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Name Pluto’s moons

Image showing Pluto's known moons

This image, taken by NASA’s Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the unnamed moon, designated P5, as photographed by Hubble’s Wide Field Camera 3 on July 7 2012. The unnamed moon P4 was uncovered in Hubble imagery in 2011.

THE DISCOVERER OF PLUTO’S two tiniest moons are inviting the public to help select names for the new moons. By tradition, the moons of Pluto have names associated with Hades and the underworld.

“The Greeks were great storytellers, and they have given us a colourful cast of characters to work with,” said Mark Showalter, Senior Research Scientist at the Carl Sagan Centre of the SETI Institute in Mountain View, California.

Pluto has five moons – Charon (discovered 1978), Nix and Hydra (discovered 2005), and two known simply as P4 and P5, discovered in 2011 and 2012 respectively. Astronomers are now looking for names for P4 and P5.

Moons of the underworld

All the bodies in the Pluto system are named after mythological figures of the underworld – Pluto, the god of the underworld; Charon, the ferryman of the dead; Nix, Greek goddess of darkness and night; and Hydra, the nine-headed serpent that battled Hercules.

Showalter and the teams of astronomers who made the discoveries will select two names based on the outcome of the voting. Like Pluto’s three other moons, Charon, Nix and Hydra, they need to be assigned names derived from Greek or Roman mythology.

Artist's impression of the New Horizons spacecraft passing Pluto in 2015

Artist’s impression of the New Horizons spacecraft passing Pluto in 2015.

Beginning today, people can vote by visiting, and select from a list of suggest ‘underworld’ names.

Visitors to the website will also be able to submit their own suggestions. These will be reviewed by the team and could be added to the ballot. Voting will end February 25, 2013. The final names will be announced after their formal approval by the International Astronomical Union.

First mission to Pluto

P4 was discovered in 2011 in images taken by the Hubble Space Telescope. P5 was discovered a year later during a more intensive search for previously unseen objects orbiting the distant, dwarf planet. The moons are only 20 to 30 kilometres across.

Currently, Pluto is receiving special scrutiny by astronomers, because NASA’s New Horizons spacecraft is slated to arrive there in July 2015.

Launched in 2006, the craft is carrying some of the ashes of the man who discovered Pluto in 1930, Clyde Tombaugh.

A Google+ Hangout is scheduled on February 11 at 11:00am US PST (19:00 GMT) with two of the scientists involved in the discovery. Mark Showalter is from the SETI Institute, and Hal Weaver is a researcher at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Questions from viewers will be taken during the event using Twitter hashtag #PlutoRocks, the SETI Institute Facebook page and the Google hangout.

Adapted from information issued by the SETI Institute. Pluto moons image courtesy NASA; ESA; M. Showalter, SETI Institute. New Horizons graphic courtesy NASA.

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Pluto has a new moon

Artist's impression of Pluto and Charon

Artist's impression of Pluto and its large moon Charon (diameter 1,043km). Hubble telescope observations have uncovered a previously unseen Plutonian moon, probably only 13 to 34km across.

ASTRONOMERS USING THE Hubble Space Telescope have discovered a fourth moon orbiting the icy dwarf planet Pluto. The tiny, new satellite, temporarily designated P4, was uncovered in a Hubble survey searching for rings around the dwarf planet.

The new moon is the smallest discovered circling Pluto. It has an estimated diameter of 13 to 34 km. By comparison, Charon, Pluto’s largest moon, is 1,043 km across, and the other moons, Nix and Hydra, are in the range of 32 to 113 km in diameter.

“I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than 5 billion km,” said Mark Showalter of the SETI Institute, who led this observing programme with Hubble.

Hubble image showing motion of Pluto's four moons

This composite of two Hubble images—taken on June 28, 2011 and July 3, 2011—shows Pluto's four satellites in motion. P4 is the as-yet-unnamed new moon.

Mission to Pluto

The finding is a result of ongoing work to support NASA’s New Horizons mission, scheduled to fly through the Pluto system in 2015. The mission is designed to provide new insights about worlds at the edge of our Solar System.

Hubble’s mapping of Pluto’s surface and discovery of its satellites have been invaluable to planning for New Horizons’ close encounter.

“This is a fantastic discovery,” said New Horizons’ principal investigator Alan Stern of the Southwest Research Institute. “Now that we know there’s another moon in the Pluto system, we can plan close-up observations of it during our flyby.”

Moons formed in a smash-up

The new moon is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Charon was discovered in 1978 at the US Naval Observatory and first resolved using Hubble in 1990 as a separate body from Pluto.

The dwarf planet’s entire moon system is believed to have formed by a collision between Pluto and another planet-sized body early in the history of the Solar System. The smash-up flung material that coalesced into the family of satellites observed around Pluto.

Artist's concept of Pluto's satellite system

An artist's concept of Pluto's satellite system with newly discovered moon P4 highlighted.

