Zodiacal Dust

Zodiacal dust is the dust found in our solar system, primarily between the Sun and Jupiter. This dust originates from comets and from asteroid collisions, and can sometimes be seen with the naked eye as a triangular glow above the horizon just before sunrise or after sunset. This glow is called the zodiacal light and is caused by sunlight being scattered off of the various dust particles which travel around the Sun. Each time a comet passes near the Sun, it loses some of its material, contributing to the dust between the planets. When asteroids collide, they also send additional dust into the solar system. How much of the zodiacal dust is due to comets and how much is due to asteroid collisions is not known. Due to the effects of the planets, the disk of dust in our solar system is full of structures such as rings and wakes. Each year the Earth collects about 40,000 tons of interplanetary dust!

The faint glow in this image is the zodiacal dust. (P. Kalas)

The zodiacal dust emits most strongly in the mid-infrared. In 1983 the Infrared Astronomical Satellite (IRAS) discovered bands of infrared emission that girdle our solar system. Called the zodiacal dust bands, these are likely to be debris from colliding asteroids. Infrared studies have shown that these bands are located between Mars and Jupiter in the region of the asteroid belt. IRAS found evidence of zodiacal dust bands around other stars as well. We now know that many stars have disks of dust around them. To the left is an infrared image of the entire sky as seen by IRAS. The bright horizontal band in the center is our Milky Way galaxy (seen edge on) and the hazy, S-shaped feature that crosses the image is the infrared radiation from the zodiacal dust in our solar system. Infrared studies of the dust in our solar system will give us information about its distribution and composition, and will help us understand the formation of dust disks around other stars.

The Spitzer Space Telescope's unique orbit will cause it to travel through a dust cloud that is trailing the Earth as it circles the Sun. This will provide a unique opportunity to study the structure of interplanetary dust at close range.