When Galileo began pointing spyglasses toward the heavens —scanning methodically, classifying what he observed — he started a trend. Four centuries later, telescopes from the huge to the massive peer at the skies with an array of technologies. They look up from all over the Earth — and from far above it. But the heavens still conceal many secrets. So over the next decade or so, Galileo’s successors plan to deploy new, super-high–definition spyglasses to view the most distant objects in the cosmos, map the Milky Way and catalog newfound solar systems. Others would survey the heavens for breaking news: stellar explosions, passing comets or the appearance of potential “killer” asteroids.
These new instruments will be far more sophisticated — and colossal — than Galileo’s original. And they’ll carry astronomical price tags.
Some ground-based telescopes will run $1 billion or more to build, with yearly outlays of $30 million or more throughout the decades they operate. “The scale of these facilities is such now that no single institution can finance them by themselves — not even a single country can,” notes Wendy Freedman, director of the Carnegie Observatories in Pasadena, Calif. At least 10 new telescopes or networks of instruments are now in production or in the late stages of design. Until construction is well under way, of course, most astronomers would acknowledge that their pet instruments may encounter delays, or get shelved.
One astronomer who is among the most confident that his instrument is a go: Markus Kissler-Patig, project scientist in Garching, Germany, for the European Extremely Large Telescope. This ground-based colossus, currently slated to begin operation in 2018, will have a primary mirror 42 meters wide (almost half as long as a U.S. football field) and made from nearly 1,000 hexagonal segments, each about 1.5 meters in diameter. Roughly 100 million euros has already been spent on the E-ELT’s design, Kissler-Patig says, and all but about a third of its projected construction cost of 1 billion euros is banked or already committed by partnering agencies.
Every 10 years, the U.S. National Academies gathers leading astronomers to assess priorities for new facilities. Results of the current survey are due out in 2010. Waiting to learn how much the astronomy community prizes their proposals has created more than a little rivalry among Pasadena astronomers. Those at the Carnegie Observatories are among scientists planning the 24.5-meter Giant Magellan Telescope, or GMT. Caltech is a lead partner in the international consortium developing the Thirty Meter Telescope, or TMT.
Design on the Giant Magellan Telescope is moving right along, but Carnegie astronomer Alan Dressler notes that “until two or three years ago, I would have bet against seeing two of these big telescopes” — or against U.S.-led consortia building both. “But lately I’ve begun to believe that GMT has at least a fifty-fifty chance.”
Hoping to boost the chances for their instrument of choice, astronomers are pointing to the new science that this coming generation of behemoth spyglasses would kick-start.
View from the ground
In orbit since 1990, the Hubble Space Telescope was the first optical telescope to operate in space. Once its flawed mirror was corrected with prescription optics in 1993, the orbiting observatory began sending back to Earth images of breathtaking clarity. But even with the approaching retirement of Hubble — and with its successor, the James Webb Space Telescope, not designed to send back photos in near-true color — astronomers aren’t panicking. Several telescopes now on the drawing board should deliver images with a resolution Hubble engineers could only dream of.
The E-ELT, for instance, will see individual objects with unprecedented detail, delivering images that are at least 15 times crisper than Hubble’s — and of much fainter objects.
E-ELT’s immense light-gathering capacity will capture “twice as many photons as the TMT could and three times as many photons as the GMT,” Kissler-Patig says. But to resolve details from these images, which would ordinarily be heavily blurred by turbulence in Earth’s atmosphere, all of the new large telescopes must employ adaptive optics. One of each telescope’s resolving mirrors will, in real-time, undergo micro-sized deformations to precisely counter fluctuations in light’s path as it moves through the atmosphere.
In the past decade, some ground-based telescopes have been retrofitted with adaptive optics. The next generation will be the first to have the optics built-in and available from day one. The superior resolution this technology enables means that, for the first time, “big ground-based telescopes will deliver better images than we’re getting in space,” says TMT adviser Richard Ellis of Caltech.
Moreover, argues Freedman, “this jump in both sensitivity and resolution is a killer application. It opens up new windows.”
For instance, she notes, “we’re very interested in peering back into the early universe. Today we can see faint smudges with Hubble and current ground-based telescopes where we know galaxies are forming.” Some of these regions date to just a few hundred million or so years after the Big Bang — prehistoric within the universe’s 13.7 billion years.
The massive ground-based facilities will finally “let us peer into what astronomers have started calling the ‘dark ages,’ ” Freedman says, “where we currently know just nothing. We’ve had ideas about what happened back then.” At last, she says, “we’ll get to witness this directly.”
Stellar census
Big telescopes peer deeply into space but can see only a tiny portion of the heavens at once. While an instrument gazes intently at a speck of sky, spectral fireworks may be breaking out elsewhere. To spot such drama, a new class of survey telescopes is rolling out.
The first to debut is Pan-STARRS, the Panoramic Survey Telescope & Rapid Response System, with a modest 1.8-meter telescope. This facility atop Haleakala on the Hawaiian island of Maui should enter full-scale operation this spring, notes Nick Kaiser, a principal scientist with the project.
Pixels, the discrete elements that make up an image, are a measure of resolution, and Pan-STARRS will capture pixels in abundance. The field of view will be vast — 7 square degrees for each mirror in its four planned telescopes. Each will have a 1.4-gigapixel camera, so even this wide view will encompass a high resolution. The telescope will train its eye on a patch of sky for about 30 seconds and then move to another. By photographing 1,000 segments nightly, “we’ll image the entire sky once a week,” Kaiser predicts.
One high priority “is being able to detect 90 percent of all killer asteroids, near-Earth asteroids bigger than 300 meters,” he says. “That should take us about 10 years,” which is the projected duration of the mission.
