Herschel intercepts asteroid Apophis

ESA's Herschel space observatory made new observations of asteroid Apophis as it approached Earth this weekend. The data shows the asteroid to be bigger than first estimated, and less reflective. Catalogued as asteroid (99942) Apophis (previously 2004 MN4), it is often nicknamed 'the doomsday asteroid' in popular media, after initial observations made after its discovery in 2004 gave it a 2.7% chance of striking Earth in April 2029. With additional data, however, an impact in 2029 was soon ruled out, although the asteroid will pass within 36 000 km of Earth's surface, closer even than the orbits of geostationary satellites. The asteroid will return to Earth's neighbourhood again in 2036, but quite how close it will come then is uncertain, as the 2029 approach is predicted to alter its orbit substantially. Obtaining improved physical parameters for Apophis and its orbit is thus of great importance in being able to make better predictions of its future trajectory. Herschel had a good opportunity at the weekend, observing the asteroid for about two hours on its approach to Earth, ahead of today's closest encounter at a little less than one tenth of the distance from Earth to the Sun: about 14.5 million km.