Seeking One of Astronomy’s Holy Grails : Telescopes: New method of altering mirror to compensate for atmospheric distortion may enable scientists to detect planets orbiting around stars.
A handful of pioneering astronomers are trying to do something they once thought couldn’t be done--build a ground-based telescope so sophisticated that it can detect the light from a planet circling another star.
Finding other planets around other stars is one of the holy grails of astronomy because it strikes at the heart of the ageless question of whether life exists elsewhere in the universe. But any planet is at least a billion times dimmer than its star, so finding one is harder than seeing a glowing candle in front of a huge spotlight.
Add to that the blurring caused by the Earth’s atmosphere, and even the best ground-based telescopes are unable to separate the image of other planets--if they do exist--from other stars. So far, scientists have only been able to infer the presence of other planets by observing the “wobbling” of certain stars, presumably from the pull of orbiting planets.
That is why people such as Roger P. Angel of the University of Arizona once thought only space-based telescopes larger than the now orbiting Hubble had any chance of detecting planets around other stars.
But Angel, who created the university’s famed spinning furnace in which large telescope mirrors are being cast at a fraction of what they used to cost, has changed his mind.
The soft-spoken British scientist is at the forefront of an effort to build telescopes designed to remove atmospheric distortion from ground-based images. If successful, the technology--called adaptive optics--could make it possible for telescopes on Earth to find large, Jupiter-size planets around other stars on almost any good night. If there are other planets, that is.
“It looks quite feasible now,” Angel told the American Astronomical Society meeting in Tucson.
The Air Force is funding the program because of intense interest in atmospheric effects on telescopes and ballistic guidance systems.
At Angel’s Mirror Lab beneath the bleachers at the university’s football stadium, glass is melted in a spinning furnace, which slowly cools, allowing the glass to harden with the curved surface of a telescope mirror.
When the mirrors are tested in the lab, he said, they produce images “three times as sharp as the Hubble Space Telescope’s.” But when the same mirrors are installed in mountaintop observatories and focused on the heavens, the images degrade “horribly” because of atmospheric distortion.
Angel and a group of fellow researchers plan to test a new system in New Mexico later this year designed to virtually wipe out that problem. The system will measure the distortion in an image from a nearby star and use that information to warp an “adaptive mirror” in such a way as to offset the effects of the atmosphere. In short, they will introduce deliberate errors to cancel out errors caused by the atmosphere.
The mirror will be warped 2,000 times each second, quickly responding to even the faintest changes in the atmosphere above the telescope.
If the system works as well as Angel expects, it will be installed on two 6.5-meter telescopes, one in Arizona and one in Chile, within about three years at a cost of about $8 million, he said.
By concentrating on about 30 nearby stars that are similar to our sun, Angel believes that Jupiter-size planets should be detected soon after the system becomes operational.
If Angel succeeds, scientists might know in a few years whether other planets are common in the universe. But it may be much longer before it is known if any of them have life. The answer to that question would require the construction of a space-based telescope much larger than the Hubble.
