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Nancy Neal
Headquarters, Washington        April 22, 2003
(Phone: 202/358-2369)

Jane Platt
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-0880)

RELEASE: 03-148

GALAXY EVOLUTION EXPLORER LOOKS BACK IN TIME

NASA's Galaxy Evolution Explorer (GALEX) will carry a
telescope into Earth orbit that will observe a million 
galaxies, across 10 billion years of cosmic history, to help 
astronomers determine when the stars we see today had their 
origins. 

GALEX is set to launch, no earlier than April 28, 2003, from 
Cape Canaveral Air Force Station, Fla. A Pegasus XL rocket, 
released by an L-1011 jet aircraft, will launch the 
satellite. The aircraft will climb to approximately 39,000 
feet and release the launch vehicle and payload. The science 
mission will start after an initial month of in-orbit 
testing.

From its orbit high above Earth, the spacecraft will sweep 
the skies, for up to 28 months, using state-of-the-art 
ultraviolet detectors. Looking in the ultraviolet will 
single out galaxies dominated by young, hot, short-lived 
stars that give off a great deal of energy at that 
wavelength. These galaxies are actively creating stars, 
therefore providing a window into the history and causes of 
galactic star formation.

"The Galaxy Evolution Explorer is crucial to understanding 
how galaxies, the basic structures of our universe, form and 
function," said Anne Kinney, director of astronomy and 
physics in the Office of Space Science, NASA Headquarters, 
Washington. "Its ultraviolet observations will round out the 
knowledge we gain from observations in infrared and other 
wavelengths," she said.

Astronomers believe the universe originated approximately 
13.7 billion years ago in the cataclysmic "Big Bang." 
Galaxies, the basic building blocks of the universe, began 
to appear as the fireball of hydrogen and helium gas 
expanded and cooled. Recent observations suggest star 
formation peaked eight to 10 billion years ago. This mission 
is specifically designed to investigate whether this 
occurred and why.

The centerpiece of the satellite is a 50-centimeter-diameter 
(19.7-inch) telescope. It is equipped with sensors that will 
gather continuous images of galaxies in the ultraviolet to 
study their shape, brightness and size. Ultraviolet light, 
the type of invisible energy responsible for sunburn, is at 
the higher end of the electromagnetic spectrum, just above 
visible light in frequency, but below X-rays and gamma rays.

A device called a spectrometer will break down the light 
into component colors, just as a prism separates white light 
into a rainbow. These measurements will enable scientists to 
determine the distances of galaxies, and thus, their places 
in cosmic history. Combined with precise measurements of the 
ultraviolet brightness of galaxies, astronomers will be able 
to determine the rate at which stars are forming within 
those galaxies. 

"This mission will provide the first comprehensive map of a 
universe of galaxies under construction and bring us closer 
to understanding how they, and our own Milky Way, were 
built," said Christopher Martin, the mission's principal 
investigator and an astrophysics professor at the California 
Institute of Technology in Pasadena.

Scientists will use data from the mission to learn when 
carbon, oxygen and other chemical elements were created 
inside blazing stars. Most of the elements found in the 
human body originated in stars. We are literally made of 
stardust. The mission will also conduct the first 
ultraviolet surveys of the entire sky beyond our own galaxy, 
including the first wide-area spectroscopic surveys. Rich in 
objects, from galaxies to quasars to white dwarf stars, this 
vast data archive will serve as a resource for the entire 
astronomical community.

The GALEX mission is led by the California Institute of 
Technology, which is also responsible for science operations 
and data analysis. NASA's Jet Propulsion Laboratory, 
Pasadena, Calif., a division of Caltech, manages the mission 
and built the science instrument. The mission was developed 
under NASA's Explorers Program, managed by the Goddard Space 
Flight Center, Greenbelt, Md. GALEX international partners 
include South Korea and France.

For information about the mission and NASA's Explorers 
Program on the Internet, visit:

http://www.srl.caltech.edu/galex

http://explorers.gsfc.nasa.gov

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