A 250m-diameter (600ft) asteroid passed by the Earth this morning (29 January, closest approach at 0833 GMT). The asteroid, 2007 TU24, came as close as 538,000km (334,000 miles), just beyond the Moon’s orbit.
NASA estimates that there are around 7000 near-Earth asteroids as large as 2007 TU24, and a similar object can be expected to pass this close to Earth about every five years or so. However, Earth impacts for an object this size only occur every 37,000 years on average.
According to NASA’s Near Earth Objects (NEOs) fact sheet, ‘There are no known NEOs on a collision course with the Earth. There is a possibility that an as yet undiscovered large NEO may hit the Earth, but the probability of this happening over the next 100 years is extremely small.’
An asteroid is considered potentially hazardous if it is larger than 100m, and is expected to pass the Earth within 20 times the Earth-Moon separation. The Earth-Moon distance is about 0.0026 AU (1 AU = 149.6 million km).
It’s hoped that detailed observations of 2007 TU24 will reveal how the asteroid is composed – i.e. whether it is a single solid object or a loose collection of rubble, information which could help plan our defence against future hazardous asteroids.
As mentioned in a recent post, the considerably smaller asteroid 2008 AF3 (27-metre diameter) passed by the Earth as close as the Moon just over two weeks ago. A 600m-wide asteroid, 2004 XP14, flew past the Earth at roughly the same distance just over six months ago.

No comments.