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New Horizons Mission Spies Pluto's Entire Moon Family

Having already discerned the dwarf planet has distinct surface features, NASA's New Horizons mission has now spotted not just Pluto's largest moons, but the smallest natural satellites too.

Having already discerned the dwarf planet has distinct surface features, perhaps even a polar ice cap, NASA's New Horizons mission has now spotted not just Pluto's largest moons, but the smallest natural satellites too.

Imaged at a distance of over 55 million miles (88 million kilometers) from the Plutonian system between April 25 and May 1, this animated sequence of five 10 second observations by New Horizons' Long Range Reconnaissance Imager (LORRI) instrument show Pluto's largest moon Charon, plus smaller moons Nix and Hydra, and it has also pinpointed, for the first time, the recently-discovered moons Kerberos and Styx.

ANALYSIS: NASA Probe Spies Possible Polar Ice Cap on Pluto

"New Horizons is now on the threshold of discovery," said mission science team member John Spencer, of the Southwest Research Institute in Boulder, Colo., in a NASA news release. "If the spacecraft observes any additional moons as we get closer to Pluto, they will be worlds that no one has seen before."

The diminutive Kerberos and Styx measure only 4 to 13 miles (6 to 21 kilometers) and 6 to 20 miles (10 to 32 kilometers) in diameter and were discovered in 2011 and 2012, respectively, by the New Horizons science team using Hubble Space Telescope data. As a comparison, Charon is 750 miles (1,200 kilometers) wide, Nyx is between 29 and 85 miles (47 and 137 kilometers) wide and Hydra is between 37 and 92 miles (60 and 148 kilometers) wide. These uncertainties in moon diameters will be greatly reduced as New Horizons rapidly approaches its July 14 flyby.

"Detecting these tiny moons from a distance of more than 55 million miles is amazing, and a credit to the team that built our LORRI long-range camera and John Spencer's team of moon and ring hunters," said principal investigator Alan Stern, of the Southwest Research Institute.

NEWS: After Pluto, Where Will NASA's New Horizons Go?

The imaging and processing techniques used by the team will now be used to continue exploration of the neighborhood surrounding Pluto. It has long been assumed, with the discovery of the dwarf planet's growing family of natural satellites, that many more moons exist. There may even be a ring of debris, signifying a possible ancient impact event in the Kuiper belt.

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

Interestingly, all the moons except Charon were discovered after New Horizons was launched from Cape Canaveral Air Force Station, Fla., in 2006. Since then, the growing Pluto family has sparked excitement - and worry - as the spacecraft plowed through the solar system ahead of its flyby date with the dwarf planet nearly a decade later.

Of principal concern is any unforeseen rings or clouds of debris that could present an impact risk to the New Horizons probe. As more moons were discovered, so did the likelihood of more, sub-resolution moons and debris. So by carrying out these observations ahead of its Pluto flyby, it may be possible to assess the region for hazards and, indeed, possibly discover more Pluto moons.

ANALYSIS: Pluto's New Moons Get Names From Hell

On May 15, any observations made by New Horizons will beat the resolution of the best Hubble observations of Pluto, so some of the most exciting and historic discoveries in the outer solar system may only be days away.

And as we are only weeks away from the long-awaited July flyby, expect the science to start streaming in thick and fast.

Source: NASA

The term "dwarf planet" wasn't defined until the infamous International Astronomical Union (IAU) vote in 2006, but this year, 9 years later, we are beginning to get our first ever close-up views of two of our solar system's most famous dwarf planets: Pluto and Ceres.

VIDEO: Pluto Flyby and Black Holes: Top Space Events for 2015

Currently spiraling in on Ceres, the innermost dwarf planet inhabiting the asteroid belt between the orbits of Mars and Jupiter, NASA's Dawn spacecraft is slowly revealing a cratered and complex world, details of which that have so far eluded even Hubble's powerful vision. Dawn is scheduled to make final orbital insertion around Ceres in March 2015 where it is destined to remain after its fuel runs out as a permanent human-made satellite of Ceres. A comparison image of the Hubble and Dawn views of Ceres is shown above.

ANALYSIS: NASA Spacecraft Ready to Unlock Ceres' Mysteries

But Dawn is just the first dwarf planet encounter of 2015. In July, NASA's New Horizons mission will flyby Pluto and its system of moons, exploring the mysterious Kuiper Belt. Between Hubble's blurry observations of Ceres and Pluto and this year's NASA encounters, many artists' impressions of these enigmatic worlds have guessed at what lies in store for our robotic explorers. But how do they measure up now we are beginning to see Ceres' and Pluto's surfaces?

