Astronomers have long scrutinized the vast and layered clouds of the Orion nebula, an industrious star-making factory visible to the naked eye in the sword of the famous hunter constellation. Yet, Orion is still full of secrets. This new image from NASA's Spitzer Space Telescope probes deep into the clouds of dust that permeate the nebula and its surrounding regions. The striking false-color picture shows pinkish swirls of dust speckled with stars, some of which are orbited by disks of planet-forming dust.
Spitzer, with its powerful infrared vision, was able to unearth nearly 2,300 such planet-forming disks in the Orion cloud complex, a collection of turbulent star-forming clouds that includes the well-known Orion nebula. The disks -- made of gas and dust that whirl around young suns -- are too small and distant to be seen by visible-light telescopes; however, the infrared glow of their warm dust is easily spotted by Spitzer's infrared detectors. Each disk has the potential to form planets and its own solar system.
A look at Orion's demographics reveals that the potential solar systems populate a variety of environments. Astronomers have found that about 60 percent of the disk-sporting stars in the Orion cloud complex inhabit clusters, containing hundreds of young stars. About 15 percent reside in smaller groups, and a surprising 25 percent prefer to go it alone, living in isolation. Prior to the Spitzer observations, scientists thought that up to 90 percent of young stars, both with and without disks, dwelled in clusters like those of Orion. The Spitzer image shows that many stars seem to form in isolation or in small groups of stars.
This new information may help us learn more about the environment in which our sun formed. Astronomers do not know whether our middle-aged sun grew up in a large cluster or in a smaller group of stars, though most favor a large cluster scenario. Newborn stars like the ones in Orion tend to drift away from their siblings over time, so it is hard to trace an adult star's origins. It is estimated that about 60 to 70 percent of the stars in the Orion cloud complex have disks. Spitzer's infrared vision also uncovered 200 stellar embryos in the Orion cloud complex, most of which had never been seen before. Stellar embryos are still too young to have developed disks.
The Orion cloud complex is about 1,450 light-years from Earth and spans about 240 light-years of space. Spitzer's wide field of view allowed it to survey most of the complex, an area of the sky equivalent to 28 full moons. The featured image shows a slice of this survey, the equivalent of four full moons-worth of sky, and includes the Orion nebula itself. This image was taken by the infrared array camera on Spitzer. It is a three-color composite of invisible light, showing emissions from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange), and 8.0 microns (red). A micron is one millionth of a meter; a human hair is about 100 microns thick. The Jet Propulsion Laboratory, California Institute of Technology, manages the Spitzer Space Telescope for NASA.