Lunar rocks returned to Earth from the Apollo missions led to the theory that our moon was the result of a similar collision between Earth and a Mars-sized body 4.4 billion years ago.

Scientists believe material blasted off Pluto’s moons by micrometeoroid impacts may form rings around the dwarf planet, but the Hubble photographs have not detected any so far.

No sign of rings yet

“This surprising observation is a powerful reminder of Hubble’s ability as a general purpose astronomical observatory to make astounding, unintended discoveries,” said Jon Morse, astrophysics division director at NASA Headquarters in Washington.

P4 was first seen in a photo taken with Hubble’s Wide Field Camera 3 on June 28. It was confirmed in subsequent Hubble pictures taken on July 3 and July 18. The moon was not seen in earlier Hubble images because the exposure times were shorter.

There is a chance it appeared as a very faint smudge in 2006 images, but was overlooked because it was obscured.

Adapted from information issued by NASA. Images and graphics courtesy NASA / A. Feild (STScI) / ESA.

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Pluto has a CO glow

Artist's impression of Pluto and Charon

An artist's impression of Pluto and its largest moon, Charon. Astronomers have detected thin traces of carbon monoxide gas in the dwarf planet's atmosphere.

ASTRONOMERS HAVE DISCOVERED carbon monoxide in the atmosphere of Pluto, capping off nearly two decades of work to detect the gas in the ‘air’ of the distant, icy world.

Pluto, discovered in 1930, was long considered the Sun’s smallest and most distant planet. Since 2006, though, it has been regarded by many astronomers as a ‘dwarf planet’…one of a handful of such bodies with sizes of hundreds of kilometres that orbit in the distant reaches of the Solar System, out beyond Neptune.

Pluto is the only dwarf planet known to have an atmosphere. The thin layer of gases was detected in 1988 when it dimmed the light of a distant star as Pluto passed in front of it.

The new results, obtained using the 15-metre James Clerk Maxwell Telescope in Hawaii, show a strong signal of carbon monoxide gas.

Team leader Dr Jane Greaves of the University of St Andrews will present the new discovery today at the UK National Astronomy Meeting in Wales.

Fragile atmosphere

Previously, Pluto’s atmosphere was known to be over a hundred kilometres thick, but the new data raise this height to more than 3,000 kilometres—a quarter of the way out to Pluto’s largest moon, Charon.

In 1989 Pluto made its closest approach to the Sun, a comparatively recent event given that it takes 248 years to complete each orbit. The gases probably result from solar heating of surface ice, which sublimates (goes directly from ice to gas) as a consequence of the slightly higher temperatures during this period.

The resulting atmosphere is probably the most fragile in the Solar System, with the top layers blowing away into space.

“The height to which we see the carbon monoxide agrees well with models of how the solar wind strips Pluto’s atmosphere,” commented team member Dr Christiane Helling, also of the University of St Andrews.

Artist's impression of the view from the surface of Pluto

Artist's impression of the view from the surface of Pluto, showing a thin, hazy atmosphere.

Deep space cold snap

The gas is extremely cold, about -220 degrees Celsius. A big surprise for the team was that the CO measurement was more than twice as strong as an upper limit obtained by another group, who used the IRAM 30-metre telescope in Spain in 2000.

“It was thrilling to see the signal gradually emerge as we added in many nights of data”, said Dr Jane Greaves, the team leader from the University of St Andrews.

“The change in brightness over the last decade is startling,” she added. “We think the atmosphere may have grown in size, or the carbon monoxide abundance may have been boosted.”

Such changes have been seen with Pluto before, but only in the lower atmosphere, where methane—the only other gas ever positively identified—has also been seen to vary.

Critical balance

Unlike the greenhouse gas carbon dioxide, carbon monoxide acts as a coolant, while methane absorbs sunlight and so produces heating. The balance between the two gases—which are just trace elements in what is thought to be a nitrogen-dominated atmosphere—is critical for its fate during the many-decades long seasons.

The newly discovered carbon monoxide may hold the key to slowing the loss of Pluto’s atmosphere. But if the chilling effect is too great, it could result in nitrogen snowfalls and all the gases freezing back onto the ground.

“Seeing such an example of extra-terrestrial climate-change is fascinating”, says Dr Greaves. “This cold, simple atmosphere that is strongly driven by the heat from the Sun could give us important clues to how some of the basic physics works, and act as a contrasting test-bed to help us better understand the Earth’s atmosphere.”

The JCMT is operated jointly by the UK, Canada and the Netherlands and is approaching its twenty-fifth anniversary.

The team has another Pluto observing run scheduled at the JCMT for the end of April, and in the long-term, they hope to continue tracking the changes in the atmosphere at least up to the fly-by of NASA’s New Horizons space probe in 2015.

Adapted from information issued by RAS. Images courtesy ESO / L. Calcada.

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