This artist's impression of Ceres shows NASA's Dawn spacecraft in orbit around the dwarf planet. As opposed to an ice encrusted world, this visualization shows a cratered, moon-like surface.

NEWS: Tantalizing Detail Seen on Mysterious Dwarf Planet

Again with Dawn in view, this artist's impression shows an active Ceres complete with water vapor escaping from a possible sub-surface ocean. Water vapor was detected in the vicinity of Ceres by Hubble, so Dawn will be on the look-out for any trace of geysers venting water.

ANALYSIS: Water Plume 'Unequivocally' Detected at Dwarf Planet Ceres

As seen by Hubble from afar, curious white patches and possible variations in Ceres' surface composition can be seen. However, any detail in these images have so far prevented planetary scientists from fully understanding the dwarf planet's true nature.

NEWS: What is That Mysterious White Blob on Ceres?

But now, as Dawn fast approaches orbital insertion, we're being treated to a bounty of data that shows a possibly ancient, rocky surface. Those curious white patches originally spied by Hubble are also snapping into view -- but what are they? Theories abound, but they may be tentative signs of subsurface water escaping to space and freezing on the surface. These are all signs of cryovolcanism, a dynamic that may dominate dwarf planet surface morphology.

NEWS: Dwarf Planet's Puzzling Landscape Snaps into View

From afar, NASA's Dawn mission is able to watch Ceres rotate, as this series of observations on Feb. 4 shows.

ANALYSIS: Craters Pop as NASA’s Dawn Probe Approaches Ceres

As Dawn gets up-close and personal with Ceres, the drama in the outer solar system is only just beginning to unfold. After 9 years of flying toward Pluto, NASA's New Horizons mission has begun approach preparations for its flyby in July.

VIDEO: Pluto Getting Bigger in New Horizons Probe's Window

From ground-based and Hubble observations, there at tantalizing clues that this frozen world has a surprisingly dynamic surface with a thin atmosphere that changes during Pluto's 248 year orbit around the sun. In this artist's impression of New Horizons flying over Pluto, an atmosphere has been included with cryovolcanos -- the latter of which planetary scientists hope to confirm in July.

Pluto has a system of known moons, the largest of which, Charon, may be considered to be Pluto's binary partner. As Charon orbits Pluto, its powerful gravitational field tugs the dwarf planet off center, a dynamic that New Horizons has observed as it approaches.

ANALYSIS: NASA Probe Captures First Pluto Approach Photos

This artist's conception shows Pluto's moon Charon eclipsing the dwarf planet. Twice every orbit around the sun, each world eclipses the other.

NEWS: Tally-Ho on Targets for New Horizons After Pluto

When Hubble spies on Pluto, it can see the different shades of the dwarf planet's surface rotate. As shown here in these blotchy images, little detail is obvious, but large regions with differing albedo (reflectiveness) may reveal huge craters, vast plains or mountains. But until New Horizons gets close, these regions will remain a mystery.

In this digital illustration rendered from 3-D NASA data of Pluto, an attempt has been made at matching observations with possible surface features.

In July 2014, NASA's New Horizons looked ahead and spied its ultimate goal: Pluto and Charon. Although tiny pinpricks of light, the pair can be seen orbiting one another in a binary dance that shifts Pluto off center. Both masses actually orbit an invisible point in space, above Pluto's surface, known as the Pluto-Charon barycenter. These observations have increased calls for Pluto to be redefined (yet again) as a 'binary planet.'

MORE: Can We Call Pluto and Charon a 'Binary Planet' Yet?

Having spotted Charon months ago, New Horizons is now beginning to see Pluto's wider family of moons pop into view. Shown here are moons Nix (yellow diamond) and Hydra (orange diamond).

MORE: Pluto's Tiny Moons Spied by Incoming NASA Probe

Once NASA's New Horizons mission careens through the Pluto-Charon system, assuming it doesn't hit any debris on its way through, its mission in the Kuiper Belt has only just begun. Hubble is currently being used to identify possible icy targets

after

the spacecraft's Pluto encounter. Shown here is an artist's impression of another dwarf planet, Eris, that was discovered in 2005. Originally thought to be the

tenth

planet of the solar system, its discovery led to the IAU's decision to reclassify these small worlds as dwarf planets, demoting Pluto in the process, leaving us with 8 planets. But as we approach Pluto and begin to understand Ceres, just because they are dwarf planets doesn't mean they're not rich and dynamic places to explore. Our voyage of dwarf planet discovery has only just begun and regardless of our need to classify celestial objects, Pluto and Ceres hold some fascinating clues to planetary formation and solar system evolution.

For more, regularly check on the

NASA Dawn

and

NASA New Horizons

mission web sites.