Page 37 - 新思维科学学生用书9 样章

1 Photosynthesis and the carbon cycle

Could other objects collide with Earth?

Objects in space that are smaller than an asteroid are called meteoroids. When meteoroids enter
Earth’s atmosphere they are called meteors. Some people call meteors shooting stars because they
appear like stars moving very fast across the sky. They usually present little risk because they burn in

the atmosphere due to heat from friction. Some large ones can create shockwaves; in 2013 a meteor
exploded over Russia and shattered windows. The parts of meteoroids that do collide with Earth are
called meteorites. Around 500 of these reach Earth’s surface each year.

If an object is large enough, it can cause local damage, or even damage that affects the whole planet.

In 1998, scientists started making detailed observations of objects that could possibly cause damage to
Earth. When assessing the possible risk to Earth, scientists look at:
• the mass or diameter of the asteroid

• the closest possible approach to Earth.

An asteroid passing further from Earth may be a greater risk than one passing closer if its mass is
greater.

The picture shows an asteroid, called 2006 DP14,
that passed 2 400 000 km from Earth in 2014.

This asteroid measures 200 m × 400 m so is
considered a potential risk. An asteroid such
as 2006 DP14 colliding with Earth would
cause an explosion equivalent to about
20 million tonnes of explosives.

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