Charon Passes in Front of a Star

An artist’s conception of Pluto and its moon Charon. Image credit: NASA. Click to enlarge
On a clear summer night, the stars aligned for MIT researchers watching and waiting for one small light in the heavens to be extinguished, just briefly.

Thanks to a feat of both astronomical and terrestrial alignment, a group of scientists from MIT and Williams College succeeded in observing distant Pluto’s tiny moon, Charon, hide a star. Such an event had been seen only once before, by a single telescope 25 years ago, and then not nearly as well.

The MIT-Williams consortium spotted it with four telescopes in Chile on the night of July 10-11.

The team expects to use data from this observation to assess whether Charon has an atmosphere, to measure its radius and to determine how round it is.

The data and results from the observation will be presented at the 2005 meeting of the American Astronomical Society’s Division of Planetary Sciences meeting to be held in Cambridge, England, in September.

MIT team leader James L. Elliot headed the group at the Clay Telescope at Las Campanas Observatory in Chile.

“We have been waiting many years for this opportunity. Watching Charon approach the star and then snuff it out was spectacular,” said Elliot, a professor in the Department of Earth, Atmospheric and Planetary Science and the Department of Physics at MIT in Cambridge, Mass.

Jay M. Pasachoff, team leader from Williams College in Williamstown, Mass., and a professor in that school’s Department of Astronomy, said, “It’s amazing that people in our group could get in the right place at the right time to line up a tiny body 4 billion miles away. It’s quite a reward for so many people who worked so hard to arrange and integrate the equipment and to get the observations.”

With the Clay Telescope’s 6.5-meter mirror (more than 21 feet across, the size of a large room) the researchers were able to observe changes throughout the event, which lasted less than a minute. While their electronic cameras sensitively recorded data, the light of the faint star was seen to dim and then, some seconds later, brighten. This kind of disappearance of a celestial body behind a closer, apparently larger one is known as an occultation.

Studying how the light dimmed and brightened will let the MIT-Williams consortium look for signs that Charon has an atmosphere. It has very little mass and thus little gravity to hold in an atmosphere, but it is so cold (being some 40 times farther from the sun than the Earth) that some gases could be held in place by the small amount of Charon’s gravity.

Other telescopes around Chile used by the MIT-Williams consortium included the 8-meter (more than 26 feet across) Gemini South on Cerro Pachon, the 2.5-meter (more than 8 feet across) DuPont Telescope at Las Campanas Observatory and the 0.8-meter (almost 3 feet across) telescope at the Cerro Armazones Observatory of Chile’s Catholic University of the North near Cerro Paranal.

The team had searched for a distribution of telescopes along a north-south line in Chile since the predictions of the starlight shadow of Charon were uncertain by several hundred kilometers. Since the star that was hidden is so far away, it casts a shadow of Charon that is the same size as Charon itself, about 1,200 kilometers in diameter. To see the event, the distant star, Charon and the telescopes in Chile had to be perfectly aligned. All of these telescopes had clear views of the event.

Other MIT affiliates involved in the observation were MIT graduate students Elisabeth Adams, Michael Person and Susan Kern and postdoctoral associate Amanda Gulbis.

The images from three telescopes in Chile, including the Clay Telescope, and one in Brazil, were taken with new electronic cameras and computer control obtained by MIT and Williams with an equipment grant from NASA. The expeditions were sponsored by NASA’s Planetary Astronomy Program.

A video showing the star dimming as Charon passes in front of it and then brightening again is posted on the Web at http://occult.mit.edu/research/occultations/Charon/C313.2/C313OccMovie.html.

Teams from the Observatory of Paris at Meudon and from the Southwest Research Institute in Boulder, Colo., also observed the occultation.

Original Source: MIT News Release

New Horizons Prepares to Zoom to Pluto

Artist impression of the New Horizons spacecraft sweeping past Pluto. Image credit: JHUAPL/SwRI. Click to enlarge.

If all goes well, the first mission to the farthest known planet in our Solar System will launch in early 2006, and give us our first detailed views of Pluto, its moon Charon, and the Kuiper Belt Region, while completing NASA’s reconnaissance of all the planets in our Solar System.

“We’re going to a planet that we’ve never been to before,” said Dr. Alan Stern, Principal Investigator for the New Horizons mission to Pluto. “This is like something out of a NASA storybook, like in the 60’s and 70’s with all the new missions that were happening then. But this is exploration for a new century; it’s something bold and different. Being the first mission to the last planet really ‘revs’ me. There’s something special about going to a new frontier, about

Pluto is so far away (5 billion km or 3.1 billion miles when New Horizons reaches it) that no telescope, not even the Hubble Space Telescope, has been able to provide a good image of the planet, and so Pluto is a real mystery world. The existence of Pluto has only been known for 75 years, and the debate continues about its classification as a planet, although most planetary scientists classify it in the new class of planets called Ice Dwarfs. Pluto is a large, ice-rock world, born in the Kuiper Belt area of our solar system. Its moon, Charon, is large enough that some astronomers refer to the two as a binary planet. Pluto undergoes seasonal change and has an elongated and enormous 248-year orbit which causes the planet’s atmosphere to cyclically dissipate and freeze out, but later be replenished when the planet returns closer to the sun.

