IT’S the end of the line. As New Scientist went to press, mission controllers were awaiting a signal from NASA’s New Horizons probe confirming it has survived its rapid journey past Pluto. If all went well, images and data from the last stop on our grand tour of the solar system will trickle in over the next year (see “View from the solar system’s edge“). “It doesn’t feel real yet,” says Casey Dreier of the Planetary Society, a space exploration advocacy group in Pasadena, California. “Emotionally, most of us grew up with the nine planets, and this caps that off.” But the mission also offers an opportunity to look back at how far we have come. We have been exploring worlds beyond our own since 1959, when both the US and Soviet Union sent probes to the moon, and we have sent robotic adventurers to every planet in the solar system, plus moons, comets and asteroids. These missions have inspired millions to wonder about our place in the cosmos and have indirectly taught us more about the planet we call home. The fly-by of New Horizons is the last of the firsts – we will never set eyes on an uncharted world in our solar system again. So what’s next? “We are running out of unknown territory, but we can now go back to places we have visited briefly and explore them more fully,” says Curt Niebur, who oversees NASA’s robotic missions. That means drawing inwards. There are currently no missions beyond Jupiter on the books of any space agency, and given the lead time in planning and travel, it could be more than 20 years before we see another long-range flight like that of New Horizons. But the moon, Mars and Jupiter, where most future missions will be heading, still hold many secrets. They are also easier to reach, reducing mission risks and cost. And efforts such as NASA’s planned 2020s jaunt to Europa offer our best, if slim, chance of finding life on other worlds...