Cracks in Pluto's moon could indicate it once had an underground ocean

Jun 13, 2014
Cracks in Pluto's moon could indicate it once had an underground ocean
This is a mosaic of images showing cracks in Saturn's moon Enceladus taken by the Cassini spacecraft during its close flyby on March 9 and July 14, 2005. Credit: NASA/JPL/Space Science Institute

If the icy surface of Pluto's giant moon Charon is cracked, analysis of the fractures could reveal if its interior was warm, perhaps warm enough to have maintained a subterranean ocean of liquid water, according to a new NASA-funded study.

Pluto is an extremely distant world, orbiting the sun more than 29 times farther than Earth. With a surface temperature estimated to be about 380 degrees below zero Fahrenheit (around minus 229 degrees Celsius), the environment at Pluto is far too cold to allow liquid water on its surface. Pluto's moons are in the same frigid environment.

Pluto's remoteness and small size make it difficult to observe, but in July of 2015, NASA's New Horizons spacecraft will be the first to visit Pluto and Charon, and will provide the most detailed observations to date.

"Our model predicts different fracture patterns on the surface of Charon depending on the thickness of its surface ice, the structure of the moon's interior and how easily it deforms, and how its orbit evolved," said Alyssa Rhoden of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "By comparing the actual New Horizons observations of Charon to the various predictions, we can see what fits best and discover if Charon could have had a subsurface ocean in its past, driven by high eccentricity." Rhoden is lead author of a paper on this research now available online in the journal Icarus.

Cracks in Pluto's moon could indicate it once had an underground ocean
This artist concept shows Pluto and some of its moons, as viewed from the surface of one of the moons. Pluto is the large disk at center. Charon is the smaller disk to the right. Credit: NASA, ESA and G. Bacon (STScI)

Some moons around the gas giant planets in the outer solar system have cracked surfaces with evidence for ocean interiors – Jupiter's moon Europa and Saturn's moon Enceladus are two examples.

As Europa and Enceladus move in their orbits, a gravitational tug-of-war between their respective parent planets and neighboring moons keeps their orbits from becoming circular. Instead, these moons have eccentric (slightly oval-shaped) orbits, which raise daily tides that flex the interior and stress the surface. It is thought that tidal heating has extended the lifetimes of subsurface oceans on Europa and Enceladus by keeping their interiors warm.

In Charon's case, this study finds that a past high eccentricity could have generated large tides, causing friction and surface fractures. The moon is unusually massive compared to its planet, about one-eighth of Pluto's mass, a solar system record. It is thought to have formed much closer to Pluto, after a giant impact ejected material off the planet's surface. The material went into orbit around Pluto and coalesced under its own gravity to form Charon and several smaller moons.

Initially, there would have been strong tides on both worlds as gravity between Pluto and Charon caused their surfaces to bulge toward each other, generating friction in their interiors. This friction would have also caused the tides to slightly lag behind their orbital positions. The lag would act like a brake on Pluto, causing its rotation to slow while transferring that rotational energy to Charon, making it speed up and move farther away from Pluto.

"Depending on exactly how Charon's orbit evolved, particularly if it went through a high-eccentricity phase, there may have been enough heat from tidal deformation to maintain liquid water beneath the surface of Charon for some time," said Rhoden. "Using plausible interior structure models that include an ocean, we found it wouldn't have taken much eccentricity (less than 0.01) to generate surface fractures like we are seeing on Europa."

"Since it's so easy to get fractures, if we get to Charon and there are none, it puts a very strong constraint on how high the eccentricity could have been and how warm the interior ever could have been," adds Rhoden. "This research gives us a head start on the New Horizons arrival – what should we look for and what can we learn from it. We're going to Pluto and Pluto is fascinating, but Charon is also going to be fascinating."

Based on observations from telescopes, Charon's orbit is now in a stable end state: a circular orbit with the rotation of both Pluto and Charon slowed to the point where they always show the same side to each other. Its current orbit is not expected to generate significant tides, so any ancient underground ocean may be frozen by now, according to Rhoden.

Since is a necessary ingredient for known forms of life, the oceans of Europa and Enceladus are considered to be places where extraterrestrial life might be found. However, life also requires a useable energy source and an ample supply of many key elements, such as carbon, nitrogen, and phosphorus. It is unknown if those oceans harbor these additional ingredients, or if they have existed long enough for life to form. The same questions would apply to any ancient ocean that may have existed beneath the icy crust of Charon.

Explore further: Research pair offer three possible models of Pluto ahead of New Horizons visit

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Jonseer
1 / 5 (7) Jun 13, 2014
Fun speculation passed off as a scientific return on the investment the nation made in a flyby of Pluto and nothing more.

The researchers who lobbied for this waste of space exploration $s I hope are no longer in a position to influence future missions.

To go all that way to simply fly by is insane, especially now that it has been revealed that their claim it would all be worthwhile, because once past Pluto there'd be another object lying in the trajectory of the probe to visit was a BIG LIE.

It looks like the flyby will be it as there are NO objects along the probes path once is passes Pluto.

