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A second minor planet may possess Saturn-like rings

Researchers detect features around Chiron that may signal rings, jets, or a shell of dust.

By Jennifer Chu


CAMBRIDGE, Mass. – There are only five bodies in our solar system that are known to bear rings. The most obvious is the planet Saturn; to a lesser extent, rings of gas and dust also encircle Jupiter, Uranus, and Neptune. The fifth member of this haloed group is Chariklo, one of a class of minor planets called centaurs: small, rocky bodies that possess qualities of both asteroids and comets.

Scientists only recently detected Chariklo’s ring system — a surprising finding, as it had been thought that centaurs are relatively dormant. Now scientists at MIT and elsewhere have detected a possible ring system around a second centaur, Chiron.

In November 2011, the group observed a stellar occultation in which Chiron passed in front of a bright star, briefly blocking its light. The researchers analyzed the star’s light emissions, and the momentary shadow created by Chiron, and identified optical features that suggest the centaur may possess a circulating disk of debris. The team believes the features may signify a ring system, a circular shell of gas and dust, or symmetric jets of material shooting out from the centaur’s surface.

“It’s interesting, because Chiron is a centaur — part of that middle section of the solar system, between Jupiter and Pluto, where we originally weren’t thinking things would be active, but it’s turning out things are quite active,” says Amanda Bosh, a lecturer in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

Bosh and her colleagues at MIT — Jessica Ruprecht, Michael Person, and Amanda Gulbis — have published their results in the journal Icarus.

Catching a shadow

Chiron, discovered in 1977, was the first planetary body categorized as a centaur, after the mythological Greek creature — a hybrid of man and beast. Like their mythological counterparts, centaurs are hybrids, embodying traits of both asteroids and comets. Today, scientists estimate there are more than 44,000 centaurs in the solar system, concentrated mainly in a band between the orbits of Jupiter and Pluto.

While most centaurs are thought to be dormant, scientists have seen glimmers of activity from Chiron. Starting in the late 1980s, astronomers observed patterns of brightening from the centaur, as well as activity similar to that of a streaking comet.

In 1993 and 1994, James Elliot, then a professor of planetary astronomy and physics at MIT, observed a stellar occultation of Chiron and made the first estimates of its size. Elliot also observed features in the optical data that looked like jets of water and dust spewing from the centaur’s surface.

Now MIT researchers — some of them former members of Elliot’s group — have obtained more precise observations of Chiron, using two large telescopes in Hawaii: NASA’s Infrared Telescope Facility, on Mauna Kea, and the Las Cumbres Observatory Global Telescope Network, at Haleakala.

In 2010, the team started to chart the orbits of Chiron and nearby stars in order to pinpoint exactly when the centaur might pass across a star bright enough to detect. The researchers determined that such a stellar occultation would occur on Nov. 29, 2011, and reserved time on the two large telescopes in hopes of catching Chiron’s shadow.

“There’s an aspect of serendipity to these observations,” Bosh says. “We need a certain amount of luck, waiting for Chiron to pass in front of a star that is bright enough. Chiron itself is small enough that the event is very short; if you blink, you might miss it.”

The team observed the stellar occultation remotely, from MIT’s Building 54. The entire event lasted just a few minutes, and the telescopes recorded the fading light as Chiron cast its shadow over the telescopes.

Rings around a theory

The group analyzed the resulting light, and detected something unexpected. A simple body, with no surrounding material, would create a straightforward pattern, blocking the star’s light entirely. But the researchers observed symmetrical, sharp features near the start and end of the stellar occultation — a sign that material such as dust might be blocking a fraction of the starlight.

The researchers observed two such features, each about 300 kilometers from the center of the centaur. Judging from the optical data, the features are 3 and 7 kilometers wide, respectively.  The features are similar to what Elliot observed in the 1990s.

In light of these new observations, the researchers say that Chiron may still possess symmetrical jets of gas and dust, as Elliot first proposed. However, other interpretations may be equally valid, including the “intriguing possibility,” Bosh says, of a shell or ring of gas and dust.

Ruprecht, who is a researcher at MIT’s Lincoln Laboratory, says it is possible to imagine a scenario in which centaurs may form rings: For example, when a body breaks up, the resulting debris can be captured gravitationally around another body, such as Chiron. Rings can also be leftover material from the formation of Chiron itself.

“Another possibility involves the history of Chiron’s distance from the sun,” Ruprecht says. “Centaurs may have started further out in the solar system and, through gravitational interactions with giant planets, have had their orbits perturbed closer in to the sun. The frozen material that would have been stable out past Pluto is becoming less stable closer in, and can turn into gases that spray dust and material off the surface of a body. ”

An independent group has since combined the MIT group’s occultation data with other light data, and has concluded that the features around Chiron most likely represent a ring system. However, Ruprecht says that researchers will have to observe more stellar occultations of Chiron to truly determine which interpretation — rings, shell, or jets — is the correct one.

