Scientists Say: Oort cloud
Oort cloud (noun, “OR-t cloud”)
This is a shell of ice and rocks that surrounds our solar system and can be found out beyond Neptune and Pluto. Comets that take more than 200 years to orbit the sun are thought to come from the Oort cloud.
The Oort cloud begins about 750 million kilometers (465 million miles) away from the sun. (The Earth orbits some 146 million kilometers, or 92 million miles, from our star.) The outer edge of the Oort cloud is nearly 15 trillion kilometers (9.2 trillion miles) away. This makes for a very thick cloud. The Voyager I spacecraft, which left Earth in 1977, has been making its way out of the solar system ever since. Voyager has long left Neptune far behind. But it won’t reach the beginning of the Oort cloud for another 300 years. And it may take another 30,000 years to come out the other side.
But for all that it’s big and thick, scientists have never actually seen the Oort Cloud. The astronomer Jan Oort predicted that this cloud of bodies existed, and it now bears his name. But so far, there have been no missions to detect, let alone visit, the shell.
In a sentence
In 2013, a comet from the Oort Cloud buzzed past the sun.
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astronomy The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.
comet A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”
Neptune The furthest planet from the sun in our solar system. It is the fourth largest planet in the solar system.
Oort cloud A swarm of small rocky and icy bodies far beyond the orbit of Pluto, up to 1.5 light-years from the sun. The cloud is a source of some comets.
orbit The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.
Pluto A dwarf planet that is located in the Kuiper Belt, just beyond Neptune. Pluto is the tenth largest object orbiting the sun.
solar system The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.
star The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.
trillion A number representing a million million — or 1,000,000,000,000 — of something.