Asteroid Apophis Approaches Earth, 2036 Impact Probability Still Uncertain


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Over the past weekend, astronomers used the European Space Agency's (ESA) Herschel Space Observatory to image an asteroid that will be giving the Earth a near-miss in 2029.

The asteroid, named Apophis, was thought to have a 2.7% chance of striking the Earth in 2029 when it was discovered in 2004. New observations have ruled out an impact, but the object still might come as close as 29,450 kilometers (18,300) miles from Earth - about 13 times closer to Earth than the moon, and closer than the orbits of geostationary satellites.

Apophis will also make a close approach to Earth in 2036. The data collected over the weekend is expected to give astronomers an idea of whether an impact in 2036 can be ruled out.

“Although Apophis initially caught public interest as a possible Earth impactor, which is now considered highly improbable for the foreseeable future, it is of considerable interest in its own right, and as an example of the class of Near Earth Objects,” said Göran Pilbratt, a Herschel project scientist with the ESA. “Our unique Herschel measurements play a key role for the physical characterisation of Apophis, and will improve the long-term prediction of its orbit.”

The Apophis observations were able to refine the details known about the object using the first thermal infrared observations of the asteroid. Its estimated average diameter was was increased to around 325 meters, increasing mass estimates by around 75%. The estimate of its reflectivity, called an albedo, was narrowed to 0.23. Knowing the thermal properties, such as the albedo, of Apophis will make orbital estimates more accurate.

“As well as the data being scientifically important in their own right, understanding key properties of asteroids will provide vital details for missions that might eventually visit potentially hazardous objects,” says Laurence O'Rourke, principal investigator of the MACH-11 observing programme, from the European Space Astronomy Centre (ESAC).

(Image courtesy ESA/Herschel/PACS/MACH-11/MPE/ESAC)