By William J. Cromie

Gazette Staff

A new planet has been discovered by a team of researchers that includes astronomers from Harvard. The newly found heavenly body lies about 300 trillion miles away in the constellation Northern Crown.

Its orbit around the sunlike star Rho Coronae Borealis supports the idea that many other solar systems with worlds like Earth exist in our galaxy. The planet is estimated to be slightly larger than Jupiter, or more than 300 times more massive than Earth.

"This discovery helps show that giant planets like Jupiter may be reasonably common around ordinary stars," says Robert Noyes, professor of astronomy at the Harvard-Smithsonian Center for Astrophysics (CfA). "It's exciting to think that there may be many smaller planets much more like Earth in orbit around these stars."

At least 10 other planets have been discovered around sunlike stars in our galaxy. They range from1/20 to 10 times the size of Jupiter and orbit between 5 million and almost a billion miles from their mother stars. The new, unnamed planet orbits about 23 million miles from Rho Coronae Borealis and completes one orbit every 40 days, making its year 40 days long. Jupiter lies about 484 million miles from the sun, and its year runs about 4,329 days long.

The Northern Crown planet is closer to its star than Mercury is to the sun, making it too hot (more than 500 degrees F.) for any kind of known life to exist.

Rho Coronae Borealis can be seen without a telescope or binoculars from February through December in the Northern Hemisphere. One of the stars forming the crown of its constellation, its light takes 50 years to travel to Earth.

Seeing Gravity's Pull

Astronomers don't actually see planets orbiting stars that far away. They detect them by the gravitational changes in speed they exert on their stars. In the latest case, skywatchers used a special instrument mounted on a telescope at the Whipple Observatory near Tucson, Ariz.

"It was the star's solar similarity that led us to target it for study," said Scott Horner of Pennsylvania State University, who designed and built a key part of the instrument. "Soon after we began to look at it, we thought that its velocity was varying. Now, after 11 months of monitoring, we're sure."

The researchers had to measure a change of only 150 miles an hour over a 40-day period in a star 300 trillion miles away. The change comes from the gravitational tug of the planet as it moves from one side of the star to the other.

Its almost circular orbit suggests to astronomers that the planet formed in the same way as Earth and the other solar-system worlds. According to the most accepted theory, planets form from gas and dust left over from the birth of a sun. This material swirls around the sun in a disk billions of miles in diameter, the gas and particles attracting each other by gravity. Dust builds into rocks, small rocks into large rocks until, over millions of years, they coalesce into rocky planets like Earth, or huge gas balls like Jupiter.

Some astronomers suspect that not all of the recently discovered "planets" formed this way and so are not really planets. Stars often form in pairs. The bigger twin may attract enough material from the smaller to prevent gravity from squeezing the latter tightly enough to form a fiery globe of gas. In other words, some of the Jovian-size objects near stars may be cold, failed stars rather than planets.

If so, that burns a hole in the theory that planets, and hence places where life could begin, are as common as some scientists believe, or hope.

Timothy Brown and Edward Kennelly of the National Center for Atmospheric Research in Boulder, Colo., also participated in the discovery. "Rho Coronae Borealis appears to be about 10 billion years old, or twice as old as the sun," Brown says.

The Harvard-Smithsonian team also included Sylvain Korzennik, Martin Krockenberger, and Peter Nisenson, researchers at the Center for Astrophysics, and Saurabh Jha, a graduate student in astronomy.

Jha worked on analyzing data that would reveal any changes in the speed of Rho Coronae Borealis. "It's intriguing when you see some of the variation you're looking for," he notes. "But the 'Eureka!' phase comes when you see a pattern repeated over and over. After months of work, when you become sure of what you're seeing, it's exhilarating."