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

The debate as to whether Pluto is a planet or a dwarf planet rumbles on, but in a new animation of the small world, one can't help but imagine another definition for Pluto. Continue reading →

The debate as to whether Pluto is a planet or a dwarf planet rumbles on, but in a new animation of the small world, one can't help but imagine another definition for Pluto.

NEWS: Radio Telescope Pinpoints Pluto for Spacecraft Buddy

As NASA's New Horizons spacecraft continues its epic journey into the outer solar system, its Kuiper Belt target is becoming brighter and more defined. Seen through the mission's Long Range Reconnaissance Imager (LORRI) camera, this new set of observations clearly shows Pluto and its biggest moon Charon locked in a tight orbital dance separated by only 11,200 miles. (Compared with the Earth-moon orbital separation of around 240,000 miles, you can see how compact the Pluto-Charon system really is.)

"The image sequence showing Charon revolving around Pluto set a record for close range imaging of Pluto-they were taken from 10 times closer to the planet than the Earth is," said New Horizons mission Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colo. "But we'll smash that record again and again, starting in January, as approach operations begin.

"We are really excited to see our target and its biggest satellite in motion from our own perch," he added in a New Horizons mission update on Thursday, "less than a year from the historic encounter ahead!"

ANALYSIS: Pluto and Moon Charon May Share Same Atmosphere

We've seen fuzzy photographs of both Pluto and Charon before, but this animation shows something more.

Over the course of 5 days, LORRI snapped 12 images of the Pluto-Charon system, tracking nearly one full (6.5 day) Charon orbit. New Horizons was between 267 million to 262 million miles from Pluto at the time. As Charon orbits, however, there's a very clear wobble in Pluto's position - Charon's mass (nearly 12 percent that of Pluto's) has a powerful gravitational influence on Pluto, yanking it "off center." Therefore, both masses orbit an imaginary point above Pluto's surface. This point is called the "barycenter" of the Pluto-Charon system.

This is unique for any planetary body in the solar system - only binary asteroids have been found to have barycenters outside of either mass' body. This fact alone has led calls for Charon to be recognized as a planetary body in its own right, or that the Pluto-Charon system should be redefined as a "binary planet" - much like the definition for binary stars that are common throughout the galaxy.

OPINION: Not a Dwarf: Is Pluto a Binary Planet?

In a thought-provoking article in 2012, Discovery News' Ray Villard investigated this possibility, pointing out that the other 4 moons discovered so far around Pluto don't orbit Pluto. They follow Keplarian orbits about the Pluto-Charon barycenter - the center of mass of Pluto and Charon. They are satellites of Pluto and Charon, not just Pluto!

The international body that defines celestial classifications, however, has yet to address this fact. The International Astronomical Union (IAU) will likely need to re-examine the case of Pluto and Charon, especially after we get a close-up view of Pluto next year.

As New Horizons quickly approaches the Pluto-Charon system for its historic flyby in July 2015, we're going to see more detail in the Pluto-Charon system; evidence for surface dynamics, detailed geological features and probably more minor satellites (that may or may not prove hazardous for the NASA probe). This mission will put a new spotlight on Pluto and its "dwarf planet" status, potentially highlighting its current classification as a woefully inadequate description of such a dynamic and interesting binary system.

Perhaps re-re-defining Pluto as a binary planet or a dwarf planet binary isn't such a bad idea after all. What do you think?

Source: New Horizons mission page

This "movie" of Pluto and its largest moon, Charon, was taken by NASA's New Horizons spacecraft as it raced toward Pluto in July 2014.

Traveling through capital cities is always a stressful occasion and this time was no exception. I had left myself a whole hour to get from the train station to the Royal Observatory Greenwich in London for The Astronomy Photographer of the Year 2013, and it seems an hour was only just enough! But once I'd arrived, I settled back in the very comfortable seats of the Peter Harrison Planetarium and the lights dimmed as the winning photographs were presented to the excited audience. There was a tangible buzz as the images appeared right over our heads on the inside of the planetarium dome against a beautiful background of glittering stars.

