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Hubble Reveals 'Cosmic Dance' of Pluto's Wobbly Moons

Jun 04, 2015 11:04 AM EDT
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New horizons flyover of Pluto
Pluto
Pictured: Artist’s illustration of the chaotic spin of Pluto's moon Nix.
(Photo : NASA, ESA, M. Showalter (SETI Inst.), D. Hamilton (Univ. of Maryland, College Park), and G. Bacon (STScI))

Two of Pluto's moons, Nix and Hydra, are wobbling unpredictably in some kind of "cosmic dance," according to new data discovered by NASA's Hubble Space Telescope, adding more mystery to this former planet.

According to scientists, if you lived on Nix or Hydra, you'd have a hard time setting your alarm clock. That's because you could not know for sure when, or even in which direction, the Sun would rise. And based on Hubble's new comprehensive analysis, they believe the other two small moons, Kerberos and Styx, are likely in a similar situation, pending further study.

"Hubble has provided a new view of Pluto and its moons revealing a cosmic dance with a chaotic rhythm," John Grunsfeld, associate administrator of NASA's Science Mission Directorate in Washington, DC, said in a statement. "When the New Horizons spacecraft flies through the Pluto system in July we'll get a chance to see what these moons look like up close and personal."

So what makes Pluto's moon so topsy-turvy? It is reportedly because the moons are situated inside a shifting gravitational field, which is created as the system's two central bodies, Pluto and Charon, rotate around each other. This phenomenon induces torques that send the smaller moons tumbling erratically. And since the moons are football-shaped rather than spherical, this torque is strengthened.

"Prior to the Hubble observations nobody appreciated the intricate dynamics of the Pluto system," noted Mark Showalter, who conducted the Hubble research. "Our report provides important new constraints on the sequence of events that led to the formation of the system."

Pluto and Charon.
(Photo : Flickr/Lunar and Planetary Institute) Pluto and Charon.

Clues to this chaos first crossed astronomers' radar when they measured variations in the light reflected off of the two moons Nix and Hydra, and noticed that their brightness changed unpredictably.

Not only that, but to their surprise, Hubble also found that of Pluto's four outer moons, three of them - Nix, Styx and Hydra - are locked together in such a way that there is a precise ratio among their orbital periods. Meaning, for example, Styx orbits Pluto twice for every three orbits made by Hydra. This motion is very similar to that of three of Jupiter's large moons.

But these moons aren't the only wobbly ones in this system. There is also evidence that the satellites are orbiting chaotically, leaving scientists wondering if Pluto and its moons may soon completely derail.

"However, that does not necessarily mean that the system is on the brink of flying apart," Showalter added. "We need to know a lot more about the system before we can determine its long-term fate."

And scientists will soon get that chance. NASA's New Horizons probe is scheduled to fly by the Pluto-Charon system in July 2015.

Furthermore, not only do these findings shed light on distant Pluto, but it may offer insights into how planets orbiting a double-star might behave.

"We are learning that chaos may be a common trait of binary systems," Hamilton said. "It might even have consequences for life on planets in such systems."

Hubble has just given us a taste of the secrets that have yet to be discovered on Pluto, and with the New Horizon's flyby and future observations, scientists may finally start to peel back the mysteries.

The results are described in further detail in the journal Nature.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

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