The wheels of the Mars Curiosity rover have square hole cutouts that leave a pattern of tracks in the dirt. Along with rear-facing cameras, these "visual odometry markers" are used to monitor the rover's progress and tell if it's stuck.

A sharp-eyed space reporter noticed that the patterns are Morse code, and here's what they spell out:

. - - - (J)
. - - . (P)
. - . . (L)

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