An Earth Hidden in Dust
Dusty Disk around Nearby Star May Hide Earth-Like Planet
A recent survey by a team of Japanese astronomers may have found an Earth-like planet hidden in the dust around a nearby star. Searching for Earth-like planets is a major goal for astrobiologists who are attempting to estimate the number of habitable worlds beyond our Solar System.
Using an instrument called the Coronagraphic Imager with Adaptive Optics (CIAO) at the Subaru Telescope, researchers in Japan recently resolved a circumstellar disk around the young lightweight star FN Tau. The diminutive star is located in a star-forming region toward the Constellation Taurus at a distance 460 light years from Earth. This star is a youthful 100 thousand years old and weighs only one tenth of the Sun.
A circumstellar disk is a mixture of gas and dust around a newly forming star. The disk accompanies almost most, if not all, sun-like star formation processes, and planets commonly form in this disk. The disk can also be referred to as a protoplanetary disk because the solid particles inside the disk collide and stick together and grow into planetesimals, which then crash into each other eventually accumulating enough mass to be stabilized as planets.
In response to this scenario, the study of young stars and their surrounding structures provide details into the formation of planetary systems, and the search for planets outside our solar system motivates much of modern astronomy. Although hundreds have been found through indirect methods, being the first to directly image a planet around a nearby star is one of the primary goals of Subaru. The findings at FN Tau show that Subaru is on the right path toward planet discovery.
The FN Tau researchers pointed the Subaru Telescope toward the tiny star trying to detect lightweight disks. Their study found a thick, compact, and roughly circular protoplanetary disk with a radius 260 times the Earth-Sun distance. The disk is rather featureless, and does not have any anomalies or asymmetries, such as rings, spirals, or arms. The mass of the disk was estimated to be 6% of the central FN Tau star, and, by far, the least massive one directly detected. In result, the discovery is the combination of the most lightweight protoplanetary disk around the least massive star.
One of the questions to come out during the study was what kind of planets can be formed from the disk around FN Tau? To date, astronomers worldwide have found 270 extrasolar planets using the indirect detection method, and all are primarily Jupiter-like giant planets; the least massive exoplanet is still 5 times heavier than Earth.
Because it surrounds a smaller star, the disk about FN Tau is believed to more likely contain Earth-like planets. The best-fit model used during this study shows that the lightweight disk around FN Tau could only produce Earth-like planets. The planetary system formation theory also predicted that the disk is able to form planets lighter than the Earth within 30 astronomical units (AU), the distance where we find planets in our Solar System. For the future, astronomers are hopeful of using Subaru’s newest technologies for resolving the detailed structure of the disk to analyze the size and composition of the dust, culminating in the first image of a terrestrial planet near FN Tau.
This discovery is reported in the Astrophysical Journal Letters in its January 20, 2008 issue, Volume 673, page L67. Dr. Tomoyuki Kudo, principal investigator, presented the findings of this project to the public in a press conference at the NAOJ headquarters in Mitaka, Japan on Friday, February 8, 2008. Further details about this study, other research findings, and the state-of-the art technologies at the Subaru Telescope are found on our website at www.subarutelescope.org.
Related Web Sites
Astrobiology Roadmap Goal 1: Habitable Planets
Donuts and Banana Splits
Beta Pic’s Dust Bunnies
Racing to Picture a Planet
Mapping an Alien World
Astrobiology Top 10: Astronomers Find Habitable Earth-like Planet