Category: Pluto

The International Astronomical Union approved new names for Pluto’s recently discovered tiny moons. Previously designated S/2005 P 1 and 2, the moons will now bear the names Hydra and Nix. In mythology, Nix is the goddess of darkness and night, while the hydra is a monster with the body of a serpent and nine heads. Although they’re faint dots right now, NASA’s New Horizons probe will fly pas them in 2015, and map them in much more detail.
Continue reading “Pluto’s New Moons are Named Nix and Hydra”

Pluto has been considered a planet since its discovery, but this position has come under threat with the discovery of 2003 UB313 (aka Xena), an object larger than Pluto orbiting out further in the Solar System. The International Astronomical Union will be meeting in August to decide on the fate of Pluto. By September, we could have 8 or 10 planets in the Solar System, but there won’t be 9 any more.
Continue reading “Pluto’s Planethood Will Be Decided Shortly”

An artist’s illustration of Xena with its moon. Image credit: NASA Click to enlarge
The powerful Hubble Space Telescope has finally been brought to bear on the newly discovered 10th planet (aka Xena), to help answer the question: is it really bigger than Pluto? Hubble is the only instrument that can make an actual visible light observation of Xena’s diameter. Hubble found that Xena is is about 2400 km (1,490 miles) across, which makes it only 113 km (70 miles) larger than Pluto. This makes the 10th planet unusually bright, probably covered in brilliant white methane snow.

For the first time, NASA’s Hubble Space Telescope has seen distinctly the “tenth planet,” currently nicknamed “Xena,” and has found that it is only slightly larger than Pluto.

Though previous ground-based observations suggested that Xena’s diameter was about 30 percent greater than Pluto, Hubble observations taken Dec. 9 and 10, 2005, showed Xena’s diameter as 1,490 miles (with an uncertainty of 60 miles). Pluto’s diameter, as measured by Hubble, is 1,422 miles.

“Hubble is the only telescope capable of getting a clean visible-light measurement of the actual diameter of Xena,” said Mike Brown, planetary scientist at the California Institute of Technology in Pasadena, Calif. Brown’s research team discovered Xena, officially cataloged as 2003 UB313, and its results have been accepted for publication in the Astrophysical Journal.

Only a handful of images were required to determine Xena’s diameter. Located 10 billion miles from Earth with a diameter a little more than half the width of the United States, the object is 1.5 pixels across in Hubble’s view. That’s enough to make a precise size measurement.

Because Xena is smaller than previously thought, but comparatively bright, it must be one of the most reflective objects in the solar system. The only object more reflective is Enceladus, a geologically active moon of Saturn whose surface is continuously recoated with highly reflective ice by active geysers.

Xena’s bright reflectivity is possibly due to fresh methane frost on its surface. The object may have had an atmosphere when it was closer to the sun, but as it moved to its current location farther away this atmosphere would have “frozen out,” settling on the surface as frost.

Another possibility is that Xena leaks methane gas continuously from its warmer interior. When this methane reaches the cold surface, it immediately freezes solid, covering craters and other features to make it uniformly bright to Hubble’s telescopic eye.

Xena’s takes about 560 years to orbit the sun, and it is now very close to aphelion (the point on its orbit that is farthest from the sun).Brown next plans to use Hubble and other telescopes to study other recently discovered Kuiper Belt objects that are almost as large as Pluto and Xena. The Kuiper Belt is a vast ring of primordial icy comets and larger bodies encircling Neptune’s orbit.

Finding that the largest known Kuiper Belt object is a virtual twin to Pluto may only further complicate the debate about whether to categorize the large icy worlds that populate the belt as planets. If Pluto were considered to be the minimum size for a planet, then Xena would fulfill this criterion, too. In time, the International Astronomical Union will designate the official name.

The Hubble Space Telescope is an international cooperative project between NASA and the European Space Agency. The Space Telescope Science Institute in Baltimore conducts Hubble science operations. The Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington

For electronic images and more Hubble news, visit: http://www.nasa.gov/hubble

Original Source: NASA News Release

Update, Pluto is no longer a planet. Why is Pluto not a planet?

Pluto and its three moons. Image credit: Hubble. Click to enlarge.
New photographs from the Hubble Space Telescope provide evidence that Pluto and its three moons probably formed at the same time, out of the same material. Scientists believe that the 4 objects were created when two Pluto-sized Kuiper Belt objects collided together. Hubble revealed that that Pluto and its moons have identical colours; exactly what you’d expect from this kind of an origin.

