The interplanetary dust cloud, also called the zodiacal cloud (because it creates the zodiacal light), is made up of tiny particles, known as cosmic dust, that float in the space between planets in a planetary system, like our Solar System. Scientists have studied these particles for many years to learn about their makeup, where they come from, and how they are connected to larger objects in space. There are several ways to measure the amount of space dust.

In the Solar System, interplanetary dust particles help scatter sunlight and emit thermal radiation, which is the most noticeable type of radiation in the night sky. This radiation has wavelengths between 5 and 50 micrometers. The sizes of dust particles that produce infrared light near Earth’s orbit usually range from 10 to 100 micrometers. Small craters found on moon rocks brought back by the Apollo Program showed the sizes of cosmic dust particles that hit the Moon’s surface. The "Grün" distribution describes how much dust of different sizes, from nanometers to millimeters, exists at a distance of 1 astronomical unit (AU) from the Sun.

The total mass of the interplanetary dust cloud is about 3.5 × 10 kg, which is similar to the mass of an asteroid with a radius of 15 kilometers and a density of about 2.5 grams per cubic centimeter. This dust cloud spreads along the zodiac, which is the path of the planets in the Solar System, and can be seen as the zodiacal light in a dark sky without the Moon. It is most visible when looking toward the Sun during astronomical twilight.

Observations from the Pioneer spacecraft in the 1970s showed that the zodiacal light is caused by the interplanetary dust cloud in the Solar System. Additionally, the VBSDC instrument on the New Horizons probe was designed to detect dust particles from the zodiacal cloud in the Solar System.

Origin

Interplanetary dust particles (IDPs) come from several sources, including asteroid collisions, comet activity and collisions in the inner Solar System, collisions in the Kuiper Belt, and grains from space beyond our solar system (Backman, D., 1997). The origin of the zodiacal cloud has been a long-debated topic in astronomy.

It was once thought that IDPs came from comets or asteroids, with their particles spreading throughout the cloud. However, more recent studies have shown that dust from storms on Mars may play a role in forming the zodiacal cloud.

Life cycle of a particle

The main physical processes that influence interplanetary dust particles are: being pushed away by radiation pressure, being pulled inward by Poynting-Robertson (PR) radiation drag, being affected by solar wind pressure (including electromagnetic effects), sublimation (turning from solid to gas), collisions with other particles, and the gravitational and movement effects of planets (Backman, D., 1997).

These dust particles do not last very long compared to the age of the Solar System. If scientists find dust grains around a star that is older than about 10,000,000 years, the grains must have come from recently broken-off pieces of larger objects, not from the original material left over from the formation of the Solar System (Backman, private communication). This means the grains are "later-generation" dust. In the Solar System, zodiacal dust is 99.9% later-generation dust and 0.1% dust that came from outside the Solar System. All of the original dust from the Solar System's formation has already been removed.

Dust particles that are mainly affected by radiation pressure are called "beta meteoroids." These particles are usually smaller than 1.4 × 10 grams and are pushed outward from the Sun into space beyond the Solar System.

Cloud structures

The interplanetary dust cloud has a complicated structure (Reach, W., 1997). In addition to a general amount of dust, it includes:

• At least 8 dust trails—these are likely from short-period comets.
• Several dust bands, which are thought to come from groups of asteroids in the main asteroid belt. The three strongest bands are from the Themis family, the Koronis family, and the Eos family. Other groups that may contribute include the Maria, Eunomia, and possibly the Vesta and/or Hygiea families (Reach et al. 1996).
• At least 2 dust rings that form due to gravitational interactions (for example, the Earth-resonant dust ring, though scientists believe every planet in the Solar System has a similar ring with a "wake") (Jackson and Zook, 1988, 1992) (Dermott, S.F. et al., 1994, 1997).

Interplanetary dust has been found to create rings in the space around Mercury and Venus. The dust ring around Venus is thought to come from unknown asteroids that trail Venus, dust moving in waves between different areas of space, or leftover material from the Solar System’s early disk, which eventually formed the planets and the Solar System itself.

Dust collection on Earth

In 1951, Fred Whipple suggested that tiny particles smaller than 100 micrometers might slow down when entering Earth's upper atmosphere without melting. The study of these particles in laboratories began in the 1970s when Donald E. Brownlee and his team collected them from the stratosphere using balloons and later U-2 aircraft.

Some of the particles found were similar to materials in current meteorite collections. However, other particles had tiny holes and a chemical makeup that did not match typical space materials. These features suggested the particles originally formed as clusters of nonvolatile materials and cometary ice. Scientists later confirmed these particles came from space by studying noble gases and tracks left by solar flares.

In response, a program to collect and carefully preserve these particles was created at Johnson Space Center in Texas. Along with presolar grains from meteorites, these stratospheric micrometeorites are rare sources of extraterrestrial material. They are also small astronomical objects that scientists can study in laboratories today.

Experiments

Spacecraft that have carried dust detectors include Helios, Pioneer 10, Pioneer 11, Ulysses (which orbits the Sun and reaches as far as Jupiter's distance), Galileo (a spacecraft that orbits Jupiter), Cassini (a spacecraft that orbits Saturn), and New Horizons (which includes the Venetia Burney Student Dust Counter).

Obscuring effect

Dust in the solar system blocks light from outside our galaxy. This makes it hard to observe this light from within our solar system.

Major review collections

Books that collect reviews on different topics related to interplanetary dust and similar areas were published in the following works:

In 1978, Tony McDonnell edited the book Cosmic Dust. This book includes chapters about comets, zodiacal light as a sign of interplanetary dust, meteors, interstellar dust, and studies of tiny particles using sampling methods and space instruments. It also discusses lunar and planetary erosion from impacts, particle movement, and methods used in laboratories to simulate effects caused by micrometeoroids.

In 2001, Eberhard Grün, Bo Gustafson, Stan Dermott, and Hugo Fechtig published the book Interplanetary Dust. Topics covered include historical background, cometary dust, the near-Earth environment, meteoroids and meteors, properties of interplanetary dust, data from collected samples, measurements of cosmic dust in their natural environment, models of the structure of the Zodiacal Cloud, synthesis of observations, tools used for research, physical processes, optical characteristics of interplanetary dust, how interplanetary dust moves through space, dust around planets, observations and basic physics, interstellar dust, and dust around stars.

In 2019, Rafael Rodrigo, Jürgen Blum, Hsiang-Wen Hsu, Detlef V. Koschny, Anny-Chantal Levasseur-Regourd, Jesús Martín-Pintado, Veerle J. Sterken, and Andrew Westphal compiled reviews in the book Cosmic Dust from the Laboratory to the Stars. This book includes discussions about dust in different environments, such as planetary atmospheres, airless objects, interplanetary dust, meteoroids, comet dust, emissions from active moons, interstellar dust, and protoplanetary disks. It also covers various research methods and findings, including in-situ measurements, remote observations, laboratory experiments, models, and analysis of samples brought back from space.