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 |  | New 'Vulcan' Planet Tantalizes Astronomers
By Ray Villard
Special to SPACE.com
posted: 07:01 am ET
13 August 2000
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Astronomers have long had their eye on Epsilon Eridani, the relatively nearby star around which a "vulcan" planet orbits
Astronomers interested in other worlds have long had their eyes on Epsilon Eridani, a relatively nearby star which gained media attention last week when astronomers announced that a planet orbits it.
One of the nearest sun-like stars to Earth, Epsilon Eridani beckoned the imagination of a young astronomer 40 years ago. In a bold and provocative experiment Frank Drake aimed a radio telescope in Green Bank, West Virginia, at Epsilon Eridani to listen for radio transmissions from an alien civilization.
Epsilon Eridandi is a 3rd magnitude star in the southern constellation Eridanus the River. Its newly detected planet has not yet been seen directly. The planet is 100 million times fainter than the star, and lost in its glare. Epsilon Eridani is much younger than the sun, only about 0.5-1 billion years old while the sun is 4.5 billion years old. The star is about one third the sun's temperature, but is very bright because it is only 10 light-years away.
Drake was startled to pick up a signal once he targeted the star. To Drake's disappointment it turned out to be a radio transmission from an airplane. No one was out there – 10 light years away -- sending us a radio message saying "hello."
Interest in Epsilon Eridani perked again 38 years later when astronomers found a huge ring of dust around the star. The ring was considered a "construction yard" of raw material for planet building. A bright spot within the ring was thought to be dust trapped by the gravity of an unseen planet.
Now, astronomers believe they have found a planet slightly larger than Jupiter orbiting Epsilon Eridani – making it the closest extrasolar planet ever found to our sun. Epsilon Eridani may eventually be the first star ever visited by an interstellar probe. It's a mere puddle jump in the galaxy - no need for a "warp drive" envisioned in science fiction.
Earth potential
Now, the planetary finding at Epsilon Eridani brings to bear more details that intrigue those searching for worlds beyond ours. For instance, the planet's orbit is so big that it takes a leisurely seven years to make one circuit about the star (as opposed to Jupiter's 12-year period).
"That’s what made this star really interesting," says astrophysiscist Mario Livio of the Space Telescope Science (STScI) Institute in Baltimore. "If there were any rocky planets inside the orbit of the discovered planet, they would be inside a ‘habitable zone’ where temperatures would be just right for liquid water to exist on planetary surfaces."
This is in striking contrast to many of the previously discovered giant planets that are dubbed "star huggers." They whirl about their parent star in dizzying small orbits, some taking only a matter of days to complete one trip around the star.
According to planet formation theory, these " hot Jupiters" must have migrated to these tight orbits from farther out, in a cooler region where they could amass a great deal of interstellar gas. Along the way they would have scattered any earthlike planets.
Disruptive orbits
Many extrasolar giants discovered previously are in elliptical orbits that swing close by and then far away from their star. They would derail the orbits of any rocky siblings, or prevent their formation in the first place.
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Some astronomers caution that the bubbly excitement over finding this nearest Jovian extrasolar world has to be dampened by the fact that it too is in a disruptive roller-coaster style orbit too. It swings as close to the star as Mars, and as far away as Jupiter.
"The fact that the detected planet is in an eccentric orbit also suggests that it has interacted with another massive body in the planetary system that we have not yet discovered," adds stellar formation expert John Bally of the University of Colorado. "Such a second body would further restrict the possible locations of stable orbits for smaller objects."
Planet formation specialist Alan Boss of the Carnegie Institutions in Washington D.C. flatly dismisses the chances for any earthlike planets around Epsilon Eridani. "The big planet would prevent the planetary embryos from growing to Earth size. Instead you would get more of an asteroid belt in the habitable zone."
This telescopic image of the region around Epsilon Eridani, take in submillimeter wavelengths, shows the emission from dust particles, each a fraction of a millimeter in size, orbiting around the star. It is likely that that tiny dust particles around Epsilon Eridani will gradually accumulate into comets like those in the Solar System's Kuiper Belt. The false-color scale shows where the brightest regions are (yellow/red), in contrast to the areas with very little dust (blue/black). The dust lies mainly in a ring around the star, with a radius of 60 times the size of the Earth's orbit. The bright spot at the 7:00 position is a large concentration of dust perhaps caused by the gravity of an unseen planet.
His point: Epsilon Eridani is yet another star where its biggest planet interferes with the possibility of having habitable earthlike planets – sorry Mr. Spock (Epsilon Eridani was the home of Spock’s native planet Vulcan in the Star Trek film and TV series).
Someday: stabilizing Jupiters
Optimistic astronomers say it is inevitable that, with improvements in observational techniques and accumulating years of data monitoring stellar wobbles (aliens would have to watch our sun for 12 years to see it wobble because of Jupiter’s tug), Jupiter-like planets in circular long-period orbits will eventually be found. And then astronomers will surmise that terrestrial planets are protectively nested inside the giant’s orbit.
More than simply staying out of the way of nascent Earths, a Jupiter-sized planet at the right distance from its star and in a circular orbit would foster the evolution of life on the terrestrial worlds.
Its powerful gravitational influence would keep the terrestrial planets in stable, circular orbits. The gas giant’s immense gravity would deflect wayward comets that would otherwise crash into the terrestrial worlds to repeatedly disrupt life’s evolution.
Until a true template of our solar system is at last found, we will have the lingering uncertainty that maybe -- due to some freaky and rare set of circumstances -- our planetary family happens to be arranged the way it is around our sun. Despite the current "big bang" of planet discoveries, we are still left to ponder whether our solar system is the exception and not the rule in the galaxy.
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