'Zombie' Planet's Rogue Orbit Around Star Shocks Scientists

The unbalanced orbit of a so-called "zombie planet" in a dusty star system has astronomers struggling to explain the exoplanet's behavior.

New observations of the planet Fomalhaut b by the Hubble Space Telescope revealed the oddball orbit, which has wild extremes between its closest and farthest points from the parent star and appears to cross through a vast minefield of dusty debris. 

"We are shocked. This is not what we expected," said study leader Paul Kalas, an astronomer with the University of California at Berkeley and the SETI Institute in Mountain View, Calif., in a statement Tuesday (Jan. 8).

'Zombie planet' gets weirder

Fomalhaut b is a giant alien planet that is nearly three times the mass of Jupiter. It was the first alien planet ever directly imaged in visible light. The planet orbits the dust-shrouded star Fomalhaut and is located about 25 light-years away in the constellation Piscis Austrinus. 

In October, scientists dubbed the world a "zombie planet" because it appeared to rise from the academic grave. After first being discovered in 2008, subsequent studies suggested the planet was nothing more than a huge dust cloud. In 2012, astronomers resurrected Fomalhaut b's planet status when new observations proved there was a planetary object embedded in a free-floating dust cloud. [Gallery: The Strangest Alien Planets]

The latest observations of the odd planetary system revealed that the dusty debris disk surrounding the star Fomalhaut is much wider than previously thought. The debris belt spans a vast region of space between 14 billion and 20 billion miles (22.5 billion to 32.1 billion kilometers) around the star.

Stranger still: The planet Fomalhaut b appears to approach with 4.6 billion miles (7.4 billion km) of its star at the closest point in its orbit, then swing way out to a point about 27 billion miles (43.4 billion km) away at the farthest point. Scientists call the extremes of such a planet’s path a highly eccentric orbit.

Fomalhaut b's path, scientists say, sends the planet crashing through the surrounding debris disk during its 2,000-year orbit around its parent star. The research was unveiled Tuesday at the 221st meeting of the American Astronomical Society in Long Beach, Calif.

A hidden planet around Fomalhaut?

Among the several theories to explain Fomalhaut b's extreme orbit is the possibility that the exoplanet had an encounter with another planet, a yet-to-be discovered neighbor. The cosmic close encounter could have gravitationally ejected Fomalhaut b into its current orbit, scientists said.

"Hot Jupiters get tossed through scattering events, where one planet goes in and one gets thrown out," study co-investigator Mark Clampin, of NASA's Goddard Space Flight Center in Greenbelt, Md., said in a statement.  "This could be the planet that gets thrown out."

Hubble telescope images revealed an apparent gap in the dust and ice debris around Fomalhaut, a region that could have been swept clean by the presence of the undetected planet, researchers said.

Another theory suggests that Fomalhaut b could have once had a small dwarf planet as a neighbor, but that the giant planet obliterated the smaller world in a catastrophic collision. Such a crash could explain why the star Fomalhaut has a narrow outer debris disk that is less than 10,000 years old, scientists said.

Does Fomalhaut b have rings?

Another tantalizing theory suggests Fomalhaut b may have Saturn-like rings and be destined for a spectacular crash through the debris disk around the star Fomalhaut in the year 2032. [Photos of Saturn’s Glorious Rings]

A set of rings or a nearby shroud of dust and ice could explain why Fomalhaut b appears so bright in visible light images, but is relatively dim in infrared light, according to Kalas. The rings or dust around the planet would reflect starlight, making the planet bright. A dust cloud could be created impacts on moons around Fomalhaut b, if they exist, researchers said.

In 2032, astronomers expect to solve one riddle that has perplexed scientists since Fomalhaut b's discovery: Is the exoplanet in the plane of the debris disk around its star, or not?

If the planet is on the same plane as the debris disk, than it will be bombarded by dust and ice in 2032 when it crosses through the disk during the outbound leg of its orbit, researchers said. That would make the planet increase its brightness in infrared light, they added. Impacts from the debris could create a celestial light show on the planet similar to that seen on Jupiter when the comet Shoemaker-Levy 9 battered the gas giant in 1994.

