Wednesday, September 29, 2010

Spring on Titan Brings Sunshine and Patchy Clouds

False-color image of cloud cover dissolving over Titan's north pole and clouds appearing in the southern mid latitudes.

September 21, 2010
The northern hemisphere of Saturn's moon Titan is set for mainly fine spring weather, with polar skies clearing since the equinox in August last year. The visual and infrared mapping spectrometer (VIMS) aboard NASA's Cassini spacecraft has been monitoring clouds on Titan regularly since the spacecraft entered orbit around Saturn in 2004. Now, a group led by Sébastien Rodriguez, a Cassini VIMS team collaborator based at Université Paris Diderot, France, has analyzed more than 2,000 VIMS images to create the first long-term study of Titan's weather using observational data that also includes the equinox. Equinox, when the sun shone directly over the equator, occurred in August 2009.

Rodriguez is presenting the results and new images at the European Planetary Science Congress in Rome on Sept. 22.

Though Titan's surface is far colder and lacks liquid water, this moon is a kind of "sister world" to Earth because it has a surface covered with organic material and an atmosphere whose chemical composition harkens back to an early Earth. Titan has a hydrological cycle similar to Earth's, though Titan's cycle depends on methane and ethane rather than water.

A season on Titan lasts about seven Earth years. Rodriguez and colleagues observed significant atmospheric changes between July 2004 (early summer in Titan's southern hemisphere) and April 2010 (the very start of northern spring). The images showed that cloud activity has recently decreased near both of Titan's poles. These regions had been heavily overcast during the late southern summer until 2008, a few months before the equinox.

Over the past six years, the scientists found that clouds clustered in three distinct latitude regions of Titan: large clouds at the north pole, patchy clouds at the south pole and a narrow belt around 40 degrees south. "However, we are now seeing evidence of a seasonal circulation turnover on Titan – the clouds at the south pole completely disappeared just before the equinox and the clouds in the north are thinning out," Rodriguez said. "This agrees with predictions from models and we are expecting to see cloud activity reverse from one hemisphere to another in the coming decade as southern winter approaches."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate, Washington, D.C. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.

Mars Rover Opportunity Approaching Possible Meteorite

NASA's Mars Exploration Rover Opportunity used its panoramic camera to capture this view of a dark rock that may be an iron meteorite. Part of the rim of Endurance Crater is on the horizon. Image Credit: NASA/JPL-Caltech/Cornell University

September 21, 2010
PASADENA, Calif. -- Images that NASA's Mars Exploration Rover Opportunity took at the end of an 81-meter (266-foot) drive on Sept. 16 reveal a dark rock about 31 meters (102 feet) away. The rover's science team has decided to go get a closer look at the toaster-sized rock and determine whether it is an iron meteorite.

"The dark color, rounded texture and the way it is perched on the surface all make it look like an iron meteorite," said science-team member Matt Golombek of NASA's Jet Propulsion Laboratory, Pasadena, Calif. Opportunity has found four iron meteorites during the rover's exploration of the Meridiani Planum region of Mars since early 2004. Examination of these rocks has provided information about the Martian atmosphere, as well as the meteorites themselves.

The newfound rock has been given the informal name "Oileán Ruaidh" (pronounced ay-lan ruah), which is the Gaelic name for an island off the coast of northwestern Ireland. The rock is about 45 centimeters (18 inches) wide from the angle at which it was first seen.

Opportunity has driven 23.3 kilometers (14.5 miles) on Mars. The drive to this rock will take the total combined distance driven by Opportunity and its twin, Spirit, to more than 31 kilometers (19.26 miles).

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover mission for the NASA Science Mission Directorate, Washington. Opportunity landed on Mars in January 2004 for what was planned as a three-month mission.

NASA Selects Investigations for First Mission to Encounter the Sun

The Solar Probe Plus spacecraft with solar panels folded into the shadows of its protective shield, gathers data on its approach to the Sun.  

