What is an Asteroid ?

Ground-based observatories and facilities such Pan-STARRS, the Catalina Sky Survey, and ATLAS are constantly on the hunt to detect near-Earth asteroids. NASA also has a small infrared observatory in orbit about the Earth: NEOWISE. In addition to detecting asteroids and comets, NEOWISE also characterizes these small bodies.

Buddy system. Roughly one-sixth of the asteroid population have a small companion moon (some even have two moons). The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993

Earthly visitors. Several NASA space missions have flown and observed asteroids. The NEAR Shoemaker mission landed on asteroid Eros in 2001 and NASA’s Dawn mission was the first mission to orbit an asteroid in 2011. In 2005, the Japanese spacecraft Hayabusa landed on asteroid Itokawa. Currently, NASA’s OSIRIS-REx is en route to a near-Earth asteroid called Bennu; it will bring a small sample back to Earth for study.

The leading theory about how our neighborhood came to be is this: the Sun coalesced from a compressed grouping of gas that eventually began fusing atoms and creating a protostar. Meanwhile, the dust and debris nearby the Sun began to coalesce. Small grains became small rocks, which crashed into each other to form bigger ones. The survivors of this chaotic period are the planets and the moons that we see today … as well as a few smaller bodies. By studying asteroids, for example, we get a sense of what the Solar System used to look like billions of years ago.

While there are asteroids all over the Solar System, there’s a huge collection of them between the orbits of Mars and Jupiter. Some astronomers think that could have formed into a planet if Jupiter was not nearby.

An asteroid is a small body orbiting the Sun that is composed primarily of rock or metal.

In general, an asteroid’s composition is determined by how close it is to the Sun. Our nearby star’s pressure and heat tends to melt ice that is close by and to blow out elements that are lighter. There are many kinds of asteroids, but these are the three main types, according to NASA:

Dark C (carbonaceous) asteroids, which make up most asteroids and are in the outer belt. They’re believed to be close to the Sun’s composition, with little hydrogen or helium or other “volatile” elements.

In 1801, Giuseppe Piazzi discovered what he believed to be a new planet. He named the newfound object Ceres, after the Roman goddess of the harvest. Soon after Ceres’ discovery similar objects were found. It was soon realized that these new objects were not, in fact, planets, but some other type of celestial body

The majority of the known asteroids in the Solar System orbit the Sun in a band between the orbits of Mars and Jupiter. This band is commonly referred to as the Asteroid Belt.

Bright S (silicaceous) asteroids and are in the inner belt. They tend to be metallic iron with some silicates of iron and magnesium.

Asteroids are small, rocky objects that orbit the Sun.

The first asteroid was Ceres, discovered by Giuseppe Piazzi in 1801.

While we think of moons as something that orbits a planet, asteroids also have smaller bodies that orbit them! The first known one was Dactyl, which was discovered in 1993 to be orbiting a larger asteroid called Ida. More than 150 asteroids are known to have moons

There are currently over 600,000 known asteroids in our solar system.

We have flown by, orbited and even landed on asteroids. NASA says there are more than 10 spacecraft that accomplished at least one of these, so we’ll just cover a couple of examples here. NEAR Shoemaker touched down and survived for weeks on 433 Eros in 2001 despite not being designed to do it.

Most asteroids are found orbiting in the Asteroid Belt, a series of rings located between the orbits of Mars and Jupiter.

NASA’s Dawn spacecraft spent months orbiting Vesta — the second-largest member of the asteroid belt — in 2011 and 2012. And in 2010, Japan’s Hayabusa spacecraft made an astonishing return to Earth bearing samples of asteroid Itokawa that it nabbed in 2005.

Astronomer William Herschel first coined the word asteroid, which means “star like” in 1802.

Asteroids are too small to support life as we know it. That’s because they’re too tiny to even hold on to atmospheres. Their gravity is too weak to pull their shape into a circle, so they’re irregularly shaped. To get a sense of just how small they are in aggregate, NASA says the mass of all the asteroids in the Solar System is less than our Moon — which only has a tenuous “exosphere” itself.

As well as being the first asteroid discovered, Ceres is also the largest known asteroid at 933 kilometers (580 miles) across. The smallest known asteroid, 1991 BA, is only 6 meters (20 feet) across.

Despite their small size, water may flow on asteroid surfaces. Observations of Vesta released in 2015 show gullies that may have been carved by water. The theory is that when a smaller asteroid slams into a bigger one, the small asteroid releases a layer of ice in the bigger asteroid it hit.

Current theory suggest that asteroids are planetisimals – the building blocks of planets – that were never incorporated into one of the eight planets in our solar system.

An asteroid could have killed the dinosaurs. The fossil record for dinosaurs and other creatures of their era show them rapidly disappearing around 65 million or 66 million years ago.

Apollo objects are asteroids whose orbit crosses the orbit of Earth.