Using new Hubble Space Telescope observations, a research team led by Dr. Hal Weaver of the Johns Hopkins University Applied Physics Laboratory and Dr. Alan Stern of Southwest Research Institute has found that Pluto’s three moons are essentially the same color – boosting the theory that the Pluto system formed in a single, giant collision.

Publishing their findings in an International Astronomical Union Circular (No. 8686), the team determined that Pluto’s two “new” satellites, discovered in May 2005 and provisionally called S/2005 P 1 and S/2005 P 2, have identical colors to one another and are essentially the same, neutral color as Charon, Pluto’s large moon discovered in 1978.

All three satellites have surfaces that reflect sunlight with equal efficiency at all wavelengths, which means they have the same color as the Sun or Earth’s moon. In contrast, Pluto has more of a reddish hue.

The new observations were obtained March 2 with the high-resolution channel of the Hubble’s Advanced Camera for Surveys. The team determined the bodies’ colors by comparing the brightness of Pluto and each moon in images taken through a blue filter with those taken through a green/red filter. The images are available on the Hubble Web site at http://hubblesite.org/newscenter/newsdesk/archive/releases/2006/15/image/.

“The high quality of the new data leaves little doubt that the hemispheres of P1 and P2 that we observed have essentially identical, neutral colors,” says Weaver.

The new results further strengthen the hypothesis that Pluto and its satellites formed after a collision between two Pluto-sized objects nearly 4.6 billion years ago. “Everything now makes even more sense,” says Stern. “If all three satellites presumably formed from the same material lofted into orbit around Pluto from a giant impact, you might well expect the surfaces of all three satellites to have similar colors.”

The researchers hope to make additional Hubble color observations, in several more filters, to see if the similarity among the satellites persists to longer (redder) wavelengths. They have proposed to obtain compositional information on the new satellites by observing them at near-infrared wavelengths, where various ice and mineral absorptions are located. The researchers also hope to better refine the orbits of P1 and P2 and measure the moons’ shapes and rotational periods.

The Hubble observations were made in support of NASA’s New Horizons mission to Pluto and the Kuiper Belt. New Horizons launched on Jan. 19, 2006, and will fly through the Pluto system in July 2015, providing the first close-up look at the ninth planet and its moons. Stern leads the mission and science team as principal investigator; Weaver serves as the mission’s project scientist. The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., manages the mission for NASA’s Science Mission Directorate and operates the New Horizons spacecraft. For more information on the mission, visit http://pluto.jhuapl.edu.

The other members of the Hubble Space Telescope-Pluto satellite observing team include Max Mutchler of the Space Telescope Science Institute, Baltimore; Drs. William Merline, John Spencer, Andrew Steffl, Elliot Young and Leslie Young of Southwest Research Institute, Boulder, Colo.; and Dr. Marc Buie of Lowell Observatory, Flagstaff, Ariz.

Original Source: JHUAPL News Release

Update: Pluto is not a planet.

Artist’s illustration showing a giant collision similar to Pluto’s newly discovered moons scenario. Image credit: Don Davis Click to enlarge
In a paper published today in Nature, a team of U.S. scientists led by Dr. S. Alan Stern of Southwest Research Institute (SwRI), concludes that two newly discovered small moons of Pluto were very likely born in the same giant impact that gave birth to Pluto’s much larger moon, Charon. The team also argues that other, large binary Kuiper Belt Objects (KBOs) may also frequently harbor small moons, and that the small moons orbiting Pluto may generate debris rings around Pluto.

The team making these findings included Drs. Bill Merline, John Spencer, Andrew Steffl, Eliot Young and Leslie Young of SwRI; Dr. Hal Weaver of the Johns Hopkins University Applied Physics Laboratory; Max Mutchler of the Space Telescope Science Institute; and Dr. Marc Buie of the Lowell Observatory. This team discovered Pluto’s two small moons in 2005 using sensitive images obtained by the Hubble Space Telescope, as reported by Weaver et al. in an accompanying paper in the February 23 issue of Nature.

“The evidence for the small satellites being born in the Charon-forming collision is strong; it is based around the facts that the small moons are in circular orbits in the same orbital plane as Charon, and that they are also in, or very near, orbital resonance with Charon,” says lead author Stern, executive director of the SwRI Space Science and Engineering Division.

“Tests of this scenario will come from refined orbital data, from measuring the rotational periods of these moons, and from determinations of their densities and surface compositions,” says co-author Weaver.

Collisions, both large and small, are major processes that shaped many aspects of our solar system. Scientists use computer simulations to study the origin of planetary systems formed by impact events of a scale much larger than could be simulated in a laboratory. Another large collision, like the one thought to have created Charon and Pluto’s small moons, is believed responsible for the formation of the Earth-moon pair.

