University of Arizona
Contact(s): Phil Hinz, 520-621-7866, email@example.com
September 16, 1998
Astronomers test a way to see planets of other stars
Astronomers at the Center for Astronomical Adaptive Optics (CAAO) at The
University of Arizona in Tucson have recently demonstrated a technique with
the potential for imaging planets circling nearby stars. The observations,
which are reported in the current (Sept. 17) issue of the science journal,
Nature, were made at the Multiple Mirror Telescope (MMT) atop Mount Hopkins, Ariz., by a team led by graduate student Phil Hinz.
Astronomers know of several planets orbiting nearby stars, revealed by the
wobble of the star, but none of these planets can be seen directly, even with
the Hubble Space Telescope. This is because, Hinz says, they lie so close to
the dazzling brightness of their parent stars, roughly millions of times
brighter. By current methods the planet is simply washed out in the glare of
The trick for getting past all of that glare is a technique called nulling
interferometry, which can be used to cancel out the light from the bright star
while leaving the image of the planet intact. The experiment at the MMT is the
first time nulling interferometry has been demonstrated on a telescope. Light
from two of the MMT's mirrors are combined in such a way that the waves of
starlight from one mirror cancel out those from the other, while the light
waves from very dim objects close by to these stars are reinforced.
To demonstrate this the astronomers took images of Betelgeuse, a nearby
supergiant star in the familiar constellation of Orion. With the light from
the Betelgeuse canceled they were able to see clearly an image of a faint dust
cloud that surrounds the star. While astronomers have known of this dust cloud previously, nulling interferometry provided the first direct images of it,
free of contamination from star light.
These experiments are the first step in a succession of advances needed to
image extrasolar planets and determine if they contain any signs of life.
Using the same method, the much more powerful Large Binocular Telescope,
currently under construction on Mt. Graham, Ariz., will be able to see planets
the size of Jupiter and larger, while NASA's planned Terrestrial Planet Finder,
a space-based nulling interferometer, is planned for detection and spectral
analysis of planets as small as the Earth around nearby stars.