Tim Furniss/LONDON
THE DESIGNERS of NASA's Galileo probe have been vindicated after 57min of data were returned from the craft as it descended through the predominantly hydrogenous atmosphere of Jupiter on 7 December. The data, however, disappointed scientists, who had been expecting them to reveal far more about the Jovian atmosphere. NASA says that they now "...have to rethink their theories of planetary evolution".
The Hughes-designed probe had experienced the "...most difficult planetary atmospheric entry ever attempted", says NASA. During its 600km (370 miles) descent, it survived speeds of more than 91,500kt (169,600km/h), temperatures twice as high as those on the surface of the Sun, and deceleration forces 230 times greater than the Earth's gravity.
The probe's six instruments transmitted data during 156km of the descent after the deployment of its parachute. Critics had earlier cast doubt, on the probe's ability to survive, the descent long enough to transmit sufficient data.
The data was described on 22 January as "fantastic" by William O'Neil, the Galileo project manager. "There are thousands of things, that could have gone wrong - but we got it all," he says. The quality of the data "...exceeds our most optimistic predictions" according to Wesley Huntress, NASA associate administrator, for space science.
The capsule encountered more severe winds than expected, up to 528km/h, indicating that the Jovian weather's energy source, is heat escaping from the planet's interior. The data reveal that there is very little water vapour, or the expected three-tiered atmosphere, which was thought to consist of ammonia ice crystals, ammonium hydrosulphide, and water and ice crystals. Ammonia ice crystals were nonetheless found to be present in the upper atmosphere.
Scientists suggest, that this was because the probe, descended through a part of the Jovian atmosphere which was clear of cloud. The level of helium in the atmosphere was half that expected and neon, carbon, oxygen and sulphur were practically non-existent. The probe did not collide with any solid matter, but the atmospheric density was higher than expected.
Lightning was detected, but at a frequency rate ten times less than that recorded on Earth - a blow to scientists hoping to find organic molecules. A new, intense radiation belt was detected more than 49,000km from the planet.
Source: Flight International
