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| A NASA Hubble Space Telescope image of a region of the Great Nebula in Orion, one of the closest areas of recent star formation, offers a glimpse into cosmic creation. The nebula, a vast gas cloud 1,500 light-years away, is illuminated by young, hot stars. Many fainter stars are encircled by dust and gas disks, slightly over twice the Solar System's diameter. A plume of gas in the upper left reveals material ejected from a newly formed star. The image, taken on December 29, 1993, spans 1.6 light-years and uses color to depict emissions: red for Nitrogen, green for Hydrogen, and blue for Oxygen. |
In 1993 — Observations with the Hubble Space Telescope have provided the most compelling evidence yet that planet formation is a common occurrence in our galaxy. A team led by Dr. C. Robert O'Dell of Rice University has uncovered clear indications that disks of dust, the essential material for planet formation, are present around many stars in the Orion Nebula, a prominent star-forming region located about 1,500 light-years from Earth.
Dr. O'Dell, along with Zheng Wen, formerly of Rice University and now at the University of Kentucky, examined 110 stars in the Orion Nebula and identified dust disks around 56 of them. These disks, termed "proplyds" by O'Dell, were initially discovered in 1992 through Hubble images. The recent, more detailed observations confirm that these structures are indeed pancake-shaped disks rather than dust shells, strengthening the theory that they are the precursors to planetary systems.
These disks are composed of carbon, silicates, and other materials similar to those that formed the planets in our solar system about 4.5 billion years ago. While current technology makes it easier to detect the stars than the disks, O'Dell suggests that many more stars likely have such protoplanetary material. He has even measured portions of the mass of these disks, finding they contain enough material to form Earth-like planets.
The only confirmed planetary system known to date comprises three Earth-sized planets orbiting a neutron star, an atypical example as these planets likely formed after a stellar explosion. The findings in the Orion Nebula, however, suggest that planet-forming disks are abundant in young star clusters, implying that planetary systems like our own might be widespread in the universe.
This revelation holds significant implications for the search for extraterrestrial life. Planets are essential for life as we know it, offering the necessary conditions and materials. The widespread presence of planet-forming disks increases the probability that planets, and possibly life, are common in the universe.
Moreover, the Hubble images have resolved young stars at the center of each disk, showing that stars with masses comparable to or smaller than our Sun are likely to possess these disks. Stars hotter than our Sun may destroy their dust disks before planets can form, but the majority of stars in regions like Orion could potentially host planets.
One of Hubble's striking images shows a dark elliptical disk silhouetted against the bright background of the Orion Nebula, providing the most direct evidence to date for protoplanetary disks. The resolution of these images has allowed O'Dell to accurately determine the mass of the disks, finding them to be several times the mass of Earth and spanning 53 billion miles across, with the central star being about one-fifth the mass of our Sun.
These discoveries support long-standing theories about the formation of planetary systems and highlight the significance of circumstellar disks in this process. O'Dell's findings will be detailed in the November 20 issue of *The Astrophysical Journal*, marking a significant milestone in our understanding of planetary genesis and the potential for life beyond Earth.
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