Pluto’s unexpected surface and moons

Combined 3-D topography mapThe New Horizons mission team reported several unusual findings concerning Pluto this week at the 47th Annual Meeting of the Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS).  Among the biggest was the discovery of two large and distinct mountains that New Horizons geologists think could be recently active “cryovolcanoes”.  So-called cryovolcanoes are thought to spew a semi-frozen slurry of water ice, nitrogen or other gases instead of fire, smoke and lava like traditional volcanoes.  The two geological features were discovered by combining images of Pluto’s surface to make 3-D topographical maps (see left).

Crater counts supposedly revealed other geological oddities on Pluto, namely a wide range of surface ages that indicate Pluto has been geologically active for much of its 4 billion year existence.  It is unknown if the mission team has any speculation as to how a minor planet smaller than our moon,  located over 1.6 billion km (1 billion miles) from its nearest neighbor and over 40 times the distance from the Sun as the Earth could experience any type of geological activity for such a long period of time.  Other interesting information revealed by the New Horizons mission team concerns the highly eccentric properties of Pluto’s moons.

Most of the moons in our solar system are in synchronous rotation around their respective planets with one side always facing the planet.  Four of Pluto’s five moons rotate at much faster speeds, with the largest Charon being the exception.  And all the moons wobble much more than scientists expected and are described as “behaving like spinning tops”.  Of course their first suspect is Charon and its gravitational influence upon the other moons.  They also proposed that the double-lobed shape of several of Pluto’s smaller moons could be the result of the merger of even smaller moons caused by a large impact in the past that formed Charon.  These double-lobed shapes are very similar to the shapes of 67P/Churyumov–Gerasimenko and other observed cometary bodies in our solar system.  Can all of these objects really be the result of slow-moving collisions between two separate objects as has been proposed for Comet 67P despite the difficulty of replicating such collisions and mergers in computer simulations?  Perhaps some sort of electrically-driven erosion is a better explanation?

Back in July, after its historic fly-by of Pluto, New Horizons detected a huge tail of ionized plasma trailing far behind the planet like a comet.  And just days before the fly-by the spacecraft encountered communications problems that corresponded with a spike in solar activity that included a CME and increased “solar wind” output.  Yet despite these observations, electrodynamic effects are in no way being considered in explaining the recent findings made by New Horizons even though electromagnetic forces could account for many, if not all of them.  With gravity the only force being considered, the New Horizons team members and other scientists are unsurprisingly very perplexed and scrambling for explanations.  To quote Jim Green, director of planetary science at NASA Headquarters in Washington, DC: “The New Horizons mission has taken what we thought we knew about Pluto and turned it upside down.”

Full press release:

Image credit:
NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Pluto's unexpected surface and moonsShannon Sims

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