The first one is the monolith chondritic asteroid, so that's the real brick of the solar system," Jourdan explained. "I would say there are three types of asteroids. Each pixel in the image corresponds to roughly 0.88 miles (1.4 kilometers) (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA) (opens in new tab) It was taken from a distance of about 9,500 miles (15,000 kilometers) away from the protoplanet Vesta. NASA's Dawn spacecraft obtained this image with its framing camera on July 17, 2011. Some asteroids are one solid monolithic body, while others like Bennu are essentially floating rubble piles, made of smaller bodies loosely bound together gravitationally. This means asteroids can also differ by how solid they are. "During the next few billions of years until the present, some asteroids smashed into each other and destroyed each other, and the debris recombined and formed what we call rubble pile asteroids." "All that happened 4.5 billion years ago but the solar system has remained a very dynamic place since then," Jourdan added. Further collisions shattered apart these planetesimals, with these fragments and rocks forming the asteroids we see today. In the chaotic conditions of the early solar system, this material repeatedly clashed together (opens in new tab) with small grains clustering to form small rocks, which clustered to form larger rocks and eventually planetesimals - bodies that don't grow large enough to form planets. "So all the material that formed all those asteroids is about 4.55 billion years old."įred Jourdan is a planetary scientist at Curtin University. They are the initial bricks that built the planets," Fred Jourdan, planetary scientist at Curtin University. "Simply put, asteroids are leftovers rocky material from the time of the solar system formation. While most of this disk collapsed to form the planets some material was left over. Using NASA definitions (opens in new tab), an asteroid is "A relatively small, inactive, rocky body orbiting the sun," while a comet is a "relatively small, at times active, object whose ices can vaporize in sunlight forming an atmosphere (coma) of dust and gas and, sometimes, a tail of dust and/or gas."Īdditionally, a meteorite is a "meteoroid that survives its passage through the Earth's atmosphere and lands upon the Earth's surface" and a meteor is defined as a "light phenomenon which results when a meteoroid enters the Earth's atmosphere and vaporizes a shooting star." What are asteroids made of?īefore the formation of the planets of the solar system, the infant sun was surrounded by a disk of dust and gas, called a protoplanetary disk. What's the difference between asteroids, comets and meteorites? government in planning for a response to a possible impact threat. But don't worry, NASA's Planetary Defense Coordination Office (opens in new tab) is keeping a watchful eye on near-Earth objects (NEOs), including asteroids, to assess the impact hazard and aid the U.S. Though a majority of asteroids lurk in the asteroid belt, NASA says (opens in new tab), the massive gravitational influence of Jupiter, the solar system's largest planet, can send them hurtling through in random directions, including through the inner solar system and thus towards Earth. Most asteroid surfaces are pitted with impact craters from collisions with other space rocks. Ceres is the largest object in the main asteroid belt while Vesta is the second largest.Īs well as coming in a range of sizes, asteroids come in a variety of shapes from near spheres to irregular double-lobed peanut-shaped asteroids like Itokawa. Vesta recently snatched the "largest asteroid title" from Ceres, which NASA now classifies (opens in new tab) as a dwarf planet. Asteroids are also often referred to as "minor planets" and can range in size from the largest known example, Vesta, which has a diameter of around 326 miles (opens in new tab) (525 kilometers), to bodies that are less than 33 feet (10 meters) across.
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