[meteorite-list] NASA's Hubble Finds Pluto's Moons Tumbling in Absolute Chaos

[Ron Baalke]

June 03, 2015

RELEASE 15-111

NASA's Hubble Finds Pluto's Moons Tumbling in Absolute Chaos

If you lived on one of Pluto's moons, you might have a hard time 
determining when, or from which direction, the sun will rise each day. 
Comprehensive analysis of data from NASA's Hubble Space Telescope shows 
that two of Pluto's moons, Nix and Hydra, wobble unpredictably.

"Hubble has provided a new view of Pluto and its moons revealing a cosmic 
dance with a chaotic rhythm," said John Grunsfeld, associate administrator 
of NASA's Science Mission Directorate in Washington. "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."

[Graphic]
This set of computer modeling illustrations of Pluto's moon Nix shows how 
the orientation of the moon changes unpredictably as it orbits the "double 
planet" Pluto-Charon.
Credits: NASA/ESA/M. Showalter (SETI)/G. Bacon (STScI)

The moons wobble because they're embedded in a gravitational field that 
shifts constantly. This shift is created by the double planet system of Pluto 
and Charon as they whirl about each other. Pluto and Charon are called a 
double planet because they share a common center of gravity located in the 
space between the bodies. Their variable gravitational field sends the 
smaller moons tumbling erratically. The effect is strengthened by the 
football-like, rather than spherical, shape of the moons. Scientists believe 
it's likely Pluto's other two moons, Kerberos and Styx, are in a similar 
situation.

The astonishing results, found by Mark Showalter of the SETI Institute in 
Mountain View, California and Doug Hamilton of the University of Maryland at 
College Park, will appear in the June 4 issue of the journal Nature.

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

Showalter also found three of Pluto's moons are presently locked together 
in resonance, meaning there is a precise ratio for their orbital periods.

"If you were sitting on Nix, you would see that Styx orbits Pluto twice for 
every three orbits made by Hydra," noted Hamilton.

Hubble data also reveal the moon Kerberos is as dark as a charcoal briquette, 
while the other frozen moons are as bright as sand. It was predicted that 
dust blasted off the moons by meteorite impacts should coat all the moons, 
giving their surfaces a homogenous look, which makes Kerberos' coloring 
very surprising.

NASA's New Horizons spacecraft, which will fly by the Pluto system in July, 
may help settle the question of the asphalt-black moon, as well as the other 
oddities uncovered by Hubble. These new discoveries are being used to plan 
science observations for the New Horizons flyby.

The turmoil within the Pluto-Charon system offers insights into how planetary 
bodies orbiting a double star might behave. For example, NASA's Kepler 
space observatory has found several planetary systems orbiting double stars.

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

Clues to the Pluto commotion first came when astronomers measured variations 
in the light reflected off Nix and Hydra. Analyzing Hubble images of Pluto 
taken from 2005 to 2012, scientists compared the unpredictable changes in the 
moons' brightness to models of spinning bodies in complex gravitational 
fields.

[Graphic]
This illustration shows the scale and comparative brightness of Pluto's 
small satellites. The surface craters are for illustration only and do not 
represent real imaging data.
Credits: NASA/ESA/A. Feild (STScI)

Pluto's moons are believed to have been formed by a collision between the 
dwarf planet and a similar-sized body early in the history of our solar 
system. The smashup flung material that consolidated into the family of moons 
observed around Pluto today. Its binary companion, Charon, is almost half the 
size of Pluto and was discovered in 1978. Hubble discovered Nix and Hydra in 
2005, Kerberos in 2011, and Styx in 2012. These little moons, measuring just 
tens of miles in diameter, were found during a Hubble search for objects that 
could be hazards to the New Horizons spacecraft as it passes the dwarf planet 
in July.

Researchers say a combination of Hubble data monitoring and New Horizon's 
brief close-up look, as well as future observations with NASA's James Webb 
Space Telescope will help settle many mysteries of the Pluto system. No 
ground-based telescopes have yet been able to detect the smallest moons.

"Pluto will continue to surprise us when New Horizons flies past it in 
July," Showalter said. "Our work with the Hubble telescope just gives us 
a foretaste of what's in store."

The Hubble Space Telescope is a project of international cooperation between 
NASA and the European Space Agency. NASA's Goddard Space Flight Center in 
Greenbelt, Maryland, manages the telescope. The Space Telescope Science 
Institute (STScI) in Baltimore conducts Hubble science operations. STScI is 
operated for NASA by the Association of Universities for Research in 
Astronomy, Inc., in Washington.

For images and more information about Hubble, visit:

http://www.nasa.gov/hubble

and

http://hubblesite.org/news/2015/24

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