This is it!
Pluto is the last of the classical nine planets to be visited by a spacecraft from Earth. The New Horizons spacecraft will take close-up images and capture other useful data as it speeds by Pluto and its moons on July 14, 2015. This will complete the imaging grand tour of our solar system that began on July 14, 1965 when Mariner 4 took the first close-up image of another planet, Mars. In the past fifty years Mercury, Venus, Mars, Jupiter, and Saturn have all had dedicated orbital missions, and Uranus and Neptune have had flyby missions.
Now it is Pluto’s turn.
New Horizons is traveling over a million kilometers closer to the system every day. There are just 36 million kilometers and 30 days left until closest approach. The mission is releasing raw images daily. New Horizons’s LORRI camera took the image above on June 13, 2015. When comparing this image to previous images, you can already see how Pluto and Charon are getting slightly bigger each day. Charon is on the verge of being wide enough to see surface “features,” or at least tantalizing light and dark patches. Around July 10th, according to the simulation of the image data set put together by Emily Lakdawalla of The Planetary Society, two more moons of Pluto—Hydra and Nix—should start showing up in the images, and Styx and Kerberos, as well as any moons not yet discovered, should show up during closest approach. Before then, I look forward to seeing results from amateurs and professionals already pulling out even more details from the current images through various image processing techniques.
What have we learned in these first 50 years of close-up exploration of our neighborhood? The solar system, including the outer, colder worlds, is a lot more active and dynamic than predicted. Earth is no longer alone when it comes to surface liquids (hydrocarbon seas on Titan and brief trickles of water on the surface of Mars) or oceans (under the shells of several moons around Jupiter and Saturn and perhaps even Pluto.) These other oceans increase the number of potentially habitable worlds in our solar system to several. In addition to the classical nine planets, other spacecraft missions have targeted asteroids, comets, and dwarf planets (of which Pluto is now considered the largest under the modern classification scheme.) Many of these worlds warrant even more detailed investigation, not just from orbit, but also by landers and rovers and other vehicles yet to be developed.
Over the next 50 years, robotic vehicles will dig, drill, climb, sail, and swim these other worlds, giving us our first glimpses of alien caves, oceans, and other underground features, even as the surfaces of these worlds are captured in higher and higher resolution. The robots will also look for signs of life, extinct or extant. Will we join our technology out there, on the first human missions to Mars and other worlds? Will we found our first extraterrestrial colonies?
Now that the initial survey of the solar system is nearly complete, anything seems possible!