“If we want to make a strong case for rings around Chiron, we’ll need observations by multiple observers, distributed over a few hundred kilometers, so that we can map the ring geometry,” Ruprecht says. “But that alone doesn’t tell us if the rings are a temporary feature of Chiron, or a more permanent one. There’s a lot of work that needs to be done.”

Nevertheless, Bosh says the possibility of a second ringed centaur in the solar system is an enticing one.

“Until Chariklo’s rings were found, it was commonly believed that these smaller bodies don’t have ring systems,” Bosh says. “If Chiron has a ring system, it will show it’s more common than previously thought.”

This research was funded in part by NASA and the National Research Foundation of South Africa.

Source: MIT News Office

Timeline of the approach and departure phases — surrounding close approach on July 14, 2015 — of the New Horizons Pluto encounter.
Image Credit: NASA/JHU APL/SwRI

NASA’s New Horizons Spacecraft Begins First Stages of Pluto Encounter

NASA’s New Horizons spacecraft recently began its long-awaited, historic encounter with Pluto. The spacecraft is entering the first of several approach phases that culminate July 14 with the first close-up flyby of the dwarf planet, 4.67 billion miles (7.5 billion kilometers) from Earth.

“NASA first mission to distant Pluto will also be humankind’s first close up view of this cold, unexplored world in our solar system,” said Jim Green, director of NASA’s Planetary Science Division at the agency’s Headquarters in Washington. “The New Horizons team worked very hard to prepare for this first phase, and they did it flawlessly.”

The fastest spacecraft when it was launched, New Horizons lifted off in January 2006. It awoke from its final hibernation period last month after a voyage of more than 3 billion miles, and will soon pass close to Pluto, inside the orbits of its five known moons. In preparation for the close encounter, the mission’s science, engineering and spacecraft operations teams configured the piano-sized probe for distant observations of the Pluto system that start Sunday, Jan. 25 with a long-range photo shoot.

 

 

Timeline of the approach and departure phases — surrounding close approach on July 14, 2015 — of the New Horizons Pluto encounter. Image Credit: NASA/JHU APL/SwRI
Timeline of the approach and departure phases — surrounding close approach on July 14, 2015 — of the New Horizons Pluto encounter.
Image Credit: NASA/JHU APL/SwRI

The images captured by New Horizons’ telescopic Long-Range Reconnaissance Imager (LORRI) will give mission scientists a continually improving look at the dynamics of Pluto’s moons. The images also will play a critical role in navigating the spacecraft as it covers the remaining 135 million miles (220 million kilometers) to Pluto.

“We’ve completed the longest journey any spacecraft has flown from Earth to reach its primary target, and we are ready to begin exploring,” said Alan Stern, New Horizons principal investigator from Southwest Research Institute in Boulder, Colorado.

LORRI will take hundreds of pictures of Pluto over the next few months to refine current estimates of the distance between the spacecraft and the dwarf planet. Though the Pluto system will resemble little more than bright dots in the camera’s view until May, mission navigators will use the data to design course-correction maneuvers to aim the spacecraft toward its target point this summer. The first such maneuver could occur as early as March.

“We need to refine our knowledge of where Pluto will be when New Horizons flies past it,” said Mark Holdridge, New Horizons encounter mission manager at Johns Hopkins University’s Applied Physics Laboratory (APL) in Laurel, Maryland. “The flyby timing also has to be exact, because the computer commands that will orient the spacecraft and point the science instruments are based on precisely knowing the time we pass Pluto – which these images will help us determine.”

The “optical navigation” campaign that begins this month marks the first time pictures from New Horizons will be used to help pinpoint Pluto’s location.

Throughout the first approach phase, which runs until spring, New Horizons will conduct a significant amount of additional science. Spacecraft instruments will gather continuous data on the interplanetary environment where the planetary system orbits, including measurements of the high-energy particles streaming from the sun and dust-particle concentrations in the inner reaches of the Kuiper Belt. In addition to Pluto, this area, the unexplored outer region of the solar system, potentially includes thousands of similar icy, rocky small planets.

More intensive studies of Pluto begin in the spring, when the cameras and spectrometers aboard New Horizons will be able to provide image resolutions higher than the most powerful telescopes on Earth. Eventually, the spacecraft will obtain images good enough to map Pluto and its moons more accurately than achieved by previous planetary reconnaissance missions.

APL manages the New Horizons mission for NASA’s Science Mission Directorate in Washington. Alan Stern, of the Southwest Research Institute (SwRI), headquartered in San Antonio, is the principal investigator and leads the mission. SwRI leads the science team, payload operations, and encounter science planning. New Horizons is part of the New Frontiers Program managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama. APL designed, built and operates the spacecraft.

