Thereafter, as Ganymede continued to move on, the shadow began to advance, appearing before it, first a sliver, then a thicker crescent, until both left Jupiter's globe.
The entire eclipse lasted three hours.
The Jovian Moon reached and passed the orbit of Ganymede when that satellite was at the other end of its seven-day orbit about Jupiter.
There was a special celebration when that happened. Men with ordinary ships (not often, to be sure) had reached Ganymede and landed on it, but no one, not one human being, had ever penetrated closer than that to Jupiter. And now the Jovian Moon did.
The ship passed within one hundred thousand miles of Europa, Jupiter Two. It was the smallest of Jupiter's major satellites, only nineteen hundred miles in diameter. It was slightly smaller than the moon, but its closeness made it appear twice the size of the moon as seen from Earth. Dark markings could be made out that might have been mountain ranges. Ship's telescopes proved they were exactly that. The mountains resembled those on Mercury, and there was no sign of moon-like craters. There were brilliant patches, too, resembling ice fields.
And still they sank downward, and left Europa's orbit behind.
Io was the innermost of Jupiter's major satellites, in size almost exactly equal to Earth's moon. Its distance from Jupiter, moreover, was only 285,000 miles, or little more than that of the moon from Earth.
But there the kinship ended. Whereas Earth's gentle gravitational field moved the moon about itself in the space of four weeks, Io, caught in Jupiter's gravity, whipped about in its slightly larger orbit in the space of forty-two hours. Where the moon moved about Earth at a speed of a trifle over a thousand miles an hour, Io moved about Jupiter at a speed of twenty-two thousand miles an hour, and a landing upon it was that much more difficult.
The ship, however, maneuvered perfectly. It cut in ahead of Io and wiped out Agrav at just the proper moment.
With a bound, the hum of the hyperatomics was back, filling the ship with what seemed a cascade of sound after the silence of the past weeks.
The Jovian Moon curved out of its path, finally, subject once again to the accelerating effect of a gravitational field, that of lo. It was established in an orbit about the satellite at a distance of less than ten thousand miles, so that lo's globe filled the sky.
They circled about it from dayside to nightside, coming lower and lower. The ship's batlike Agrav fins were retracted in order that they might not be torn off by Io's thin atmosphere.
Then, eventually, there was the keen whistling that came with the friction of ship against the outermost wisps of that atmosphere.
Velocity dropped and dropped; so did altitude. The ship's sidejets curved it to face stern-downward toward Io, and the hyperatomic jets sprang into life, cushioning the fall. Finally, with one last bit of drop and the softest jar, the Jovian Moon came to rest on the surface of Io.
There was wild hysteria on board the Jovian Moon. Even Lucky and Bigman had their backs pounded by men who had been avoiding them constantly all voyage long.
One hour later, in the darkness of Io's night, with Commander Donahue in the lead, the men of the Jovian Moon, each in his space suit, emerged one by one onto the surface of Jupiter One.
Sixteen men. The first human beings ever to land on Io!
Correction, thought Lucky. Fifteen men.
And one robot!
12. The Skies and Snows of Io
It was Jupiter they stopped to look at. It was Jupiter that held them frozen. There was no talk about it, no babble over the helmet radios. It was beyond talk.
Jupiter was a giant globe which, from rim to rim, extended one eighth of the way across the visible sky. Had it been full, it would have been two thousand times as bright as the Earth's full moon, but the night shadow cut a third of it away.
The bright zones and dark belts that crossed it were not merely brown now. They were close enough to show full clear color: pink, green, blue, and purple, amazingly bright. The edges of the bands were ragged and slowly changed shape as they watched, as though the atmosphere were being whipped into gigantic and turbulent storms, as most probably it was. Io's clear, thin atmosphere didn't obscure the smallest detail of that colored shifting surface.
The Great Red Spot was heaving ponderously into sight. It gave the impression of a funnel of gas, swirling lazily.
They watched for a long time, and Jupiter did not change position. The stars moved past it, but Jupiter remained fixed where it was, low in the western sky. It could not move, since Io presented only one side to Jupiter as it revolved. On nearly half of Io's surface Jupiter never rose, and on nearly half it never set. In an in-between region of the satellite, a region making up nearly a fifth of the total surface, Jupiter remained forever on the horizon, part showing, part hidden.
"What a place for a telescope!" murmured Bigman on the wave length allotted to Lucky during the pre-landing briefing.
Lucky said, "They'll have one soon and a lot of other equipment."
Bigman touched Lucky's face-plate to attract his attention and pointed quickly. "Look at Norrich. Poor guy, he can't see any of this!"
Lucky said, "I noticed him before. He's got Mutt with him."
"Yes. Sands of Mars, they go to trouble for that Norrich! That dog suit is a special job. I was watching them put it on the dog when you were keeping tabs on the landing. They had to test to make sure he could hear the orders and obey them and if he'd let Norrich use him once Norrich got into a space suit. Apparently it all worked out."
Lucky nodded. On impulse he moved rapidly in Norrich's direction. Io's gravity was just a trifle over that of the moon, and both he and Bigman could handle that neatly.
A few long, flat strides did the job. "Norrich," said Lucky, shifting to the engineer's wave length.
One cannot tell direction of a sound when it comes out of earphones, of course, and Norrich's blind eyes looked about helplessly. "Who is it?"
"Lucky Starr." He was facing the blind man, and through the face-plate could make out clearly the look of intense joy on Norrich's face. "You're happy to be here?"
"Happy? You might call it that. Is Jupiter very beautiful?"
"Very. Would you want me to describe it to you?"
"No. You don't have to. I've seen it by telescope when-when I had eyes, and I can see it in my mind now. It's just that… I don't know if I can make you understand. We're some of the few people to stand on a new world for the first time. Do you realize what a special group that makes us?"
His hand reached down to stroke Mutt's head and contacted only the metal of the dog's helmet, of course. Through the curved face-plate, Lucky could see the dog's lolling tongue, and his uneasy eyes turning restlessly this way and that, as though disturbed by the strange surroundings or by the presence of his master's voice without the familiar body that went with it.
Norrich said quietly, "Poor Mutt! The low gravity has him all confused. I won't keep him out much longer."
Then, with an increase of passion again, "Think of all the trillions of people in the galaxy. Think how few of them have had the luck to be the first on a world. You can almost name them all off. Janofski and Sterling were the first men on the moon, Ching the first man on Mars, Lubell and Smith on Venus. Add them all up. Even count in all the asteroids and all the planets outside the solar system. Add up all the firsts and see how few there are. And we're among those few. I'm among those few."
He flung his arms out as though he were ready to embrace the whole satellite. "And I owe that to Summers, too. When he worked out a new technique for manufacturing the lead contact point-it was just a matter of a bent rotor, but it saved two million dollars and a year's time, and he not even a trained mechanic -they offered to let him be in the party as reward. You know what he said. He said I deserved it in his place. They said sure, but I was blind, and he reminded them why I was blind and said he wouldn't go without me. So they took us both. I know you two don't think much of Summers, but that's what I think of when I think of him."