365betÌåÓýÔÚÏßÊÀ½ç±­

Looking up at the moon in the night sky, it’s difficult to grasp just how dramatic the topography of its surface really is. But for David Kring, the reality of that terrain isn’t too hard to imagine.

Kring is the principal scientist at the Lunar and Planetary Institute (LPI) in Houston and divides his time between Houston and Flagstaff, where he also serves on the board of trustees for the Museum of Northern Arizona. His focuses on two immense lunar canyons known as Vallis Schrödinger and Vallis Planck, and draws upon his lifelong experiences with northern Arizona’s most famous natural feature to convey the scale of these far-away chasms.

“I love my river trips through the Grand Canyon. And I have to say, I’ve known about these two canyons on the moon for a long time,� Kring said. “And every time I’m in the bottom of the Grand Canyon on the river, I look up at the canyon walls, and I just mentally map onto that view the walls of these two canyons on the moon.�

Kring’s paper, fittingly titled “Grand canyons on the Moon,� was published on Feb. 4 in the journal Nature Communications with coauthors Danielle Kallenborn and Gareth Collins. It’s one component of ongoing research intended to lay the groundwork for future lunar exploration missions.

Vallis Schrödinger and Vallis Planck radiate outward from the Schrödinger impact basin, a crater roughly 200 miles across that was created by an asteroid impact around 3.8 billion years ago. That basin, Kring said, is “the single-best place on the moon to study the largest number of the highest-priority science objectives.� And while previous studies have focused on the Schrödinger crater itself, this new study offers “a closer look at the debris that was ejected from the basin and the scientific opportunities that that generated,� he explained.

The debris flung up by the asteroid impact included two concentrated streams of rock that created clusters of overlapping craters as they fell back to the surface, collectively carving out the two canyons discussed in the paper. Vallis Schrödinger and Vallis Planck “are just monsters,� Kring said. “They’re akin to the Grand Canyon in scale, and actually a little bit bigger�: around 170 miles long, up to 16 miles wide, and over 2 miles deep in some places.

(The Grand Canyon is longer overall, but not as deep -- its maximum depth from the North Rim is 6,393 feet, or about 1.2 miles.)

Unlike the Grand Canyon, which formed gradually over millions of years through slow processes of uplift and erosion, Vallis Schrödinger and Vallis Planck formed over a span of mere minutes -- a rapid, violent process that uplifted older rocks and deposited them along the canyon rims, potentially allowing astronauts to collect samples of strata that would otherwise be buried miles deep.

It was only relatively recently that researchers were able to understand the formation processes confidently behind these lunar canyons, Kring noted.

“We now have available spacecraft data to measure them properly and see them properly,� he said. “The Lunar Reconnaissance Orbiter� -- an unmanned spacecraft launched in 2009 -- “has imaged them and provided detailed elevation data that allowed us to start making measurements that allowed us, in turn, to begin calculating the impact cratering processes that produced them.�

Understanding the geologic history of potential lunar landing sites is critical for designing exploratory missions and guiding sample collection.

“You can land an astronaut on the surface, but if they do not understand the geology of that surface, then they are inevitably going to be collecting samples that will not be as useful as some of the other samples at that site,� Kring said.

At Arizona’s Meteor Crater, for example, �175 million metric tons of rock were excavated when that crater was produced. You have to understand the geology of that crater to know which rocks, among those 175 million metric tons, to collect,� he explained.

And few locations, if any, are as well-suited as northern Arizona for such geological training.

The area around Flagstaff was key to preparation for NASA’s Apollo missions, and “put a geological stamp on that program,� Kring said.

When he was initially recruited to the LPI from his previous position at the University of Arizona, Kring was tasked with reviewing potential sites to train future astronauts to walk on the surface of the moon. He considered all the past Apollo training sites, as well as other candidate sites across North America and the world.

“At the end of the day,� Kring said, “I recommended Flagstaff as the primary training and lunar mission simulation site.� The training program that he helped develop included work at Meteor Crater, SP Crater and the Black Point Lava Flow -- all areas that Kring is deeply familiar with.

“I’ve been taking Ph.D. students up here since 1989," he noted.

If all goes to plan for NASA’s Artemis program, the first mission to return humans to the moon in over 50 years is scheduled for 2027. The program, however, has already experienced numerous delays. If and when astronauts do return to the lunar surface, Kring believes the samples they collect there could shed new light on the early history of the earth.

“What people may not realize is the oldest epoch of earth is gone. It’s been eroded. It’s been subducted by plate tectonics,� he explained. “Even at the Grand Canyon, you can go down and you can get down to 1.7-, 1.8-billion-year-old rocks. But what about those 4-, and 4.2-, and 4.3-billion-year-old rocks? They’ve been consumed.�

On the moon, however, samples from that time period may still be accessible. And acquiring such samples, according to Kring, “would be an extraordinary scientific triumph.