Right now, Pan-STARRS relies on a single telescope. If funds hold out, it should get three clones. Each of the four telescopes would simultaneously view the same patch of sky. Sometimes a digital detector registers a false positive, perhaps from a stray cosmic ray, Kaiser says. With four images of the same spot, he says, three will veto any false report.
The far more ambitious Large Synoptic Survey Telescope is scheduled to see first light in 2014 from a Chilean mountaintop. Its 8.4-meter mirror is in production, and the completed system would use the world’s largest digital camera to get a resolution of 3.2 gigapixels. By 2016, LSST is expected to be scanning not only for asteroids and supernovas but also for details of dark matter — the majority of the universe’s mass, now unseen — and the dark energy serving as a mysterious, accelerating force (SN: 2/2/08, p. 74).
Compared with the recently completed set of data from the ongoing Sloan Digital Sky Survey, even the smaller Pan-STARRS will offer “a lot more pixels,” Kaiser observes. “So we’ll see a lot fainter objects.”
Galactic archaeology
Other new missions will put communities of stars in perspective — literally.
“At the moment we don’t know the distances to most stars in the Milky Way,” observes Ellis, “so we don’t have a three-dimensional map of even the galaxy that we inhabit.” But Gaia, a European Space Agency project due to launch in 2011, will correct that, he predicts.
The mission will carry two telescopes into orbit, each focused at a different angle to provide the equivalent of binocular vision. And the spacecraft itself will spin slowly to scan the entire celestial sphere. Over several years, its precision measurements —its accuracy is expected to be the equivalent of measuring the diameter of a human hair at a distance of 1,000 kilometers —should provide a 3-D map of all the stars within 30,000 light-years of the sun.
During its five-year mission, Gaia should map about a billion stars and other objects roughly 70 times — each time charting their position, distance and brightness, with unprecedented precision, to track changes over time.
Another mission will offer a historical perspective on stars, what’s being called “galactic archaeology,” notes Mike Irwin of the University of Cambridge in England. Its data will be the chemical fingerprints of stars as read by a new Wide-Field Multi-Object Spectrograph, or WF-MOS. This instrument is being designed for use, perhaps by 2014, with Japan’s refurbished 8.2-meter Subaru telescope atop Hawaii’s Mauna Kea.
Star trajectories can become jostled, as passing galaxies kidnap stars or as maturing stars take up relationships with strangers. But wherever it goes, a star carries the chemical fingerprint unique to its nursery environment, Irwin explains. By analyzing a star’s spectral, or chemical, fingerprint, he says, astronomers hope to identify which stars in a throng are related, and which trace back to other regions of the galaxy. Similarly, he says, “as our galaxy cannibalizes a neighboring one, we can look for traces of the disrupted satellite galaxy by fingerprinting its stars in the great trail of debris left behind.”
WF-MOS will simultaneously measure the spectra of up to 2,400 objects at once, the most ever. “So we can rapidly build a very large database” that points to the history — and, in some ways, the genealogy — of residents across a wide swath of the Milky Way, Irwin predicts.
New synergies
Because Earth’s atmosphere screens out some wavelengths of electromagnetic radiation, WF-MOS can’t collect a full fingerprint of distant stars. Only space-based telescopes have access to full spectra. And NASA will be launching a powerful successor to Hubble around 2013 that will not only chemically fingerprint stars but also collect images of them.
The James Webb Space Telescope will have seven times Hubble’s light-collecting area and 15 times its field of view. And whereas Hubble collects radiation in multiple wavelengths, including visible, its successor is being optimized to pick up the infrared radiation associated with the oldest, most distant objects. This spectral specificity means, however, that the JWST won’t be able to cover for the Chandra X-ray Observatory, which has completed 10 of its 15 projected years (Chandra scientists say it could last even longer).
The new space telescope will orbit the sun with Earth — but not circle Earth. Because Hubble did orbit Earth, astronauts could service its instruments. At 1.5 million kilometers from Earth, roughly four times as far as the moon, the JWST will not be accessible for repairs or upgrades. And carrying fuel for only about 10 years, the mission will likely be far shorter than that of Hubble, which is now 19 years old.
Like Hubble, the JWST will serve as a scout. But unlike Hubble, this scout will leave the rest of the work to the next generation of ground-based telescopes that have the capacity to produce high-resolution, super-crisp images. This crispness means that individual objects will be easier to discern, as will each object’s spectral fingerprint.
Those big ground-based observatories will also be turning to spacecraft such as Gaia as well as NASA’s recently launched Kepler mission to find planets beyond the solar system. Relatively small ground-based telescopes will also be recruited for detailed observations of distant solar systems. “Looking for planets has become big business in astronomy,” Ellis says.
More than 345 extrasolar planets have been logged. “But we can only easily spot planets today that are Jupiter-sized,” Ellis says. What everyone wants to find are rocky, Earth-sized planets that have atmospheres. And that, he says, is about to become possible.
Even GMT, the smallest of the three next-generation big-bruiser telescopes, “can essentially mask out the light from a parent star so that we can directly image its planet and study the spectra of the planet’s atmosphere,” Freedman says.
This is “exciting and very inspirational,” says her colleague Dressler. Cosmologists are starting to investigate not only how to uncover Earthlike planets in the sun’s region of the Milky Way, “but also whether such planets might have the elements of life. Even whether their atmospheres show evidence of seasons, or signatures of likely vegetation.”
Although the new generation of telescopes will likely make inroads into understanding extrasolar planets, Dressler suspects astronomers will probably need far bigger space telescopes to “break the field open.” But the growing trend in astronomy, he says, is that instead of focusing primarily on “the broad scope of things over vast distances and eons of time, we’re starting to examine how all of those grand but simple processes in the universe have led to great complexity.” Like life on Earth.
