On March 19, 2012, I was observing and imaging Mars in my observatory. I noticed something peculiar on the limb of the planet, but attributed it to either seeing or miscollimation of my scope. I recollimated mid-session, but the strange protrusion from the limb remained. The seeing was quite good at the time, but those of you who have spent much time behind an eyepiece know that there are always very slight ripple or disturbances, so I didn’t think too much of it until the next day while I was processing the data into images.
As I created images, I noticed the anomaly again in each image but it eventually faded away toward the end of the session. After initially toying with the idea of just erasing it in Photoshop, I decided to create an animation (a simple sequence) with the images. As you can see below, the protrusion moves with the planet. It wasn’t an artifact of bad seeing, it’s something real.
I sent the initial images to some experienced observers and we agreed that it couldn’t be any of Mars’ moons. They would be too dim to see against the planet at that distance and are typically impossible to image via amateur telescope unless they’re near aphelion from the planet and captured in a highly overexposed image. So, the question became, what is the “Mars Anomaly”?
Once I notified the amateur community, others were able to review their images and identify the same protrusion. As we gathered the data, we conferred with various professional astronomers in attempts to identify the phenomena. Ultimately, we gathered 19 observations of the plume from across the world in a very short period of time. In the meantime, NASA/JPL directed their Mars-orbiting satellites to the region to see if the source of the plume was from the planet, but nothing appeared at ground level or within the atmosphere. When we calculated the height of the cloud, however, it was outside the bounds of what we would consider Mars’ atmosphere as it was somewhere between 120 and 160 miles above the planet’s surface. Even on Earth that would be considered well into orbit (there are space stations not much higher than that altitude over Earth!) On Mars it’s completely impossible for any cloud to reach that high. Yet we have enough pictures from enough observers to prove there is something there.
What is it? We don’t know. We eventually published our observation in the Journal Nature. In the article, we note that the Hubble Space Telescope had imaged a similar phenomena (below) back in 1996. Articles on this discovery were published in numerous journals, many websites covered the story, it was in each of the cable news channel’s new cycles for a day, was an APOD, and even was covered a number of times on “Nasa’s Unexplained Files” on the Discovery Channel. I’m even listed on imdb.
There hasn’t been another occurrence of the terminator cloud recorded in over 10 years since my observation back in 2012, so my initial theory that this was somehow related to a series of crater that appeared on Mars shortly after the cloud was observed.