New Horizons: Team spot Charon, the tiny moon of Pluto

Artist’s conception of the New Horizons spacecraft flying past Pluto and Charon, one of the dwarf planet’s moons. 

Credit: Johns Hopkins University/APL 

The New Horizons team spotted Charon, the tiny moon of Pluto in July, about six months ahead of when they expected to.

You can check it out in the images below.

The find is exciting in itself, but it also bodes well for the spacecraft's search for orbital debris to prepare for its close encounter with the system in July 2015.

Most of Pluto's moons were discovered while New Horizons was under development, or already on its way.

Mission planners are thus concerned that there could be moons out there that aren't discovered yet, moons that could pose a danger to the spacecraft if it ended up in the wrong spot at the wrong time.

That's why the team is engaging in long-range views to see what else is lurking in Pluto's vicinity.

"We're thrilled to see it, because it shows that our satellite-search techniques work, and that our camera is operating superbly, but it's also exciting just to see a third member of the Pluto system come into view, as proof that we're almost there," stated science team member John Spencer, of the Southwest Research Institute.

Hydra was spotted using the spacecraft's Long Range Reconnaissance Imager (LORRI), which took 48 images of 10 seconds apiece between July 18 and July 20.

Then the team used half the images, the ones that show Hydra better, to create the images you see above.

The spacecraft was still 267 million miles (430 million kilometers) from Pluto when the images were taken.

Another moon discovered around the same time as Hydra, Nix, is still too close to be seen given it's so close to Pluto, but just wait.

Meanwhile, scientists are busily trying to figure out where to send New Horizons after Pluto.

In July, researchers using the Hubble Space Telescope began a full-scale search for a suitable Kuiper Belt Object, which would be one of trillions of icy or rocky objects beyond Neptune's orbit.

Flying past a KBO would provide more clues as to how the Solar System formed, since these objects are considered leftovers of the chunks of matter that came together to form the planets.

Watch the difference: Pluto’s moon Hydra stands out in these images taken by the New Horizons spacecraft on July 18 and 20, 2014. 

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

What is beneath the cracked surface of Pluto's moon Charon?

An artist’s concept of Pluto as viewed from the surface of one its moons. 

Pluto is the large disk at the center of the image. Charon is the smaller disk to the right. 

Credit: NASA, ESA and G. Bacon (STScI)

Is there evidence of an ocean-past or present-waiting to surprise us on Charon?

It isn't impossible. In fact, it might be likely.

What used to be the smallest planet in our solar system has, comparatively, the biggest moon.

Pluto, now classified as a dwarf planet, has a moon, Charon, almost 1/8th its own mass and almost half its physical volume.

Our Moon, by comparison, has about 1% of the Earth's mass and only 2% of its volume.

Charon is so large compared to Pluto that some astronomer's consider the two to be a sort of binary dwarf-planet system, as opposed to a moon-and-planet system.

Both Charon and our Moon are believed to have formed in the same way: when they were knocked off their parent planets.

Enormous collisions liquified parts of the Earth and Pluto. The debris was thrown into orbit where it later cooled.

In the process of cooling into solid bodies around the Earth and Pluto, the Moon and Charon became locked to their parent planets' orbits.

That locking of the planets to moons results in tides: here on Earth, on the Moon, and, we believe, on Pluto and Charon.

An analysis by scientists at Goddard suggests that tides on Pluto and Charon could have been especially high as Charon cooled.

This is because the part of Pluto knocked into orbit didn't get very far. Charon formed incredibly close to Pluto: only 19,000 km (12,000 miles) away.

By comparison, our Moon is currently 384,000 km (238,855 mi) from Earth. Initially, the orbit might not have been very circular, either: it might have been more eccentric or elliptical-shaped.

Eccentrically-moving, close-by Charon would have pulled on Pluto, and Pluto would have pulled back, resulting in heating of both planets and, maybe, an ocean under Charon's ice shell.

Alyssa Rhoden

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 Alyssa Rhoden of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"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."

Artist impression of the New Horizons spacecraft as it approached Jupiter en route to Pluto. 

Credit: NASA

On icy moons like Europa and Enceladus, tidal forces exerted by their parent planets cause massive surface cracks to form.

Those cracks are easily appreciated by passing spacecraft. According to Rhoden and colleagues' model, Charon's surface should be similarly cracked.

We expect to see evidence of this fractured surface geology as the New Horizons spacecraft approaches Pluto. New Horizons will pass directly over Pluto and Charon, briefly, on July 15th 2015.

Charon was discovered thirty-five years ago, in 1978, but well-photographed for the first time by New Horizons in 2013.

With the 2015 close-up just around the corner, scientists are working swiftly to make best use of surface photographs returned by the spacecraft.

New Horizons will give us the ability to resolve objects as small as a football field on part of the surface of Pluto and Charon.

With pictures of that detail and models such as this one, we may be able to look backwards in time to determine details about both bodies, such as how thick their ice shells were when they formed.

Studying patterns of fractures in Charon's surface is critical to building accurate models of the ice shell and layers beneath.

"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 Rhoden.

"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."

The oceans of certain icy moons with surface fractures are considered to be places where extraterrestrial life might be found.

