HALF of Jupiter鈥檚 helium is not missing after all. Earlier this week,
NASA admitted that it was wrong to announce that the giant planet鈥檚 atmosphere
contains unexpectedly little of the gas. Results from the Galileo probe, which
plunged into the swirling clouds of Jupiter in December, initially suggested
that the planet鈥檚 upper layers contain only 13.7 per cent helium, about half the
amount present in the primordial gas cloud that condensed to form the Solar
System (New 杏吧原创, Science, 3 February, p 16).
杏吧原创s speculated that vast quantities of helium must be raining towards
Jupiter鈥檚 centre, releasing energy and heating the planet. Some even argued that
the results could mean that Jupiter does not have a dense, rocky core.
But after reanalysing the results, Galileo scientists say that this
speculation was premature. The helium-measuring team, headed by Ulf von Zahn of
the University of Rostock in Germany, has revised its estimate of the abundance
of helium to 24 per cent. 鈥淭his sort of thing often happens,鈥� says Fred Taylor
of the University of Oxford, who works on another Galileo experiment. 鈥淚t鈥檚 just
a question of having a more careful look at the data.鈥�
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