年9月高口阅读上半场第三篇
Question 11-15
LIKE the space telescope he championed, astronomer Lyman Spitzer faced some perilous moments in his career. Most notably, on a July day in 1945, he happened to be in the Empire State building when a B-25 Mitchell bomber lost its way in fog and crashed into the skyscraper 14 floors above him. Seeing debris falling past the window, his curiosity got the better of him, as Robert Zimmerman recounts in his Hubble history, The Universe in a Mirror. Spitzer tried to poke his head out the window to see what was going on, but others quickly convinced him it was too dangerous.
Spitzer was not the first astronomer to dream of sending a telescope above the distorting effects of the atmosphere, but it was his tireless advocacy, in part, that led NASA to launch the Hubble Space Telescope in 1990. Initially jubilant, astronomers were soon horrified to discover that Hubble's 2.4-metre main mirror had been ground to the wrong shape. Although it was only off by 2.2 micrometres, this badly blurred the telescope's vision and made the scientists who had promised the world new images and science in exchange for $1.5 billion of public money the butt of jokes. The fiasco, inevitably dubbed "Hubble Trouble" by the press, wasn't helped when even the limited science the crippled Hubble could do was threatened as its gyroscopes, needed to control the orientation of the telescope, started to fail one by one.
By 1993, as NASA prepared to launch a rescue mission, the situation looked bleak. The telescope "probably wouldn't have gone on for more than a year or two" without repairs, says John Grunsfeld, an astronaut who flew on the most recent Hubble servicing mission. Happily, the rescue mission was a success. Shuttle astronauts installed new instruments that corrected for the flawed mirror, and replaced the gyroscopes. Two years later, Hubble gave us the deepest ever view of the universe, peering back to an era just 1 billion years after the big bang to see the primordial building blocks that aggregated to form galaxies like our own.
The success of the 1993 servicing mission encouraged NASA to mount three more (in 1997, 1999 and 2002). Far from merely keeping the observatory alive, astronauts installed updated instruments on these missions that dramatically improved Hubble's power. It was "as if you took in your Chevy Nova [for repairs] and they gave you back a Lear jet," says Steven Beckwith, who from 1998 to 2005 headed the Space Telescope Science Institute (STScI) in Baltimore, Maryland, where Hubble's observations are planned. Along the way, in 1998, Hubble's measurements of supernovas in distant galaxies unexpectedly revealed that the universe is expanding at an ever-increasing pace, propelled by a mysterious entity now known as dark energy. In 2001 the space observatory also managed to make the first measurement of a chemical in the atmosphere of a planet in an alien solar system.
Despite its successes, Hubble's life looked like it would be cut short when in 2004, NASA's then administrator Sean O'Keefe announced the agency would send no more servicing missions to Hubble, citing unacceptable risks to astronauts in the wake of the Columbia shuttle disaster of 2003, in which the craft exploded on re-entry, killing its crew. By this time, three of Hubble's gyroscopes were already broken or ailing and no one was sure how long the other three would last. Citizen petitions and an outcry among astronomers put pressure on NASA, and after a high-level panel of experts declared that another mission to Hubble would not be exceptionally risky, the agency reversed course, leading to the most recent servicing mission, in May 2009.
No more are planned. The remainder of the shuttle fleet that astronauts used to reach Hubble is scheduled to retire by the year's end. And in 2014, NASA plans to launch Hubble's successor, an infrared observatory called the James Webb Space Telescope, which will probe galaxies even further away and make more measurements of exoplanet atmospheres.
According to Grunsfeld, now STScI's deputy director, plans are afoot for a robotic mission to grab Hubble when it reaches the end of its useful life, nudging it into Earth's atmosphere where most of it would be incinerated. Only the mirror is sturdy enough to survive the fall into an empty patch of ocean.
But let's not get ahead of ourselves - Hubble is far from finished. The instruments installed in May 2009, including the Wide Field Camera 3, which took this image of the Butterfly nebula, 3800 light years away, have boosted its powers yet again. It might have as much as a decade of life left even without more servicing. "It really is only reaching its full stride now, after 20 years," says Grunsfeld.
A key priority for Hubble will be to explore the origin of dark energy by probing for it at earlier times in the universe's history. Hubble scientist Malcolm Niedner of NASA's Goddard Space Flight Center in Greenbelt, Maryland, is not willing to bet on what its most important discovery will be. "More than half of the most amazing textbook-changing science to emerge from this telescope occurred in areas we couldn't even have dreamed of," he says. "Expect the unexpected."
