Asteroids: The Cosmic Entity that Ended the Dinosaurs

Asteroids are rocky objects, sometimes called Planetoids or minor planets, revolving around Sun in elliptical orbits and, sometimes quite erratically, tumbling. Asteroids are too small to be called Planets. These are airless remnants left over from the formation of our solar system (about 4.6 million years ago). There are millions of these rocky objects, mostly orbiting the Sun between Mars and Jupiter, within a region called the main Asteroid belt. There are millions of asteroids with 1,113,527 known asteroids, ranging from hundreds of miles to several feet across, with the most giant known Asteroid Vesta at 325 miles (525 kilometers) followed by Pallas at 320 miles (510 kilometers). The most minor known Asteroids are members of the Near-Earth Objects (NEOs) group, some of which approach Earth to within a few hundredths of 1AU, some of which are classified as "Potentially hazardous Asteroids (PHAs)" by astronomers. These asteroids come within about 4.64 million miles (7.48 million kilometers) of Earth's orbit and are larger than about 500 feet (140 meters) across, according to NASA's center of near-earth objects Studies (CNEOS). However, the classification does not imply that the asteroids pose a certain threat to Earth. As of November 2021, 27,323 near-earth asteroids have been discovered, and 2224 of them are classified as potentially hazardous asteroids, according to CNEOS. Although Asteroids orbit the Sun-like planets, they are much smaller than planets. The total mass of all the asteroids is less than Earth's Moon.

The asteroid belt lies between Mars and Jupiter (Image credit: Getty )

Some of these Asteroids go in front and behind Jupiter, called Trojan Asteroids, which lie outside the main Asteroid belt, and the Asteroids which come close to Earth are known as Near-Earth Objects (NEO).

Scientists also suspect that many of the solar system's moons, before they were eventually captured by a planet's gravity and became satellites. They were once Asteroids like Mars' moons, Phobos and Dermos, and most of the outer moon of Jupiter, Saturn, Uranus, and Neptune.

Limb View of Ceres
Source: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The first and the largest asteroid, Ceres, orbiting between Mars and Jupiter in the main asteroid belt, was discovered accidentally in 1801 by Italian priest and astronomer Giuppe Piazzi while making a star map. Although Ceres is considered a dwarf planet today, it accounts for a quarter of all the mass of the known asteroids in or near the main asteroid belt.

Nearly all the asteroids are irregular in shape, but a few of the largest are roughly spherical. The surface of most of the asteroids is thought to be covered in dust. According to NASA, some asteroids are also known to have a small companion moon.

The average temperature of the surface of a typical asteroid is -100F (-73C) and has stayed mostly unchanged for billions of years. There are also binary asteroids, in which two asteroids of nearly equal size orbit each other.

Despite their small size, asteroids can be dangerous. Many of them have hit Earth in the past, and most likely, many will crash in the future. They are said to be the cause of catastrophic events that caused dinosaurs' extinction at the end of the Cretaceous period.

Overall, we could say they are some of the extinction-level threats to living species on Earth.