After taking a brief look at Venus, the Galileo spacecraft is speeding toward a close encounter with Earth Dec. 8 on its long journey to Jupiter and it is expected to hit its desired course almost on the button, scientists reported Thursday.
Environmentalists had tried to block the launch of Galileo last year because its instruments draw their energy from nuclear power, and some feared that a launch failure or a subsequent collision with Earth could release deadly radioisotopes into the atmosphere. But there is no chance of that, scientists said, because Galileo will be within about 16 miles of its desired course, passing 590 miles over the surface of the Earth.
Galileo will make an even closer Earth flyby in two years, passing less than 200 miles from the planet on its way to its ultimate destination, Jupiter. But nothing about the spacecraft has given officials with the National Aeronautics and Space Administration anything to worry about.
“The spacecraft’s health is excellent,” said Galileo project manager William J. O’Neil of NASA’s Jet Propulsion Laboratory.
Galileo is functioning so well that “we don’t have to do anything on the ground or anything on the spacecraft” to successfully zip by the Earth and use gravity to boost its speed by about 15,000 m.p.h. That is one of several maneuvers that Galileo will go through in order to reach Jupiter, where it will conduct a two-year study of the Jovian system.
Originally, plans did not call for Galileo to fly past either Venus or Earth, but a new course had to be developed after changes in the space program resulting from the Challenger disaster precluded the use of a rocket powerful enough to send it on a direct course to Jupiter. So both Venus and Earth are bonuses along the way, and scientists expect to make full use of both opportunities to study planets that are very similar in some ways, but quite different in others.
The Earth flyby will be unique in that, for the first time, a spacecraft will reveal the Earth as it would appear to an alien spacecraft flying through the solar system. The flyby is expected to produce some first-ever pictures of the Earth and the moon.
“We will see portions of the far side of the moon that have never been looked at with modern sensors,” said Torrence V. Johnson of JPL, the project scientist.
The images that Galileo will send back as it speeds toward Earth, as well as the thousands of photographs it will take of Jupiter and that planet’s moons, could be exceptionally rewarding because the camera aboard Galileo is capable of creating extremely sharp images in very low light, scientists said.
According to Michael Belton, leader of the imaging team, Galileo’s camera is about 100 times as sensitive to light as the cameras that sent back spectacular images from the two Voyagers as they explored the outer reaches of the solar system.
Galileo’s visit to Venus has been upstaged by JPL’s Magellan spacecraft, which uses a radar camera to pierce through the sulfur dioxide clouds that hide the planet’s surface, but at least it gave scientists a chance to check out their instruments and pick up a little precious data on the brilliant white planet.
The data, collected in February, was stored aboard the spacecraft until last week, when Galileo was close enough to Earth to transmit it back. Scientists have spent the last few days devouring the information.
“Christmas came early this year,” Johnson said.
And there were a few surprises.
For instance, Galileo’s instruments detected a concentration of electrons traveling at far higher speeds than would have been expected.
The electrons apparently were accelerated to the extraordinary speeds because of some “interaction” of Venus with the million-mile-an-hour wind blowing off the sun. Asked the significance of the discovery, Louis Frank of the University of Iowa, head of the plasma science team, said:
“It shows our ignorance of how to push particles around the solar system.”
The photos of Venus taken by Galileo do not rival the sharp radar images that Magellan has been sending back for the last few weeks, but scientists embraced them anyway because they reveal additional details about the clouds that cover Venus. That, in turn, is important because it gives scientists a chance to study the atmosphere of a planet that evolved quite differently from the Earth.
“We are living in an atmosphere that we are changing,” Belton said, referring to the global warming effect that many scientists believe is taking place on Earth. “If you don’t want the Earth to change into something like that (Venus), then you better learn about atmospheres.”
Venus has an atmosphere that is rich in carbon dioxide, so it has already experienced the greenhouse effect. It is also devoid of life.