Scientists Say: Comet | Science News for Students

Scientists Say: Comet

This speeding object can have a pretty tail when it passes near the sun
Oct 17, 2016 — 7:00 am EST
comet 67P

This is comet 67P/Churyumov-Gerasimenko.


Comet (noun, “COM-et”)

A small object in the solar system that orbits the sun. Comets are clumps of rocks, ice, dust and frozen gases. They may come from the Kuiper Belt — a strip of rocky clumps beyond Neptune. Comets may also come from the Oort cloud — the cloud of icy objects at the very edge of the solar system. Comet orbits can be very variable. Some comets are visible from Earth once every few years. Others might take thousands of years to revisit our planet.

A comet differs from an asteroid because it has a tiny bit of gassy atmosphere surrounding it; asteroids are mostly rock. A comet’s frozen ice and gases are what causes the most spectacular feature: When a comet passes close to the sun, these frozen chemicals melt, surrounding the comet and trailing after it as it streaks across the sky.

In a sentence

The European Space Agency sent a craft called Rosetta to orbit a comet named 67P/Churyumov-Gerasimenko (or just 67P). Rosetta ended its mission by landing on the comet’s surface.

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Power Words

(for more about Power Words, click here)

asteroid     A rocky object in orbit around the sun. Most orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.

atmosphere     The envelope of gases surrounding Earth or another planet.

chemical     A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

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.”

Kuiper belt     An area of the solar system beyond the orbit of Neptune. It is a vast area containing leftovers from the formation of the solar system that continue to orbit the sun. Many objects in the Kuiper belt are made of ice, rock, frozen methane and ammonia.

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.

solar system     The eight major planets and their moons in orbit around the sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

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. Or a sunlike star.


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