One or more large planets may shepherd a lopsided dusty ring that encircles the nearby star Fomalhaut, according to new images released today from the Hubble Space Telescope. The discovery gives astronomers a chance to find some of the closest young planets that may exist.
At a distance of just 25 light-years, Fomalhaut is one of the brightest stars seen from Earth. Astronomers think the youthful, 200-million-year-old star is more than twice as massive as our sun. Satellite data from the mid-1980s first showed that a faint shroud of debris surrounds Fomalhaut, probably from collisions of asteroids and comets. Recent images suggested that this dusty envelope is lopsided, as if a planet perturbs the particles. But Fomalhaut is so bright that its glare washed out attempts to see details.
Now, a Hubble camera has unveiled the full band of dust by placing a small disk in front of the star to eclipse its blazing light. Images taken over a 5-month period in 2004 reveal a sharp ring of reflected light from sand-sized grains, says astronomer Paul Kalas of the University of California, Berkeley. The giant ring spans about four times the width of our solar system. The pictures clearly show that the ring is centered not on Fomalhaut but on a point in space 2 billion kilometers away from the star. That's a sure sign of gravitational bullying by unseen objects, Kalas maintains. "Taken together, the offset and the [sharp] edge point to a planetary system contained within the belt," he says.
One or more large, young planets--possibly the size of Neptune or Jupiter--must dictate the shape of the dust, according to simulations. The planets would loop around Fomalhaut on eccentric paths and confine small particles to remote orbits. Kalas and his colleagues think they might see a big enough planet directly with high-resolution observations in July by the 10-meter Keck Telescope in Hawaii. The team reported its work today at a NASA news briefing and in the 23 June issue of Nature.
Further studies will illuminate the "final stages of the planetary assembly line" in Fomalhaut's rich belt of material, says astrophysicist Jane Greaves of the University of St. Andrews in Fife, Scotland. "This is a very impressive achievement," she says. "The image is really clear and sharp."