Almost 1000 million $ will have been spent on a fly by, money that would have been better spent going to Europa, or probably Ceres should New Dawn discover that yes indeed it has easily accessed large stores of water.
alfie_null
5 / 5 (5) Jun 14, 2014
Almost 1000 million $ will have been spent on a fly by

That's an exaggeration. More like $650 million.

I don't know what your beef is with the researchers. After all, they weren't the ones who approved the mission.
Jantoo
5 / 5 (1) Jun 14, 2014
This article is indeed a space exploration promo, but it points to possibility of life formation in binary systems of small asteroids completely outside of any solar system (compare the panspermia hypothesis and F. Hoyle ideas in this regard). So I wouldn't throw out the child together with bath water here.
Torbjorn_Larsson_OM
5 / 5 (7) Jun 14, 2014
"Fun speculation passed off as a scientific return on the investment the nation made in a flyby of Pluto and nothing more."

Since that shows how the comment is a completely ignorant trolling of the subject, I would suggest stop reading right there. (I did.)

- Everyone interested in the science should know, from earlier articles, that the planetary physicists are preparing what to study in the system as New Frontiers approach. It has to know what to study at approach given the most recent, including its own continually ever closer up data, and what to follow up as it gets away.

- Everyone interested in the science should know that there has been a multiyear, still ongoing, survey of possible other Kuiper Belt Objects that is possible with the remaining fuel that was always designed for suh a followup mission.

I'm interested in astrobiology, and this is an important mission. Pluto should have the same ice covered ocean that Europa (or likely Ceres) have, amping up habitability.
Jantoo
1 / 5 (5) Jun 14, 2014
that the planetary physicists are preparing what to study in the system as New Frontiers approach
Wait, wait... Nobody here doubts the importance of this research for planetary physicists. But how it will help the people, who are actually paying it? Are we doing the science as a occupational program for scientists, or as a stuff useful for the human civilization? The ignorance of this difference will not pay off - the scientists will otherwise prefer the research of their abstract stuffs into account of practically important findings (many of them are already lurking behind the corner for many years: the cold fusion, antigravity drives and beams, scalar wave applications, magnetic motors, etc.) How is it possible, that for example NASA develops antigravity drive, while no peer-reviewed study deals with it? Well, this is just the result of the above ignorance.
Torbjorn_Larsson_OM
5 / 5 (8) Jun 14, 2014
[ctd] If Charon also once had an ocean, and we can detect both oceans by ice tectonics, it is even better. Goes towards range of habitability.
Torbjorn_Larsson_OM
5 / 5 (8) Jun 14, 2014
@Jantoo: Read the NASA papers on their site that has studied the ROI of science. It is among the best ROI activities we can do.

And it is all interconnected, doing I's is mutually increasing R. Conversely, you can't feasibly predict what specific I's will give R's.

Your aspirations on science doesn't go very far, since you are describing atypical science. [/shrugs]
Jantoo
1 / 5 (5) Jun 14, 2014
The opinion that investments into science always pay off is very naive one: in some areas (genomic research of viruses, the GMO spreading, the artificial intelligence domination) it may harm the civilization instead, if they will be developed earlier, than we can safely handle the risks of this research. But even if we would completely ignore the risk of these investments, there still remains the risk in development of ignorance of scientists for findings of practical importance, once these findings would accidentally violate their established pet theories.

If you didn't realize, I'm not talking here about ROI of research, which SHOULD NOT be done - but on the contrary: about ROI of research, which SHOULD be done and the scientists just prohibit it. I'm not limiting the science in its work, on the contrary: I'd like to eliminate the selfish constrains, which the contemporary science applies to its research by itself.
Jantoo
1 / 5 (4) Jun 14, 2014
since you are describing atypical science
Well, this is just the sad aspect of every breakthrough research, it's atypical. It's not the research, which is loudly anticipated in media for many years in advance (Higgs boson), because in this case we are actually confirming the already confirmed theories (Standard Model). As Feynman once said, the actual research is, if you don't know what you're actually doing, everything else is just a stamp collection. The true breakthrough it this one, which no one expects and it's ignored or even better: this one, which makes everyone upset and its covered before public, because it could be useful for it more, than the existing findings.
ViperSRT3g
5 / 5 (3) Jun 14, 2014
I don't see how your argument pertain to the New Horizons mission.
Captain Stumpy
5 / 5 (7) Jun 14, 2014
(genomic research of viruses, the GMO spreading, the artificial intelligence domination) it may harm the civilization instead
@jantoo-ZEPHIR
this is almost as absurd as your AW/DAW religion and your clinging to ANY fringe crackpot debunked philosophy in science...
the SAME argument was made against Nuclear
and AIRPLANES
and COMPUTERS
and the INTERNET
and CARS
and ENGINES (including TRAINS)
and likely Cities, domesticated animals, keeping dogs around the camp, or the flint hand axe or club.
whenever there is new technology that has applications-good or bad, there are crackpots like you condemning them. It is NOT the SCIENCE that is dangerous, or harmful, it is THE APPLICATION of the science, to which it is the INDIVIDUAL/GROUP APPLYING SAID SCIENCE, so your objections are based upon your fear of change and the future and your moral beliefs.