NICMOS missed

Infrared astronomy is experiencing a boom as powerful ground-based telescopes have been outfitted in recent years to make remarkable observations of stellar dust disks. Astronomers are also seeing early hints of nascent planets, or protoplanets, that may form in the disks.

Big telescopes like Keck, Gemini, and the European Southern Observatory's Very Large Telescope have worked to fill the gap left by the NICMOS instrument.

"NICMOS has been sorely missed by infrared astronomers, especially by those of us who study protoplanetary and debris disks around young stars," says Ray Jayawardhana, an astronomer at the University of California, Berkeley.

Terrestrial telescopes suffer from blurring effects of Earth's atmosphere, which Hubble is above. Several ground observatories now partially overcome this problem with adaptive optics systems, which deform mirrors to cancel some of blurring and make finer observations of faraway objects.

Mark McCaughrean of the Astrophysical Institute in Potsdam, Germany, has used NICMOS in the past and hopes to use it again. He said NICMOS "definitely has a few tricks up its sleeves" when observing objects in certain portions of the infrared band.

Cool stars and young giant planets, for example, contain steam in their atmospheres, which is difficult to study when Earth's atmosphere intervenes.

Shrinking niche

In other studies, however, observations can be done just as well from Earth, where telescopes with larger light-collectors (8 to 10 meters compared to 2.4 meters with Hubble) and adaptive optics systems make up for the limiting effects of the atmosphere. Further, the electronic devices that actually record the image collected by an infrared telescope are much more advanced now than those attached to NICMOS.

Recently, McCaughrean and a colleague used the Very Large Telescope in Chile to peek inside possible starbirth regions in the Eagle Nebula, structures in space made famous by Hubble.

Ironically, one of NICMOS' swan songs involved infrared pictures of the same features. McCaughrean said the broad band of wavelengths studied meant both telescopes were equally well suited to the task.

"Its niche is growing smaller by the day, and many projects you might have tried to use NICMOS for in 1997 are now getting done from the ground very effectively," McCaughrean said.

That's not to say there isn't room for improvement. Future space telescopes will employ the latest technology to make further strides in the quality of infrared observations.

Beyond planet

The Advanced Camera for Surveys, on the other hand, will offer unparalleled views of the universe in visible and ultraviolet light.

Astronomers who explore the origin and evolution of galaxies are excited about the expected improvement in resolving objects that are intrinsically bright but are so far away as to be nearly impossible to see.

Among these objects are quasars, brilliant galaxies at the edges of the universe thought to contain very active supermassive black holes at their centers. These gravity wells hold the mass of billions of stars in a small region. Matter swirling into them is accelerated to nearly the speed of light, superheated, and then becomes the cause of gigantic emissions that make the galaxies so prominent.>

With the coronagraph on ACS blocking out the bright centers of quasars, astronomers may get their best views ever of what goes on in the outer reaches of these early and puzzling galaxies.

"We're looking forward to taking images of quasars, and seeing the structures that surround the quasars much better with the ACS's higher resolution and higher sensitivity," says Holland Ford, an astronomer at Johns Hopkins who led the team that built the ACS.

Discerning fireflies

Ford and his colleagues say the new instrument's ability to resolve objects will be twice as good. And its sensitivity will increase four-fold.

"If you had two fireflies six feet apart in Tokyo, Hubble's vision with ACS will be so fine that it will be able to tell from Washington that they were two different fireflies instead of one," Ford said.

Importantly, the ACS will be able to survey large fields of distant objects 10 times more quickly. All this adds up, the researchers say, to 10 times greater ability to make discoveries.

McCaughrean, of the Astrophysical Institute agrees that the increased speed, larger sky coverage, and improved spatial resolution will make Hubble a super survey machine.>

The ACS, he said, "will be a great asset to astronomy, no doubt about it, and it'll place many of our existing ideas about the universe on much firmer footings."

McCaughrean adds, however, that the "shock of the new" with the Hubble Space Telescope may well be over.

"While there will hopefully be new and paradigm-changing discoveries made with it, it's not entirely obvious where they'll come. Then again", he noted wryly, "that's what's so great about astronomy -- having your cherished preconceptions overturned at regular intervals."