Charon is Pluto’s largest moon and, despite being so cold and remote from the Sun, has been revealed to be a fascinating and active world, just like Pluto itself. Residing in the far outskirts of the Solar System, it had been expected that Charon – and Pluto for that matter – would be little more than frozen, dead worlds. But just like the rest of the Solar System, there were surprises waiting to be found. Thanks to the New Horizons spacecraft, we got our first close-up views of the Pluto system in July 2015. It soon became evident that not only were Pluto and Charon geologically active in the ancient past, but they perhaps still are in some ways even now. One of the most surprising findings was both Pluto and Charon likely had subsurface water oceans; while it is thought that Pluto’s is probably still liquid, Charon’s is likely completely frozen, and now additional evidence for its existence has been published by researchers.
To say that the New Horizons mission has been a success would be a massive understatement; this first-ever spacecraft to visit Pluto has revolutionized our understanding of this distant, small world. Pluto and its moons are complex and active places, more so than thought possible by most scientists. Even though New Horizons flew past Pluto instead of orbiting it in July 2015, it still collected an enormous amount of information, which has taken more than a year to be sent back to Earth. That process is now complete, NASA just announced.
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.
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.
After a lull of several weeks, the downlinking of new data from the New Horizons spacecraft has begun, including stunning new images of Pluto and its largest moon, Charon, as well as a treasure trove of other scientific data. There is so much to come that it will take about one year to downlink everything from the spacecraft and send back to Earth. Those first amazing images of Pluto and its moons were only the beginning.