Final answer:
The major challenges for spacecraft landing on Venus are its extreme atmospheric pressure and high surface temperature, conditions caused by a dense atmosphere primarily composed of CO2 and an intense greenhouse effect.
Step-by-step explanation:
The main problem spacecraft have encountered in landing on Venus is the extreme atmospheric pressure and high surface temperature. Venus' surface is incredibly hostile; pressure measures at about 90 bars, which is equivalent to the pressure found approximately 900 meters underwater on Earth.
Additionally, the temperature on Venus can reach upwards of 730 Kelvin (457°C; 855°F), hot enough to melt lead. The corrosive nature of Venus' atmosphere, which consists of thick clouds made of sulfuric acid, and a composition of approximately 96% carbon dioxide (CO2), further exacerbates the challenge of space missions on this planet. The CO2 greenhouse effect has led to these high temperatures. Despite this inhospitable environment, the Russian Venera missions in the 1970s landed successfully, relaying crucial data about Venus' surface and atmosphere before succumbing to the harsh conditions.