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FUSE mission graphic

Far Ultraviolet Spectroscopic Explorer

Phase: Past

Launch Date: June 24, 1999

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Program(s):Astrophysics Explorers, Explorers

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The Far Ultraviolet Spectroscopic Explorer FUSE was a NASA supported mission that launched June 24, 1999 and observed the universe using high resolution far-ultraviolet spectroscopy, a region of the electromagnetic spectrum that is blocked by Earth’s atmosphere.

After a highly successful eight year observational period, on-orbit activities concluded in mid-October 2007 with the decommissioning of the satellite. FUSE provided a wealth of data that will be studied for years to come.

FUSE false-color image of the star AE Aurigae
This is a false-color image of the star AE Aurigae (bright source of light slightly off center of image) embedded in a region of space containing smoke-like filaments of carbon-rich dust grains, a common phenomenon. Such dust might be hiding deuterium, an isotope of hydrogen, and stymieing astronomers' efforts to study star and galaxy formation. The FUSE satellite has surveyed the local deuterium concentration in the galaxy and found far more than expected. Because deuterium is a tracer of star and galaxy evolution, this discovery could radically alter theories about how stars and galaxy form.
Credit: T.A. Rector and B.A. Wolpa, NOAO, AURA, and NSF.

Science Highlights

One of FUSE’s discoveries was the detection of molecular nitrogen in interstellar space, something astronomers have been searching for signs of for decades. Another long sought discovery was that of Eta-Carinae’s companion star. Eta-Carinae is one of the most massive and highly studied stars in our galaxy, weighing in at more than 100 times the mass of our sun. It resides in the heart of a star forming factory, and is expected to explode as a Type II supernova within the next million years.

FUSE showed that a large amount of water has escaped from Mars, enough to form a global ocean 100 feet deep, by measuring abundances of molecular hydrogen (made of two hydrogen atoms).

FUSE also observed a debris disk that is surprisingly rich in carbon gas orbiting the young star Beta Pictoris. The carbon overabundance indicates either the star is forming planets that could end up as exotic, carbon-rich worlds of graphite and methane, or Beta Pictoris is revealing an unsuspected phenomenon that also occurred in the early solar system.

FUSE discovered far more deuterium, a form of hydrogen with a proton and a neutron instead of just one proton, in the Milky Way galaxy than astronomers had expected. Deuterium was produced in the early universe, but this isotope is destroyed easily in stellar nuclear reactions. FUSE showed that less deuterium has been burned in stars over cosmic time which is in agreement with modern models for the evolution of the galaxy and the recent Wilkinson Microwave Anisotropy Probe results.

By detecting highly ionized oxygen atoms in intergalactic space, FUSE showed that about 10 percent of matter in the local universe consists of million-degree gas floating between the galaxies. This discovery might help resolve the long-standing mystery of the universe's "missing baryons." Baryons are subatomic particles, often protons and neutrons. Calculations of how many baryons were produced in the very early universe predict about twice as many baryons as astronomers have observed. The rest of the missing baryons might exist as even hotter gas, which could be observed by future X-ray observatories.

FUSE vastly increased scientists’ understanding of our galaxy's evolution and many exotic phenomena and has left a strong legacy on which to build the next generation of investigations and missions.

Last updated: May 28, 2015

Related Links
  • FUSE archive website -