The cosmic dust It consists of tiny particles that fill the space between planets and stars, sometimes accumulating to form clouds and rings. They are particles of matter whose size is less than 100 micrometers, where a micrometer is one millionth of a meter. Larger particles are now called "meteoroids".
For a long time it was believed that the vast interstellar spaces were devoid of matter, but what happens is that not all that exists is condensed in the form of planets or stars..
There is a large amount of matter of very low density and diverse origins, which with time and the appropriate conditions turns into stars and planets.
But it is not necessary to go that far to find cosmic dust, since the Earth receives about 100 tons of dust and fragments every day that arrive from space at high speed. Most of it goes to the oceans and is distinguished from household dust, which is produced by volcanic eruptions and sand storms in large deserts..
Cosmic dust particles are capable of interacting with radiation from the Sun and also ionizing, that is, capturing or giving up electrons. Its effects on Earth are diverse: from scattering sunlight to modifying temperature, blocking infrared radiation from the Earth itself (heating) or the Sun (cooling).
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Here are the main types of cosmic dust:
When approaching the Sun and being exposed to its intense radiation, part of the comet disintegrates, the gases are expelled forming the hair and the tails composed of gas and dust. The straight tail seen in the comet is made of gas and the curved tail is made of dust..
Several planets in our solar system have rings of cosmic dust, originating from collisions between asteroids..
The remnants of collisions travel through the solar system and frequently impact the surface of the moons, breaking up into tiny particles. The surface of our Moon is covered in fine dust from these impacts..
Some of the dust remains around the satellite forming a faint halo, like that of the large Jovian satellites Ganymede and Callisto. And it also spreads along the satellite orbits, forming rings, which is why it is also called circumferential dust.
This is the origin of Jupiter's faint rings, first detected by the Voyager probe. Asteroidal impacts are due on the small Jovian moons Metis, Adrastea, Amalthea and Thebe (figure 3).
The Jovian system also sends large amounts of dust into space thanks to volcanic eruptions on the moon Io. But the gas giant is not the only one to have cosmic dust rings, as Uranus and Neptune have them too..
As for the famous rings of Saturn, their origin is somewhat different: they are believed to be the remains of an icy moon that collided with the newly formed giant planet..
Stars expel large amounts of mass at the end of their lives and then when they explode as supernovae, leaving behind a nebula. A small part of this material condenses into powder..
And although there is barely 1 hydrogen atom for every cubic centimeter of space, the dust is large enough to cause starlight fading and flushing..
The space between galaxies also contains cosmic dust, and as for the galaxies themselves, spirals are richer in cosmic gas and dust than ellipticals. In the former, the dust is rather concentrated towards the disk and in the spiral arms.
It is found throughout the solar system and comes in part from the original cloud that gave rise to it, in addition to cometary dust and that produced by asteroidal collisions and impacts on moons..
On particles just a few microns in diameter, the pressure exerted by sunlight is significant, pushing dust out of the solar system. It is responsible for the tails of comets when they get close enough to the Sun.
Cosmic dust particles are also subject to the so-called Poynting-Robertson effect, which counteracts the pressure of solar radiation and causes a slow spiral movement towards the Sun. It is a noticeable effect on very small particles but negligible when the size exceeds subway.
Magnetic fields also affect the movement of cosmic dust particles, deflecting them when ionized, which happens easily, since dust grains are easily electrified by capturing or giving up electrons..
It is not surprising that these forces generate dust currents moving at 70 km per second or more through space..
Cosmic dust that comes from stars is rich in graphite and silicon crystallized by high temperatures. On the other hand, that of asteroids is rich in metals such as iron and nickel..
What is surprising is that biologically important molecules can also settle in grains of cosmic dust. On its surface, hydrogen and oxygen atoms meet to form water, which despite the low temperatures of deep space, can still be mobilized.
Other simple organic compounds are also present, such as methane, ammonia, and carbon monoxide and dioxide. Scientists do not rule out that some living beings such as tardigrades and some plants and bacteria are capable of leaving the planet transporting themselves in the dust. Nor do they rule out the idea that life has come to our planet from some remote place by this same path..
Observing the evidence for cosmic dust is simple. There is a band of diffuse light in the shape of a cone or triangle called zodiacal light, that appears in the sky just where the ecliptic emerges. It is sometimes called "false dawn" and Domenico Cassini studied it in the 17th century..
Finally for those who are in equatorial latitudes, the zodiacal light is visible throughout the year.
The name is due to the fact that the luminosity seems to be over the constellations of the Zodiac and the best time to see it is during clear, moonless nights, away from light pollution, preferably in the two weeks after the full moon..
The zodiacal light is due to the cosmic dust accumulated in the equatorial plane of the Sun scattering the light of the star.
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