The best way to get to know a world is by touching it. Scientists have observed the planets and moons in our solar system for centuries and have flown in spacecraft passing the spheres for decades. But to truly understand these worlds, researchers need to get their hands dirty, or at least the pillows of a spaceship.
Since the dawn of the space age, Mars and the moon have won almost all of Lander’s love. Only a handful of spacecraft landed on Venus, our other nearest neighboring world, and none touched Europe, a frozen moon of Jupiter that is believed to be one of the best places in the solar system to search for current life (SN: 02/05 / 14).
Researchers are working to change that. In several talks at the American Geophysical Union virtual meeting held Dec. 1-17, planetary scientists and engineers discussed new tricks that the hypothetical future spacecraft may have to land on unknown terrain on Venus and Europe. The missions are still in the design phase and are not on NASA’s launch schedule, but scientists want to be prepared.
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Sailing in a Venusian glove
Venus is a notoriously difficult world to visit (SN: 13/02/18). Their scorching temperatures and overwhelming atmospheric pressure destroyed all the ships that were lucky enough to reach the surface in about two hours after arrival. The last landing was more than 30 years ago, despite increasing confidence among planetary scientists that the surface of Venus was already habitable (SN: 26/08/16). That possibility of past and perhaps current life on Venus is one of the reasons scientists are eager to return (SN: 28/10/20).
In one of the proposed plans discussed at the AGU meeting, scientists have a bent mountainous terrain on Venus called Teselas. “Landing safely on tile grounds is absolutely necessary to meet our scientific goals,” planetary scientist Joshua Knicely of the University of Alaska Fairbanks said in a recorded recording for the meeting. "We have to do it."
Knicely is part of a study led by geologist Martha Gilmore of Wesleyan University in Middletown, Connecticut, to design a hypothetical mission to Venus that could be launched in the 2030s. and analyze tile rock samples. It is believed that this terrain formed where the edges of the continents slipped on top of each other beneath each other, bringing new rocks to the surface in what could be a version of plate tectonics. On Earth, this type of resurgence may have been important in making the planet hospitable to life (SN: 22/04/20).
JPL-Caltech / NASA
But landing in these areas on Venus could be especially difficult. Unfortunately, the best maps of the planet – from NASA’s Magellanic orbiter in the 1990s – can’t tell engineers how steep the slopes are in tile terrain. These maps suggest that most are less than 30 degrees, which the lander could handle with four telescopic legs. But some could reach 60 degrees, which will leave the vulnerable ship collapsing.
“We have very little understanding of what the surface is like,” Gilmore said in a recorded recording for the meeting. "What is the size of the stone? What is the distribution of the size of the rock? Is it spongy?"
Therefore, the lander will need some kind of smart navigation system to choose the best places to land and head there. But that need for direction brings another problem: unlike landers on Mars, a Venus lander cannot use small rocket engines to slow down when descending.
The shape of a rocket is adapted to the density of air against which it will push. That is why rockets launching spacecraft from Earth have two sections: one for the Earth's atmosphere and another for the almost emptiness of space. Venus' atmosphere changes density and pressure so fast between space and the planet's surface that "falling a mile would go from the rocket working perfectly, until it's going to fire and possibly fall apart," Knicely says.
Instead of rockets, the proposed lander would use fans to push, almost like a submarine, turning the disadvantage of dense atmosphere into an advantage.
The planet’s atmosphere also presents the biggest challenge of all: seeing the ground. The dense atmosphere of Venus scatters light more than that of Earth or Mars, blurring the view of the surface to the last miles of descent.
What’s worse, the scattered light makes it look like the lighting is coming from all directions at once, like making a fog lantern shine. There are no shadows to help show steep slopes or reveal large boulders that the lander could collide with. That’s an important issue, according to Knicely, because all existing navigation software assumes that light comes from a single direction.
“If we can’t see the ground, we can’t figure out where things are safe,” Knicely says. "And we can't figure out where science is either." Although the proposed solutions to the other challenges of landing on Venus are almost feasible, he says, this remains the biggest hurdle.
Sticking to landing in Europe
For its part, Jupiter's icy moon Europe has no air to blur the surface or break rockets. A hypothetical future lander from Europe, which was also discussed at the AGU meeting, would be able to use the “sky crane” technique (SN: 8/6/12). That method, in which a platform is placed on the surface using rockets and drops a spacecraft to the ground, was used to land the Curiosity rover on Mars in 2012 and will be used for the terrifying Perseverance in February 2021.
“Engineers are very excited about not having to deal with an atmosphere when going down,” spacecraft engineer Jo Pitesky of NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a recorded recording for the meeting.
Still, there are many that scientists don’t know about the surface of Europe, which could have implications for any lander it touches, planetary scientist Marissa Cameron of the Jet Propulsion Laboratory said in another talk.
The best views of the moon landscape are from the Galileo orbiter in the 1990s, and the smallest features I could see were half a mile in diameter. Some scientists have suggested that Europe could carry irregular ice peaks called penitents, similar to the ice features of the Chilean Andes that get their name from their resemblance to hooded monks with bowed heads – although more recent work shows that Europe's lack of atmosphere should prevent penitents from forming. .
Another mission, the Europa Clipper, which is already underway will take higher resolution images when the orbiter visits the Jovian moon at the end of this decade, which should help clarify the problem.
Meanwhile, scientists and engineers are conducting elaborate clothing tests for a landing in Europe, from simulating ice cream with different chemical compositions in the vacuum chambers to dropping a crane called Olaf from a crane to see how it is supported.
“We have a requirement that says the terrain can have any configuration – jagged, potholes, so – and we have to be able to adjust to that surface and be stable on it,” says John Gallon, an engineer at Jet Propulsion Laboratory. (The Lander mannequin was named after his 4-year-old daughter's favorite character in the movie Frozen).
Olaf, a scale model of a possible European lander, is helping NASA engineers test different strategies for landing on Jupiter's icy moon. The rover is named after the snowman from the movie Frozen.
For the past two years, Gallon and colleagues have tested different feet, legs, and landing configurations in a lab by suspending the ceiling scare like a puppet. That suspension helps simulate the gravity of Europe, which is one-seventh that of Earth.
Without much gravity, a massive terrifier could jump and be easily damaged when trying to land. “She’s not going to hit the landing like a gymnast coming out of the bars,” Gallon says. His team tested sticky feet, cup-shaped feet, springs that compress and push on the surface, and legs that lock in to help the lander be placed on multiple terrains. The lander can crouch like a frog or be rigid like a table, depending on the type of surface it lands on.
While Olaf is working hard helping scientists figure out what it will take to build a successful European lander, the mission itself, like its Venusian counterpart, only remains on the wish lists of some planetary scientists for now. Meanwhile, other researchers dream of trips to completely different worlds, including Saturn's geyser moon Enceladus.
“Some people will pick favorites,” Cameron says. "I just want to land somewhere we've never been and other than Mars. I'd love to."