How likely is an asteroid collision with Earth?
We don’t know for sure, but in 2005 NASA set a goal “to detect, track and characterise 90 per cent of the near-Earth objects that are 140 metres across or larger by the end of 2020” (New Scientist, 22 January 2020). As a result, we now have an unprecedented amount of data on the orbits of near-Earth objects (NEOs).
NASA’s Center for Near-Earth Object Studies (CNEOS) has a database of near-Earth objects and the times and distances of their closest approaches to Earth.
[Click for an interactive version.]
The visualization shows each object as a grey disk, sized according to how big the object’s diameter is. The position of the object shows its closest approach: the x-axis shows the date of closest approach, and the y-axis shows the predicted distance from Earth. The distance is measured in multiples of Lunar distance (abbreviated LD). (Clearly, the distance scale for distance from the Earth is different to the distance scale for the object’s diameter!)
The band of small NEOs to the left of the year 2020 suggests that NASA’s goal is being realized, since it shows a large number of small objects are being detected and catalogued when their orbit brings them closer to Earth.
The good news is that most NEOs are outside the Moon’s orbit (the horizontal yellow line), which as this visualization shows, is a long way from Earth (about 384,400 km). However, 20 LD (approximately 0.05au) is considered the distance threshold for defining NEOs as “potentially hazardous”.
If you click on the image above you can try out the interactive version, which allows you to get information on an NEO by hovering over it. If you click on an NEO it will show other close approaches that the same object has made (or will make in the future). (Remember that NEOs are in orbit around the Sun, so they may approach the Earth many times. The record holder for this dataset is 2019 BE5, which has 40 approaches.)
You can also filter the NEOs by diameter. By adjusting the sliders you can see the NEOs that are between 100m and 1km, say. As a rule of thumb, objects of around a metre or less don’t cause damage, ~100m could destroy a city, ~1km could affect an entire continent, and ~10km would cause global damage (source New Scientist).
Visualization type: bubble plot
Data source: CNEOS Close Approach Data, CSV, 3 MB
See also: Inside the mission to stop killer asteroids from smashing into Earth, New Scientist, 22 January 2020; NEO Basics, CNEOS