This years winners did not disappoint, there was a wide range of skills and techniques on show from the stunning "Deep Space" category where the photos had taken literally days to capture and process to the simple yet enigmatically beautiful "People and Space" category. As I watched the beautiful images appearing above me it reminded me just how powerful images of space can be in communicating the wonder of the Universe. The shortlisted photographs entered into the competition came from 49 countries. The overall winning image was taken by Mark Gee from Australia and was titled 'Guiding Light to the Stars' (shown here), depicting the stunning sight of the Milky Way with a glowing beacon of a lighthouse to the right of the scene. The composition reflects the way the stars used to be employed as a way of navigation in contrast to modern navigation techniques. Mark's image also won the "Earth and Space" category.

Adam Block from the United States won the Deep Space category with his image called "Celestial Impasto." The picture beautifully captures the delicate shades in the dust and dark nebulae of Sh2-239 in the Taurus molecular cloud about 450 light-years away.

The winner of the "Solar System" category was Man-To Hui from China with this beautifully captured image of the Australian solar eclipse of 2012. Phenomenal levels of detail can be seen in the usually hidden solar corona which can only be seen at the moment of totality during a solar eclipse.

Jacob Marchio from the United States was the winner of the Young Astronomy Photographer of the Year and at the age of 14 was able to capture this beautiful image captioned simply "The Milky Way." The image is a beautiful reminder of our place in the Universe as the stars from our galaxy shine with a lovely warm glow.

There were three special categories too this year, the first "People and Space" was won by Mark Gee with this beautifully composed image of an observation platform silhouetted against the moon. Mark took this picture from a distance of about 3 kilometers and used a zoom lens to get the shot.

The winner of the Sir Patrick Moore Prize for Best Newcomer was Sam Cornwell form the UK who managed, against the odds of the British weather, to capture a glimpse of the 2012 Venus transit just before it finished. The cloud really adds atmosphere to the picture and wonderfully represents the challenges facing astronomers suffering adverse weather conditions.

The Robotic Scope Image of the Year was picked up by László Francsics from Hungary with an amazing picture of the famous Trapezium Cluster in the Orion Nebula.

The shifting lights of the Aurora Borealis can take on many shapes and forms as they are molded by the Earth’s complex magnetic field. Sheets and planes of glowing gas appear to be twisted into a giant vortex above Grøtfjord in Norway.

All of the light which reaches the ground from space must first travel through the Earth’s atmosphere. During its journey the light can be altered by all sorts of atmospheric phenomena. Tiny ice crystals high above the ground refract the moonlight diverting it into a number of beautiful halos.

Like the snowy mountains in the foreground, the nucleus of Comet Panstarrs is composed largely of ice and rock. The nucleus itself is just a few kilometers across but as it neared the Sun in early 2013, ice evaporating from the surface formed a tail of gas and dust hundreds of thousands of kilometers long.

A great deal of careful planning, a long night of photography and hours of painstaking image processing have gone into creating this startling composite image of the Perseid meteor shower. The Perseid meteors get their name from the constellation of Perseus from where they appear to come. However, even at the peak of the shower it is impossible to predict exactly when or where the next meteor will appear. The photographer has combined 23 individual stills to convey the excitement and dynamism of this natural firework display.

The smoky appearance of the dust clouds in this image is fitting, since the grains of dust which make up the nebula are similar in size to particles of smoke here on Earth. The dust can reflect the light of nearby stars, as seen in the blue and yellow regions. It can also block and absorb the light of more distant stars, appearing brown and black in this image. To the right a bright star is ionizing a cloud of hydrogen gas, causing it to glow red, while below it far in the distance, is a globular cluster containing thousands of stars.

First discovered by astronomer Caroline Herschel in 1783, NGC 253 is a rare example of a ‘starburst galaxy’ with new stars being formed at many times the rate in our own galaxy, the Milky Way. Its mottled appearance comes from extensive lanes of dust which thread through the galactic disk. These are studded with many red clouds of ionized hydrogen gas, marking the sites where new stars are being born.

