New technique could uncover planets that harbor life
By: David Campbell
Princeton University astrophysicist Bohdan Paczynski was among the international team of astronomers who have discovered the smallest planet found outside of our solar system using a technique that researchers believe could uncover other planets that harbor life.
The rocky ice planet is about 5½ times the mass of Earth and located more than 20,000 light years away in the constellation Sagittarius, near the center of the Milky Way galaxy.
The discovery, which is detailed in the Jan. 26 issue of Nature, was made by a partnership of astronomers from around the world, including the Optical Gravitational Lensing Experiment group co-founded by Professor Paczynski, 66, who is the Lyman Spitzer Professor of Theoretical Astrophysics at Princeton.
He said this week that life on other planets probably won’t be discovered during his lifetime, but maybe sometime in the future.
"At this time, the most advanced and expensive NASA project aiming at direct imaging of planets is the Terrestrial Planet Finder," he said of a space telescope NASA hopes to launch sometime between 2012 and 2015.
"It will cost several billion dollars," he continued. "Prior to spending all these funds, NASA would like to know if there are terrestrial planets to look after. At this time, gravitational microlensing is the only way to find out."
Researchers do not believe that life could be sustained on the icy new planet that was discovered, which has an estimated surface temperature of minus 364 degrees Fahrenheit similar to Pluto’s. The planet orbits its star at a distance of more than three times that of the Earth orbiting the sun. Its star is about one-fifth the mass of our sun.
But astronomers are optimistic that the gravitational microlensing technique referenced by Professor Paczynski, used to find the new planet, will lead to the discovery of other planetscloser in size to Earth or smaller, and that may exist in orbits around stars where temperatures could sustain liquid surface water.
Three planets have been found in the last two years using the method, which allows astronomers to detect changes in the brightness of a star when a massive object in space like a planet or star or even a black hole crosses in front of it.
The object’s strong gravitational pull bends the light rays from the distant star and magnifies them like a lens. By analyzing the patterns of the brightening of the distant star’s light rays, researchers can identify the object passing in front of it.
Previously, more than 150 planets were discovered outside our solar system with a technique known as the radial velocity method, which observes a wobble in stars caused by the planet’s gravitational effects. But Professor Paczynski said that method, while effective at finding massive planets, such as Jupiter, or close-orbiting ones, cannot match the observational sensitivity of gravitational microlensing for detecting small planets with wide orbits around their suns.
Professor Paczynski co-founded the OGLE project with Andrzej Udalski of Warsaw University, who designed and leads the effort to survey millions of stars. OGLE researchers first detected the microlensing event that led to the new planet discovery in July with its telescope at the Las Campanas Observatory in Chile.
The OGLE team collaborated with several other international research groups to confirm the presence of the new planet. In total, the effort included 73 researchers from 32 institutions, Princeton said.
Two planets previously discovered using gravitational microlensing were much larger than the most recent finding. Both were roughly three to five times the size of Jupiter, the largest planet in our solar system with a mass 318 times that of Earth.
Professor Paczynski first proposed using gravitational microlensing to search for planets in 1991 along with his graduate student, Shude Mao, now a professor at Manchester University in England. He predicts that as OGLE and other research teams employ the technique to find smaller planets very far from Earth, their work will aid NASA’s efforts to make similar discoveries closer to our solar system.
"Unfortunately, gravitational microlensing detects stars at very large distances many thousands of light years so it is not possible to image those planets," he said, and noted that hopefully will be done with the Terrestrial Planet Finder.
"It is sensible to find out if there are planets with the Earth’s mass in orbits similar to ours," Professor Paczynski said. "This search can be done with gravitational microlensing, spending far smaller funds. Once we know such planets are common, it will make sense for NASA to look for them."
The American Astronomical Society certainly has taken note of his achievements.
Professor Paczynski has been awarded the society’s highest honor, the Henry Norris Russell Lectureship, in recognition of a lifetime of eminence in astronomical research, Princeton announced this week.