The tracks are pale brown trails where green trees and plants have been uprooted, leaving disturbed ground. Though faint, the center track runs from southwest of Tuscaloosa, through the gray city, and extends northeast towards Birmingham. Two other tracks run parallel to the center track. The northernmost track is in an area where the National Weather Service reported a tornado, but no tornado was reported in the vicinity of the more visible southern track. In the southern region, strong winds were reported.

The tornadoes were part of a larger weather pattern that produced more than 150 tornadoes across six states, said the National Weather Service. The death toll had nearly reached 300 on April 29, making the outbreak the deadliest in the United States since 1974.

For more information visit http://www.nasa.gov/topics/earth/features/severe-storms-20110429.html

"Collisions between asteroids create rock fragments, from fine dust to huge boulders, that impact planets and their moons," said Dennis Bodewits, an astronomer at the University of Maryland in College Park and lead author of the Swift study. "Yet this is the first time we've been able to catch one just weeks after the smash-up, long before the evidence fades away."

Asteroids are rocky fragments thought to be debris from the formation and evolution of the solar system approximately 4.6 billion years ago. Millions of them orbit the sun between Mars and Jupiter in the main asteroid belt. Scheila is approximately 70 miles across and orbits the sun every five years.

"The Hubble data are most simply explained by the impact, at 11,000 mph, of a previously unknown asteroid about 100 feet in diameter," said Hubble team leader David Jewitt at the University of California in Los Angeles. Hubble did not see any discrete collision fragments, unlike its 2009 observations of P/2010 A2, the first identified asteroid collision.

The studies will appear in the May 20 edition of The Astrophysical Journal Letters and are available online.

Astronomers have known for decades that comets contain icy material that erupts when warmed by the sun. They regarded asteroids as inactive rocks whose destinies, surfaces, shapes and sizes were determined by mutual impacts. However, this simple picture has grown more complex over the past few years.

During certain parts of their orbits, some objects, once categorized as asteroids, clearly develop comet-like features that can last for many months. Others display much shorter outbursts. Icy materials may be occasionally exposed, either by internal geological processes or by an external one, such as an impact.

On Dec. 11, 2010, images from the University of Arizona's Catalina Sky Survey, a project of NASA's Near Earth Object Observations Program, revealed Scheila to be twice as bright as expected and immersed in a faint comet-like glow. Looking through the survey's archived images, astronomers inferred the outburst began between Nov. 11 and Dec. 3.

Three days after the outburst was announced, Swift's Ultraviolet/Optical Telescope (UVOT) captured multiple images and a spectrum of the asteroid. Ultraviolet sunlight breaks up the gas molecules surrounding comets; water, for example, is transformed into hydroxyl and hydrogen. But none of the emissions most commonly identified in comets, such as hydroxyl or cyanogen, show up in the UVOT spectrum. The absence of gas around Scheila led the Swift team to reject scenarios where exposed ice accounted for the activity.

Images show the asteroid was flanked in the north by a bright dust plume and in the south by a fainter one. The dual plumes formed as small dust particles excavated by the impact were pushed away from the asteroid by sunlight. Hubble observed the asteroid's fading dust cloud on Dec. 27, 2010, and Jan. 4, 2011.

The two teams found the observations were best explained by a collision with a small asteroid impacting Scheila's surface at an angle of less than 30 degrees, leaving a crater 1,000 feet across. Laboratory experiments show a more direct strike probably wouldn't have produced two distinct dust plumes. The researchers estimated the crash ejected more than 660,000 tons of dust -- equivalent to nearly twice the mass of the Empire State Building.

"The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1 during NASA's UMD-led Deep Impact mission," said co-author Michael Kelley, also at the University of Maryland. "Collisions allow us to peek inside comets and asteroids. Ejecta kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila's interior shows that it's entirely unlike comets."

NASA's Goddard Space Flight Center in Greenbelt, Md., manages Hubble and Swift. Hubble was built and is operated in partnership with the European Space Agency. Science operations for both missions include contributions from many national and international partners.

For more information visit http://www.nasa.gov/topics/universe/features/asteroid-collision.html

The event will be held at NASA Headquarters in Washington and will be broadcast live on NASA Television and streamed at http://www.nasa.gov . In addition, the event will be carried live on Ustream, with a live chat box available, at http://www.ustream.tv/nasajpl2 .

After 33 years in space, the spacecraft are still operating and returning data from about 16 billion kilometers (10 billion miles) away from our sun. The Voyagers also carry a collection of images and sounds from Earth as a message to possible life elsewhere in the galaxy.

The participants are:
-- Ed Stone, Voyager project scientist and professor of physics, California Institute of Technology, Pasadena, Calif.
-- Ann Druyan, creative director, Voyager Interstellar Message Project; Carl Sagan's co-author and widow
-- Suzanne Dodd, Voyager project manager, NASA’s Jet Propulsion Laboratory, Pasadena, Calif.
-- Merav Opher, Voyager guest investigator and assistant professor of astronomy, Boston University

For more information visit http://www.nasa.gov/mission_pages/voyager/voyager20110426.html

"It's inspiring to learn that STEREO, which was designed to teach us more about the Sun's influence on our solar system, is able to detect other solar systems," said STEREO project scientist Joseph Gurman at NASA's Goddard Space Flight Center in Greenbelt, Md.

Although STEREO is primarily a solar mission, the team realized that the stability of the Heliospheric Imagers (HI) aboard the twin spacecraft could be used to monitor variations in the brightness of stars.

"STEREO's Heliospheric Imagers were designed for stable, accurate measurements to allow us to subtract out the stellar background and see faint coronal mass ejections --- but that same stability allows us to make the incredibly precise measurements necessary to detect such small changes in the brightness of stars,” Gurman remarked.

According to one of the leads in this survey, STEREO's ability to sample continuously for up to 20 days, coupled with repeat viewings from the spacecraft during the year, makes it an invaluable resource for researching variable stars. Observations from the HI cameras are enabling scientists to pin down the periods of known variables with much greater accuracy.

In addition to studying variable stars, the U.K. team announced that HI measurements may be useful for exoplanet and astroseismology research. Very small changes to the brightness of stars can be detected, which could reveal the presence of transiting exoplanets, or trace a star’s internal structure by measuring their seismic activity.

Teams from the Open University, University of Central Lancashire and the Science and Technologies Facilities Council Rutherford Appleton Laboratory carried out the study and their findings were presented at the Royal Astronomical Society’s National Astronomy Meeting in Llandudno, Wales, on April 19.

STEREO is the third mission in NASA's Solar Terrestrial Probes program. The mission, launched in October 2006, has provided a unique and revolutionary view of the Sun-Earth System. The two nearly identical observatories - one ahead of Earth in its orbit, the other trailing behind - have traced the flow of energy and matter from the sun to Earth. STEREO is also key to the fleet of space weather detection satellites by providing more accurate alerts for the arrival time of Earth-directed solar ejections with its unique side-viewing perspective.

For more information visit http://www.nasa.gov/mission_pages/stereo/news/binary-stars.html