Planet?

Update
15 JULY 1998. In early June, scientists revealed a digital photo of a planet being flung away from a binary star system. Then in July, other scientists announced the discovery of a planet around Gliese 876, a star that's just 15 light-years from Earth. The planet registers at 1.6 times the mass of Jupiter, and it orbits close to the star. But because Gliese 876 is a lightweight -- about one-third the mass of our sun -- the planet's surface is calculated to be about -75 degrees Celsius. That's inhospitable to life, but the fact that 12 planets have already been discovered outside our solar system should encourage those who suspect we're not alone in the universe. (See "Two Teams Find..." in the bibliography)

Planets on their minds
POSTED JUNE 1996 When astronomer George Gatewood described the discovery of orbital companions around a small star called Lalande 21185, he seemed to be discussing an old friend. And in a sense, he was, since his predecessors at Allegheny Observatory started staring at the star, the fourth-closest to Earth, 66 years ago.
About nine months ago, after a long period of precise measurement Gatewood measured a periodic wobble in the star's motion across the sky. On June 11, Gatewood announced at a meeting of the American Astronomical Society, that these deviations in the star's path signaled the presence of one or two planets orbiting around it.
When a planet orbits a star, both objects actually orbit around the center of mass (defined) of the entire planetary system. Since stars are much more massive than planets, the planets do most of the moving, but with extremely sensitive instruments you can detect movement in stars, especially if they're close by.
center of mass image Although only the planet seems to be moving, they both orbit around a point called the "center of mass" (X). In this one-planet system, the star and the planet are always on opposite sides of the center of mass. If you can see periodic movement in the star, you have indirect proof that something is in orbit around it.
Still, the movement was so small that Gatewood picked his words cautiously: "I see something going around this star," and the best explanation was that a planet with a mass equal to or twice that that of Jupiter was orbiting Lalande 21185 every 30 years or so.
How small is that deviation? It's about .002 arc seconds (defined). Gatewood translates that angle as follows: if you were viewing the moon through a telescope and an astronaut passed a flashlight from one hand to the other, that would be the same angular movement.
That small deviation occurred regularly in Gatewood's data, which stretched back to photos taken 66 years ago.
Gatewood took his time before making an announcement, since he'd made of a name for himself debunking previous "planet" discoveries. "I was nervous," he says. "I'd been a naysayer for a long time. I spent three months trying to make this go away."
But other telescopes showed a similar deviation, reducing the chance for a systematic error (defined). The thing that would not go away, Gatewood, says, is "probably a planet. It's perfectly possible that there are two."
Meet your neighbor
Lalande 21185 is red dwarf star (defined), with about one-third of our sun's mass. It's the fourth-closest "star system" to us (that wording reflects the fact that nearby Alpha Centauri actually contains three stars). Still, it's a fair hike to Lalande 21185: 8.2 light years (about 48 trillion miles), and you can't see it without binoculars.
However, Lalande 21185's proximity explains some of the excitement over the discovery, since details about size, orbit, composition, and even possibly the presence of life, are all easier to see in such a nearby system.
Even more exciting is the fact that this planet looks "familiar" to students of planetary systems.

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		Update 15 JULY 1998. In early June, scientists revealed a digital photo of a planet being flung away from a binary star system. Then in July, other scientists announced the discovery of a planet around Gliese 876, a star that's just 15 light-years from Earth. The planet registers at 1.6 times the mass of Jupiter, and it orbits close to the star. But because Gliese 876 is a lightweight -- about one-third the mass of our sun -- the planet's surface is calculated to be about -75 degrees Celsius. That's inhospitable to life, but the fact that 12 planets have already been discovered outside our solar system should encourage those who suspect we're not alone in the universe. (See "Two Teams Find..." in the bibliography)

Planets on their minds POSTED JUNE 1996 When astronomer George Gatewood described the discovery of orbital companions around a small star called Lalande 21185, he seemed to be discussing an old friend. And in a sense, he was, since his predecessors at Allegheny Observatory started staring at the star, the fourth-closest to Earth, 66 years ago. About nine months ago, after a long period of precise measurement Gatewood measured a periodic wobble in the star's motion across the sky. On June 11, Gatewood announced at a meeting of the American Astronomical Society, that these deviations in the star's path signaled the presence of one or two planets orbiting around it. When a planet orbits a star, both objects actually orbit around the center of mass (defined) of the entire planetary system. Since stars are much more massive than planets, the planets do most of the moving, but with extremely sensitive instruments you can detect movement in stars, especially if they're close by. Although only the planet seems to be moving, they both orbit around a point called the "center of mass" (X). In this one-planet system, the star and the planet are always on opposite sides of the center of mass. If you can see periodic movement in the star, you have indirect proof that something is in orbit around it. Still, the movement was so small that Gatewood picked his words cautiously: "I see something going around this star," and the best explanation was that a planet with a mass equal to or twice that that of Jupiter was orbiting Lalande 21185 every 30 years or so. How small is that deviation? It's about .002 arc seconds (defined). Gatewood translates that angle as follows: if you were viewing the moon through a telescope and an astronaut passed a flashlight from one hand to the other, that would be the same angular movement. That small deviation occurred regularly in Gatewood's data, which stretched back to photos taken 66 years ago. Gatewood took his time before making an announcement, since he'd made of a name for himself debunking previous "planet" discoveries. "I was nervous," he says. "I'd been a naysayer for a long time. I spent three months trying to make this go away." But other telescopes showed a similar deviation, reducing the chance for a systematic error (defined). The thing that would not go away, Gatewood, says, is "probably a planet. It's perfectly possible that there are two." Meet your neighbor Lalande 21185 is red dwarf star (defined), with about one-third of our sun's mass. It's the fourth-closest "star system" to us (that wording reflects the fact that nearby Alpha Centauri actually contains three stars). Still, it's a fair hike to Lalande 21185: 8.2 light years (about 48 trillion miles), and you can't see it without binoculars. However, Lalande 21185's proximity explains some of the excitement over the discovery, since details about size, orbit, composition, and even possibly the presence of life, are all easier to see in such a nearby system. Even more exciting is the fact that this planet looks "familiar" to students of planetary systems.