A comet is an icy object which orbits the sun. It produces steam when it nears the sun and develops a tail of dust and gas. A meteor is a particle of rock that burns up in Earth’s upper atmosphere, leaving a streak of light. An asteroid is a small rocky object in the solar system. Asteroids range in size from 930 km (578 miles) across down to dust particles. A meteorite is a piece of rock that has survived passage through Earth’s atmosphere, thought to be a fragment of an asteroid, not of a comet.
Comets are chunks of ice and rock left over from the birth of the solar system. Astronomers believe that these icy rocks are located in a zone called the Oort cloud, named after the Dutch astronomer Jan Oort (1900 to 1992), that lies beyond the furthest planet in the solar system.
The nucleus of a comet is a chunk of rock and ice lying at its core. As the comet nears the sun, the heat melts the ice. Gas jets spring from the sun-facing side. Fragments of rock break off to form the dust tail.
Every 76 years Halley’s Comet returns to the center of the solar system. In 1705, English astronomer Edmond Halley (1656 to 1742) correctly predicted its return in the year 1758. On the last return in 1986, the space probe Geodon penetrated to within 600 km (370 miles) of the comet’s nucleus.
- The longest known surviving comet lasted for 24 million years. The comet, known as Delavan’s comet, was last seen in 1914.
- The most frequently seen comet is Encke’s comet, which returns every 3.3 years.
- The brightest comet known to science was seen in daylight in 1910. It was as bright as the planet Venus.
Each comet has a dust tail and a gas tail. These are blown back by the solar wind, which forces the dust and gas away from the sun. As a comet recedes from the sun its tail always points away from the sun. The dust tail follows the curve of the comet’s path. The gas tail is forced back by electrically charged particles in the solar wind.
The comet with the longest known tail was the Great Comet of 1843, which trailed for 330 million km (205 million miles). The tail could have wrapped around Earth 7000 times. It will not return to the center of the solar system until 2356.
Meteors, or shooting stars, are streaks of light that appear briefly in the night sky. They occur when particles of rock or dust, left my comets, burn up in Earth’s atmosphere at speeds of up to 70 km/s (43 mi/s).
Comets leave trails of dust and debris along their orbits around the sun. When Earth crosses one of these trails, the dust burns up in the atmosphere and we see a meteor shower in the sky.
Asteroids are pieces of rock smaller than planets that orbit the sun. More than 4000 have been found. They range in size from tiny fragments of rock to bodies hundreds of kilometers across.
Ceres, discovered in 1801, is the biggest known asteroid with a diameter of 930 km (578 miles). If Ceres were placed on earth it would cover France.
Vesta is smaller than Ceres, but its highly reflective surface makes it the brightest asteroid.
Psyche is irregularly shaped, made out of iron, and about 260 km (160 miles) long. It’s the same size as Jamaica.
Most asteroids line the asteroid belts between the orbits of Mars and Jupiter. The Trojan asteroids, though, follow Jupiter’s orbit in two groups. Others orbit the sun alone.
An estimated 2000 collisions have occurred between asteroids and Earth in the last 600 million years.
If an asteroid of average size collided with Earth, it could destroy an entire country.
In January 1991, an asteroid measuring about 10 m (33 feet) across passed between the moon and the earth.
In the future, asteroids may be mined for metals as resources on Earth grow scarce.
Asteroid 2309 is called Mr Spock, after the character in the television series and film franchise, Star Trek.
Ceres, the largest asteroid, contains a quarter of all the rock in the asteroid belts combined.
A meteorite is a piece of rock from space that escapes destruction in Earth’s atmosphere, and is able to reach the ground. There are 3 kinds of meteorites: Stony, iron, and stony-iron.
- Stony meteorites
Stony meteorites are the most common type. They consist mainly of the minerals olivine and pyroxene.
- Iron meteorites
Iron meteorites come from small asteroids that broke up in space. They’re rarer than stony meteorites.
- Stony-iron meteorites
Stony-iron meteorites contain both rock and metal. In many cases a casing of bright metal encloses the mineral base.
The oldest meteorites, called carbonaceous chondrites, are 4.55 billion years old.
The largest meteorite landed at Fontaine, Namibia. It is called Jojoba, is 2.75 m (9 feet) long, made of iron, and weighs 59 tons. That’s as much as eight adult elephants.
The only person ever injured by a meteorite was Mrs A. Hodges of Alabama, USA. A four kilogram (9 lbs) meteorite crashed through her roof in November 1954 and injured her arm.
The only death caused by a meteorite was a dog killed in Egypt in 1911.
Throughout the ages natural phenomena have often been explained, in the absence of scientific understanding, by superstitious beliefs. The Black Stone of Mecca, housed in a shrine in Saudi Arabia, is the sacred stone of Islam. It is believed to be a meteorite that fell to Earth hundreds of years ago. The famous “Star of Bethlehem” that according to Christian myth led the Magi to the baby Jesus, may have been a comet. And many other natural cosmic phenomena have been mistaken for gods or angels, signs and portents, around the world.
That brings us to the end of our exploration of fascinating and fun facts about comets, meteors, and asteroids. I hope you’ve enjoyed the journey and learned something along the way. While we now know a great deal more about the universe and its wonders than ever before, there is still much more to discover. Perhaps one day you will be a scientist or an astronomer and help add to the body of knowledge for future generations.