It has been 14 months since the New Horizons spacecraft flew past Pluto and its moons, but data still continues to come in, and new discoveries are still being made. The dwarf planet has surprised scientists by its geological activity, for the most part unexpected for such a small, cold body. Now two new results are adding to the mystery of Pluto: the detection of x-rays emanating from the surface and new evidence that Pluto “spray-paints” the north pole of its largest moon Charon a rusty red colour.
Pluto is a tiny world in the outer fringes of the Solar System; for many decades it was only a mere speck of light in even the best telescopes, with only vague hints of surface features. Then, in July 2015, the New Horizons spacecraft flew past Pluto, the first time ever that humanity would get to see this mysterious place up close – and it did not disappoint. An enormous amount of data has continued to be sent back by New Horizons since the flyby, and now five new papers have been published which provide an in-depth overview of the findings so far about Pluto and its moons. Pluto is an active world, with its own unique geology different from anywhere else in the Solar System.
It has been a year now since the Dawn spacecraft first reached the dwarf planet Ceres in the main asteroid belt between Mars and Jupiter, and during that time has shown Ceres to be a unique and complex little world. At first glance, Ceres just seems to be a heavily battered place, covered in craters like the Moon or Mercury, but a closer look reveals something more interesting: a small rocky world with large fractures, unusual “bright spots” randomly dispersed across the surface and an odd conical “mountain” which sits in isolation with nothing else like it around. Dawn has already acquired an enormous amount of data about Ceres, but now, in its lowest possible orbit, will continue to do for some time to come.
As the data from New Horizons continues to come in, we are learning more about what an incredible little world Pluto really is, with tall mountains of rock-hard water ice, as well as glaciers and vast icy plains composed of nitrogen ice. In some ways, these features are visually reminiscent of similar ones on Earth, and now this week another cool discovery was revealed: methane snow on some of Pluto’s mountain peaks.
One of the most surprising discoveries in recent years in the outer Solar System is that there are small moons which have oceans inside them. Jupiter’s moon Europa and Saturn’s moon Enceladus are now known to have global oceans of water beneath their icy crusts, and others are thought to as well, including Ganymede, Titan, and possibly others. These moons have a lot of ice and rock as well, and gravitational tugging and heating from the large gas giant planets helps maintain a deep layer of liquid water inside them, where otherwise they would most likely be frozen solid in the deep cold so far from the Sun. Now it seems that another moon also once had an ocean, although in this case it is thought to now be solid ice: Pluto’s largest moon, Charon.
New Horizons has shown Pluto to be a diverse world, more so than many scientists had anticipated, with tall mountain ranges, vast glaciers, a blue-colored layered atmosphere, and possible ice volcanoes. One thing, however, which seemed to be relatively lacking, was exposed water ice. Not much had been seen on the surface, not even in the glacial regions, which are composed of other ices instead. But now, new data indicates there actually is more water ice than had originally been thought.
Another beautiful view of Pluto, taken by New Horizons as it passed by the dwarf planet on July 14, 2015. Pluto is backlit by the Sun, showing the hazy blue colour of its thin atmosphere, a view never possible from Earth. Image processing by Roman Tkachenko. It is also now the current header image for the blog. Larger version available here.