New Horizons will provide the first close-up look at Pluto and the surrounding region. The grand piano-sized spacecraft will map and analyze the surface of Pluto and Charon, study Pluto’s escaping atmosphere, look for an atmosphere around Charon, and perform similar explorations of one or more Kuiper Belt Objects.

The spacecraft, built at the Johns Hopkins Applied Physics Laboratory, is currently being flight tested at the Goddard Space Flight Center. Dr. Stern has been planning a mission to Pluto for quite some time, surviving through the various on-again, off-again potential missions to the outer solar system.

“I’m feeling very good about the mission,” he said in an interview from his office at the Southwest Research Institute in Boulder, Colorado. “I’ve been working on this project for about 15 years, and the first 10 years we couldn’t even get it out of the starting blocks. Now we’ve not only managed to get it funded, but we have built it and we are really looking forward to flying the mission soon if all continues to go well.”

Of the hurdles remaining to be cleared before launch, one looms rather large. New Horizons’ systems are powered by a Radioisotope Thermoelectric Generator (RTG), where heat released from the decay of radioactive materials is converted into energy. This type of power system is essential for a mission going far from the Sun like New Horizons where solar power is not an option, but it has to be approved by both NASA and the White House. The 45-day public comment period ended in April 2005, so the project now awaits final, official approval. Meanwhile, the New Horizons mission teams prepare for launch.

“We still have a lot of work in front of us,” Stern said. “All this summer we’re testing and checking out the spacecraft and the components, getting all the bugs out, and making sure its launch ready, and flight ready. That will take us through September and in October we hope to bring the spacecraft to the Cape.”

The month-long launch window for New Horizons opens on January 11, 2006.

New Horizons will be the fastest spacecraft ever launched. The launch vehicle combines an Atlas V first stage, a Centaur second stage, and a STAR 48B solid rocket third stage.

“We built the smallest spacecraft we could get away with that has all the things it needs: power, communication, computers, science equipment and redundancy of all systems, and put it on the biggest possible launch vehicle,” said Stern. “That combination is ferocious in terms of the speed we reach in deep space.”

At best speed, the spacecraft will be traveling at 50 km/second (36 miles/second), or the equivalent of Mach 85.

Stern compared the Atlas rocket to other launch vehicles. “The Saturn V took the Apollo astronauts to the moon in 3 days,” he said. “Our rocket will take New Horizons past the moon in 9 hours. It took Cassini 3 years to get to Jupiter, but New Horizons will pass Jupiter in just 13 months.”

Still, it will take 9 years and 5 months to cross our huge Solar System. A gravity assist from Jupiter is essential in maintaining the 2015 arrival date. Not being able to get off the ground early in the launch window would have big consequences later on.

“We launch in January of 2006 and arrive at Pluto in July of 2015, best case scenario,” said Stern. “If we don’t launch early in the launch window, the arrival date slips because Jupiter won’t be in as good a position to give us a good gravity assist.”

New Horizons has 18 days to launch in January 2006 to attain a 2015 arrival. After that, Jupiter’s position moves so that for every 4 or 5 days delay in launch means arriving at Pluto year later. By February 14 the window closes for a 2020 arrival. New Horizons can try to launch again in early 2007, but then the best case arrival year is 2019.

New Horizons will be carrying seven science instruments:

  • Ralph: The main imager with both visible and infrared capabilities that will provide color, composition and thermal maps of Pluto, Charon, and Kuiper Belt Objects.
  • Alice: An ultraviolet spectrometer capable of analyzing Pluto’s atmospheric structure and composition.
  • REX: The Radio Science Experiment that measures atmospheric composition and surface temperature with a passive radiometer. REX also measures the masses of objects New Horizons flies by.
  • LORRI: The Long Range Reconnaissance Imager has a telescopic camera that will map Pluto?s far side and provide geologic data.
  • PEPSSI: The Pluto Energetic Particle Spectrometer Science Investigation that will measure the composition and density of the ions escaping from Pluto’s atmosphere.
  • SWAP: Solar Wind Around Pluto, which will measure the escape rate of Pluto?s atmosphere and determine how the solar wind affects Pluto.
  • SDC: The Student Dust Counter will measure the amount of space dust the spacecraft encounters on the voyage. This instrument was designed and will be operated by students at the University of Colorado in Boulder.

