection

Having found the Perseverance trackable, the next step is to go to the website, log in or create an account, then find the Perseverance trackable page at and type in the code on the geocoin: 221BBAKER.

Be sure to click the Found It? Log It! link and then click the Add to Watchlist link too. And if you’re interested in all the markings on the rover, definitely look at the NASA page that describes them all.

Learn More

Calibration Target on NASA Website

Calibration Target on Mars IRL

Geocoin Trackable

Mars 2020 Perseverance Rover Markings

Interview with Francis McCubbin

Perseverance Trackable on

International Space Station Geocache on

Geocaching and Perseverance/Space Timeline

The Detective Aboard NASA’s Perseverance Rover


  • Tim Slavin

    Tim is an award-winning writer and technologist who enjoys teaching tech to non-technical people. He has many years experience with web sites and applications in business, technical, and creative roles. He and his wife have two kids, now teenagers, who are mad about video games.

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