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Astronomy & Astrophysics 101: Asteroids

Animation of an asteroid rotating in space.

Asteroids are rocky celestial bodies that orbit the Sun, but do not meet the requirements to be classified as a planet.

The term asteroid covers a very broad range of Solar System objects, including debris left behind by objects that did not successfully grow into planets. They are irregularly shaped, which disqualifies them from being classified as planets or dwarf planets. The asteroid belt is a region of space between the orbits of MarsMars is the second smallest planet in our solar system and the fourth planet from the sun. Iron oxide is prevalent in Mars' surface resulting in its reddish color and its nickname "The Red Planet." Mars' name comes from the Roman god of war.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Mars and JupiterJupiter is the largest planet in the solar system and the fifth planet from the sun. It is a gas giant with a mass greater then all of the other planets combined. Its name comes from the Roman god Jupiter.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Jupiter that is densely populated with asteroids. The majority of known asteroids are found within the asteroid belt. Asteroids and comets are partially distinguished from one another by their composition: asteroids are rocky, whereas comets comprise dust and ice. When comets pass close to the Sun, some of their icy composition heats up sufficiently to be released as gas. This gas forms a loosely bound atmosphere known as a ‘coma’, and this gives comets their distinctive appearance of having a tail streaming behind them. In contrast, asteroids tend to remain solid. In practice, however, the distinction between asteroids and comets can be rather arbitrary.

The asteroid 6478 Gault is seen with the NASA/ESA Hubble Space Telescope, showing two narrow, comet-like tails of debris that tell us that the asteroid is slowly undergoing self-destruction. The bright streaks surrounding the asteroid are background stars. The Gault asteroid is located between the orbits of Mars and Jupiter. Credit: NASA, ESA, K. Meech and J. Kleyna, O. Hainaut

Hubble has observed various asteroids over the course of more than three decades of observations. For example, in 2017 Hubble studied the asteroid Vesta — which is only 500 km in diameter — from a distance of 250 million kilometers. The observations created a map of its surface and were even able to capture the asteroid’s changing appearance as it rotated.

Hubble also observed the spectacular asteroid collision P2010/A2 in 2010. Using Hubble to study the aftermath of the collision over five months, astronomers watched a strange, comet-like debris trail slowly evolve as the collision site orbited the Sun. This research gave clues about how asteroids behave when they collide, and how the fall-out from these impacts contributes to the dust that pervades the Solar System.

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Asteroids are rocky celestial bodies that orbit the Sun, but do not meet the requirements to be classified as a planet. Credit: NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. It's vision is "To discover and expand knowledge for the benefit of humanity."” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>NASA & ESA

In 2017 a German-led group of astronomers used Hubble to observe two asteroids, orbiting each other in the asteroid belt between Mars and Jupiter, that exhibited comet-like features, including a bright coma and a long tail. This was the first known binary asteroid to also be classified as a comet. It was Hubble’s images that revealed that it was actually not a single object, but two asteroids of almost the same mass and size, orbiting each other at a distance of about 100 kilometers. That discovery was in itself an important find; because they orbit each other, the masses of the objects in such systems can be measured. Understanding the origin and evolution of main-belt comets — asteroids orbiting between Mars and Jupiter that show comet-like activity — is a crucial element in our understanding of the formation and evolution of the whole Solar System.

Credit: ESA/Hubble, NASA, ESA, K. Meech and J. Kleyna (University of Hawaii), O. Hainaut (European Southern Observatory)

In 2019, Hubble observed a rare self-destructing asteroid called 6478 Gault. The images provided new insights into the asteroid’s past: the object was 4–9 kilometers wide and had two narrow, comet-like tails of debris that indicated that the asteroid was slowly undergoing self-destruction. Each tail is evidence of an active event that released material into space. The direct observation of this activity by the Hubble Space TelescopeThe Hubble Space Telescope (often referred to as Hubble or HST) is one of NASA's Great Observatories and was launched into low Earth orbit in 1990. It is one of the largest and most versatile space telescopes in use and features a 2.4-meter mirror and four main instruments that observe in the ultraviolet, visible, and near-infrared regions of the electromagnetic spectrum. It was named after astronomer Edwin Hubble.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Hubble Space Telescope provided astronomers with a special opportunity to study the composition of asteroids. By researching the material that this unstable asteroid releases into space, astronomers can get a glimpse into the history of planet formation in the early Solar System.

Source: SciTechDaily