Caused by sunlight scattered by space dust in the zodiacal cloud, it is so faint that either moonlight or light pollution renders it invisible.
The dust forms a thick pancake-shaped cloud in the Solar System collectively known as the zodiacal cloud, which occupies the same plane as the ecliptic.
Regardless of the sources, the diffuse zodiacal cloud
has a total mass of perhaps [10.sup.19] grams, equaling the Martian moon Phobos.
The dusty disk, also called the zodiacal cloud
, radiates from near the sun out beyond the orbit of Mars, toward Jupiter.
They estimate that there must be some 20 trillion tons of dust in the zodiacal cloud
(twice the mass of the Martian moon Phobos), and that 100 000 tons of the stuff falls to Earth every year!
These stars are more than 1 billion years old, an age by which the Sun's debris disk already looked much like today's tenuous zodiacal cloud
. In both cases, Spitzer has provided exquisite spectral data showing hot, fresh dust located within about 1 a.u.
Nesvorny and Jenniskens, with the help of Harold Levison and William Bottke of the Southwest Research Institute, David Vokrouhlicky of the Institute of Astronomy at Charles University in Prague, and Matthieu Gounelle of the Natural History Museum in Paris, showed that these comet disruptions can account for the observed thickness of the dust layer in the zodiacal cloud
With seven of its 40 chapters devoted to comets, cometary dynamics, the Kuiper Belt, asteroids, near-Earth asteroids, interplanetary dust and the zodiacal cloud
, and meteorites, Encyclopedia of the Solar System pays greater respect to the solar system's small objects than one might naively expect.