Journey to the Beginning of Time
Wilkie, Tom, The Independent (London, England)
After a voyage of 2.3 billion miles, lasting six years and costing about $1.6bn, the Galileo space mission to Jupiter has ushered in a new age of astronomy.
The results from Jupiter, just released by Nasa, represent "a major contribution to our understanding of the development of the solar system," says Dr Paul Murdin, head of astronomy for the Particle Physics and Astronomy Research Council. Astronomers are no longer passive, Earthbound observers of the planets and stars - the technology of spaceflight means they can now reach out and touch parts of the nearby universe.
Galileo's observations are not of arcane interest. Jupiter and the other "gas giant" planets such as Saturn and Uranus are important because they are so far from the Sun that gases in its atmosphere have not boiled off and so their composition should reflect the primordial stuff from which the solar system was made. They also have strong gravity, which holds the gas more tightly. In contrast, the inner rocky planets such as the Earth and Mars are much more differentiated. So in theory, at least, sending a probe into Jupiter is the closest we can get to sending it into the very earliest moments in the life of the solar system.
Galileo found that Jupiter was quite different from the planet scientists had expected to find based on observations from telescopes on Earth and passing spacecraft such as the Voyager missions to Jupiter and the outer planets. The finding suggests that either Jupiter has developed more than we had expected and that it isn't a good guide to the way our planets were formed or that we must rethink the very origins of our solar system.
Hydrogen and helium are the most abundant elements in the universe, but astronomers believed the disc of dust and gas from which our solar system evolved must also have contained carbon and sulphur and other heavier elements forged in the hearts of stars and then ejected across the galaxy in supernova explosions. We are, quite literally, stardust. But Galileo's findings do not accord with a simple interpretation of this theory. It found that Jupiter's atmosphere is drier than Nasa scientists had anticipated and it contained about half of the expected helium concentrations. In addition, neon, carbon and sulphur were less abundant than predicted.
There are also fewer lightning storms on Jupiter than there are on Earth, the probe discovered. This is consistent with the lack of water vapour, says Professor Alec Boksenberg, former director of the Royal Greenwich Observatory and now professor of experimental astronomy at Cambridge University. Lightning occurs when electric charges have been transported across the atmosphere. If there are not enough water droplets to act as the carriers of charge, lightning will be that much rarer.
Jupiter is a fearful place, according to the observations sent back by the little probe that the Galileo mother ship dispatched on a suicide mission into the planet's atmosphere.
Dr Richard Young, the project scientist in charge of the mission at the Nasa-Ames research centre, says: "The probe detected extremely strong winds and very intense turbulence during its descent through Jupiter's thick atmosphere. The origin of Jupiter's winds appears to be an internal heat source that radiates energy up into the atmosphere from the planet's deep interior."
This is in stark contrast to Earth, whose weather is driven by heat from the Sun warming the atmosphere. Jupiter is so far from the Sun that it gets little solar heat, so the driving force for its weather is its gravitational energy and the heat from radioactive decay of elements deep within the planet.
The probe measured wind speeds of up to 330mph. The characteristic swirling patterns visible on Jupiter's surface appear to come, Dr Young says, from "a jet stream-like mechanism rather than swirling hurricane or tornado-like storms". …