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How many NEOs are there?
It has been estimated that there are roughly 100 million ten metre objects, some 100,000 one hundred metre objects, about 10,000 five hundred metre objects and perhaps 1000 which are one kilometre or larger. There is in general an exponential increase in the number of smaller objects.
We estimate how many NEOs there are from the rate at which they are discovered. This is very much like telling how many apples are in a barrel. Take out ten apples and mark them with a cross as 'discovered' then return them to the barrel. Shake the barrel to mixing up the apples and then remove another ten. If one of these apples has a cross then there are probably 100 apples in the barrel. On a much larger scale this works with asteroids and comets in the night sky.
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How do we search for NEOs?
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