Lying at a distance of twelve million light years from Earth, M81 and M82 are galaxies with a difference. Close encounters between the two objects have forced gas down into their central regions. In M81 this influx of gas is being devoured by a supermassive black hole. In neighboring M82 the gas is fueling a burst of new star formation which in turn is blasting clouds of hydrogen (shown in red) back out into space.

Omega Centauri is a globular cluster, a spherical cloud containing several million stars. As this image shows, the stars are more densely clustered towards the center. The pronounced red color of several of the stars gives away the cluster’s great age: it is thought to have been formed billions of years ago. The cluster was first noted by the astronomer Ptolemy almost 2000 years ago and cataloged by Astronomer Royal Edmond Halley in 1677.

The awesome scale presented in this image depicts what as far as we’re concerned, are the three most significant objects in the Universe. The Sun and Moon each play an important role to us on Earth, and both are seen here, reddened by our vital atmosphere, presiding over the horizon. The third object is the Earth itself, and here its land, sea and sky meet around an amazing human megastructure, San Francisco’s Golden Gate Bridge.

The Great Nebula, also referred to as The Orion Nebula and M42 is found in the well-known constellation of Orion, just below the hunter’s belt. To the naked eye the nebula looks like another star in Orion’s sword. However, this skilful young photographer has shown there is more to it than meets the eye by producing this beautiful image that not only shows the stunning formation of this popularly observed nebula but also it diffuse nature.

The Moon seems to be emerging from the interplanetary darkness, and the young photographer has captured the contrast been the dark lava-filled lunar ‘seas’ and the mountainous southern highlands.

By keeping the camera shutter open this young photographer gathers precious light, making the desert scenery seem as bright as day. But the stars in the blue sky give the game away, showing that this dramatic photograph was actually taken in the middle of the night.

Appearing like a column of smoke rising from the horizon, a dark lane of dust marks the plane of the Milky Way in this photograph. This dust plays a vital role in the life story of our galaxy. Formed from the ashes of dead and dying stars, the dust clouds are also the regions in which new stars will form.

The darkest patches or ‘umbrae’ in this image are each about the size of Earth, with the entire region of magnetic turmoil spanning the diameter of ten Earths. This image captures rich details directly around the sunspots, and further out in the so-called ‘quiet’ Sun where simmering hot plasma rises, cools and falls back. This produces a patchwork surface like a pot of boiling water, but on an epic scale – each bubbling granule is about the size of France.

At a glance, this image may seem like a post-processed montage of objects from three separate images. However the truth is that they were all captured together providing the viewer with an amazing view of the Solar System, galaxy and Universe. Comet Lemmon only comes into our neighborhood every 11,000 years, racing around our Sun and back out to the far reaches of the Solar System. The light from the globular cluster in the center of this image took a journey of over 16,000 years to reach Earth. The furthest object in the image is a dwarf galaxy called the Small Magellanic Cloud whose starlight takes 200,000 years to reach us.

The Moon’s orbit about the Earth is not perfectly circular, so that at different times the Moon can be slightly closer or further away than usual. If the Moon passes in front of the Sun when it is at its furthest point, it will appear to be too small to entirely cover the solar disc. This is an ‘annular eclipse’ in which a ring, or annulus, of the Sun remains visible. This composite shot shows the progress of an annular eclipse in May 2013. Close to the horizon the distorting effects of Earth’s atmosphere can also be seen.

This incredibly sharp portrait brilliantly captures the jewel of our solar system, revealing the subtle banding around the orb that results from the planet’s weather. It also shows the exquisite gradation of brightness and color in the planet’s rings. The ultra-faint inner ‘D-Ring’ and outermost Encke gap are clearly visible. The hexagonal storm at the North Pole – a scientific curiosity – shows off three of its angular kinks. Images with this much clarity challenge our ideas of what can be achieved with amateur telescopes.

Full resolution versions of these photographs can be found on the National Maritime Museum ( All photographs are credited to the respective photographers and the National Maritime Museum. Photo captions for the winning entries are written by Mark Thompson; captions for runners up and highly commended entries are courtesy of the National Maritime Museum and Astronomical Photographer of the Year 2013.