A remarkable, first-of-a-kind movie shot by the Galileo probe as it raced past Earth earlier this month shows the blue planet spinning in the vast night of space, giving elated scientists a taste of the view they can expect of Jupiter in 1995.
Captured by Galileo's state-of-the-art solid-state cameras, the movie showed the blue-and-white Earth from a vantage point below the planet, a view that included snowy white Antarctica and brownish Australia that extended as far north as Florida and the Persian Gulf region.As the cloud-streaked planet rotated on its axis in the black night of space, the glint of sunlight off oceans and rivers repeatedly flared into view as entire continents rolled by as if on parade.
While Apollo-era photographs of the planet exhibit greater sharpness in some instances, the Galileo movie marked the first time humanity's home planet has been seen rotating on its axis.
"The movie is unique in the sense it's from a single point in space and you see the Earth rotating," said Michael Belton, Galileo imaging team leader. "There have been no sequences of pictures that show the Earth in motion."
Galileo was launched Oct. 18, 1989, from the shuttle Atlantis on a convoluted trajectory requiring three gravity-assist planetary flybys to boost the spacecraft on to a 1995 encounter with distant Jupiter.
The nuclear-powered spacecraft whipped past Venus Feb. 9 and completed the first of two Earth flybys Dec. 8 at an altitude of just 600 miles. The second Earth encounter, at an altitude of less than 200 miles, is set for Dec. 8, 1992, a velocity-boosting flyby that will finally put Galileo on course for Jupiter.
The Earth movie was assembled by scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., using images taken by Galileo as the robotic explorer raced past on Dec. 8.
As it approached and then receded, the $1.5 billion spacecraft's instruments recorded more than 58 billion bits of data, including more than 2,600 pictures of the Earth and moon and priceless data about the planet's space environment.
As an intellectual exercise, scientists studied the data for evidence of life on Earth. While they were able to see clear signs of biological activity, there was no direct evidence of intelligent life in the data.
"The accumulated evidence we have from all the spectral data, gas compositions and so forth, would give your hypothetical extra-terrestrial explorer a very strong indication that you had biological activity occurring on the Earth," said Galileo project scientist Torrence Johnson.