The Johns Hopkins Gazette: February 26, 2001
February 26, 2001
VOL. 30, NO. 23


FUSE Completes First Year of Observations

Scientists use satellite observatory to study nearly 700 astronomical objects

By Michael Purdy

Johns Hopkins Gazette Online Edition

The Far Ultraviolet Spectroscopic Explorer, a NASA satellite observatory operated by Johns Hopkins, sailed through the end of its first year of science observations in early December 2000.

A month later, the world got a better sense of how much FUSE had accomplished during that first year of observations.

"We were at the meeting of the American Astronomical Society in early January, and I'd given all the researchers who were making presentations based on FUSE data a FUSE banner to put up, and I'd look down the hall and see the banners everywhere," says Ken Sembach, lead science coordinator and planner for FUSE.

Scientists presented more than 40 papers based on FUSE data at the meeting, the first where the astronomy community heard results from both the FUSE team and guest investigators, astronomers from around the world selected by NASA to perform observations with FUSE.

"One of the things that was particularly astounding was the range of subjects covered," Bill Blair, chief of observatory operations, says. "Everything from planets in our solar system to quasars halfway across the universe were discussed in those papers."

At the meeting, FUSE researchers also were elated to see that a NASA planning chart showed the FUSE mission extending into 2004--two years beyond the satellite's original planned mission. Scientists had applied for the extension last summer and received favorable results from a NASA review panel.

Although Warren Moos, FUSE principal investigator and Gerhard H. Dieke Professor of Physics and Astronomy, noted that nothing can be guaranteed until the NASA long-range project plan appears with the new presidential budget, many FUSE scientists saw the chart as evidence that FUSE is likely to be in operation beyond its original three-year mission.

"FUSE is producing absolutely beautiful data, and the community has now recognized that fact and is actively participating in the Guest Observer Program," says Sembach, an associate research scientist, who notes that early problems in operation of the satellite have faded to a nearly routine level typical for any orbiting observatory.

"FUSE observed close to 700 astronomical objects in the first year of operations, for a total of nearly 9 million seconds of exposure time," adds Blair, an associate research professor.

An announcement is expected within the next several months of significant progress on one of FUSE's primary missions: quantifying the cosmic ratio of deuterium to hydrogen.

Deuterium is an isotope of hydrogen created only in the Big Bang, the cataclysmic explosion that astronomers believe started the universe. It is converted to other elements in stars. Astronomers can use a detailed assessment of the relative amounts of deuterium and hydrogen to infer more about conditions in the early universe shortly after the Big Bang, and to glean important insights into how various elements are created, distributed and destroyed by star formation.

In addition to progress on FUSE's planned research objectives, other unexpectedly fruitful areas of investigation have "popped up."

"That's the 'explorer' part of this mission," Sembach says. "There are some things that you discover that you didn't think about beforehand, and those can actually be some of the more interesting things that you come across in science, the things that make science fun."

As an example, Sembach notes that FUSE has proved exceptionally good at finding hydrogen gas present in the vast, dark gulfs between galaxies.

"It could be that half of the mass in the local universe is in these clouds, and we haven't seen them before," Sembach says. The Hubble Space Telescope and some ground-based telescopes can detect such clouds in the very distant universe, but FUSE is the only observatory able to investigate them in the local universe.

"There appears to be as much material in these clouds as there is in stars, and gas, and galaxies that we know about," he says. "It's not clear whether these clouds are big envelopes around galaxies, or whether they're material that is left over when clusters of galaxies form."

To detect these clouds, FUSE observes distant 'background' sources of ultraviolet light, such as quasars or active galaxies, and measures how each object's light is attenuated (or not) by the intervening gas clouds.

"Along some of these sight lines you don't see these clouds, and on others you see several of them," Blair says. "By observing many objects, FUSE can be used to build a three-dimensional picture of these structures and their relationship to galaxies and clusters of galaxies, and to measure characteristics such as their chemical composition."

Looking ahead, Sembach says, "Interestingly enough, a year from now we'll probably have something completely different and unexpected to talk about. It is really important to emphasize the 'explorer' aspect of this mission. There's a lot of universe out there that hasn't been explored yet."