How much space junk is there?
Around 40,000 objects larger than 10 cm are tracked individually. Below that, the numbers come from models: roughly 1.1 million fragments between 1 and 10 cm, and over 130 million between 1 mm and 1 cm. The small ones matter because orbital closing speeds reach 15 km/s, at which a 1 cm aluminium fragment carries the kinetic energy of a hand grenade. Two events — China's 2007 anti-satellite test and the 2009 Iridium-Cosmos collision — produced a substantial share of the tracked catalogue between them.
How the figure is arrived at
Objects above about 10 cm in low orbit are tracked directly by ground radar. Smaller fragments cannot be seen, so their population is inferred two ways: statistical radar sampling that detects fragments without cataloguing them, and physically counting impact craters on hardware returned from orbit, such as the Space Shuttle windows and retrieved Hubble solar arrays.
How confident it is
- Low estimate
- 36,000
- High estimate
- 45,000
- Spread
- 1.3× between the bounds
Other space and the universe counts
- How many stars are there in the universe? about 200 billion trillion
- How many stars are there in the Milky Way? between 100 billion and 400 billion
- How many atoms are there in the universe? about 10^80
- How many galaxies are there? hundreds of billions — possibly 2 trillion
- How many satellites are in orbit? about 12,000 active satellites
- How many moons are there in the solar system? about 900 confirmed, and the number keeps moving
- How many planets are there in the galaxy? at least 100 billion — probably more planets than stars
- How many stars can you see with the naked eye? about 9,000 over the whole sky; roughly 2,500 at once
- How many constellations are there? exactly 88
- How many asteroids are there? about 1.4 million catalogued
Common questions
- How much space junk is there?
- about 40,000 tracked objects, and over 130 million fragments too small to track
- How is that estimated?
- Objects above about 10 cm in low orbit are tracked directly by ground radar. Smaller fragments cannot be seen, so their population is inferred two ways: statistical radar sampling that detects fragments without cataloguing them, and physically counting impact craters on hardware returned from orbit, such as the Space Shuttle windows and retrieved Hubble solar arrays.
Related pages
- How many stars are there in the universe? about 200 billion trillion
- How many stars are there in the Milky Way? between 100 billion and 400 billion
- How many atoms are there in the universe? about 10^80
- How many galaxies are there? hundreds of billions — possibly 2 trillion
- How many satellites are in orbit? about 12,000 active satellites
- How many moons are there in the solar system? about 900 confirmed, and the number keeps moving
- How many planets are there in the galaxy? at least 100 billion — probably more planets than stars
- How many stars can you see with the naked eye? about 9,000 over the whole sky; roughly 2,500 at once
- How many people are there in the world? Living things and the natural world
- How many countries are there in the world? Things people built
- How many bones are in the human body? The human body
- How many grains of sand are there on Earth? Living things and the natural world
- How many ants are there in the world? Living things and the natural world
- How many trees are there in the world? Living things and the natural world
Sources
- NASA — National Aeronautics and Space Administration (Public domain (US Government))