We keep sending rovers to the same spot on Mars for 1 fascinating reason

"Mars is a very risky place to go. Nearly 50 percent of missions have failed, so engineers are pretty goosey."
Grant Currin
This elevation image created by Google shows the region where many missions to Mars have landed. The deep blue depression shows Utopia Planitia, and the red arrow (added by Interesting Engineering) shows Zhurong's present location..Google Mars

China's Mars rover, Zhurong, touched down on the Red Planet a little over a year ago. Earlier this week, scientists published the first significant report of what Zhurong has seen so far.

The paper details the rover's first 60 Martian Sols, which are 37 minutes longer than Earth days. During that time, the rover made a quarter-mile journey across the planet's surface and found plenty of wind erosion and possibly some evidence of liquid water.

Zhurong is exploring the planet's northern lowlands. Specifically, it's on a plain called Utopia Planitia, which is about as wide as the continental United States.

Zhurong has plenty of company on its patch of Mars

Zhurong is the first rover on Mars that isn't controlled by NASA scientists based at the Jet Propulsion Laboratory in Southern California. Instead, the rover is a project of the China National Space Administration.

Surprisingly, the rover is exploring terrain just a few hundred miles from NASA's active rovers, Curiosity, and Perseverance. 

Geographer Christine M. Rodrigue, who worked with NASA on the Cassini mission, tells IE the reason those probes are relatively close instead of exploring the farthest reaches of the planet comes down to a classic clash in space exploration: engineers vs. scientists.

Well, she was more diplomatic:

Mission planners have a pair of "sometimes almost oppositional goals [they're] trying to maximize," she says.

"Engineers tend to be extremely concerned about the safety of a mission, and so they will often insist on landing in very smooth, low-slope locations." On the other hand, researchers have specific interests — intriguing spots they want to scope out.

“Sometimes the engineering-safe sites may be a little bit less interesting to the scientists."

"Sometimes the engineering-safe sites may be a little bit less interesting to the scientists," she says.

History shows it's a critical decision.

"Mars is a very risky place to go," Rodrigue says. "Nearly 50 percent of missions have failed, so engineers are pretty goosey."

The problem is that Mars is an incredibly bumpy place.

Martian geography is a record of Martian history

"Mars had the crap kicked out of it" by meteors and asteroids for billions of years, Rodrigue says. The same thing happened to pretty much every large object in the Solar System. The only reason that Earth isn't as pockmarked is that our planet's geologic activity has erased most of the evidence (but try telling that to the dinosaurs).

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The southern two-thirds of Mars is a highland. On a map showing elevation (check one out here), it's much more rugged than the lowlands to the north. Rodrigue calls the southern highlands "pristine" because that portion of the planet contains the well-preserved evidence of the regular and violent battering Mars got for billions of years until meteor activity in the Solar System calmed down about 3.7 billion years ago.

Rodrigue says researchers are still trying to figure out what happened to form the northern lowlands. The going theory is that "a huge impact basically chopped off the northern part of the planet." This kind of collision wasn't incredibly unusual billions of years ago.

The young Earth was hit by an object the size of Mars. The rubble formed rings around the planet and eventually merged into — wait for it, this is so cool — the Moon.

Anyway, the thinking is that the northern highlands are a crater so large it "basically defines the northern hemisphere" of Mars, Rodrigue says.

The Great Dichotomy is a sweet spot

It's not impossible to land in the southern highlands. It's where the first successful mission to the Martian surface touched down. The Soviets landed the Mars 3 Lander there in 1971, just a couple of years after American astronauts walked on the Moon.

But it's tough — Mars 3 Lander was both the first and the last successful landing in the rugged highlands.

But there's a compromise. 

It turns out the boundary between the southern highlands and the northern lowlands is "very, very sharp," Rodrigue says.

"It's like a cliff that's one to three kilometers high." 

At its maximum, that's close to thirty times the height of the white cliffs of Dover.

While it would be a suicide mission for a mission to try landing right on the Great Dichotomy, the land just to the north of it offers a compromise for safety-concerned engineers and scientists who want to check out fascinating topography (and more).

There are more geographic details at finer scales, of course. Zhurong, Curiosity, and Perseverance are close to Olympus Mons, the largest volcano in the Solar System. If it were on Earth, the volcano would completely cover Arizona and be visible from Los Angeles.

Many even smaller geographic details are very relevant to landing. Mars may not have been as active for a few billion years, but it has plenty of craters, boulders, and other spots too rough for a delicate robot from Earth to safely land and navigate.

In the end, Rodrigue says there aren't that many suitable spots when looking for a landing on Mars. There are just "two or three" good places when everything is considered.


Correction: This article has been updated to reflect that Zhurong is a few hundred miles from the Perseverance and Curiosity rovers.