“Landing,” in robotic space missions, refers to a controlled descent of a probe onto a celestial body’s surface without significant damage. This intricate maneuver allows for close-up examination of distant worlds, providing insights unattainable through remote observation alone.
The Lunar Landings
The Moon, Earth’s closest celestial neighbor, was the first body beyond our planet where humanity achieved successful landings. The Soviet Union initiated robotic lunar exploration, with Luna 9 performing the first soft landing in February 1966, followed by Luna 13 later that year, both returning panoramic images from the surface. The United States followed with its Surveyor program, achieving five soft landings, demonstrating the technology needed for human missions.
The Apollo program landed humans on the Moon. Apollo 11, in July 1969, saw Neil Armstrong become the first person to step onto the lunar surface, joined by Buzz Aldrin. In total, six Apollo missions successfully landed astronauts on the Moon, with the last being Apollo 17 in December 1972. These missions returned lunar samples and deployed scientific instruments, advancing understanding of the Moon’s geology and formation.
Landings on Other Planets
Beyond the Moon, successful landings on other planets have been limited to Mars and Venus, presenting unique engineering and environmental challenges. Mars has been the most frequently targeted planet for landings, with numerous missions exploring its diverse terrain. Early successes include NASA’s Viking 1 and 2 landers in 1976, which conducted experiments to search for signs of life and analyzed the Martian soil and atmosphere.
Later missions like the Mars Exploration Rovers, Spirit and Opportunity, which landed in 2004, provided extensive geological data and evidence of past water activity. The Curiosity rover, landing in 2012, confirmed that Mars once had environmental conditions suitable for microbial life within Gale Crater. More recently, the Perseverance rover, which touched down in 2021, is collecting and caching Martian rock and atmospheric samples for potential return to Earth, while also testing technologies for future human exploration.
Venus poses challenges due to its dense, hot, and corrosive atmosphere. Despite these difficulties, the Soviet Venera program achieved the only successful soft landings on its surface. Venera 7 became the first spacecraft to soft-land on another planet in 1970, transmitting data for a brief period. Subsequent Venera missions, such as Venera 9 and 10 in 1975, sent back the first images from the Venusian surface, enduring the harsh conditions for less than two hours.
Beyond Planets: Moons, Asteroids, and Comets
Space exploration has extended beyond planets to other celestial bodies. Saturn’s largest moon, Titan, is one example, where the European Space Agency’s Huygens probe landed in January 2005. Huygens descended through Titan’s hazy, nitrogen-rich atmosphere, providing the first direct measurements of its atmospheric composition and revealing evidence of liquid methane rivers and lakes on its surface. The probe continued to send data for about 90 minutes after touching down on what was described as a consistency similar to wet sand.
Asteroids have also been targets for successful landings or touch-and-go sample collection missions. Japan’s Hayabusa mission achieved the first successful sample return from an asteroid, Itokawa, in 2010, after briefly touching down on its surface. Its successor, Hayabusa2, landed on asteroid Ryugu multiple times in 2019, collecting both surface and subsurface samples that were returned to Earth in 2020. NASA’s OSIRIS-REx mission also successfully collected a sample from asteroid Bennu in 2020, which was delivered to Earth in 2023. These asteroid samples offer clues about the early solar system and the origins of water and organic compounds.
Humanity has also landed on a comet, accomplished by the European Space Agency’s Philae lander in November 2014. Philae, carried by the Rosetta spacecraft, touched down on Comet 67P/Churyumov–Gerasimenko, despite its harpoons failing to deploy. The lander collected valuable data on the comet’s surface composition and properties before its batteries depleted due to an unfavorable landing orientation. This mission provided unprecedented in-situ analysis of a comet, yielding insights into these ancient icy remnants of the solar system’s formation.
The Scientific Value of Landings
Direct surface interaction through landings provides an opportunity for in-situ analysis, important for scientific understanding. Unlike orbital observations, landers can perform detailed measurements of surface materials, atmospheric conditions at ground level, and subsurface properties. For example, rovers on Mars use instruments to analyze the chemical composition of rocks and soil, search for organic molecules, and assess the planet’s past habitability.
This direct contact allows scientists to gather specific data on geological processes, such as the presence of water or volcanic activity, which are vital for reconstructing a celestial body’s history. Understanding the composition and structure of surfaces and atmospheres helps piece together the puzzle of solar system formation and evolution. By physically interacting with these environments, missions gain unique insights into the potential for life beyond Earth and the fundamental processes that shaped our cosmic neighborhood.