Dusty trails may reveal new planet

Great blobs of dust may signal the presence of a planet orbiting Vega, the brightest star in the summer sky.

The dusty structures have been suspect since the early 1980s when astronomer/writer Carl Sagan located an alien listening-station near Vega in his novel “Contact,” later made into a movie starring Jodie Foster.

Last year, astronomers at the Harvard-Smithsonian Center for Astrophysics took a closer look at the dust with the help of a large telescope array in the French Alps. “It’s one of the closest and brightest stellar dust clouds visible from the Northern Hemisphere,” notes astronomer David Wilner. “These clouds are much easier to detect than the planets because of their larger area. It’s like seeing the wake of a boat from an airplane when the boat itself is too small to see.”

Such dust litters our solar system. It comes from collisions between small meteors and asteroids, and from comets spiraling inward toward the sun. The gravity of planets pushes, pulls, and traps this dust into various structures that would not otherwise appear.

Just as sky-watches on Earth can see these signs around Vega, some 150 trillion miles away, aliens on a Vegaian planet or listening post could see grimy evidence of planets orbiting the sun. Jupiter, the largest planet in the solar system, sweeps out a pattern of dust that would be visible from Vega with the same type of telescopes available on Earth. Our planet creates an enriched ring of dust along its orbit, but the trail is too small to see from very far.

From the size and location of its cosmic dust bunnies, Wilner and colleagues estimate that the alleged Vegaian planet would be least as big as Jupiter, which is 300 times as massive as Earth. It would probably be cloaked in poisonous gases and lacking a solid surface, water, or life. (That doesn’t mean that its neighborhood couldn’t support a listening post of the type envisioned in “Contact.”)

If further observations actually reveal such a planet, it wouldn’t be very exciting from the point of view of locating intelligent extraterrestrials. However, it would provide a promising new tool for easily finding other worlds. Besides Vega, astronomers are peering closely at dusty structures around three other stars, Epsilon Eridani, Fomalhaut, and Beta Pictoris. Fomalhaut has been used for centuries as a navigation star, and Epsilon Eridani is a mere 60 trillion miles away. Earthlings could get a message to Epsilon Eridani in 10 years as opposed to the 25 years it took aliens near Vega to receive television transmissions from the 1936 Olympics in the movie “Contact.”

Wobbling into view

Virtually all of the 70-plus planets found outside the solar system were discovered by irregular movements of their mother stars. The tug of gravity from these planets produces slight wobbles in the paths of their suns, which can be detected by changes in their light. Vega, which appears in the constellation Lyra, faces us nearly pole-on, making such minute vacillations almost impossible to see.

However, Vega makes an excellent target for the study of dust clouds, which circle it like rings around a bull’s eye. From this perspective, the planet seems to be in an elliptical orbit that takes it almost 3 billion miles from Vega, or about the distance from the sun to Neptune. The gravity of a planet like that would act like a wave, trapping dust into concentrations 5.4 billion miles to the southwest and 6.75 billion miles to the northeast of the star.

“In other words, peaks of dust seen at such positions are best explained by the influence of an unseen planet in an eccentric orbit around Vega,” Wilner says.

Circumsteller dust does not present an easy target to see with an optical telescope. Rather, the dust is warmed by radiation from the star, which it then re-radiates at microwave or infrared wavelengths (about 0.5 millimeters). The Vegaian radiation was first detected in 1983 by instruments aboard the Infrared Astronomy Satellite. Wilner and his colleagues employed an array of five 50-foot-diameter antennas to search the radiation for evidence of interesting structures. These antennae sit atop the 8,400-foot-high Plateau de Bure, near Grenoble, France.

Wilner, along with Matt Holman, Paul Ho, and Marc Kuchner, found the first evidence of a planet in data collected last year. They reported the find last month at a meeting of the American Astronomical Society in Washington, D.C. More details, along with photographs, have been submitted for publication to The Astrophysical Journal.

Meanwhile, the Harvard astronomers are looking through powerful optical telescopes near the summit of 13,796-foot-high Mauna Kea in Hawaii to see if they can spot the planet. Later, they will use an array of eight antennas being built on that mountain by the Smithsonian Astrophysical Observatory and astronomers from Taiwan. This new facility will be the best in the world for looking at radiation from cold dust, which commonly occurs in star- and planet-forming regions.

“It may take us five to 10 years to conform the existence of a planet near Vega,” says Wilner. But it will only take one such sighting to show that cosmic dust can be used as a planetary signpost anywhere in the universe.

Then felt I like some watcher of the sky/When a new planet swims into his kin.
– Keats