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Venusian rendezvous results: chapter one   As NASA’s MESSENGER departed from Venus on 5 June 2007 to continue its journey towards Mercury, its Wide Angle Camera captured a sequence of 50 images (480-nm wavelength filter) showing the planet disappearing in the distance. At the start of the sequence the spacecraft was 60 688 km from the planet, by the end it was at 89 310 km. Initially, images were acquired at a rate of one of every 20 minutes and then, with increasing distance, the timing interval was increased to 60 minutes. Besides a joint observation campaign of the planet with ESA’s Venus Express, the flyby provided the MESSENGER mission operations team with an opportunity to successfully complete a full test of the complicated series of spacecraft motions required to build up high-resolution image mosaics at Mercury.
Mariner 10 imaged only one hemisphere of Mercury in 1974-75. During the upcoming flyby, in January 2008, the MESSENGER instruments will photograph and make measurements of half of the hemisphere viewed by Mariner 10 and half of the hemisphere never before imaged by spacecraft. MESSENGER will capture the rest of the planet in subsequent flybys in October 2008 and September 2009. In March 2011 MESSENGER will be inserted into orbit about Mercury, allowing detailed observations of the planet for a full Earth year.  This grey-scale image, obtained by the VIRTIS instrument on board ESA’s Venus Express, shows the atmospheric region of Venus over which NASA’s MESSENGER passed on 5 June 2007. The region of MESSENGER’s closest approach is in the night side (marked by a circle). VIRTIS obtained this image at 2.3 micrometres from about 35 000 kilometres from the planet, on the night side. This wavelength makes it possible to probe the atmosphere down to about 30 kilometres from the surface. Much of the contrast in this image is due to the structure of the lower clouds. The bright areas correspond to radiation from the lower atmospheric layers, indicating that the clouds are thinner in those areas. At the 2.3-micrometre wavelength it is possible to study not only the morphology of the cloud layers, but also its chemical composition (carbon monoxide, water, sulphur-dioxide, etc). A version of this image without an indication of the region of fly-by and one indicating the planetary latitude can be downloaded here [ VI410_01_23_no_layers.gif, VI410_01_23.gif ]  The images in this panel were obtained by the VIRTIS imaging spectrometer on board Venus Express on 5 and 6 June 2007, before and after MESSENGER’s closest approach to the planet. These panels from VIRTIS provide a night-side view of the same region that Messenger flew over and imaged. The images where obtained at 1.7 micrometres, revealing atmospheric details down to an altitude of 50 km from the surface. Two stills from these images can be downloaded here [ VI0410_00_prj_17.tif, VI0411_03_prj_17.tif ]  This movie consists of a sequence of six images obtained by the VIRTIS imaging spectrometer on board ESA’s Venus Express on 5 and 6 June 2007, before and after NASA MESSENGER’s closest approach to the planet. The image sequence, obtained by VIRTIS, provides a night-side view of the same region that Messenger flew over and imaged. They were obtained at 1.7 micrometres, revealing atmospheric details down to an altitude of 50 km from the surface. A combined image made of the six images featured in this video can be downloaded here [ ORB410_411_tot.tif ]  An unprocessed thermal map of the Venusian surface obtained by VIRTIS on 5 June 2007 (left) is compared here with a radar image of the same area obtained by NASA’s Magellan spacecraft in the 1990s (right). VIRTIS, the imaging spectrometer on board Venus Express, obtained this image at 1 micrometre, a wavelength that allows detection of radiation originating from the surface. The imaged region is that which NASA’s MESSENGER flew over as it made its closest approach to the planet. Magellan’s radar imaging and altimetry maps made it possible to measure the elevation and the radio-optical properties of the surface. Venus Express’ VIRTIS is providing the first complete set of thermal maps of the surface of Venus. Correlations between topographic and thermal data similar to the ones shown in this image-composite will allow the scientists to understand if the measured temperature of the surface depends only on the altitude – where higher altitudes simply corresponds to colder, temperatures such as on Earth – or if it depends on the presence of previously undetected sources of heat such as active volcanoes.  ESA’s Venus Express, in orbit around Venus since 11 April 2006, was joined for a few hours by NASA’s MESSENGER spacecraft, flying by Venus while on its way to Mercury. This animation shows both the Venus Express and MESSENGER spacecraft in orbit around Venus at the time of the fly-by.
Earth-based observatories and telescopes in orbit around Earth were also watching. Looking at Venus together, spacecraft and ground observatories obtained a unique set of data each, so many different ‘eyes’ observed the same regions and phenomena during the same time frame. Release date: 10 October 2007 |