Private spacecraft circling moon snaps photo with strange optical illusion

A Japanese commercial spacecraft has sent home another close-up image of the moon, its intended landing destination in a matter of days, but this picture can play tricks on the eyes. 

Tokyo company ispace released a fresh photo from its lunar lander Resilience as it orbits the moon. The snapshot reveals the rugged landscape of the lunar south pole, a highly sought region by NASA and other spacefaring competitors because of its ice within permanently shadowed craters. That ice could be a valuable commodity for future space voyages if it can be converted into rocket fuel, oxygen, and drinking water. 

But some viewers may not see the pictured craters denting the surface as they are. 

"This image presents an optical illusion to some," the company said in a post on X. "Although the image is filled with concave craters, from this orientation they may look like they are convex to the eye."

Engineers for ispace load the Resilience lunar lander into a transport container before shipping it to Cape Canaveral, Florida. Credit: ispace

Make no mistake: Those are hollowed out dips, not bumps. The reason they may appear as the latter, though, is a relief inversion phenomenon — a common problem when interpreting spacecraft photography. Astronomers have even coined names for it, calling it the "crater illusion" or "crater-dome illusion."

"Upon first glance, it is difficult to tell if ground is rising up, sinking down, or a mix of both," according to the European Space Agency. 

The crater-dome illusion, explained

The optical illusion occurs because people are used to interpreting shadows as coming from an overhead light source. But that's not necessarily the orientation of spacecraft. In many satellite photos, the light source is almost horizontal to the surface. That makes it easy for the patterns of light and shade to fool our brains. 

Where sunlight illuminates south-facing slopes and leaves northern slopes in shadow, for instance, many viewers experience the issue, according to NASA's Earth Observatory. For that reason, astronomers often orient satellite images so that north is up.

Four months after Resilience's mid-January launch, it reached the moon and has flown laps around it since in preparation for ispace's second attempt at a lunar landing. The company's first try two years ago failed when its spacecraft ran out of fuel and crashed on the moon. 

The new mission, dubbed Hakuto-R, is gearing up for a touchdown near the center of Mare Frigoris at 3:24 p.m. ET on June 5. (It will be June 6 in Japan.) Livestream coverage will begin about one hour earlier, at 2:15 p.m. ET, with English translation. 

If the Hakuto-R mission aces the landing, it will spend two weeks running experiments on the lunar surface before powering down for the brutally cold lunar night. Credit: ispace infographic

Landing on the moon remains onerous — demonstrated by numerous flopped landings. Though Firefly Aerospace succeeded in landing in March, another U.S. company, Intuitive Machines, didn't fare as well, ending up on its side in a crater less than a week later. 

The difficulty arises from the moon's exosphere, which provides virtually no drag to slow a spacecraft down as it approaches the ground. What's more, there are no GPS systems on the moon to help guide a craft to its landing spot. Engineers have to compensate for those challenges from 239,000 miles away.

Whether ispace is better positioned for success this time remains to be seen. For now, flight controllers are enjoying the spacecraft's scenery. And for those who are having trouble appreciating the moon's southern craters in the new image, ispace has a tip. 

"Flip the image," the company said, "or tilt your head to change your perspective!"