This story is part of Welcome to Mars, our series exploring the red planet.
Every morning, I make time to browse through raw images of Mars sent back by NASA’s rovers. I ooh and ah over the rock formations, and sometimes spot something goofy, like a mysterious black object hovering in a Perseverance rover image from Sunday.
The image comes from Percy’s left navigation camera. It shows a striking rock-strewn landscape and a hazy sky where the dark object appears.
So what’s going on here? It’s not aliens. A Reddit discussion of the image in a group dedicated to Mars resulted in some humorous takes on what it might be, like an ant or a plastic bag. The black shape resembles a speck of dirt or a piece of debris flying over Jezero Crater, but it’s not any of those things.
The dark object in the sky doesn’t actually exist. It’s a result of a camera artifact issue called «bad» pixels. «They are caused by micron-sized pieces of debris on the detector. Most/all imagers have these kinds of artifacts,» imaging scientist Justin Maki said in an email statement from NASA JPL. «They are generally only noticeable when the camera acquires images of the sky or some otherwise flat radiometric surface.»
If you’re not convinced, check out another left Navcam image from Sunday. The same dark streak appears, but this time it’s in the middle of a sandy landscape.
The bad-pixels issue has reared its head at other times. NASA’s Curiosity rover, which is exploring the Gale Crater in a different area of Mars, snapped a similar sky «object» in early October. As with the Percy image, it appeared as a dark spot floating in the air.
Perseverance camera team members addressed the «odd tiny black speck» artifacts in a blog post last year in relation to the rover’s mast-mounted cameras. Image processors are aware of the problem pixels and correct for them. We see the specks in the raw images sent back by the rovers because the photos haven’t been cleaned up yet.
Perseverance has been in residence on Mars since early 2021 and it’s already witnessed plenty of real-life oddball objects, like this spaghetti-like bundle of debris and a shiny piece of foil left over from its landing operations.
Camera specks are a fact of life for the Mars rovers. Our technology is amazing, but it’s not perfect. If anything, it’s a reminder of just how impressive an achievement the rovers are. Wheeled laboratories. On Mars. Sending snapshots home almost every day. Wow.