Destination: Solar System

In 1974, NASA's Mariner 10 became the first spacecraft to ever fly by Mercury. It took these photos on its way.

Then, in 2011, MESSENGER became the first spacecraft to orbit Mercury. This allowed it to take more detailed measurements than if it had just flown by.

At its closest, Venus is nearer to Earth than any other planet. But compared to Mars, we have only just begun to explore it.

The first spacecraft to flyby Venus — or any other planet — launched in 1962.

We have explored Mars more than any other planet in the Solar System by far. Humanity's first brush came when NASA's Mariner 4 flew by in 1964. The Soviet Union made the first intact landing in 1971. That same year NASA put the first spacecraft in orbit around Mars.

In 1997, Pathfinder became the first rover to navigate Martian terrain. It was far from the last. 

This map shows the locations of a number of landers and rovers that have since touched down on Mars. 

Mars also has two moons, Phobos and Deimos, which we have barely explored. Neither moon has been directly visited. 

That won't be the case for long, though. In 2028, the MMX mission will land on Phobos, collect rock samples, and return them to Earth.

Our first visit to Jupiter came in 1973, when Pioneer 10 flew by. We've revisited the giant planet several times since then.

The Galileo spacecraft made history as the first orbiter and first atmospheric probe of Jupiter in 1989.

Jupiter has dozens of moons, but the four largest are the most complex.

Like Jupiter, Io was first visited by a Pioneer 10 flyby in 1973. There are 
currently no plans to go back with an orbiter or lander.

Callisto was first visited by the Galileo spacecraft in 1996. There are no plans to send another spacecraft to it in the near future. 

Europa wasn't explored at all until 1996, when the Galileo spacecraft flew past. In the 2030s, the JUICE and Europa Clipper missions will both visit and study it in more detail.

The history of Saturn's exploration is similar to that of Jupiter — with one explosive difference.

This photo was taken by the Cassini spacecraft, which became the first to orbit Saturn in 1997. Twenty years later, at the end of its functional life, NASA purposely sent it crashing into Saturn's atmosphere in a dramatic "Grand Finale".

Like Jupiter, Saturn also has dozens of moons. Three of the largest — Tethys, Enceladus, and Mimas — are pictured here. All have been passed near by a few different spacecraft.

Uranus and Neptune are the least explored planets. Only one spacecraft, Voyager 2, has flown by the planets and a few of their moons. That was almost 40 years ago. 

Although "demoted" to a dwarf planet, Pluto is still worth exploring. In 2015, the New Horizons spacecraft became the first to fly by. It also visited Pluto's moon, Charon.

The Solar System is more than just planets. We have also visited comets, too. The first fly-by of a comet was by the spacecraft ISEE-3 in 1978.

This image was taken by the Stardust spacecraft, which, in 1999, became the first to land on a comet and bring back samples.

In 2004, the Philae spacecraft landed on the comet 67P/Churyumov-Gerasimenko. This is a view from the surface.

The same asteroid as previously pictured, but viewed during departure.

The next breakthrough mission to a comet will be Comet Interceptor, which will launch in 2029 to an as-yet unknown but exotic faraway comet — perhaps even one from another stellar system.

We have only taken the first few steps out our front door. But there will always be more missions, and there will always be more places to explore.