ROUGHLY a million molecules of water fall into the upper atmospheres of
Jupiter, Saturn, Uranus and Neptune each second, scientists report in this
week鈥檚 Nature (vol 389, p 159).
Using the Infrared Space Observatory, an international team of astronomers
discovered signs of water vapour on Uranus. They then found the same features on
the other gas giants. Water vapour makes up only a few parts per billion of the
atmosphere. But it must be continually falling onto the planets because it
freezes at lower altitudes, the astronomers say.
鈥淚t can come either from the rings or interplanetary meteoroids,鈥� says
Emmanuel Lellouch of the Paris Observatory.
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