The planet is in an elliptical orbit that carries it as close to the star as Earth is from the Sun, and as far from the star as Jupiter is from the Sun. Epsilon Eridani is a young star, only 800 million years old. It is still surrounded by a disk of dust that extends 30 billion kilometers from the star.For that matter, the orbit of the planet, along with the lack of proximity to the disk (which is over 18 billion miles from the star), suggests either a capture origin, expulsion, or collision.
Astronomers Track the Birth of a PlanetOur galactic neighbor, Epsilon Eridani, has long been the target of both scientific and literary speculation. Back in 1960, the star was one of two targets of the very first SETI search – Frank Drake's Project Ozma. A few years later, when Star Trek hit television screens across North America, Epsilon Eridani was designated as the sun of Vulcan, Mr. Spock's home world. Then, in the year 2000, a true planet was detected orbiting Epsilon Eridani – among the first extrasolar planets discovered, and the closest one to Earth. And now, the decades of close observation of the star have yielded a truly remarkable result: the first direct evidence that planets are formed from clouds of gas and dust swirling around young stars... Epsilon Eridani is in some ways very similar to our Sun. Only 10.5 light years away it resides practically in our galactic backyard, and its mass is estimated at 83% of the Sun. The main difference between the two is their age: whereas the Sun has reached the mature middle age of 4.5 billion years, Epsilon Eridani is a sprightly 800 million years old. Because of its youth, Epsilon Eridani is still surrounded by a swirling disk of gas and dust, whereas our Sun had lost its own disk billions of years ago. Nevertheless, according to prevailing models, Epsilon Eridani is old enough for its disk to have given birth to actual planetary companions, and it therefore came as no surprise that just such a planet was discovered orbiting the star in 2000... The authors then observed that the orbital inclination of the planet, as seen from Earth is quite substantial – a full 30 degrees. This result is important for calculating the planet's mass, because it reveals what component of its real motion is seen from Earth as the "back and forth" wobble of the star detectable in spectroscopic measurement. In this case, the mass of the planet turned out to be 1.55 Jupiters, well within the range of planetary masses. But the 30 degree tilt is important for another reason: it very closely matches the known tilt of the protoplanetary disk surrounding Epsilon Eridani. And this means that the giant Jupiter-like planet known as Epsion Eridani_b is very likely the first planet ever detected orbiting within the cloud of gas and dust from which it formed.
by Amir Alexander
Planetary Society
19 October 2006