A.S.I. - Agenzia Spaziale Italiana - The road to Space goes through Italy.

16 Nov 2009

Final flyby of the Earth for Rosetta, the ESA probe for studying minor bodies in the solar system and built with a significant Italian contribution. At precisely 8:45 on 13 November, exactly as planned, it reached the closest point to the Earth, passing about 2481 km above the Indian Ocean (109 latitude east, eight longitude south: a little below the island of Java) at a velocity of 13.34 km per second. The success of the 'swing by' was confirmed twenty minutes later, at 9:05, when contact with the probe was re-established by the Spanish control centre in Maspalomas. This is Rosetta’s third flyby, following those made in March 2005 and November 2007, after which Rosetta, will resume its voyage into deep space, given additional speed by the gravitational energy 'sling', and will reach its destination, the comet Churyumov Gerasimenko, in 2014. Its mission is to explain the many mysteries that the comets, these ancient inhabitants of our solar system, still keep. The probe was named Rosetta precisely for this reason; after the Rosetta Stone, discovered by chance on the Nile delta in 1799, that contributed decisively to decoding hieroglyphics and thus to understanding ancient Egyptian civilisation.

  
The name Osiris recalls the ancient Egyptian divinity but in fact it is initials which stand for 'Optical, Spectroscopic and Infrared Remote Image Sensing'. The camera consists of the WAC (wide angle camera) and an NAC (narrow angle camera, which can zoom in on subjects). This will serve to obtain high resolution images of the nucleus of the comet and of the asteroids that it will encounter on its long voyage into deep space. Other instruments on the probe will make readings of the Earth’s atmosphere and magnetosphere, in an attempt to contribute to our understanding of fascinating phenomena such as the aurora (the spectacular 'product' of collisions between terrestrial magnetic fields and particles bursting out from the Sun).

The image on the right shows the Earth at night, particularly the American continent, with the US West and East Coast made clearly visible by the impact of artificial light.

The spectacular image on the left shows the Earth seen from a distance of 633 thousand kilometres and was 'taken' at 13:28 on 12 November 2009 by the camera on board Osiris (the heart of which, the WAC, was built entirely in Italy, and is managed by the CISAS "Giuseppe Colombo" Centre in Padova).  In fact, this 'photo' was created by taking and superimposing three separate images (with blue, orange and green filters). The brightest area, at the bottom, is the south pole. It is the white surface of the Antarctic ice sheet, the outline of which can easily be recognised under a swirl of clouds, that is reflecting the light intensely.

The image on the right, taken on November 13, shows an anticyclone over the Southern Pacific Ocean. Cloud vortexes are shown with particular clarity.