As of March 10 we know of 4,692 planets orbiting stars beyond our own. The vast majority of these extrasolar planets circle lesser-known stars, but a potential new discovery may change that. Astronomers have discovered hints of a giant, blazingly hot planet orbiting Vega, one of the brightest stars in the night sky.
Vega pops up over the northeastern horizon around 11 p.m. local time in mid-March, the first in a wave of "summer stars" that will come to dominate the sky in July and August. Vega is the 5th brightest star — just a hair fainter than Arcturus — making it impossible to miss. It's also the brightest member of the familiar star-pattern the Summer Triangle.
Located 25 light-years from Earth, it would take about 250 million years to drive to Vega at typical freeway speeds of 70 mph (113 km/hour). That sounds far away, but astronomically speaking, it's just down the block. Such are the unhuman distances that separate the stars.
Despite Vega's fame and proximity, astronomers have yet to detect a single planet orbiting the star. That compelled Spencer Hurt, an astronomy undergraduate student at the University of Colorado (Boulder) to take a closer look. As part of a summer research fellowship he and his colleagues examined about 10 years of data on Vega collected by the Fred Lawrence Whipple Observatory.
Orbiting planets tug on their host suns and make them wobble back and forth in a repeating pattern. When the planet pulls the star in one direction, its speed increases slightly. When it's around the opposite side, it pulls the star the other way, and its speed decreases. If Hurt could find these wobbles in the Vega data, he might be on to something.
Vega didn't make things easy for the team. It's bigger and younger than the sun and rotates much faster — 16 hours compared to the sun's sluggish 27 days. But the group appears to have successfully detected a signal indicating that Vega hosts a massive, close-orbiting planet, what astronomers call a "hot Neptune" or "hot Jupiter". "Hot" because the planet orbits the star so closely it completes a revolution in just 2.4 days.
"It would be at least the size of Neptune, potentially as big as Jupiter and would be closer to Vega than Mercury is to the sun," Hurt said in a press release.
Like a marshmallow brought too close to the fire, temperatures are hot enough to puff up the planet and for iron to vaporize into a gas.
Back in 1984, astronomers using the infrared-light-sensitive satellite IRAS, detected a disk of dust orbiting Vega, exactly what you'd expect to see when protoplanets and smaller bodies collide in a newly-forming solar system. The disk or shell extends at least 330 times Earth's distance from the sun away from Vega, much farther than Pluto. Denser blobs of dust within the disk could indicate the presence of additional planets enveloped in shrouds of debris from their formation.
There's still a lot more work to do to confirm the planet's existence, but in the meantime we can look toward Vega's rising on late March nights, knowing that a star familiar to so many might be home to a planet and perhaps even a solar system.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.