After 9 years and over 3 billion miles, the New Horizons spacecraft has arrived near Pluto to fulfill its purpose of studying the dwarf planet and it's largest moon, Charon. The unmanned spacecraft - which is often described as looking like a large, gold piano - was at its closest on Tuesday, reaching a distance roughly equivalent to that between New York and Mumbai. The images seen all over the internet now were taken on Monday, and more are expected to arrive today.
The US is now the first nation to send a space probe to every known planet, and New Horizons arrived at a significant time as well: exactly 50 years after the Mariner 4 probe did a flyby of Mars.
While it will take New Horizons 16 months to beam back all of the data it is collecting, scientists have already managed to glean some important information from the received images. Firstly, this has shown us that Pluto is larger than anticipated - we now know the exact size is 1,473 miles in diameter - while the atmosphere is shallower. There are huge contrasts which appear on the surface of Pluto, with a very bright "heart" and other dark areas, reflecting very little light. This is quite rare and suggests a complex system which may have great educational value. Furthermore, apparent frost seems to change over time, suggesting seasons, and scientists claim that it snows on the surface of Pluto.
In the past, scientists considered Pluto to be very similar to Triton - Neptune's largest moon - as both have an icy surface and nitrogen-based atmospheres. However, after this flyby, scientist Bill McKinnon says that, "We thought Pluto would be a kinder, gentler version of Triton...Pluto is more like Triton on steroids".
New Horizons will now continue to analyze the atmosphere and take measurements for mapping the planet and surrounding moons, before flying further into the Kuiper Belt, an area scientists believe is filled with icy objects. NASA will then decide whether or not to extend this mission.
Follow the mission here: http://pluto.jhuapl.edu/