September 02, 2010

PASADENA, Calif. -- NASA has begun development of a mission to visit and study the sun closer than ever before. The unprecedented project, named Solar Probe Plus, is slated to launch no later than 2018.
The small car-sized spacecraft will plunge directly into the sun's atmosphere approximately 6.4 million kilometers (four million miles) from our star's surface. It will explore a region no other spacecraft ever has encountered. NASA has selected five science investigations that will unlock the sun's biggest mysteries, including one led by a scientist from NASA's Jet Propulsion Laboratory, Pasadena, Calif.
"The experiments selected for Solar Probe Plus are specifically designed to solve two key questions of solar physics -- why is the sun's outer atmosphere so much hotter than the sun's visible surface and what propels the solar wind that affects Earth and our solar
system? " said Dick Fisher, director of NASA's Heliophysics Division in Washington. "We've been struggling with these questions for decades and this mission should finally provide those answers."
As the spacecraft approaches the sun, its revolutionary carbon-composite heat shield must withstand temperatures exceeding about 1,400 degrees Celsius (2,550 degrees Fahrenheit) and blasts of intense radiation. The spacecraft will have an up-close and personal view of the sun, enabling scientists to better understand, characterize and forecast the radiation environment for future space explorers.
NASA invited researchers in 2009 to submit science proposals. Thirteen were reviewed by a panel of NASA and outside scientists. The total dollar amount for the five selected investigations is approximately $180 million for preliminary analysis, design, development and tests.

The selected proposals are:
-- Solar Wind Electrons Alphas and Protons Investigation: principal investigator, Justin C. Kasper, Smithsonian Astrophysical Observatory in Cambridge, Mass.
This investigation will specifically count the most abundant particles in the solar wind -- electrons, protons and helium ions -- and measure their properties. The investigation also is designed to catch some of the particles in a special cup for direct analysis.

-- Wide-field Imager: principal investigator, Russell Howard, Naval Research Laboratory in Washington. This telescope will make 3-D images of the sun's corona, or atmosphere. The experiment actually will see the solar wind and provide 3-D images of clouds and shocks as they approach and pass the spacecraft. This investigation complements instruments on the spacecraft, providing direct measurements by imaging the plasma the other instruments sample.

-- Fields Experiment: principal investigator, Stuart Bale, University of California Space Sciences Laboratory in Berkeley, Calif. This investigation will make direct measurements of electric and magnetic fields, radio emissions, and shock waves that course through the
sun's atmospheric plasma. The experiment also serves as a giant dust detector, registering voltage signatures when specks of space dust hit the spacecraft's antenna.

 -- Integrated Science Investigation of the Sun: principal investigator, David McComas of the Southwest Research Institute in San Antonio. This investigation consists of two instruments that will take an inventory of elements in the sun's atmosphere using a mass 
spectrometer to weigh and sort ions in the vicinity of the spacecraft.

-- Heliospheric Origins with Solar Probe Plus: principal investigator, Marco Velli of JPL. Velli is the mission's observatory scientist, responsible for serving as a senior scientist on the science working group. He will provide an independent assessment of scientific performance and act as a community advocate for the mission.

"This project allows humanity's ingenuity to go where no spacecraft has ever gone before," said Lika Guhathakurta, Solar Probe Plus program scientist at NASA Headquarters, in Washington. "For the very first time, we'll be able to touch, taste and smell our sun."

The Solar Probe Plus mission is part of NASA's Living with a Star Program. The program is designed to understand aspects of the sun and Earth's space environment that affect life and society. The program is managed by NASA'S Goddard Space Flight Center in Greenbelt, Md., with oversight from NASA's Science Mission Directorate's Heliophysics Division. The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., is the prime contractor for the spacecraft.

Amateur Astronomers are First to Detect Objects Impacting Jupiter

Caught in the Act: Fireballs Light up Jupiter 

A fleeting bright dot on each of these images of Jupiter marks a small comet or asteroid burning up in the atmosphere. The image on the left was taken on June 3, 2010, by amateur astronomer Anthony Wesley, who was visiting a friend in Broken Hill, Australia, when he obtained the image with a 37-centimeter (14.5-inch) telescope.

September 09, 2010
Amateur astronomers working with professional astronomers have spotted two fireballs lighting up Jupiter's atmosphere this summer, marking the first time Earth-based telescopes have captured relatively small objects burning up in the atmosphere of the giant planet. The two fireballs - which produced bright freckles on Jupiter that were visible through backyard telescopes - occurred on June 3, 2010, and August 20, 2010, respectively.

A new paper that includes both pros and amateurs, led by Ricardo Hueso of the Universidad del País Vasco, Bilbao, Spain, appears today in the Astrophysical Journal Letters. In the paper, astronomers estimate the object that caused the June 3 fireball was 8 to 13 meters (30 to 40 feet) in diameter. The object is comparable in size to the asteroid 2010 RF12 that flew by Earth on Wednesday, Sept. 8, and slightly larger than the asteroid 2008 TC3, which burned up above Sudan two years ago.