“The idea that Pluto’s small moons and Charon resulted from a giant impact now seems compelling. Future simulations to determine the characteristics of the impact required to produce all three satellites should provide improved constraints on the early dynamical history of the Kuiper Belt,” adds Dr. Robin Canup, director of SwRI’s Space Studies Department, who in 2005 produced the most comprehensive models to date of the Charon-forming impact.

Based on the growing realization that binary “ice dwarf” pairs like Pluto-Charon are common in the Kuiper Belt, the Pluto satellite discovery team concludes that numerous triple, quadruple and even higher-order systems may be discovered across the Kuiper Belt in years to come.

“Finding small satellites around KBOs is difficult because their large distance from the Sun makes them appear very faint. As a result, we don’t really know how common it is for KBOs to have multiple satellites,” adds co-author Steffl. “One good way to test this is to search around objects that have been ejected from the Kuiper Belt into orbits that bring them much closer to the Sun. So far, about 160 of these objects, called Centaurs, have been discovered. We hope to use Hubble to search for faint moons around some of them.”

Co-author Merline adds, “If Pluto’s small moons generate debris rings from impacts on their surfaces, as we predict, it would open up a whole new class of study because it would constitute the first ring system seen around a solid body rather than a gas giant planet.”

“The Pluto system never fails to reward us when we look at it in new ways,” concludes Stern. “What a bonanza and an illustration of the richness of nature Pluto has consistently proved to be. Our discovery of its two new moons reinforces that lesson yet again.”

The paper, “A Giant Impact Origin for Pluto’s Small Moons and Satellite Multiplicity in the Kuiper Belt,” by Stern et al. is available in the February 23 issue of Nature. NASA funded this work.

Original Source: SwRI News Release

Update: Pluto is no longer a planet.

The size of UB313 compared with Pluto, Charoon, Moon and Earth. Image credit: Max Planck Institute. Click to enlarge
Claims that the Solar System has a 10th planet are bolstered by the finding by a group lead by Bonn astrophysicists that this alleged planet, announced last summer and tentatively named 2003 UB313, is bigger than Pluto. By measuring its thermal emission, the scientists were able to determine a diameter of about 3000 km, which makes it 700 km larger than Pluto and thereby marks it as the largest solar system object found since the discovery of Neptune in 1846 (Nature, 2 February 2006).

Like Pluto, 2003 ub313 is one of the icy bodies in the so-called Kuiper belt that exists beyond Neptune. It is the most distant object ever seen in the Solar System. Its very elongated orbit takes it up to 97 times farther from the Sun than is the Earth – almost twice as far as the most distant point of Pluto’s orbit – so that it takes twice as long as Pluto to orbit the Sun. When it was first seen, UB313 appeared to be at least as big as Pluto. But an accurate estimate of its size was not possible without knowing how reflective it is. A team lead by Prof. Frank Bertoldi from the University of Bonn and the Max Planck Institute for Radio Astronomy (MPIfR) and the MPIfR’s Dr. Wilhelm Altenhoff has now resolved this problem by using measurements of the amount of heat UB313 radiates to determine its size, which when combined with the optical observations also allowed them to determine its reflectivity. “Since UB313 is decidedly larger than Pluto,” Frank Bertoldi remarks, “it is now increasingly hard to justify calling Pluto a planet if UB313 is not also given this status.”

UB313 was discovered in January 2005 by Prof. Mike Brown and his colleagues from the Californian Institute of Technology in a sky survey using a wide field digital camera that searches for distant minor planets at visible wavelengths. They discovered a slowly moving, spatially unresolved source, the apparent speed of which allowed them to determine its distance and orbital shape. However, they were not able to determine the size of the object, although from its optical brightness it was believed to be larger than Pluto.

Astronomers have found small planetary objects beyond the orbits of Neptune and Pluto since 1992, confirming a then 40-year old prediction by astronomers Kenneth Edgeworth (1880-1972) and Gerard P. Kuiper (1905-1973) that a belt of smaller planetary objects beyond Neptune exists. The so-called Kuiper Belt contains objects left from the formation of our planetary system some 4.5 billion years ago. In their distant orbits they were able to survive the gravitational clean-up of similar objects by the large planets in the inner solar system. Some Kuiper Belt objects are still occasionally deflected to then enter the inner solar system and may appear as short period comets.

