Category Science

Scientists are interested in finding out more about asteroids. Many are thought to contain minerals and metals that could benefit industries on Earth. The Near Earth Asteroid Rendezvous (NEAR) space probe (below) visited two asteroids, Mathilde and Eros, in 1997 and 1998. It took photographs that showed Mathilde to be entirely covered by craters. Soon, expeditions may be launched from Earth to mine asteroids in space.

Asteroids are minor planets, especially of the inner Solar System. Larger asteroids have also been called planetoids. These terms have historically been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observed to have characteristics of an active comet such as a tail. As minor planets in the outer Solar System were discovered that were found to have volatile-rich surfaces similar to comets, these came to be distinguished from the objects found in the main asteroid belt. In this article, the term “asteroid” refers to the minor planets of the inner Solar System, including that co-orbital with Jupiter.

There exist millions of asteroids, many the shattered remnants of planetesimals, bodies within the young Sun’s solar nebula that never grew large enough to become planets. The vast majority of known asteroids orbit within the main asteroid belt located between the orbits of Mars and Jupiter, or co-orbital with Jupiter (the Jupiter Trojans). However, other orbital families exist with significant populations, including the near-Earth objects. Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C-type, M-type, and S-type. These were named after and are generally identified with carbon-rich, metallic, and silicate (stony) compositions, respectively. The sizes of asteroids varies greatly; the largest, Ceres, is almost 1,000 km (600 mi) across and massive enough to be a dwarf planet.

Asteroids are somewhat arbitrarily differentiated from comets and meteoroids. In the case of comets, the difference is one of composition: while asteroids are mainly composed of mineral and rock, comets are primarily composed of dust and ice. Furthermore, asteroids formed closer to the sun, preventing the development of cometary ice. The difference between asteroids and meteoroids is mainly one of size: meteoroids have a diameter of one meter or less, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials.

Although most asteroids drift harmlessly around the Sun for billions of years, some are occasionally knocked out of their orbits. Some of these asteroids pass very close to Earth. In 1994, an asteroid measuring 10m (32ft) in diameter passed within 105,000km (65,000 miles) of our planet — around one third of the distance to the Moon. If a large asteroid were to collide with Earth, the impact could he powerful enough to annihilate all life on the planet. Vast waves of water, dust and fire would flatten cities in seconds, and billions of tonnes of dust entering the atmosphere would block out the Sun’s light for hundreds of years.

This is a list of examples where an asteroid or meteoroid travels close to the Earth. Some are regarded as potentially hazardous objects if they are estimated to be large enough to cause regional devastation.

Near-Earth object detection technology greatly improved about 1998, so objects being detected as of 2004 could have been missed only a decade earlier due to a lack of dedicated near-Earth astronomical surveys. As sky surveys improve, smaller and smaller asteroids are regularly being discovered. The small near-Earth asteroids 2008 TC3, 2014 AA, 2018 LA and 2019 MO are the only four asteroids discovered before impacting into Earth (see asteroid impact). Scientists estimate that several dozen asteroids in the 6–12 m (20–39 ft) size range fly by Earth at a distance closer than the moon every year, but only a fraction of these are actually detected.

There are many theories about how the asteroid belt developed. Some astronomers believe that it is the remains of a planet that was torn apart billions of years ago. Conversely, others argue that the asteroids in the belt are pieces of a planet that never formed. According to this theory, the immense gravitational pull of the young planet Jupiter prevented the rocks from forming one large body.

The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars, that is occupied by a great many solid, irregularly shaped bodies, of many sizes but much smaller than planets, called asteroids or minor planets. This asteroid belt is also called the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and Trojan asteroids.

About half the mass of the belt is contained in the four largest asteroids: Ceres, Vesta, Pallas, and Hygiea. The total mass of the asteroid belt is approximately 4% that of the Moon, or 22% that of pluto, and roughly twice that of Pluto’s moon Charon (whose diameter is 1200 km).

The asteroid belt formed from the primordial solar nebula as a group of planetesimals. Planetesimals are the smaller precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals and most of the protoplanets shattered. As a result, 99.9% of the asteroid belt’s original mass was lost in the first 100 million years of the Solar System’s history. Some fragments eventually found their way into the inner Solar System, leading to meteorite impacts with the inner planets. Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits.

