Do You See a Mountain or a Crater in This Picture?

By Nancy Atkinson - January 29, 2015 at 2:40 PM UTC | Planetary Science
ESP_011588_2225_RED.browse.jpg

Yesterday, we posted an

image taken by the HiRISE

camera on the Mars Reconnaissance Orbiter (MRO) of an unusual crater formed by a triple-asteroid. We noticed some comments on the article and on social media of people who said, "hey, that looks like a mountain, not a crater!"

Thanks to our brains, this is a common illusion! Depending on the angle of the Sun when the picture was taken, images of craters taken from overhead (i.e. from orbit) may appear to be a mountain. Here on Earth, we're used to seeing sunlight coming from overhead, and our brain interprets what we see with the assumption that the sunlight must always come from above. Satellite photos of terrain, however usually only show shadows when the light source is nearly horizontal with the surface.

There's an easy fix for this illusion: flip the image over so it appears the sunlight is coming from above. We've done that for you, below:

[caption id="attachment_118620" align="aligncenter" width="451"]

The same 1-km fresh crater on Mars, but with the image upside down. Credit: NASA/JPL/University of Arizona.[/caption]

Dr. Richard Barrans

from Newman University in Kansas

explains

this crater/mountain illusion:

When a crater is illuminated from above, the shadow inside the crater is near the top and the bright part is near the bottom. A mountain shows exactly the opposite lighting pattern: bright at the top and shadowed at the bottom. This is because the part of the crater or mountain that is most perpendicular to the incoming light reflects it the best. Anyway, your brain interprets pictures under the assumption that the light is from the top of the scene. So if a picture shows an object that is bright at the top and dark at the bottom, it interprets it as a mound lit from above, not as a crater lit from below.

We do know that any photo of anything that is concave or convex will flip in its appearance if the photo is turned upside down. Take a look at

any of these crater images from HiRISE

, and you'll likely be deceived on most of them! (remember, they are ALL craters!)

And here's the image from yesterday:

[caption id="attachment_118582" align="aligncenter" width="580"]

A triple crater in Elysium Planitia on Mars. Credit: NASA/JPL/University of Arizona.[/caption]

You can now amaze your friends. You're welcome.

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com