page_title: New Worlds Mission
section_title: Methods
hierarchical_section_title: New Worlds Mission / Methods
caption_attribution_description: English: Occulter diagram
context_page_description: The New Worlds Mission is a proposed project comprising a large occulter flying in formation designed to block the light of nearby stars in order to observe their orbiting exoplanets. The observations could be taken with an existing space telescope, possibly the James Webb Space Telescope when it launches, or a dedicated visible light optical telescope optimally designed for the task of finding exoplanets. A preliminary research project was funded from 2005 through 2008 by NASA Institute for Advanced Concepts and headed by Webster Cash of the University of Colorado at Boulder in conjunction with Ball Aerospace & Technologies Corp., Northrop Grumman, Southwest Research Institute and others. Since 2010 the project has been looking for additional financing from NASA and other sources in the amount of roughly US$3 billion including its own four-meter telescope, or $750 million for one starshade to be used with the James Webb Space Telescope. If financed and launched, it would operate for five years.
context_section_description: Traditional methods of exoplanet detection rely on indirect means of inferring the existence of orbiting bodies. These methods include:
  Astrometry – watching a star move slightly due to the gravitational influence of a nearby planet
  Observing Doppler shifts of the star's spectrum due to the star's movement
  Observing the amount of light from a star change as an extrasolar planet transits the star, preventing a portion of the light from reaching the observer
  Pulsar timing
  Gravitational microlensing
  Observing radiation from circumstellar disks in the infrared
  All of these methods provide convincing evidence for the existence of extrasolar planets, but none of them provide actual images of the planets.
  The goal of the New Worlds Mission is to block the light coming from nearby stars with an occulter. This would allow the direct observation of orbiting planets. The occulter would be a large sheet disc flown thousands of kilometers along the line of sight. The disc would likely be several tens of meters in diameter and would fit inside existing expendable launch vehicles and be deployed after launch.
  One difficulty with this concept is that light incoming from the target star would diffract around the disc and constructively interfere along the central axis. Thus the starlight would still be easily visible, making planet detection impossible. This concept was first famously theorized by Siméon Poisson in order to disprove the wave theory of light, as he thought the existence of a bright spot at the center of the shadow to be nonsensical. However Dominique Arago experimentally verified the existence of the spot of Arago. This effect can be negated by specifically shaping the occulter. By adding specially shaped petals to the outer edge of the disc, the spot of Arago will disappear, allowing the suppression of the star's light.
  This technique would make planetary detection possible for stars within approximately 10 parsecs (about 32 light years) of Earth. It is estimated that there could be as many as several thousands of exoplanets within that distance. The starshade is similar to but should not be confused with the Aragoscope, which is a proposed imaging device designed to use the diffraction of light around a perfectly-circular light-shield to produce an image. The starshade is a proposed sunflower-shaped coronagraph disc that was designed to block starlight that interferes with telescopic observations of other worlds. The "petals" of the "sunflower" shape of the starshade are designed to eliminate the diffraction that is the central feature of an Aragoscope.
  The starshade is a spacecraft designed by Webster Cash, an astrophysicist at the University of Colorado at Boulder's Center for Astrophysics and Space Astronomy. The proposed spacecraft is designed to work in tandem with space telescopes like the James Webb Telescope or a new 4-meter telescope. It would fly 72,000 km (45,000 mi) in front of a space telescope (between the telescope and a target star) and approximately 238,600 miles (384,000 km) away from Earth, outside of Earth's heliocentric orbit. When unfurled, the starshade resembles a sunflower, with pointed protrusions around its circumference. The starshade acts as a very large coronagraph: it blocks light of a distant star, making it easier to observe associated planets. The unfurled starshade could reduce collected light from bright stars by as much as 10 billion-fold. Light that "leaks" around the edges would be used by the telescope as it scans the target system for planets. With the reduction of the harsh light, astronomers will be able to check exoplanet atmospheres tens of trillions of miles away for the potential chemical signatures of life.
caption: The yellow circle represents the star, whose light is blocked by the occulter. The blue circle represents the planet, whose light passes to the observer undisturbed.
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