In optically visible light, the solar system objects are visible through the light they reflect from the Sun. Thus, the apparent brightness depends on their size as well as on the surface reflectivity. Latter is known to vary between 4% for most comets to over 50% for Pluto, which makes any accurate size determination from the optical light alone impossible.

The Bonn group therefore used the IRAM 30-meter telescope in Spain, equipped with the sensitive Max-Planck Millimeter Bolometer (MAMBO) detector developed and built at the MPIfR, to measure the heat radiation of 2003 qq47 at a wavelength of 1.2 mm, where reflected sunlight is negligible and the object brightness only depends on the surface temperature and the object size. The temperature can be well estimated from the distance to the sun, and thus the observed 1.2 mm brightness allows a good size measurement. One can further conclude that the UB313 surface is such that it reflects about 60% of the incident solar light, which is very similar to the reflectivity of Pluto.

“The discovery of a solar system object larger than Pluto is very exciting,” Dr. Altenhoff exclaims, who has researched minor planets and comets for decades. “It tells us that Pluto, which should properly also be counted to the Kuiper Belt, is not such an unusual object. Maybe we can find even other small planets out there, which could teach us more about how the solar system formed and evolved. The Kuiper Belt objects are the debris from its formation, an archeological site containing pristine remnants of the solar nebula from which the sun and the planets formed.” Dr. Altenhoff made the pioneering discovery of heat radiation from Pluto in 1988 with a predecessor of the current detector at the IRAM 30-meter telescope.

The size measurement of 2003 UB313 is published in the 2 February 2006 issue of Nature. The research team includes Prof. Dr. Frank Bertoldi (Bonn University and MPIfR), Dr. Wilhelm Altenhoff (MPIfR), Dr. Axel Weiss (MPIfR), Prof. Dr. Karl M. Menten (MPIfR), and Dr. Clemens Thum (IRAM).

UB313 is a members of a ring of some 100,000 objects on the outskirts of the solar system, beyond Neptune at distances over 4 billion km from the sun, over 30 times the distance between Earth and Sun. The objects in this “Kuiper belt” circle the sun in stable orbits with periods of about 300 years. In the middle of the last century, the existence of a ring of small planetary objects was first suggested by the astronomers Kenneth Edgeworth (1880-1972) and Gerard P. Kuiper (1905-1973), but the first discovery of a “Kuiper belt object” was not until 1992. By now, over 700 such objects are known. UB313 is somewhat different from the normal Kuiper belt in that its orbit is highly excentric and 45 degrees inclined to the ecliptic plane of the planets and Kuiper Belt. It is likely that is originated in the Kuiper Belt and was deflected to its inclined orbit by Neptune.

Original Source: Max Planck Society

Update: Pluto is demoted

Liftoff of the Atlas V carrying NASA’s New Horizons spacecraft. Image credit: NASA/KSC Click to enlarge
The first mission to distant planet Pluto is under way after the successful launch today of NASA’s New Horizons spacecraft from Cape Canaveral Air Force Station, Fla.

New Horizons roared into the afternoon sky aboard a powerful Atlas V rocket at 2 p.m. EST. It separated from its solid-fuel kick motor 44 minutes, 53 seconds after launch, and mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., where the spacecraft was designed and built, received the first radio signals from New Horizons a little more than five minutes later. The radio communications, sent through NASA’s Deep Space Network antennas in Canberra, Australia, confirmed to controllers that the spacecraft was healthy and ready to begin initial operations.

“Today, NASA began an unprecedented journey of exploration to the ninth planet in the solar system,” says Dr. Colleen Hartman, deputy associate administrator for NASA’s Science Mission Directorate, Washington, D.C. “Right now, what we know about Pluto could be written on the back of a postage stamp. After this mission, we’ll be able to fill textbooks with new information.”

The 1,054-pound, piano-sized spacecraft is the fastest ever launched, speeding away from Earth at approximately 36,000 miles per hour, on a trajectory that will take it more than 3 billion miles toward its primary science target. New Horizons will zip past Jupiter for a gravity assist and science studies in February 2007, and conduct the first close-up, in-depth study of Pluto and its moons in summer 2015. As part of a potential extended mission, the spacecraft would then examine one or more additional objects in the Kuiper Belt, the region of ancient, icy, rocky bodies (including Pluto) far beyond Neptune?s orbit.

“The United States of America has just made history by launching the first spacecraft to explore Pluto and the Kuiper Belt beyond,” says Dr. Alan Stern, New Horizons principal investigator, from Southwest Research Institute in Boulder, Colo. No other nation has this capability. This is the kind of exploration that forefathers like Lewis and Clark, 200 years ago this year, made a trademark of our nation.”