For more information about the New Horizons mission, visit:

www.nasa.gov/newhorizons

Time to Wake Up: Artist’s impression of NASA’s New Horizons spacecraft, currently en route to Pluto. Operators at the Johns Hopkins University Applied Physics Laboratory are preparing to “wake” the spacecraft from electronic hibernation on Dec. 6, when the probe will be more than 2.9 billion miles from Earth. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

New Horizons Set to Wake Up for Pluto Encounter

NASA’s New Horizons spacecraft comes out of hibernation for the last time on Dec. 6. Between now and then, while the Pluto-bound probe enjoys three more weeks of electronic slumber, work on Earth is well under way to prepare the spacecraft for a six-month encounter with the dwarf planet that begins in January.

“New Horizons is healthy and cruising quietly through deep space – nearly three billion miles from home – but its rest is nearly over,” says Alice Bowman, New Horizons mission operations manager at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. “It’s time for New Horizons to wake up, get to work, and start making history.”

Since launching in January 2006, New Horizons has spent 1,873 days in hibernation – about two-thirds of its flight time – spread over 18 separate hibernation periods from mid-2007 to late 2014 that ranged from 36 days to 202 days long.

In hibernation mode much of the spacecraft is unpowered; the onboard flight computer monitors system health and broadcasts a weekly beacon-status tone back to Earth. On average, operators woke New Horizons just over twice each year to check out critical systems, calibrate instruments, gather science data, rehearse Pluto-encounter activities and perform course corrections when necessary.

New Horizons pioneered routine cruise-flight hibernation for NASA. Not only has hibernation reduced wear and tear on the spacecraft’s electronics, it lowered operations costs and freed up NASA Deep Space Network tracking and communication resources for other missions.

Ready to Go

Next month’s wake-up call was preprogrammed into New Horizons’ on-board computer in August, commanding it come out of hibernation at 3 p.m. EST on Dec. 6. About 90 minutes later New Horizons will transmit word to Earth that it’s in “active” mode; those signals, even traveling at light speed, will need four hours and 25 minutes to reach home. Confirmation should reach the mission operations team at APL around 9:30 p.m. EST. At the time New Horizons will be more than 2.9 billion miles from Earth, and just 162 million miles – less than twice the distance between Earth and the sun – from Pluto.

Time to Wake Up: Artist’s impression of NASA’s New Horizons spacecraft, currently en route to Pluto. Operators at the Johns Hopkins University Applied Physics Laboratory are preparing to “wake” the spacecraft from electronic hibernation on Dec. 6, when the probe will be more than 2.9 billion miles from Earth. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Time to Wake Up: Artist’s impression of NASA’s New Horizons spacecraft, currently en route to Pluto. Operators at the Johns Hopkins University Applied Physics Laboratory are preparing to “wake” the spacecraft from electronic hibernation on Dec. 6, when the probe will be more than 2.9 billion miles from Earth. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

After several days of collecting navigation-tracking data, downloading and analyzing the cruise science and spacecraft housekeeping data stored on New Horizons’ digital recorders, the mission team will begin activities that include conducting final tests on the spacecraft’s science instruments and operating systems, and building and testing the computer-command sequences that will guide New Horizons through its flight to and reconnaissance of the Pluto system. Tops on the mission’s science list are characterizing the global geology and topography of Pluto and its large moon Charon, mapping their surface compositions and temperatures, examining Pluto’s atmospheric composition and structure, studying Pluto’s smaller moons and searching for new moons and rings.

New Horizons’ seven-instrument science payload, developed under direction of Southwest Research Institute, includes advanced imaging infrared and ultraviolet spectrometers, a compact multicolor camera, a high-resolution telescopic camera, two powerful particle spectrometers, a space-dust detector (designed and built by students at the University of Colorado) and two radio science experiments. The entire spacecraft, drawing electricity from a single radioisotope thermoelectric generator, operates on less power than a pair of 100-watt light bulbs.

Distant observations of the Pluto system begin Jan. 15 and will continue until late July 2015; closest approach to Pluto is July 14.

“We’ve worked years to prepare for this moment,” says Mark Holdridge, New Horizons encounter mission manager at APL. “New Horizons might have spent most of its cruise time across nearly three billion miles of space sleeping, but our team has done anything but, conducting a flawless flight past Jupiter just a year after launch, putting the spacecraft through annual workouts, plotting out each step of the Pluto flyby and even practicing the entire Pluto encounter on the spacecraft. We are ready to go.”

“The final hibernation wake up Dec. 6 signifies the end of an historic cruise across the entirety of our planetary system,” added New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute. “We are almost on Pluto’s doorstep!”

The Johns Hopkins Applied Physics Laboratory manages the New Horizons mission for NASA’s Science Mission Directorate. Alan Stern, of the Southwest Research Institute (SwRI) is the principal investigator and leads the mission; SwRI leads the science team, payload operations, and encounter science planning. New Horizons is part of the New Frontiers Program managed by NASA’s Marshall Space Flight Center in Huntsville, Ala. APL designed, built and operates the New Horizons spacecraft.

Source: JHUAPL