Classes of small solar System bodies in other regions are the near-Earth objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids, and the Oort cloud objects.

Bode’s law states that there is a pattern in the way the planets are spaced from the Sun. Bode started with the number 0, then took 3, and began doubling: 0, 3, 6, 12, 24, 48, 96, 192, 384, 768. He then divided each number by 10 and added 4. The numbers that he discovered were similar to planetary distances from the Sun in astronomical units. According to Bode’s theory, there should be a planet between Mars and Jupiter.

The concept was devised and first published in 1766 by Johann D. Titius, a German mathematician and physicist, based on the six planets known at the time: Mercury, Venus, Earth, Mars, Jupiter, and Saturn. The German astronomer Johann E. Bode popularized the law in a book published in 1772, and it became associated with his name.

The law relates the mean distances of the planets from the sun to a simple mathematic progression of numbers. To find the mean distances of the planets, beginning with the following simple sequence of numbers:
0   3   6   12   24   48   96   192   384

With the exception of the first two, the others are simple twice the value of the preceding number.

Adding 4 to each number results,
4   7   10   16   28   52   100   196   388

Then dividing by 10
0.4   0.7   1.0   1.6   2.8   5.2   10.0   19.6   38.8

Most of the asteroids in the Solar System orbit the Sun in a band between Mars and Jupiter. This band is nearly 550 million km (340 million miles) wide and is called the asteroid belt. There are billions of asteroids in this zone, each moving independently around the Sun and spaced many thousands of kilo-metres from each other.

The asteroid belt is located between the inner and the outer planets and is home to thousands of rocks and debris known as asteroids and some of the dwarf planets. All of these orbit the Sun.

Some asteroids do orbit in space near to Earth and some are forced out of the asteroid belt by gravity and sent towards the outer solar system instead. There are hundreds of thousands of asteroids in the asteroid belt, but almost half of the entire mass is made up of just four objects. These objects are the dwarf planet Ceres, and three other asteroids called Vesta, Pallas and Hygiea. The diameters of Vesta, Pallas and Hygiea are over 400km and Ceres is even bigger at 950km diameter.

Of the many thousands of asteroids in the asteroid belt, Ceres is the only one large enough to be classified as a “dwarf planet”. Apart from these four objects, the remaining objects in the asteroid belt range in size from small rocks right down to dust particles.

The asteroid belt is between the planets Mars and Jupiter. It is located about 2.2 to 3.2 Astronomical Units (AU) from the Sun. That is somewhere between 329-478 million km away. The asteroid belt is huge and the space between each of the asteroids is over 600,000 miles. The circumference of Earth is only 24,901.45 miles, which means that the distance between objects in the asteroid belt is more than 24 times the circumference of Earth.

Planets and their moons are not the only objects in our Solar System. Billions of small rocky bodies, called asteroids, also orbit the Sun. An asteroid, often called a minor planet, is a small body made up of rock and metal left over from the formation of the Solar System. Asteroids can range in size from almost 1000km (610 miles) in diameter, to the size of a small car.

4.6 billion Years ago, our solar system formed from a collection of gas and dust surrounding our nascent sun. While much of the gas and dust in this protoplanetary disk coalesced to form the planets, some of the debris was left over.

Some of debris was shattered remnants of planetesimals – bodies within the young sun’s solar nebula that never grew large enough to become planets, and scientists theorize that large collisions in the early, chaotic solar system pulverized these planetesimals into smaller pieces. Other debris never came together due to the massive gravitational pull from Jupiter.

These rocky remnants are now the asteroids that travel about our solar system. Since these “leftovers” contain clues about the early days of our solar system, scientists are eager to study them.

Asteroids are rocky, metallic bodies that orbit the sun. They are made from different kinds of rock and metals, with the metals being mostly nickel and iron. They are sometimes called “minor planets” but they are much, much smaller than the planets or moons. They don’t have atmospheres, but about 150 asteroids are known to have small “moons” orbiting them, and some even have two moons. There are also binary (double) asteroids, where two rocky bodies of roughly equal size orbit each other, as well as triple asteroid systems.

At least one asteroid has rings. This surprise discovery was made in 2013 when scientist watched Asteroid Chariklo pass in front of a star. The asteroid made the background star “blink” several times, which led to the discovery that two rings are surrounding the asteroid.