EARTH received its first confirmed interplanetary visitor Saturday as the spacecraft Galileo came within 590 miles of its home planet's surface, scientists said. Earth greeted the spacecraft by giving it a hefty push in a slingshot effect, increasing its speed from 67,000 m.p.h. to 78,000 m.p.h.
Galileo, which received a similar boost from Venus in February, will return to Earth in exactly two years, Dec. 8, 1992, for another push to speed it on its way to its eventual target, the planet Jupiter, which it will reach Dec. 7, 1995.
``We are having a great day today,'' Galileo project manager William O'Neil told reporters at the National Aeronautics and Space Administration's Jet Propulsion Laboratory here.
``Galileo just completed a virtually perfect Earth gravity assist. We hit our target altitude to within five miles, and our arrival time to within half a second. That's not bad for a 14-month trip of two-thirds of a billion miles,'' he said.
Mr. O'Neil said Galileo will achieve many firsts during its interplanetary wanderings, one of which will be a close encounter with an asteroid in October next year when the craft comes across the asteroid ``Gaspar.'' It will take pinpoint maneuvering by scientists in Pasadena to get the craft close enough to Gaspar to take pictures and get scientific data from it, as the asteroid is only 10 miles in diameter.
Environmentalists went to court in an attempt to stop the launch of Galileo from the space shuttle Atlantis in October last year because it has a small nuclear plant on board to power its many instruments.
They feared an accident during the launch or a collision with Earth on its return would send deadly nuclear radiation into the atmosphere.
But Galileo performed perfectly, O'Neil said, sending back video pictures of the moon and central Australia ``somewhere near Alice Springs'' as it sped toward Earth.
As it leaves, the craft is expected to send back the first-ever pictures of Earth and moon together, as well as views of the dark side of the moon. It will also measure for the first time the amount of methane gas in Earth's atmosphere. Methane is an important gas in the global warming that some scientists fear is occurring.