If Fomalhaut b is not in the same plane as the debris disk, then it should gradually get dimmer as it gets farther and farther from its parent star, researchers said. One way or another, the clues should come out starting in 2032, scientists said.

Hubble telescope officials said astronomers plan to continue to monitor the Fomalhaut star system over the next few years and decades to see how the star system changes over time.

You can follow SPACE.com Managing Editor Tariq Malik on Twitter @tariqjmalik. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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Moons Around Asteroid Reveal a Giant Rubble Pile (SPACE.com)

Nola Taylor Redd, SPACE.com Contributor
Space.com Nola Taylor Redd, Space.com Contributor
space.com – 1 hr 20 mins ago

Like the ancient Egyptian queen it was named for, the asteroid Kleopatra has birthed twins — a pair of moons that have helped scientists learn that the huge space rock is a rubble pile rather than a chunk of solid rock.

These two moons, named Alexhelios and Cleoselene after the twin children of the queen, were discovered in 2008. Now, astronomers studying their orbits have deduced that their parent asteroid is a jumble of loosely held rocks.

"That's the point of looking for triple and binary asteroids," study co-author Franck Marchis of the University of California, Berkeley told SPACE.com. "They're the only ones that allow us to measure the mass of the system." [See asteroid Kleopatra and its rocky moons]

Studying the asteroid system

Since the researchers knew Kleopatra's orbit, they were able to use data from various telescopes — including several operated by amateur astronomers — to observe Kleopatra as she passed between Earth and various bright stars.

They also used measurements from as far back as 1980 to examine other, similar passes. For each transit, they timed how long the star "winked" out of view from various positions on the planet. [Photos: Asteroids in Deep Space]

Because each location views the asteroid differently, combining these observations allowed the team to calculate the space rock's size and shape, as well as to view the moons and measure their orbit.

Having determined the orbits of Kleopatra's satellites, the team, lead by primary author Pascal Descamps of the Institut de Mecanique Celeste et de Calculs des Ephemerides (IMCCE) of the Observatoire de Paris, then was able to calculate the mass of the system as a whole.

With mass and size in hand, figuring out the asteroid's density was a breeze. The researchers concluded that the asteroid was not a solid rock.

"Our observations of the orbits of the two satellites of 216 Kleopatra imply that this large metallic asteroid is a rubble pile, which is a surprise," Marchis said in a statement.

The team reported its results in the February issue of the journal Icarus.

Big asteroid surprise

There are a number of smaller asteroids throughout the solar system that are loose, gravitationally bound piles of rock rather than solid objects.

But to find one in such a large system is surprising. At about 135 miles (217 km) in length, Kleopatra is among the largest of these rubble pile asteroids discovered over the past few years, topped only by 174-mile (280 km) 87 Sylvia.

"You expect something (this size) to be less porous," Marchis told SPACE.com.

In fact, given the density of its likely primary iron components, Kleopatra is between 30 and 50 percent empty space.

The rubble pile structure of the asteroid provides clues to its formation, as well as that of its satellites, researchers said. The collision of two larger, rocky asteroids likely resulted in the destruction of one, and the resulting rubble was held together by gravity.

As the pile continued to spin, it slowly shed mass, including its two moons. The outermost moon, Alexhelios, likely spiraled out around 100 million years ago, while the inner moon, Cleoselene, began its journey within the last 10 million years.

Kleopatra was discovered in 1880. Astronomers used stellar transits to determine it was elongated, but it wasn't until 2000 that it was revealed to be shaped more like a dog bone than a cigar. Descamps' team wanted to study whether the bulges at the end were connected to the body of the asteroid or were separate pieces entirely.

The team continues to study other binary or triple asteroid systems, but the tools that allow them to do so are limited.

"The only telescope in the world that can detect these (types of systems) is the Keck, because it has the largest aperture and the best AO (adaptive optic) system," Marchis said.  

However, thousands of astronomers vie for the use of the largest optical and infrared telescope. Marchis expressed his hope that more telescopes like the 33-foot (10-meter) giants in Hawaii will be built, allowing more research to be done.

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