We have only just begun to explore the Solar System. One lifetime ago, we had no idea what a planet as far away as Neptune really looked like, let alone the surface of Mars. Our neighborhood is full of planets, moons, asteroids, and comets that we have barely laid eyes on. Where have we already traveled? Where will we go in the near future?
Explore this list of space exploration milestones for every planet (and then some), from first visits to first landings, and find out what we'll do next.
Photomosaic of Mercury - Inbound View (2001-01-17) by NASA/JPLNASA
In 1974, NASA's Mariner 10 became the first spacecraft to ever fly by Mercury. It took these photos on its way.
MESSENGER at Mercury Artist Concept (2011-03-02) by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of WashingtonNASA
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.
This is one of the photos MESSENGER took. It shows the "terminator", the border between day and night on the planet.
The next spacecraft to visit Mercury, a joint ESA/JAXA mission called BepiColombo, will arrive in orbit in 2025.
Global view of Venus from Magellan, Pioneer, and Venera data (1991-10-29)NASA
At its closest, Venus is nearer to Earth than any other planet. But compared to Mars, we have only just begun to explore it.
Mariner 2 Artist Concept (2003-06-27) by NASA/JPLNASA
The first spacecraft to flyby Venus — or any other planet — launched in 1962.
Venus - 3-D Perspective View of Maat Mons (1996-03-14) by NASA/JPLNASA
After Mariner 2, the Soviet Union sent several spacecraft to Venus. The first one to try to land, Venera 3, crashed in 1966. But in 1967, Venera 7 became the first spacecraft to successfully land on another planet, period.
It and the other landers that followed are the source of all our direct measurements of Venus' surface. They enabled the computer simulation you see here.
Other spacecraft have flown by since then, like Pioneer, which took this photo. NASA's DAVINICI+ and VERITAS missions will send an orbiter, plus a probe that will descend through Venus' atmosphere, in 2029.
NASA's Hubble Sees Martian Moon Orbiting the Red Planet (2017-07-20) by NASA/ESA/STScINASA
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.
LIFE Photo Collection
Pathfinder Makes History
In 1997, Pathfinder became the first rover to navigate Martian terrain. It was far from the last.
Landing Area Narrowed for 2016 InSight Mission to Mars (2013-09-04) by NASA/JPL-CaltechNASA
Map of Mars
This map shows the locations of a number of landers and rovers that have since touched down on Mars.
Martian Moon Deimos in High Resolution (2009-03-09) by NASA/JPL-Caltech/University of ArizonaNASA
Deimos From Two Perspectives
Mars also has two moons, Phobos and Deimos, which we have barely explored. Neither moon has been directly visited.
Phobos from 6,800 Kilometers Color (2008-04-09) by NASA/JPL-Caltech/University of ArizonaNASA
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.
Jovian Stormy Weather (2017-02-17) by NASA/JPL-Caltech/SwRI/MSSS/John LandinoNASA
Our first visit to Jupiter came in 1973, when Pioneer 10 flew by. We've revisited the giant planet several times since then.
Galileo Spacecraft (1987)LIFE Photo Collection
The Galileo spacecraft made history as the first orbiter and first atmospheric probe of Jupiter in 1989.
The Moons Have It
Though other spacecraft have studied Jupiter since Galileo, the planet's moons have also grown into a major focus of past and future exploration. The moons Europa, Callisto, and Io are caught in serendipitous alignment here.
The Galilean Satellites (1998-05-08) by NASA/JPL/DLRNASA
The Galilean Satellites
Jupiter has dozens of moons, but the four largest are the most complex.
Io Pele Hemisphere After Pillan Changes (1999-01-18) by NASA/JPL/University of ArizonaNASA
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.
Global Callisto in Color (2001-08-22) by NASA/JPL/DLRNASA
Callisto was first visited by the Galileo spacecraft in 1996. There are no plans to send another spacecraft to it in the near future.
There are grander plans to explore Ganymede than any other moon of Jupiter. In 2032, the JUICE mission will arrive in orbit around Ganymede, becoming the first orbiter around a moon of another planet. Two years later, it will purposely crash down on Ganymede to collect data.
Europa, Jupiter's Icy Moon (2014-11-21) by NASA/JPL-Caltech/SETI InstituteNASA
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.
A Farewell to Saturn (2017-11-21) by NASA/JPL-Caltech/Space Science InstituteNASA
The history of Saturn's exploration is similar to that of Jupiter — with one explosive difference.
Basking in Light (2016-12-26) by NASA/JPL-Caltech/Space Science InstituteNASA
The North Pole
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".
Three Times the Fun (2016-02-22) by NASA/JPL-Caltech/Space Science InstituteNASA
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.
Titan may host environments suitable to life, so it is by far the most explored of Saturn's moons. The Hyugens lander touched down on its surface in 1997, and in 2029, the Dragonfly rotorcraft will launch. It will perform the first aerodynamic flight on another moon.
Webb Explained Slide 14NASA
The Ice Giants
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.
Imagine a Landing on Pluto (2016-07-14) by NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research InstituteNASA
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.
Comet Halley (1986-03-14) by NASA/ESA/Giotto ProjectNASA
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.
Wild 2 Close Look (2004-06-17) by NASA/JPL-CaltechNASA
This image was taken by the Stardust spacecraft, which, in 1999, became the first to land on a comet and bring back samples.
Welcome to a Comet, from Lander on Surface (2014-11-13) by Copyright: Copyright: ESA/Rosetta/Philae/CIVANASA
On a Comet
In 2004, the Philae spacecraft landed on the comet 67P/Churyumov-Gerasimenko. This is a view from the surface.
Rosetta Comet Marches On (2015-06-19) by ESA/Rosetta/NAVCAMNASA
Goodbye, For Now
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.
Looking Up at Mars Rover Curiosity in Buckskin Selfie (2015-08-19) by NASA/JPL-Caltech/MSSSNASA
To Be Continued...
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.