Discover the space rocks NASA keeps an eye on near our planet.
An asteroid is a small rocky world that travels around the Sun. Some pass near Earth, but “near” can still mean several million kilometres away.
NASA watches asteroids like a playground helper watches bikes: knowing their path helps avoid surprises.
Most asteroids are found between Mars and Jupiter.
Passing near Earth does not mean hitting it.
Scientists work out their path a long time in advance.
Objects near Earth are sorted by their size and by how close they come. A scientific alert means an object deserves to be followed, not that a collision is going to happen.
Compare an asteroid’s flyby with the distance to the Moon. Which one is farther away?
Answer two questions about the lesson to stamp your passport.
Question 1 of 2
An asteroid is a big rock travelling through space! Most are found between Mars and Jupiter, in the “asteroid belt”, but some sometimes pass near Earth. NASA watches them day and night with special telescopes.
Scientists call some asteroids “potentially hazardous” when they can pass within 7.5 million km of Earth AND are more than 140 metres across. To compare: the Eiffel Tower is 330 metres tall, and a football pitch is 100 metres long.
Planetary defence: since the DART mission in 2022, humans know how to push an asteroid off course by hitting it with a spacecraft. It was the first time anyone changed the orbit of an object in space!
Each bar grows more slowly than the real size, so that small objects stay visible.
The most studied asteroid. The OSIRIS-REx probe brought samples of it back to Earth in 2023! It has about a 1 in 2,700 chance of hitting Earth in 2182.
Bennu spins once every 4 h 17 min and sometimes throws small pebbles into space!
In 2004, the first calculations gave a 2.7% chance of a collision in 2029. That risk has been ruled out: it will pass about 32,000 km from Earth on 13 April 2029.
It will pass closer than some satellites. We may even see it with the naked eye!
The Japanese probe Hayabusa2 touched down on it and brought samples back in 2020. Amino acids, building blocks of life, were found in them!
Ryugu is shaped like a spinning top and is so porous that it is about half empty space.
The first asteroid whose orbit humans have changed! NASA’s DART mission hit it in 2022 to test planetary defence.
The impact made a trail of debris more than 10,000 km long and shortened its orbit by about 33 minutes.
The biggest object in the asteroid belt, classed as a “dwarf planet”. The Dawn probe studied it from 2015 to 2018.
Ceres may hold more fresh water than the whole Earth, hidden as ice under its crust.
The second biggest asteroid. Vesta has a huge impact crater (Rheasilvia) almost as wide as the asteroid itself!
Pieces of Vesta have fallen to Earth as meteorites. Some were found in Antarctica!
The DART mission that hit the asteroid Dimorphos in 2022.
A European Space Agency video about asteroids and how scientists keep watch on them.
66 million years ago, an asteroid about 10 km wide changed Earth’s history.
The end of the journey of the probe that brought samples of the asteroid Bennu back to Earth.