The talk at Fuerte’s observatory was absolutely delightful. While I didn’t learn much myself, it’s always delightful to be presented with the fascinating scope of our universe. It’s a combination of harrowing and humbling, and the view of the moon was a delightful conclusion. That, however, is not the purpose of my post. Caleb Koch, Jake Januzelli, and myself have spent the last hour trying to come to an answer about a placard in the museum in the observatory associated with the following photo:

While I can’t recall exactly what the placard said, it was something akin to what is the official description of the photo from the Jet Propulsion Laboratory (JPL):

“This approximate true-color image taken by the panoramic camera on the Mars Exploration Rover Opportunity shows the impact crater known as “Endurance.” Scientists are eager to explore Endurance for clues to the red planet’s history. The crater’s exposed walls provide a window to what lies beneath the surface of Mars and thus what geologic processes occurred there in the past. While recent studies of the smaller crater nicknamed “Eagle” revealed an evaporating body of salty water, that crater was not deep enough to indicate what came before the water. Endurance may be able to help answer this question, but the challenge is getting to the scientific targets: most of the crater’s rocks are embedded in vertical cliffs. Rover planners are currently developing strategies to overcome this obstacle.

Presently, Opportunity is perched 40 centimeters (15.7 inches) away from the crater’s edge. Endurance is roughly 130 meters (430 feet) across.

This image mosaic was taken by the panoramic camera’s 480-, 530- and 750-nanometer filters on sols 97 and 98. It consists of a total of 258 individual images.

Image credit: NASA/JPL/Cornell ” Source: https://mars.nasa.gov/mer/gallery/panoramas/opportunity/2004.html

Notice that the description clearly suggests that the crater in the picture, Endurance crater, and the previously investigated crater, Eagle crater, possessed quickly evaporating but nevertheless liquid brines on the surface of Mars. If this is true, this is direct evidence of liquid water on Mars. Caleb was skeptical, and I’m glad he was. A quick google search reveals that there does not seem to be such a radical consensus in the literature. No one seems to have suggested direct evidence for liquid water on Mars, and articles discussion these evaporating brines don’t cite any having been found, but rather provide evidence that the conditions could create them and that they were once present (https://www.nature.com/articles/ngeo2412).

There is a mystery about this description – but I do not think anything malicious is going on. On the contrary the story behind the photo provides fascinating insight into the workings of the Opportunity Rover. The photo in question is composed of 258 individual images and gives a 180 degree panorama of the crater. As far as I can tell, half of these are from the left lens of the camera, and the other half are from the right lens. These are then doctored together and recolored (more on that later) to create the final image we see. Notably, the images from the left lens

and right lens

Source: https://mars.nasa.gov/mer/gallery/panoramas/opportunity/2004.html

Both show the same fluid like substance at the center of the crater. Since these are from May 4th, 2004, two days before the May 6th publication of the original photo, I believe this convincingly shows that the doctoring of the photo did not add any substantial changes to the fluid appearance of what is at the base of the crater. Fun fact – Cornell assisted with creating this photo in some way (presumably this is partly why a nice copy is at the museum). The question then remains – what is at the base of the crater? The discussion of the photo from JPL on May 6th (http://www.spaceref.com/news/viewpr.html?pid=14175) includes the following:

“”That was the last dying gasp of a body of water,” Squyres said. “The question that has intrigued us since we left Eagle Crater is what preceded that. Was there a deep body of water for a long time? Was there a shallow, short-lived playa? We don’t know.””

The individual quoted is Dr. Steve Squyres of Cornell University. The suggestion of this description is that what we are seeing is the remnant of some body of water – not the water itself. This is corroborated further with the following image:

Source: https://mars.nasa.gov/mer/gallery/press/opportunity/20040806a.html

The source claims that this is a photo of the center of Endurance Crater taken by Opportunity in 2004. As far as we can tell, this is the exact same “fluid” substance appearing at the center of the crater in the main image. However, the source states that this is sand – and it certainly looks like it is sand as well. So I think it is perfectly satisfying to say that what is in the original photo is not an evaporating body of water itself, but instead the last remnants of a recently eliminated brine. The only question remaining is then why does it appear so much like water in the original image? JPL actually has an explanation:

“Also evident is a “blue” tint on the flat surfaces as compared to the dune flanks. This results from the presence of the hematite-containing spherules (“blueberries”) that accumulate on the flat surfaces.” https://mars.nasa.gov/mer/gallery/press/opportunity/20040806a.html

This explains why the sand in the original photo appears so gray. I’m guessing that this is in part because of these “blueberries” – they provided the discoloration we see. All together, this is what we concluded. The original photo is in no way unusually doctored – but what appears to be a salty brine is actually sand, discolored by strange minerals in the surface of Mars. The sand itself, however, is evidence of a recently evaporated brine, and clear evidence that there was once water on Mars.