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June 22, 2005 01:00 PM (EDT)

News Release Number: STScI-2005-10

Elusive Planet Reshapes a Ring Around Neighboring Star

June 22, 2005: The top view, taken by NASA's Hubble Space Telescope is the most detailed visible-light image ever taken of a narrow, dusty ring around the nearby star Fomalhaut (HD 216956). The image offers the strongest evidence yet that an unruly and unseen planet may be gravitationally tugging on the ring. The left part of the ring is outside the telescope's view. Hubble unequivocally shows that the center of the ring is a whopping 1.4 billion miles (15 astronomical units) away from the star. This is a distance equal to nearly halfway across our solar system. The geometrically striking ring, tilted obliquely toward Earth, would not have such a great offset if it were simply being influenced by Fomalhaut's gravity alone.

The view at bottom points out important features in the image, such as the ring's inner and outer edges. Astronomers used the Advanced Camera for Surveys' (ACS) coronagraph aboard Hubble to block out the light from the bright star so they could see the faint ring. The dot near the ring's center marks the star's location. Despite the coronagraph, some light from the star is still visible in this image, as can be seen in the wagon wheel-like spokes that form an inner ring around Fomalhaut.

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Q & A: Understanding the Discovery

  1. 1. Is more than one planet orbiting Fomalhaut?

  2. Astronomers said it is possible that several planets are circling the star. If the planets exist, they are too small and too dim to be seen by telescopes.

  3. 2. How do astronomers know that the object orbiting Fomalhaut is a planet?

  4. Astronomers have collected solid evidence for a planetary-mass object orbiting Fomalhaut. They think they have found a planet because Hubble would have detected an object larger and brighter than a planet, such as a brown dwarf. Planets, however, are too small and too dim to be seen by Hubble.

  5. 3. How big is the putative planet?

  6. Because Hubble could not see the planet, it was unable to measure its mass. Astronomers will conduct computer simulations of the ring's dynamics to estimate the planet's mass.

  7. 4. Could the suspected planet support life, as we know it?

  8. The putative planet is too far away from Fomalhaut and therefore too cold to support life. The suspected planet may be orbiting far away from Fomalhaut, inside the debris ring's inner edge, between 4.7 billion and 6.5 billion miles (50 to 70 astronomical units) from the star. Even planets that may be closer to the star - and therefore warmer - would not sustain life. Fomalhaut's lifespan is only 1 billion years. If Earth is a typical example, life takes billions of years to evolve. The star would burn out before life had a chance to begin on the planet.

  9. 5. Is Fomalhaut like the Sun?

  10. Fomalhaut, a type A star, is bigger, brighter, hotter, and younger than the Sun. The star is about 2.3 times the mass of the Sun and is about 200 million years old. The Sun is about 4.5 billion years old.

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Credit: NASA, ESA, P. Kalas and J. Graham (University of California, Berkeley), and M. Clampin (NASA's Goddard Space Flight Center)