Newly Discovered Baby Planet Confounds Expectations: Raw Materials For Habitable Planets Around Surprisingly Young Stars

The critical infrared “eyes” of the infrared telescope were designed in part by physics and astronomy professors Judith Pipher, William Forrest, and Dan Watson, a team that has been among the world leaders in opening the infrared window to the universe. It was Forrest and Pipher who were the first U.S. astronomers to turn an infrared array toward the skies: In 1983, they mounted a prototype infrared detector onto the University telescope in the small observatory on top of the Wilmot Building on campus, taking the first-ever telescopic pictures of the moon in the infrared, a wavelength range of light that is invisible to the naked eye as well as to most telescopes. The effort attracted colleagues and supporters, culminating 20 years later in the launch of the Spitzer Space Telescope and the discovery of the possible toddler planet.

Watson, Forrest and members of the Spitzer Infrared Spectrograph instrument team detected substantial amounts of icy organic materials sprinkled throughout several “planetary construction zones,” or dusty planet-forming disks, around five young, sun-like stars in the constellation Taurus, 420 light-years from Earth. These materials, mostly microscopic dust particles coated with water, methanol and carbon dioxide ices, may help explain the origin of icy planetoids like comets. Scientists believe these comets may have endowed Earth with some of its water and many of its biogenic, life-enabling materials.

“We’ve seen the building blocks of habitable planets for the first time unambiguously” in stars that will turn out like our sun, says Watson.

The planet cannot be seen directly, but Spitzer’s Infrared Spectrograph instrument clearly showed that an area of dust in the disk was missing, strongly suggesting the presence of a planet. The dust in the disk is hotter in the center near the star and so radiate most of their light at shorter wavelengths than the cooler outer reaches of the disk. The research team found that there was an abrupt dearth of light radiating at all short infrared wavelengths, strongly suggesting that the central part of the disk was absent. Scientists know of only one phenomenon that can tunnel such a distinct “hole” in the disk during the short lifetime of the star—a planet at least 100,000 years old.

CoKu Tau 4, the million-year-old star around which the new planet circles, is a baby by stellar standards. By comparison, our sun is roughly 4.5 billion years old. The presence of a planet around so young a star challenges the leading theories of how planets form, most of which suggest the process takes at least several million years.

The $458 million Spitzer telescope (originally called SIRTF for Space Infrared Telescope Facility) was launched into orbit on Aug. 25, 2003, after more than a year and a half of delays. The telescope circles the sun—not the Earth—as it peers into the cosmos in the infrared spectrum for the next five years. Spitzer’s Infrared Spectrograph is able to break apart infrared light to detect the signatures of various chemicals, such as the organic ices and the clearing within CoKu Tau 4’s disk. Papers on the research will appear in the Sept. 1 issue of Astrophysical Journal Supplement Series. For images and information about the research on the Internet, visit: http://www.spitzer.caltech.edu and http://photojournal.jpl.nasa.gov.