This painting by Donald E Davis shows an asteroid slamming into the tropical, shallow seas of the Yucatan Peninsula, in what is today south-east Mexico. The aftermath of this immense asteroid collision, which occurred approximately 65 million years ago, is believed to have caused the extinction of the dinosaurs and many other species on Earth (Image: JPL / NASA)

Video: A large space rock zoomed past Earth at just twice the altitude of the most distant communications satellites (Video courtesy of Dave Herald)

Updated 11 March: Infrared observations of 2009 DD45 suggest it is a member of a class of rocky asteroids called “S-type”. Based on the average surface brightness of these asteroids, DD45’s size appears to be about 19 km across, on the lower end of its estimated size range. Its size and stony makeup suggest it would break up high in Earth’s atmosphere if it were ever found on a collision course with Earth, and would not cause damage on the ground, says NASA’s David Morrison in an email newsletter.

An asteroid about the size of the one that levelled the forest in Tunguska, Siberia, a century ago flew past Earth on Monday – well within the Moon’s orbit. The risk of a future impact with the object is not yet known.


The asteroid, dubbed 2009 DD45, whizzed just 72,000 kilometres above the Earth’s surface. That is less than a fifth of the distance to the Moon and just twice the distance to geosynchronous satellites.

The object was first reported on Saturday by members of the Siding Spring Survey, a near-Earth object search programme based in Australia.

Based on its brightness, the asteroid seems to be between 20 and 50 metres across, says Timothy Spahr of the International Astronomical Union’s Minor Planet Center. That rivals the size of the asteroid, estimated to be as small as 30 metres, that slammed into Tunguska, Siberia in 1908, creating a powerful blast that levelled 2000 square kilometres of forest.

Spotted in advance

Astronomers hope to get a better estimate of DD45’s span by observing it at infrared wavelengths to estimate how well the rock reflects light.

By modelling the rock’s orbit over the coming days, astronomers also hope to have a better sense of the threat it may pose to Earth in the next 100 years or so, Spahr told New Scientist. DD45 seems to orbit the Sun once every 1.5 years.

Some 6100 objects have been discovered passing within 1.3 astronomical units (AU) of Earth (1 AU is the distance from the Earth to the Sun). Of those, more than 1000 have been classified as potentially hazardous, because they pass within 0.05 AU of Earth.

DD45, which passed just 0.00048 AU from Earth, is one of a growing list of potentially hazardous asteroids that have been spotted by astronomers in advance of their closest approach.

Scanning the skies

In October 2008, astronomers spotted the first space rock on a certain collision course with Earth. Pieces of the asteroid, which seems to have measured no more than 5 metres across, were recently recovered in Sudan.

The closest observed asteroid to pass Earth so far has been 2004 FU162, a 5- to 10-metre rock that skimmed by Earth in 2004, flying just 6500 kilometres above the surface.

NASA aims to discover at least 90% of near-Earth objects that span a kilometre or more.

But since smaller objects can also pack a punch, some argue that NASA must do more to identify threatening asteroids as small as 140 metres.