Linking of Mauna Kea telescopes enhances visibility
By Jan TenBruggencate
Advertiser Science Writer
The twin Keck telescopes on Mauna Kea are now linked, and their combined resources promise new insight into stars and distant planet systems.
Astronomers hope to learn about the formation of solar systems by studying the dust clouds around nearby stars.
The twin Keck telescopes on Mauna Kea are connected by an underground tunnel, which allows light from both to simultaneously meet at an interferometer, which gives clearer images than what can be obtained with either telescope independently.
They hope to determine the temperature and composition of hot Jupiter-sized planets and to detect previously unknown Uranus-sized planets. They also hope to collect images like none before.
The technology they are perfecting will be used on a space mission designed to search for the Holy Grail of astronomy: planets the size of Earth.
The Keck work is financed by NASA and performed by the Jet Propulsion Laboratory and the California Association for Research in Astronomy, which runs the Keck telescopes.
The telescopes are linked using a device called an interferometer, which combines the light from multiple telescopes and creates levels of detail equivalent to what might be obtained with a mirror vastly larger than either or both together.
The identical Keck telescopes, each outfitted with a segmented mirror 30 feet across, were first successfully joined through the interferometer in March.
Since then, physicists, astronomers and engineers have been fine-tuning it.
They hope to be performing actual astronomical research by the end of the year, said Mark Colavita, the engineer heading the project for the Jet Propulsion Laboratory.
"The big milestone for any interferometer is getting the first fringes. In March, we got light from the two Kecks and detected fringes, which tells us that all the fundamental pieces work," he said.
An interferometer relies on manipulation of the wave-like nature of light. If the peaks of two ocean waves coincide, a much higher peak is created. This is called constructive interference.
It's similar with light: If scientists match the peaks in light waves, they get much brighter signals.
In an interferometer, astronomers can manipulate the light from two telescopes that are looking at the same object and bring light waves into synchronization. When the light waves match, the system is said to have fringes.
There are other interferometer systems working on other telescopes, but none as large as the one on Mauna Kea.
The Keck telescopes are among the largest in the world, and they already have independently been used to produce images of objects never before detected in deep space.
Combining their light through interferometry is expected to lead to breakthroughs in astronomy.
But first, some kinks have to be worked out.
One of the main problems is vibration. The interferometer is a long instrument, consisting of the Keck telescope mirrors and a series of other mirrors that transmit their light down into the tunnel between them and then through the tunnel to the guts of the interferometer.
Any shakiness anywhere in the system degrades the quality of the signal, and the scientists have found there's quite a bit of shake, even though it's so slight that humans might not even notice it. It comes from the pumps that pressurize the oil bed on which the giant mirrors float. It comes from air-conditioning motors. It comes from fans.
"We're taking a three-pronged approach," said Mark Swain, a Jet Propulsion Laboratory physicist and astronomer.
One is to identify the sources of shuddering and isolate them. Another is to change the ways mirrors are handled so they are not affected so much by vibrations. A third is to actively measure the vibration and counteract it with compensating vibration.
The scientists will have the Kecks up and running tonight to see how their fixes so far have done.
The degree to which they succeed will help the future of two major NASA projects.
One is the Space Interferometry Mission. The other is the Terrestrial Planet Finder, not scheduled to be launched for another decade.
Its goal is to find small planets like Earth, which no known land-based astronomy platform can do.
