End of the line for Hubble? Astronomers ponder space telescope's final years

Science News, July 24, 2004 by Ron Cowen

Black Friday. That's how Steve Beckwith, director of the Baltimore-based Space Telescope Science Institute and his colleagues refer to Jan. 16, 2004, the day that the Hubble Space Telescope got its death sentence. Sean O'Keefe, a NASA Administrator, handed down the judgment to Beckwith and about 100 other Hubble scientists and engineers in a conference room above Hubble's flight operations center at NASA's Goddard Space Flight Center in Greenbelt, Md.

Citing safety concerns that had come to light after the Columbia space shuttle tragedy in February 2003, O'Keefe told the gathering that NASA wasn't going to send any more shuttle missions to upgrade or repair the orbiting observatory. With its 3-decades-old batteries in danger of petering out and its spacecraft-stabilizing gyroscopes vulnerable to failure, the telescope could cease to function as early as 2007. Scientists had hoped to use shuttle missions to maintain it until as late as 2013.

The decision to end Hubble's life prematurely has set off a public furor. From snapshots of ultraviolet auroras shimmering above Jupiter to pictures of exploding stars and images of dozens of the most distant galaxies so far detected, Hubble hasn't only revolutionized astronomy. Around the world, its images have become icons of scientific discovery.

On June 1, O'Keefe announced that NASA is proposing to send robots, rather than astronauts, to repair and upgrade Hubble. Although many astronomers, including Beekwith, say they are heartened by this proposal, they also point out that an unmanned servicing mission has never before been attempted. The scientists are skeptical that even state-of-the art robots can deliver batteries and gyroscopes, let alone carry out current plans to install a new infrared camera and ultraviolet spectrograph.

Asked by Congress to consider the future of the Hubble Space Telescope, a National Academy of Sciences panel came out with a preliminary recommendation on July 14. It urges that NASA not preclude the use of the shuttle for a repair mission while the space agency considers the feasibility of robotic servicing.

"My advice to young astronomers is to treat each night on [any] telescope like it was the last night" says John Huchra of Harvard University. "In this ease, this may be the last years on the Hubble Space Telescope."

"It's definitely a race with the clock," adds John Tonry of the University of Hawaii in Honolulu. Which prompts the question, What observations should take priority in Hubble's last few years?

"We're not going to do all the good things that everybody has in mind before the batteries wear out," says Robert Kirshner of Harvard University. "We're going to have to make some very difficult, unpleasant choices."

DO OR DIE In May, scientists gathered at the Space Telescope Science Institute to discuss priorities. They agreed that they couldn't count on the success of a robotic mission. The astronomers expressed diverse opinions on what problems Hubble should tackle next, but they found a consensus on some issues. "The big question is, Should we dedicate a lot of Hubble time to one or two compelling problems, and the answer at the meeting was 'no," says Beckwith.

Much of the telescope's time is assigned almost a year in advance, but the space telescope director reserves some Hubble time for special projects or on-the-fly follow-up of new discoveries.

Last fall, Beekwith gave away more than 11 days of this discretionary time for astronomers to take the most detailed snapshot yet of the distant universe. As astronomers plumb this goldmine of imagery and spectrographic data, known as the Hubble Ultra Deep Field, they are asking whether the images in this narrow slice of the universe are representative of the rest of the cosmos.

To find out, Hubble should image at least two other deep fields before its time runs out to more accurately reveal the distribution of the colors, shapes, and clusterings of the first galaxies, says Marijn Franx of Leiden Observatory in the Netherlands.

Other astronomers at the May meeting urged that Hubble continue its pioneering work in determining the size and atmospheric composition of planets that lie beyond the solar system. By carefully gathering a star's light, Hubble can provide spectrographic signatures of closely orbiting planets that circle it. Astronomers don't have images of those extrasolar planets, so Hubble has provided the only direct data on them. Other telescopes have insufficiently clear vision and lack Hubble's spatial resolution.

Hubble examines extrasolar planets as they periodically pass in front of their stars as seen from Earth--a process known as a transit. At that time, the planets block a small but detectable amount of starlight. A precision measurement of the drop in brightness can indicate the radius of the transiting planet (SN: 12/1/01, p. 346).

An even smaller amount of the starlight filters through the transiting planet's atmosphere, whose constituent atoms and molecules absorb specific wavelengths. By comparing the spectra of starlight taken during and after a transit, astronomers can in principle determine the abundance of a variety of elements and compounds in a planet's atmosphere.