Like Charon, Europa and Enceladus are very cold and very distant from the sun. In all three cases, the formation and maintenance of life would depend upon a reliable energy source as well as elements that can participate in the chemistry of life, such as carbon, nitrogen, and phosphorus.

New Horizons Long Range Reconnaissance Imager (LORRI) composite image showing the detection of Pluto’s largest moon, Charon. 

When these images were taken on July 1 and July 3, 2013, the New Horizons spacecraft was still about 550 million miles (880 million kilometers) from Pluto.

On July 14, 2015, the spacecraft is scheduled to pass just 7,750 miles (12,500 kilometers) above Pluto’s surface, where LORRI will be able to spot features about the size of a football field. 

Credit: NASA /Johns Hopkins University Applied Physics Laboratory /Southwest Research Institute (SRI)

It is unknown if a potential ocean on Charon may have harbored these ingredients or if the ocean there existed for long enough for life to form.

The same questions apply to any ancient ocean on any moon in our Solar System or any other. The first step on Charon is to find the fractures, and then go looking for the warmth that liquid water.

"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," said 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."

NASA Cassini Image: Flyby of Saturn's moon Phoebe

As it entered the Saturn system, NASA's Cassini spacecraft performed its first targeted flyby of one of the planet's moons.

On June 11, 2004, Cassini passed Phoebe, the largest of Saturn's outer or "irregular" moons, at an altitude of just 1,285 miles (2,068 kilometers).

This was the sole close flyby of one of the outer moons of Saturn in the entire Cassini mission.

This montage of two views is published by the Cassini team to mark the 10th anniversary of the Phoebe flyby.

The image on the left side shows Cassini's view on approach to Phoebe, while the right side shows the spacecraft's departing perspective.

Most of the left-side view was previously released as PIA06073; an area on its upper right side is newly filled in here.

Most of the view on the right side has not previously been released, although the crater at upper left is seen in PIA06074.

Phoebe's shape is approximately spherical (see PIA06070 and PIA15507 for more details), with a diameter of 136 miles (219 kilometers) on its longest axis and 127 miles (204 kilometers) on its shortest axis, which is also the rotation axis. This is approximately 16 times smaller than Earth's moon.

For several reasons, Phoebe is thought to be a captured object that does not share a joint origin with Saturn and the inner, "regular" satellites.

It orbits in a retrograde direction, opposite to the direction of Saturn's other major moons.

Its overall density was determined by Cassini scientists to be quite large for a moon of Saturn.

The prevailing view is that Phoebe might have formed in the Kuiper Belt, far beyond the orbit of Saturn. It might thus be a small cousin of the largest Kuiper Belt object, Pluto.

Medium sized Kuiper belt object less dense than water

Observations of the 2002 UX25 system with HST/HRC and Keck LGS-AO/NIRC2. 

The northward orientation arrow is 0.25 arcseconds long, for scale. 

In the first column, we show the image of both 2002 UX25 and its satellite. 

Credit: arXiv:1311.0553 

Michael Brown, a planetary scientist with California Institute of Technology, has found a medium sized object in the Kuiper belt (dubbed 2002 UX25) that doesn't appear to conform to theories of how such objects came to exist.

Michael Brown

In his paper to be published in Astrophysical Journal Letters, Brown notes that the mid-sized object appears to be less dense than it should be if it followed conventional thinking that suggests the larger the objects are in the belt, the more dense they should get.

The Kuiper belt, is of course, a group of rock-like objects (comets, dwarf planets, etc.) orbiting the sun that lie farther out than Neptune.

Such Kuiper belt objects (KBOs) are believed to have formed in ways similar to the way planets did, i.e. due to accretion of material over time.

Conventional theory suggests that small KBOs are less dense than water because of their porous nature—large KBOs grew more dense as they grew larger due to gravity causing them to compact.

If the theory is correct medium size KBOs should have medium density. But this new KBO that Brown has found doesn't conform to the theory at all, instead, its density is roughly the same as smaller KBOs, suggesting that it's not size that determines KBO density, but something else. And right now, Brown notes, nobody knows what that something else might be.

12 minute exposure of dwarf planet candidate (55637) 2002 UX25 with a 24" telescope.

2002 UX25 has a diameter of roughly 650 kilometers, putting it squarely in the mid-size KBO category, and it, like other KBOs, is believed to exist in very nearly the same state it's held since the formation of the solar system.

It's in studying such objects that scientists learn more about how everything in our solar system came to be the way it is.

Until now, most scientists agreed that KBOs of a size smaller than 350 kilometers across had a density less than that of water, whereas bigger ones had a greater density.

That theory might have to be changed however as 2002 UX25 is the first medium sized KBO to have its density measured and it clearly doesn't conform.

The discovery of 2002 UX25's density properties has already led to new theories, Brown notes, with some suggesting that scientists have been wrong to assume that KBOs and the planets formed at the same time.

Instead, they suggest, that it's possible that KBOs came first and afterwards as the planets were forming, eddies formed causing KBOs to knock into one another breaking them into different sized pieces.

More information: The density of mid-sized Kuiper belt object 2002 UX25 and the formation of the dwarf planets, arxiv.org/abs/1311.0553