A parting shot from outer space

With only a few days before it goes dark, the camera that arguably saved the Hubble Space Telescope has delivered a stunning image of a dying star. The picture of planetary nebula Kohoutek 4-55 was snapped just last week by Hubble's Wide Field and Planetary Camera 2 (a.k.a. WFPC2), the instrument that also imaged the iconic "Pillars of Creation" and the Hubble Deep Field.

WFPC2 was built in the 1980s as a "clone" of the space telescope's first wide-field camera, to be used as a spare in case something went wrong with the original instrument. Something went wrong, all right, but not with the camera. Shortly after Hubble's launch in 1990, scientists discovered to their horror that the telescope's primary mirror was shaped incorrectly, crippling its optics.

Fortunately, the Hubble team figured out a way to adjust WFPC2's optics to compensate for the mirror flaw - turning the tide in the telescope's favor.

Another corrective-optics package, known as COSTAR, was built for Hubble's other instruments, and WFPC2 and COSTAR were installed during a famous set of spacewalks in 1993. It wasn't long after that that Hubble came into its own. WFPC2 served as Hubble's primary observing instrument in visible-light wavelengths until the Advanced Camera for Surveys arrived in 2002.

WFPC2's best-known picture just might be 1995's Pillars of Creation - a view of the Eagle Nebula that shows fingers of gas and dust enshrouding newborn stars. NASA's science mission chief, Ed Weiler, frequently points to the Eagle Nebula as Hubble's hallmark. "You don't see Eagle Nebulas on the cover of Time magazine taken from the ground," he said recently. "You see them from Hubble. Hubble still has a unique niche."

Toward the end of 1995, Hubble's handlers pointed the telescope toward a seemingly empty patch of sky - and came up with what was then the deepest view of the universe ever captured. WFPC2's Hubble Deep Field includes some galaxies that are more than 12 billion light-years away.

Since then, there have been somewhat deeper views - including the Hubble Ultra Deep Field, created using the Advanced Camera for Surveys and the Near Infrared Camera and Multi-Object Spectrometer. But there'll never be any deep field like the first Deep Field. "It is hard to remember an image that has had such an impact in such a short time," astronomer Richard Ellis has been quoted as saying.

The camera also produced trailblazing images of Saturn, Mars, Jupiter and other planets. It was one of the best witnesses to Comet Shoemaker-Levy's impact on Jupiter in 1994. And then there are those planetary nebulae. When a star nears the end of its life, it can throw off billowing bubbles of colorful gas and dust. Back in the 18th and 19th centuries, some astronomers wondered whether these puffballs were actually planets - sparking the not-quite-accurate name for the nebulae.

WFPC2 has seen lots of nebulae in its day. The best-known may well be Eta Carinae, a supermassive star that looks as if it could go supernova any day now.

The color-coded picture of Kohoutek 4-55, taken on May 4 and released on Sunday, shows a bright inner ring surrounded by a bipolar structure reminiscent of Eta Carinae's double bubble. The entire system is shrouded by a faint, red, swirling halo - which is "fairly uncommon in planetary nebulae," according to a news release from NASA's Jet Propulsion Laboratory. The red colors represent nitrogen emissions, green represents hydrogen, and blue stands for oxygen.

Kohoutek 4-55, or K 4-55 for short, is one of a series of planetary nebulae that were named after their discoverer, Czech astronomer Lubos Kohoutek. Yes, that Kohoutek. It's nearly 4,600 light-years from Earth in the northern constellation Cygnus.

NASA and the Space Telescope Science Institute say this view of K 4-55 will serve as WFPC2's final "pretty picture." The shuttle Atlantis' astronauts are due to remove the 16-year-old camera from Hubble's chest later this week and replace it with a new, improved instrument called Wide Field Camera 3.

During the buildup to today's Atlantis launch, Weiler said he remembered the exact moment when WFPC2 was put into Hubble, and he'll remember the moment when it's taken out. "But I really look forward to the moment when I get to walk up to it and touch it someday in the Smithsonian and say, 'That is the camera that saved Hubble.'"

For more reminiscences of WFPC2's wonders, check out Universe Today's list of the camera's greatest hits, NASA's WFPC2 gallery and this tribute from Music of the Spheres. Our Space Gallery includes more stunners from all of Hubble's instruments, and our Human Spaceflight section keeps you up to date on the Atlantis mission.

Update for 11:22 a.m. ET May 12: Some commenters may have gotten the misimpression that Hubble itself is passing away. Actually, the current shuttle mission will give Hubble a new lease on life, as we've described in morethanone report. It's just WFPC2 that is going out of business. However, the camera played such a big role in reviving Hubble that it's eminently worthy of a place in the Smithsonian. I can visualize it on display alongside a mockup of the space telescope. At one time there had been talk about bringing the actual telescope back down for veneration in a space shuttle payload bay, but because the shuttle fleet is due to be retired next year, there's currently no way to bring the thing down intact.

On another matter, at least one commenter has questioned whether Eta Carinae should be classified as a planetary nebula - and just to be safe, I've revised this item to leave the question a bit more open. 

Update for 10:25 p.m. ET May 13: We may see WFPC2 at the Smithsonian sooner than I thought. D.C. Agle, a spokesman for NASA's Jet Propulsion Laboratory, told me that the camera is due to go on temporary display in October, and become a permanent part of the Smithsonian's collection later.

You might ask whatever happened to Hubble's first wide-field camera, WFPC1. Well, it's too late to put that one on display anywhere: Many of its parts were recycled to build the Wide Field Camera 3, WFPC2's replacement.