Stern says the first part of the flight will keep the mission teams busy, as they need to check out the entire spacecraft, and execute the Jupiter fly-by at 13 months.

“The middle years will be long and probably — and hopefully — pretty boring,” he said, but will include yearly spacecraft and instrument checkouts, trajectory corrections, instrument calibrations and rehearsals the main mission. During the last three years of the interplanetary cruise mission teams will be writing, testing and uploading the highly detailed command script for the Pluto/Charon encounter, and the mission begins in earnest approximately a year before the spacecraft arrives at Pluto, as it begins to photograph the region.

A mission to Pluto has been a long time coming, and is popular with a wide variety of people. Children seem to have an affinity for the planet with the cartoon character name, while the National Academy of Sciences ranked a mission to Pluto as the highest priority for this decade. In 2002, when it looked as though NASA would have to scrap a mission to Pluto for budgetary reasons, the Planetary Society, among others, lobbied strongly to Congress to keep the mission alive.

Stern said the mission’s website received over a million hits the first month it was active, and the hit rate hasn’t diminished. Stern writes a monthly column on the website, http://pluto.jhuapl.edu , where you can learn more details about the mission and sign-up to have your name sent to Pluto along with the spacecraft.

While Stern is understandably excited about this mission, he says that any chance to explore is a great opportunity.

“Exploration always opens our eyes,” he said. “No one expected to find river valleys on Mars, or a volcano on Io, or rivers on Titan. What do I think we’ll find at Pluto-Charon? I think we’ll find something wonderful, and we expect to be surprised.”

Pluto Mission Arrives at NASA for Testing

Artist illustration of New Horizons with Pluto and Charon. Image credit: JHUAPL/SwRI. Click to enlarge.
The first spacecraft designed to study Pluto, the last planet in our solar system, arrived at NASA?s Goddard Space Flight Center (GSFC) in Greenbelt, Md., today for a series of pre-launch checkouts.

“We are extremely proud to have the NASA’s New Horizons mission make Goddard the first stop in its journey to the last planet,” said Dr. Ed Weiler, GSFC Center Director. “The New Horizons mission to Pluto is an historic journey of exploration to unlock secrets from a mysterious planet so distant that the Sun is just a bright star in the sky.”

The spacecraft will be at Goddard for the next three months where team members will check New Horizons? balance and alignment in a series of spin tests; put it before wall-sized speakers that simulate the noisy vibrations of launch; and seal it for several weeks in a four-story thermal-vacuum chamber that duplicates the extreme cold and airless conditions of space. After departing Goddard in the Fall, the spacecraft will make its way to the Kennedy Space Center, Fla. for final launch preparations.

New Horizons is the first mission to Pluto and its moon, Charon. As part of an extended mission, the spacecraft would head deeper into the Kuiper Belt to study one or more of the icy mini worlds in that vast region. New Horizons is scheduled for launch in January 2006 from Cape Canaveral Air Force Station, Fla., aboard a Lockheed Martin Atlas V. New Horizons should begin its five-month-long flyby reconnaissance of Pluto-Charon in summer 2015.

New Horizons is carrying an extensive complement of science instruments. Goddard has a major role in the Southwest Research Institute?s Ralph instrument. Ralph’s main objectives are to obtain high resolution color and surface composition maps of the surfaces of Pluto and Charon. The instrument has two separate channels: the Multispectral Visible Imaging Camera (MVIC) and the Linear Etalon Imaging Spectral Array (LEISA). A single telescope with a 3-inch (6-centimeter) aperture collects and focuses the light used in both channels. MVIC, provided by Ball Aerospace in from Boulder Colo., operates at the visible wavelength to produce color maps. LEISA operates at infrared wavelengths. LEISA, provided by Goddard, will be used to map the distribution of frosts of methane, molecular nitrogen, carbon monoxide, and water over the surface of Pluto and the water frost distribution over the surface of Charon.

New Horizons is the first mission in NASA?s New Frontiers program of medium-class, high-priority solar system exploration projects. The spacecraft is managed by the John Hopkins University Applied Physics Laboratory in Laurel, Md. The Principal Investigator Dr. Alan Stern, is from the Southwest Research Institute, San Antonio, TX. The mission team includes Goddard Space Flight Center, APL, Ball Aerospace Corporation, the Boeing Company, the Jet Propulsion Laboratory, Pasadena, Calif. Stanford University, Calif. KinetX, Inc., Tempe, AZ, Lockheed Martin Corporation, University of Colorado at Boulder, the U.S. Department of Energy and a number of other firms, NASA centers and university partners.

For more information on the mission, visit: http://pluto.jhuapl.edu.

Original Source: NASA News Release

Update: Pluto is not a planet