To find the hardest planetary landing in our solar system, you have to choose between a world with no surface at all, or one where the air is hot enough to melt lead.
Attempting to land on a gas giant like Jupiter is a paradox because the planet lacks a solid surface.
Jupiter, as seen by the Cassini spacecraft in 2000. It lacks a solid surface, making a traditional landing impossible.
Jupiter is composed almost entirely of hydrogen and helium. A crewed spacecraft entering its atmosphere would experience a descent with no end. After passing through turbulent, ammonia-rich clouds and lethal radiation belts, the ship would face exponentially increasing pressures and temperatures. Eventually, the pressure becomes so immense that hydrogen gas compresses into a bizarre state called liquid metallic hydrogen. Any vessel would be crushed, melted, and assimilated into the planet's interior long before reaching the core. Because there is no rocky crust to park a vehicle on, a safe landing is physically impossible.
For a true planetary landing on a solid surface, Venus provides the most hostile environment for human survival.
An illustration of a heavily armored spacecraft descending through the thick, hostile sulfuric acid clouds of Venus.
From orbit, Venus looks like a serene, bright marble, but its atmosphere is a nightmare for aerospace engineering. The atmosphere is composed primarily of carbon dioxide, with thick clouds of sulfuric acid. The atmospheric pressure at the surface is roughly 90 times greater than that of Earth. Standing on the surface of Venus would feel akin to being submerged 900 meters (about 3,000 feet) underwater. Any unreinforced habitat or spacesuit would instantly implode from the weight of the air alone.
In addition to the crushing pressure, Venus experiences a runaway greenhouse effect. The surface temperature averages around 475 degrees Celsius (887 degrees Fahrenheit). This is hot enough to melt lead, zinc, and tin. The extreme heat would instantly cook conventional life-support systems, melt electronics, and rapidly degrade spacecraft seals.
A panoramic view of the surface of Venus captured by the Soviet Venera 13 lander in 1982.
Despite these apocalyptic conditions, Soviet engineers managed to land robotic probes on Venus during the Cold War. Because the atmosphere is so incredibly dense, the later Venera landers did not even need parachutes for the final stages of their descent; they used aerodynamic braking discs to drift down through the thick, fluid-like air.
Once on the ground, the engineering challenge shifted entirely to survival. The Venera 13 robotic lander, which touched down in 1982, holds the record for the longest survival time on the Venusian surface. It lasted for just 127 minutes before the immense heat and pressure breached its protective titanium hull and destroyed its instruments. Designing a crewed lander to keep humans alive long-term on Venus would require specialized high-temperature refrigeration, massive titanium pressure hulls, and materials that push the boundaries of materials science.
While Mars presents difficulties with its thin atmosphere and dust storms, aerospace engineers plan to eventually send humans to visit and inhabit it. On Venus, achieving even a few hours of robotic surface time represents an engineering marvel, making it the single hardest planetary surface in the solar system for humans to reach and survive on.