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Landing on a strange planet

  To explore the solar system, people not only send probes to the vicinity of distant celestial bodies to observe them, but also hope to directly land on these celestial bodies to study them up close. And landing safely on a planet is often a critical step in success or failure. Since the space age, human probes have had memorable landing moments on major planets, moons, asteroids and comets in the solar system, with Mars and the moon being the most favored by scientists.
  However, so far there are still many places that are not satisfactory. Venus, for example, although it is very close to us, landing on Venus is not easy, and only a few spacecraft have been successful. And Europa, while the frozen moon is considered one of the most ideal places in the solar system to search for life, no probe has landed on Europa so far. People often talk about the above two planets, but what they are on the surface is still unknown.
  Now, scientists are working to change this situation, and they have designed some new landing plans, and imagine what new landing techniques should be used by future spacecraft to land on Venus and Europa.
  Venus is a difficult world to visit, as scientists have learned. Venus’ scorching temperatures and enormous atmospheric pressure could destroy a probe that reaches its surface in less than two hours. But planetary scientists are still very much looking forward to going to Venus, because they are increasingly certain that Venus was once habitable. Some scientists also claim that they have found traces of microbial activity in Venus’ atmospheric clouds, which contain a chemical known as phosphine that normally coexists with certain microbes. On Earth, phosphine is released by certain bacteria, and the presence of phosphine in the clouds of Venus means there may also be microbes in the upper atmosphere of modern Venus.
  Although microbes have not yet been confirmed to exist on Venus, the idea that Venus’ environment was once habitable has been increasingly recognized by the academic community, leading scientists to rush to explore Venus. They noticed a mountainous region called “Tesera” on Venus, where mountains are ridged and folded, most likely the result of the relative motion of continental plates, suggesting that some form of tectonics may exist on Venus plate. The movement of the plates brings new rock to the surface, creating this folded mountainous terrain. On Earth, the existence and movement of tectonic plates play a very important role in the existence and evolution of life on Earth.
enter the dense atmosphere

  To this end, scientists have designed a space mission to Venus, which will have, in addition to an orbiter around Venus, a lander that can drill and analyze rock samples from the Terceira region. At present, however, it appears that it is very difficult for the lander to land in the mountains of Venus. Although in the 1990s, NASA’s Magellan orbiter produced a topographic map of Venus, the map only showed in general that most slopes on Venus were less than 30 degrees, but the specific situation did not It is unclear and impossible to determine exactly how steep the slopes in the Terceira area are. Maybe in some areas, the slope can reach 60 degrees. If the lander landed in these areas, it could easily tip over. Therefore, the lander needs some kind of intelligent navigation system to choose the best landing site and navigate.
  Because of the density and pressure of Venus’ atmosphere, the proposed lander doesn’t use small rocket engines to slow it down like the Mars lander, but instead uses a fan-style setup. Fans can slowly bring the lander closer to the surface, almost like a submarine, turning the disadvantage of Venus’ dense atmosphere into an advantage.

Image taken by the Magellan orbiter showing a mountainous region on Venus known as Terceira, whose folded mountainous terrain may be the product of tectonic activity

3D composite image of Venus’ surface

  However, the dense atmosphere on Venus will also bring another bigger challenge, that is, it is difficult to see the ground when the lander touches down on Venus. The dense atmosphere makes Venus’ surface scatter light more easily than on Earth or Mars. Once the lander descended to just a few kilometers from the ground, the view of the surface of Venus became very blurred.
  To make matters worse, the scattered light can also create the illusion that the light source is coming from all directions, like a flashlight shining into a fog. This makes it difficult for objects on Venus to appear in shadow, and steep slopes or huge rocks cannot be highlighted by shadows, which poses a great risk to a safe landing. Some scientists believe that while there are near-feasible solutions to most of the challenges of landing on Venus, the inability to see clearly remains the biggest hurdle.

A spacecraft lands on Jupiter’s icy moon Europa (imagined)
Landing on a frozen planet

  Compared with the landing on Venus, the lander will not encounter a dense atmosphere on Europa, nor will it be blocked by scorching high temperature and huge air pressure, and the scenery on Europa’s surface is also clear. But Europa’s surface is composed of ice, with ridges, ravines and cracks, and a handful of craters. The challenges of landing on such a frozen planet remain daunting. Scientists are considering using the landing technology used on Mars on Europa’s lander, a landing device called a “space crane” that first landed on Mars in 2012 when the “Curiosity” rover touched down on Mars. used this technique. It’s a suspension system with a braked rocket motor that gently “drops” the lander to the surface of the planet. The technology was also used when the Perseverance rover landed on Mars in February 2021.
  But the gravity on Europa is very small, only one-seventh of the gravity on Earth. In this case, the huge lander still has uncertainty when it touches down, because if there is a rebound or the like on the landing, the landing operation will face failure. In this regard, John Gallen, an engineer at the Jet Propulsion Laboratory in the United States, said: “Our requirement is that no matter what the shape of the planet’s surface is, the lander must be able to adapt and remain stable on it.” The lander has designed and tested various styles of supports that can lock onto the ice or allow the lander to crouch firmly on the ice like a frog.
  Europa is about the size of the moon. So far, scientists’ understanding of Europa remains superficial. In the 1990s, the “Galileo” Jupiter probe detected the moon. The detection results show that there may be a liquid water body under the ice shell of Europa. This huge subsurface ocean is the reason why scientists are deeply interested in it, because the existence of the subsurface ocean means that Europa is likely to be a A planet where life exists.
  The Galileo Jupiter probe took a careful look at Europa’s frozen surface and found that Europa has a unique double-ridged terrain, which can reach 300 meters high and extend for hundreds of kilometers. Scientists don’t yet know how this strange icy terrain formed. Some scientists believe that Europa may have jagged icicles, known as “ice blades.” However, based on the images returned by the “Galileo”, it is completely impossible to determine whether the ice blade exists. If such ice structures do exist, landing on Europa would be even more difficult. However, the latest research shows that the lack of atmosphere on Europa should make it difficult for ice blades to form.
  In order to deepen the understanding of Europa, people have also designed another space mission, called Europa Clipper, which is scheduled to launch in 2024 and reach Jupiter in 2030. It will take high-resolution images of Europa, which will help clarify whether there are ice blades on Europa. At the same time, the “Europa Clipper” will also conduct a comprehensive multi-faceted detection of Europa, which will help accelerate human beings’ further understanding of this strange planet.

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