Pluto has presented a long list of mysteries since it was first discovered by astronomer Clyde Tombaugh in 1930. The first visit by a robotic observatory to the distant body, meant to answer some of these mysteries, revealed more bizarre facts about the world, begging for explanation.
Charon, the largest moon of Pluto, is the largest satellite, relative to the size of its partner, anywhere in the solar system. This mega-moon is half the size of its larger companion. A new study shows the moon was geologically active until around two billion years ago. At that point, Charon "ran out of juice" to reshape craters and impact basins.
Pluto, on the other hand, exhibits radically different terrain over its surface. Some of the features are ancient, while other locations on the surface are newly-formed.
The atmosphere of Pluto has remained an enigma when examined by astronomers utilizing Earth-based telescopes. Observations from the New Horizon spacecraft show gases, mostly nitrogen, are escaping from the gravitational pull of the dwarf planet at a rate slower than that predicted by astronomers. The air on Pluto is losing heat through some unknown mechanism, reducing the rate of loss to the abyss of space.
"We were very surprised to observe that Pluto's atmosphere has a multi-layered bluish haze that extends from the surface to altitudes above 200 km ... We've also measured the surface pressure for the first time — about 11 microbars — and we've discovered that the temperature structure of the lower atmosphere varies with location," said David Hinson of the SETI Institute.
On Earth, methane, nitrogen and carbon monoxide exist in the form of gases. However, on Pluto, temperatures drop enough that these molecules freeze into solids. Researchers are just now starting to understand how the combination of these ices together can produce bizarre geology.
Astronomers usually assumed the four smaller moons of Pluto — Hydra, Kerberos, Nix and Styx, formed at the same time as Charon, and would be geologically similar to the larger satellite. However, New Horizons reveals the truth is not that simple.
A student-built experiment captured few particles left over from collisions between Pluto and its partners with space debris. Solar wind from the distant sun was also found to have little effect on the system.
The more we learn about Pluto and its family of moons, the stranger they seem.
