Over the past 13 years, astronomers have found more than 300 planets orbiting other stars. These planets, known as extrasolar planets, are usually detected by measuring the slight wobbles of their stars. None, however, have been viewed directly because they are too far away and too dim to be seen. Observing extrasolar planets is like trying to see a fly fluttering around a streetlight.
Now, astronomers using NASA’s Hubble Space Telescope have taken the first visible-light images of a planet orbiting the nearby, bright southern star, Fomalhaut. The star is located 25 light-years away in the constellation Piscis Australis and is a relatively young star, only 200 million years old. The images show the planet, named Fomalhaut b, as a tiny point source of light orbiting the star. Observations taken 21 months apart with the Advanced Camera for Surveys show that the planet is orbiting Fomalhaut, and therefore is gravitationally bound to it. Fomalhaut b is orbiting 10.7 billion miles from its star.
Like the hundreds of other known extrasolar planets, Fomalhaut b is a gas-giant world, estimated to be no more than three times Jupiter’s mass. Astronomers, however, suspect it might have one striking characteristic that separates the newly discovered planet from its extrasolar brethren. It may be surrounded by an immense Saturn-like ring system. “The planet is brighter than expected for an object of three Jupiter masses,” says Paul Kalas of the University of California, Berkeley, and the study’s lead researcher. “If we’re seeing light in reflection, then it must be because Fomalhaut b is surrounded by a planetary ring system so vast, it would make Saturn's rings look pocket-sized by comparison. The ice and dust reflect starlight.” Perhaps Fomalhaut b’s ring will eventually coalesce to form moons.”
An immense debris disk about 21.5 billion miles across surrounds the star. Astronomers have long considered the Fomalhaut system as a potential breeding ground for planets because of the star’s vast debris ring. “Fomalhaut b may actually show us what Jupiter and Saturn resembled when the solar system was about 100 million years old,” Kalas says. Circumstantial evidence for Kalas’ planet theory came from Hubble’s confirmation that the Fomalhaut ring is offset from the star’s center. The disk’s sharp inner edge is also consistent with the presence of a planet that gravitationally “shepherds” particles within it.
Kalas and his team plan follow-up Hubble observations in 2009 to further study the Fomalhaut system. "We hope those observations will greatly refine what we know about Fomalhaut b’s orbit,” Kalas says. “New measurements of the brightness at various wavelengths also will help in deciphering the physics that makes Fomalhaut b shine.” Perhaps future observations will turn up more planets. Fomalhaut b may be the outermost planet in a whole solar system of planets, just as Neptune is in our solar system.
Astronomers, however, may have to wait for the James Webb Space Telescope, slated to launch in 2018, to find out whether planets in the Fomalhaut system could sustain life.
“We'll probably have to wait for the James Webb Space Telescope to give us a clear view of the region closer to the star where a planet could host liquid water on its surface,” Kalas says.
"Tales of ... The first image of a planet orbiting another star" explains how the Hubble Space Telescope found and imaged a planet called Fomalhaut b. This marks the first time astronomers have captured the image of a planet orbiting another star. The planet is thought to be a gas giant that is three times larger than Jupiter, with an extensive ring system to make it bright enough for the camera to capture it.
Teachers can use this resource as:
A content reading selection. Teachers should discuss the meaning of unfamiliar vocabulary prior to having students read this selection.
An engagement activity. Have students read the selection. Ask them to identify the events that led astronomers to capture the images of the planet around the star Fomalhaut.
An inquiry tool. Propose a question, such as, "Have astronomers ever captured the image of a planet outside the solar system?" Have students read the selection and write down as many questions as they can about the information in the text.
A source of information. Students can use this as an example of how astronomers have found more than 300 planets orbiting other stars. The story also highlights the next steps in the process of finding habitable worlds around other stars.
HubbleSite press release: "Hubble Directly Observes Planet Orbiting Fomalhaut"
HubbleSite press release: "Elusive Planet Reshapes a Ring Around Neighboring Star"