Have you ever been out at night and seen a streak of light blast across the sky and disappear? Ever wonder where that shooting star came from, or how it got to be in your sky?As the director of the Peters Observatory at Hamilton College, I have seen many similar streaks across the sky, as I spend late nights at the observatory, and I am here to tell you that what you saw isn’t a star at all. You observed the end of a comet or asteroid’s 4.6-billion-year journey right before your eyes.Remnants from the early solar systemRoughly 4.6 billion years ago, the solar system was in its infancy. A vast ball of gas and dust that would become our solar system was accumulating matter in its center, forming what would eventually become our Sun. It was also condensing dust in smaller patches farther from the center that would merge into the first chunks of materials, called planetesimals.AdvertisementAdvertisementAsteroids formed from planetesimals in the inner portions of the solar system, near the Sun. This location in the center of the solar system was warm, so the planetesimals were made mostly of the rocks and metals that could withstand the heat. The biggest of these chunks would congeal with others and form the terrestrial planets: Mercury, Venus, Earth and Mars. The remaining planetesimals that did not form into the terrestrial planets are the asteroids of today, left to orbit the inner portion of the solar system.Asteroids such as Psyche, shown in this illustration, are planetary remnants typically made of metal and rock. NASAComets formed in the outer parts of the solar system, where it was cold enough that any water, or similar hydrogen-based compounds, took the form of ice. The planetesimals forming in this region were composed of not just rock and metal but these ices as well.Some of the planetesimals became big enough, fast enough, that they had enough gravitational pull to hold onto large atmospheres composed of the very abundant early solar system gases, such as hydrogen and helium. These planetesimals became the Jovian planets of today: Jupiter, Saturn, Uranus and Neptune. However, the planetesimals that did not form into the Jovian planets were left to travel through the solar system as comets.A comet named Hartley is shown in this image from NASA’s EPOXI mission. It has a thin trail of dust particles coming off its back side. NASA/JPL-Caltech/UMDOrigin of meteorsAsteroids are still abundant in the inner solar system, so inevitably some will collide with Earth. When a chunk of rock enters Earth’s atmosphere, it’s traveling at dozens of miles per second. As it enters, it may create a thunderlike sonic boom in its wake. When it travels through the air faster than the speed of sound, the asteroid produces a shock wave, which can generate that boom.AdvertisementAdvertisementDuring its journey through the atmosphere over tens of miles, the asteroid collides with air molecules, and the incredible temperatures and pressure usually vaporize it. That trail of vaporizing particles breaking off the asteroid causes a bright streak of light across the sky called a meteor, or colloquiall …
