Space exploration is the journey of people and machines beyond Earth’s atmosphere into a distant, unexplored universe. It’s a complex undertaking that requires the greatest ingenuity and investment of time, talent, and money. It’s an effort that brings nations together, regardless of their political or cultural differences. The International Space Station, for example, involves collaboration between the national space agencies of the United States, Russia, and Europe.
Space probes and artificial satellites have flown past, orbited, and landed on the Moon, Saturn’s moon Titan, Venus, and Mars. They have also explored asteroids and a comet. The longest-running spacecraft, Voyager 1, and its twin, Voyager 2, have traveled so far that they are now in interstellar space (a region beyond the solar system’s bubble of particles called the heliosphere).
Scientists use the unique conditions of space to conduct experiments on living things of all kinds—from plants and animals to microscopic bacteria. They study everything from the physics of space to the chemistry of planetary atmospheres.
People’s fascination with space has inspired exploration since the earliest days, when they first looked upward to wonder what they saw in the stars (see astronomy). Eventually they developed the technology to rise above the Earth’s surface with kites and balloons, then airplanes. Finally, rockets and spacecraft enabled them to live in orbiting space stations and to travel to the Moon and other planets, both in crewed vehicles and with mechanical stand-ins (see astronaut). They do so in response to an irresistible impulse to probe beyond the boundaries of their home world.