January 14, 2001
If video technology had been around when our solar system formed nearly five billion years ago, here's what would have been caught on tape:
A dusty, gaseous disk swirling around a blazing star, which would later be named the Sun. Inside the disk, particles clumping together to form chunks, swirling and picking up even more particles. Eventually, some chunks growing large enough to form planets - some solid and rocky, like Earth and Mars, and others remaining gaseous, like Jupiter and Saturn. All of them ultimately settling into orbit around the Sun.
Astronomers have pieced together this scenario of how our solar system was formed. Based on recent discoveries, we know that similar events are currently being played out around countless other stars. In fact, we don't know how many blazing stars in the nighttime sky have swirling dust disks that are construction zones for new planetary systems.
Scientists refer to these dusty areas as circumstellar disks. They're of great interest for two reasons. For one thing, these disks teach us how the planets in our own solar system developed. In addition, we're intrigued by the prospect of finding planets beyond our solar system with conditions suitable for life.
Disks swirling around stars are grouped into two categories according to their stage of development. One to 10 million years after a star is born, a disk of gas and dust may be observed around the newborn star. This type of disk, called a protoplanetary disk, is a signature that indicates a planetary system is in the act of formation. Perhaps 100 million years later, most of the gas has been depleted, and a disk comprised primarily of dust remains. This is called a planetary debris disk.
Even though our solar system was formed billions of years ago, and by now most of the dust has been swept away, observers far out in space would still see a lingering, faint disk around our Sun. But to do this, they would need an infrared telescope.
Here on Earth, we have developed the technology to study disks around distant stars by using infrared light. In fact, when NASA's Space Infrared Telescope Facility launches, one of its main goals will be to detect and characterize disks, particularly those where planets have already formed. The observatory will use a technique called spectroscopy to study the chemistry of the dust within the disk. Scientists will then take this information and compare it with data on the remnant dust within our solar system.
The observatory will also image the disks at various infrared wavelengths. By combining and comparing the observations with theoretical models, astronomers may be able to infer that there are gaps within the disks. Such gaps may be caused by planets sweeping out the dust and clearing the area. In a similar way, shepherd moons have created gaps in the rings of Saturn by clearing material.
The observatory will help pinpoint disks with the most active planetary development, helping to pave the way for such future NASA missions as the Space Interferometry Mission and Terrestrial Planet Finder. Those missions will hunt among distant planets for those with the right chemistry to support living organisms, or even those which already have life. At last, we may have an answer to the intriguing question - Are we alone?