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Phoenix to the pad

The Phoenix lander bound for Mars is hauled to Cape Canaveral's pad 17A on July 23 for installation atop the Delta 2 rocket that will propel the craft on its cruise from Earth to Mars.

 Part 1 | Part 2

Dawn waits for date

The Dawn spacecraft is returned to a processing facility to await a new launch date. The mission was delayed from July to September, prompting the craft's removal from the Delta rocket at pad 17B.

 Part 1 | Part 2

Spacewalk highlights

This highlights movie from the July 23 station spacewalk shows the jettisoning of a support platform and a refrigerator-size tank.

 Play

Expedition 16 crew

Members of the upcoming space station Expedition 16 crew, led by commander Peggy Whitson, hold a pre-flight news briefing.

 Play

ISS spacewalk preview

This is a preview the planned July 23 EVA by members of the space station crew to jettison two objects from the outpost and perform maintenance.

 Briefing | Animation

STS-118: The mission

Officials for Endeavour's trip to the space station present a detailed overview of the STS-118 flight and objectives.

 Briefing | Questions

STS-118: Spacewalks

Four spacewalks are planned during Endeavour's STS-118 assembly mission to the space station. Lead spacewalk officer Paul Boehm previews the EVAs.

 Full briefing
 EVA 1 summary
 EVA 2 summary
 EVA 3 summary
 EVA 4 summary

STS-118: Education

A discussion of NASA's educational initiatives and the flight of teacher Barbara Morgan, plus an interactive event with students were held in Houston.

 Briefing | Student event

Mars lander preview

A preview of NASA's Phoenix Mars lander mission and the science objectives to dig into the arctic plains of the Red Planet are presented here.

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Phoenix animation

Project officials narrate animation of Phoenix's launch from Earth, arrival at Mars, touchdown using landing rockets and the craft's robot arm and science gear in action.

 Play

Dawn launch delay

Jim Green, director of the Planetary Science Division at NASA Headquarters, explains why the agency decided to delay launch of the Dawn asteroid probe from July to September.

 Play

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Gases escaping from Jupiter's moon Io studied
BOSTON UNIVERSITY NEWS RELEASE
Posted: July 25, 2007

Boston University (BU) researchers have published the first clear evidence of how gases from volcanoes on a tiny moon of Jupiter can lead to the largest visible gas cloud in the solar system.

Jupiter, the largest planet in the solar system, has a moon named Io that is just 100 km larger in radius than Earth's Moon. According to lead researcher Michael Mendillo, professor of electrical and computer engineering and astronomy at BU, there are over 100 active volcanic sites on Io making it the most active place for volcanic activity known anywhere.

"Of the various gases that come from Io's volcanoes, sodium atoms can be detected using ground-based telescopes because the light they emit is in the visible part of the spectrum - the same familiar orange glow from sodium street lights that are in most American cities," said Mendillo. "Therefore, sodium atoms become a tracer of other elements that might be more abundant, but less easy to see."

In 1990, BU scientists discovered a large gas cloud - or nebula - of sodium atoms (Na) spanning great distances to either side of Jupiter.

"If this faint structure could be seen by the naked eye, it would be over ten times the size of the full Moon, and thus the largest permanently visible object in our solar system," Mendillo explained. "Computer models suggested the types of escape processes needed to feed this giant nebula, but actual pictures of those sources eluded observers for many years."

The research team from Boston University's College of Engineering and Center for Space Physics (CSP) solved this problem by developing a novel way to photograph these sources using a high-definition imaging (HDI) system that combines several images into one clear picture.

The new images, published in the July 19th issue of the journal Nature, reveal two distinct sources of sodium atoms escaping from Io. One is a symmetrical cloud of escaping gas produced by collisions of the streaming ions and electrons in Jupiter's so-called plasma torus. These plasma particles are trapped in Jupiter's strong magnetic field and rotate with the planet's 10-hour period, much faster than the 2-day orbital period of Io. "So, there is a continuous plasma wind hitting Io, causing sodium atoms to be sputtered from its atmosphere," Mendillo explained.

According to the scientists, this sputtering source is distinctly different from a localized source of atoms produced chemically in the wake of the streaming torus flow past Io. The images define the extent of the sputtering and stream sources for the first time.

"Since the giant sodium nebula that they create varies over periods of months to years, the source of the variability is probably not the symmetrical sputtering cloud, but the streaming-wake source that waxes and wanes with volcanic activity on Io," explained Jody Wilson, CSP senior research associate and a study co-author.

The observations were made using a 4-meter telescope operated by the U.S. Air Force on Maui, HI. To capture the faint signals from sodium atoms close to Io, the observers had to find a way to cope with the bright sunlight reflected from Io's surface, as well as from the even stronger light from nearby Jupiter. In addition, ever-present turbulence in the Earth's atmosphere causes the image of Io to jitter about randomly. Thus, any attempt to capture the faint Na light by long time-exposures would result in a highly blurred image.

"Our HDI system solved this problem in two ways. First, by taking very short exposures - 1/60th of a second - the atmosphere might be steady for that instant and thus occasional sharp images could be found; and second, by dividing the full spectrum of light from Io into a narrow wavelength range," explained CSP senior research associate Jeffrey Baumgardner, the HDI instrument designer and a co-author of the study. "That is, capturing only the color needed to see sodium above the glare of full light and then using most of the remaining light to simultaneously follow the fluctuating positions of Io."

The goal was to then reposition Io to the same place in each frame and use only the very clearest of those frames to make what Mendillo calls "the ideal time exposure, one made with the target stationary, a good spectral signal, and the best possible seeing."

The CSP observing team returned to Boston with 62,500 such images stored on a computer and Mendillo wondering how the goal would be achieved. Study co-author Sophie Laurent, a doctoral candidate at the time in Electrical and Computer Engineering, assumed responsibility for the required signal processing, with guidance from Professors Clem Karl and Janusz Konrad, signal processing experts. Dr. Laurent devised automated ways to center all of the images and then to find the highly-defined ones needed to make the best possible images.

"These images provide specific spatial scales and relative strengths of these sources that now can be put into computer models that attempt to simulate how all types of gases escape from Io to populate the vast regions of space surrounding Jupiter," Mendillo added.

This research was funded by the National Science Foundation (NSF) and the Air Force Office of Scientific Research, and the HDI instrument by the Office of Naval Research.

Founded in 1839, Boston University is an internationally recognized institution of higher education and research. With more than 30,000 students, it is the fourth largest independent university in the United States. It contains 17 colleges and schools along with a number of multi-disciplinary centers and institutes which are central to the university's research and teaching mission.