An impact of this kind on Earth would not be expected to cause damage on the ground. The energy released by the June 3 fireball as it collided with Jupiter's atmosphere was five to 10 times less than the 1908 Tunguska event on Earth, which knocked over tens of millions of trees in a remote part of Russia. Analysis is continuing on the Aug. 20 fireball, but scientists said it was comparable to the June 3 object.

"Jupiter is a big gravitational vacuum cleaner," said Glenn Orton, a co-author on the paper and an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It is clear now that relatively small objects, remnants of the formation of the solar system 4.5 billion years ago, still hit Jupiter frequently. Scientists are trying to figure out just how frequently."

Orton and colleagues said this kind of discovery couldn't have been made without amateur astronomers around the world, whose observations of Jupiter provide a near round-the-clock surveillance that would be impossible to do with the long lines of scientists waiting to use the large telescopes. Amateur astronomers, for example, were the first to see the dark spot that appeared on Jupiter in July 2009 as the result of an impact. Professional astronomers are still analyzing that impact.

Anthony Wesley, an amateur astronomer from Murrumbateman, Australia, who was also the first to take a picture of that dark spot on Jupiter in July 2009, was the first to see the tiny flash on June 3. Amateur astronomers had their telescopes trained on Jupiter that day because they were in the middle of "Jupiter season," when the planet is high in the sky and at its largest size, as seen by backyard telescopes.

Wesley was visiting an amateur astronomer friend about 1,000 kilometers (600 miles) away in Broken Hill, and he set a digital video camera to record images from his telescope at about 60 frames per second. He was watching the live video on a computer screen at his friend's house when he saw a two-and-a-half-second-long flash of light near the limb of the planet.

"It was clear to me straight away it had to be an event on Jupiter," he said. "I'm used to seeing other momentary flashes in the camera from cosmic ray impacts, but this was different. Cosmic ray strikes last only for one frame of video, whereas this flash gradually brightened and then faded over 133 frames."

Wesley sent a message out on his e-mail list of amateur and professional astronomers, which included Orton. After receiving Wesley's e-mail, Christopher Go of Cebu, Philippines -- who like Wesley, is an amateur astronomer -- checked his own recordings and confirmed that he had seen a flash, too.

Before Wesley's work, scientists didn't know these small-size impacts could be observed, Hueso explained. "The discovery of optical flashes produced by objects of this size helps scientists understand how many of these objects are out there and the role they played in the formation of our solar system," Hueso said.

For three days afterward, Hueso and colleagues looked for signs of the impact in high-resolution images from larger telescopes: NASA's Hubble Space Telescope, Gemini Observatory telescopes in Hawaii and Chile, the Keck telescope in Hawaii, the NASA Infrared Telescope Facility in Hawaii and the European Southern Observatory's Very Large Telescope in Chile. Scientists analyzed the images for thermal disruptions and chemical signatures seen in previous images of Jupiter impacts. In this case, they saw no signs of debris, which allowed them to limit the size of the impactor.

Based on all these images, and particularly those obtained by Wesley and Go, the astronomers were able to confirm the flash came from some kind of object – probably a small comet or asteroid – that burned up in Jupiter's atmosphere. The impactor likely had a mass of about 500 to 2,000 metric tons (1 million to 4 million pounds), probably about 100,000 times less massive than the object in July 2009.

Calculations also estimated this June 3 impact released about 1 to 4 quadrillion joules (300 million to 1 billion kilowatt-hours) of energy. The second fireball, on Aug. 20, was detected by the amateur Japanese astronomer Masayuki Tachikawa and later confirmed by Aoki Kazuo and Masayuki Ishimaru. It flashed for about 1.5 seconds. The Keck telescope, observing less than a day later, also found no subsequent debris remnants. Scientists are still analyzing this second flash.

Although collisions of this size had never before been detected on Jupiter, some previous models predicted around one collision of this kind a year. Another predicted up to 100 such collisions. Scientists now believe the frequency must be closer to the high end of the scale.

"It is interesting to note that whereas Earth gets smacked by a 10-meter-sized object about every 10 years on average, it looks as though Jupiter gets hit with the same-sized object a few times each month," said Don Yeomans, manager of the Near-Earth Object Program Office at JPL, who was not involved in the paper. "The Jupiter impact rate is still being refined and studies like this one help to do just that."