Over the next several weeks, mission operators at APL will place the spacecraft in flight mode, check out its critical operating systems and perform small propulsive maneuvers to refine its path toward Jupiter. Following that, among other operations, the team will begin checking and commissioning most of the seven science instruments.

“This is the gateway to a long, exciting journey,” says Glen Fountain, New Horizons project manager from APL. “The team has worked hard for the past four years to get the spacecraft ready for the voyage to Pluto and beyond, to places we’ve never seen up close. This is a once-in-a-lifetime opportunity, in the tradition of the Mariner, Pioneer, and Voyager missions to set out for first looks in our solar system.”

After the Jupiter encounter ? during which New Horizons will train its science instruments on the large planet and its moons ?? the spacecraft will “sleep” in electronic hibernation for much of the cruise to Pluto. Operators will turn off all but the most critical electronic systems and check in with the spacecraft once a year to check out the critical systems, calibrate the instruments and perform course corrections, if necessary.

Between the in-depth checkouts, New Horizons will send back a beacon signal each week to give operators an instant read on spacecraft health. The entire spacecraft, drawing electricity from a single radioisotope thermoelectric generator, operates on less power than a pair of 100-watt household light bulbs.

New Horizons is the first mission in NASA’s New Frontiers Program of medium-class spacecraft exploration projects. Stern leads the mission and science team as principal investigator. APL manages the mission for NASA’s Science Mission Directorate and is operating the spacecraft in flight. The mission team also includes Ball Aerospace Corporation, the Boeing Company, NASA Goddard Space Flight Center, NASA Jet Propulsion Laboratory, Stanford University, KinetX, Inc., Lockheed Martin Corporation, University of Colorado, the U.S. Department of Energy, and a number of other firms, NASA centers, and university partners.

Original Source: APL News Release

An artist’s conception of Pluto and its moon Charon. Image credit: NASA Click to enlarge
If you want to learn something about a place that’s billions of miles away, it helps to be in the right place at the right time.

Astronomers from MIT and Williams College were lucky enough to watch as Pluto’s largest moon, Charon, passed in front of a star last summer. Based on their observations of the occultation, which lasted for less than a minute, the team reports new details about the moon in the Jan. 5 issue of Nature.

A second paper from another group, led by French astronomer Bruno Sicardy, also appears in this issue of Nature.

The MIT-Williams team was able to measure Charon’s size to an unprecedented accuracy and determine that it has no significant atmosphere. The atmosphere on Pluto, on the other hand, has been very well established.

“The results provide insight into the formation and evolution of bodies in the outer solar system,” said lead author Amanda Gulbis, a postdoctoral associate in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

Specifically, the team found that Charon has a radius of 606 kilometers, “plus or minus 8 kilometers to account for local topography or possible non-sphericity in Charon’s shape,” Gulbis said. That size, combined with mass measurements from Hubble Space Telescope data, show that the moon has a density roughly one-third that of the Earth. This reflects Charon’s rocky-icy composition.

The team also found that the density of any atmosphere on the moon must be less than a millionth of that of the Earth. This argues against the theory that Pluto and Charon were formed by the cooling and condensing of the gas and dust known as the solar nebula. Instead, Charon was likely created in a celestial collision between an object and a proto-Pluto.

“Our observations show that there is no substantial atmosphere on Charon, which is consistent with an impact formation scenario,” Gulbis said. Similar theories exist about the formation of the Earth-moon system.

The success of the MIT-Williams team in observing the Charon occultation bodes well for future adaptations of the technique the researchers used.

“We are eager to use (it) to probe for atmospheres around recently discovered Kuiper Belt objects that are Pluto-sized or even larger,” said James Elliot, co-author of the Nature paper and a professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences and in the Department of Physics. Elliot has been observing stellar occultations by bodies in the solar system for more than three decades.

Jay Pasachoff, Williams College team leader and a professor in its Department of Astronomy, said, “It’s remarkable that our group could be in the right place at the right time to line up a tiny body 3 billion miles away. The successful observations are quite a reward for all of the people who helped predict the event, constructed and integrated the equipment and traveled to the telescopes.”

In addition to Elliot and Gulbis, members of the MIT team were Michael Person, Elisabeth Adams and Susan Kern, with support from undergraduate Emily Kramer. The Williams College team included Pasachoff, Bryce Babcock, Steven Souza and undergraduate Joseph Gangestad.

The work was supported by NASA.

Original Source: MIT News Release

Update: Pluto isn’t a planet. Why isn’t Pluto a planet?