Sifting Through Starlight To Find New Planets
July 6, 2012

Sifting Through Starlight To Find New Planets

Lee Rannals for - Your Universe Online

The first images from a new project are demonstrating a new technique that creates precise "dark holes" around stars of interest.

Dark holes are extremely difficult to see directly in an image because the light that stars emit is tens of millions to billions of times brighter than the light given off by planets.

However, astronomers working on Project 1640 presented findings of dark holes at the International Society for Optics and Photonics (SPIE) Astronomical Telescopes and Instrumentation meeting in Amsterdam.

"We are blinded by this starlight," Ben R. Oppenheimer, a curator in the Museum's Department of Astrophysics and principal investigator for Project 1640, said in a prepared statement. "Once we can actually see these exoplanets, we can determine the colors they emit, the chemical compositions of their atmospheres, and even the physical characteristics of their surfaces."

Scientists need a great level of precision in order to image the nearby stars, which are no more than 200 light years away.

"Imaging planets directly is supremely challenging," Charles Beichman, executive director of the NASA ExoPlanet Science Institute at the California Institute of Technology, said in a statement. "Imagine trying to see a firefly whirling around a searchlight more than a thousand miles away."

The project is based on four instruments that take infrared photos of light generated by stars and the warm planets that orbit them. The instruments are now operating, and produce some of the highest-contrast images ever created.

The project is helping to create images that reveal celestial objects 1 million to 10 million times fainter than the star at the center of the image.

It utilizes the world's most advanced adaptive optics systems that can manipulate light by applying more than seven million active mirror deformations per second with a precision level better than 1 nanometer about 100 times smaller than a typical bacterium.

Another tool utilized is a spectrograph built by the team from the Museum of Cambridge University that records the images of other solar systems in a rainbow of colors simultaneously. The astronomers also use a specialized wavefront sensor built by NASA's Jet Propulsion Laboratory (JPL) that is imbedded in the coronagraph, which senses imperfections in the light path at a precision of nanometer.

The project has now demonstrated a technique that can darken the speckles farther than ever before, carving a dark square in the speckle background centered on the star.

The dark region can only be created by measuring and controlling distortions in the distant star's light.

The dark hole created previously by Project 1640 had only been observed in controlled laboratory conditions, but now the effect on the star has been observed through a telescope.

"High-contrast imaging requires each subsystem perform flawlessly and in complete unison to differentiate planet light from starlight," Richard Dekany, the associate director for instrumentation at Caltech Optical Observatories, said in a press release. "Even a small starlight leak in the system can inundate our photodetectors and pull the shroud back down over these planets."

The researchers have now started a three-year survey, during which they are planning to image hundreds of young stars.

"The more we learn about them, the more we realize how vastly different planetary systems can be from our own," Jet Propulsion Laboratory astronomer Gautam Vasisht said. "All indications point to a tremendous diversity of planetary systems, far beyond what was imagined just 10 years ago. We are on the verge of an incredibly rich new field."

One of the biggest research potentials of the new project is to broadening scientists understanding about what the architectures of solar systems say about our own planet.

"In order to understand the origin of Earth, we need to understand the origin of planets in general," Lynne Hillenbrand, an astronomy professor at the California Institute of Technology, said in a statement. "How do they form, how do they evolve? How does our solar system with both gas giant and rocky small planets compare to others? These are questions that are very important to humanity."

Image 2 (below): Two images of HD 157728, a nearby star 1.5 times larger than the Sun. The star is centered in both images, and its light has been mostly removed by the adaptive optics system and coronagraph. The remaining starlight leaves a speckled background against which fainter objects cannot be seen. On the left, the image was made without the ultra-precise starlight control that Project 1640 is capable of. On the right, the wavefront sensor was active, and a darker square hole formed in the residual starlight, allowing objects up to 10 million times fainter than the star to be seen. Images were taken on June 14, 2012 with Project 1640 on the Palomar Observatory's 200-inch Hale telescope. (Courtesy of Project 1640)