Hubble Space Telescope Turns 15

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It was worth the wait. Hubble has exceeded expectations with an incredible resume of discovery.

Hubble revealed that a mysterious force called dark energy works against gravity to further the expansion of the universe. Dark energy comprises some 70 percent of the universe, yet astronomers know very little about the mysterious force.

Hubble also made the first direct measurement of planetary atmospheres outside of our own solar system, detecting sodium, hydrogen, carbon, and oxygen in the atmospheres of alien planets. Similar analysis may one day help scientists find life on other planets.

"It's not that we thought that these planets, if they were out there, would not have things like hydrogen," Livio said. "But the fact that you can actually see it is astounding."

"These two examples touch on what are arguably the most intriguing questions in science today: What is the nature of dark energy? Is there life outside Earth?" Livio said. "This is how you measure something that is truly great."

More Discoveries

By observing the expansion rate of pulsating stars, Hubble delivered the most accurate estimate of the age of the universe—13 to 14 billion years.

The telescope also captured deep-space images of "toddler" galaxies, which existed billions of years ago when the universe was young. By studying the shape and formation of galaxies in different periods of time, scientists have learned much more about how the galaxies form.

Hubble also discovered black holes at the center of most galaxies and identified the gamma-ray bursts of light that accompany the collapse of massive stars. These bursts may be the universe's biggest explosions since the original big bang.

The telescope identified planetary construction zones in the flattened disks of gas and dust, which surround young stars. These common clouds hold the building blocks of planetary systems.

Hubble has recorded cosmic births and deaths. Some of Hubble's most memorable images are of planetary nebulae, the colorful gas shrouds that form at the death of stars like our sun.

Yet for all of Hubble's scientific breakthroughs, the pure visual power of its images may be among its more lasting achievements.

"One of the most remarkable things that I find is that the public is on a first name basis with a scientific instrument," Summers said. "You can just say Hubble, and everybody knows what you're talking about."

"How many times has a microscope or a particle accelerator become part of the public vernacular?" Summers said.

Today Hubble's future is uncertain. Without a space shuttle servicing mission, the orbiting telescope will likely cease to operate sometime after 2007. Plans for such a mission were scrapped due to a negative risk assessment that followed the 2003 breakup of the space shuttle Columbia over Texas.

However NASA's new chief, Michael Griffin, recently revived hope when he said he would reconsider shuttle service to Hubble.

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