Humanity has delved into outer space for over six decades, capturing detailed images of numerous celestial entities. Notably, our spacecraft have successfully reached and photographed each planet within our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. In addition, we’ve explored two dwarf planets, Pluto and Ceres, traversed a sprawling asteroid belt, examined various moons, and navigated through the expansive and dusty interplanetary medium.
The first spacecraft to leave our solar system, the Soviet Union’s Sputnik 1 in 1957, gave astronomers their first look at the outer planets and the vast expanse of space beyond them. The momentous achievement inspired the United States to invest in space exploration, launching its first uncrewed satellite, Explorer 1, the following year.
Since then, we’ve launched a dazzling array of spacecraft to orbit, fly by, slingshot around, or land on all the planets and many of their moons. Several have even left our solar system and entered interstellar space.
Most of the planet flybys came from NASA’s Voyager 1 and Voyager 2 — two twin spacecraft designed to perform a “Grand Tour of the Outer Solar System.” They took advantage of a rare planetary alignment in 1977 and 1978 to drastically cut their travel time.
Both spacecraft transmitted data as of 2017, more than four decades after they left Earth. Their instruments were so sensitive that they now pick up the faint signals of other cosmic dust particles as they venture into interstellar space. Our solar system once existed in this region.
The Voyager probes have revealed that a bubble of gas and dust called the heliosphere, surrounds our solar system, made by the solar wind that blasts outward from our Sun. This bubble protects our planet and the inner planets from cosmic radiation and may provide clues about life in other worlds.
We’ve also seen our Sun in all its glory. The most recent mission, the Parker Solar Probe, is the most advanced spacecraft ever to fly by our star, gathering valuable information about its composition and behavior that will help us better understand how we are protected from the harmful effects of our Sun’s radiation.
Two other missions — the Magellan and Dawn spacecraft — orbited Venus for several years. Magellan discovered the planet was a barren hellhole with ferocious winds and a scalding surface. The Magellan probe lost contact with Venus in 1994, crushed by its atmospheric pressure, which is 92 times that of Earth. The Dawn mission spied a muddy crust on Pluto, and it’s possible that the dwarf planet had a liquid ocean once upon a time. In 2015, New Horizons traveled the 5.05 billion kilometers / 3.1 billion miles that separate Earth from Pluto, discovering that it may have a subsurface ocean of its own.