“Ingenious!” cried Afra. “That’s breathing! Now they’re bound to tell us the composition of their atmosphere. But how?”
As if in answer to her question, the figure on the screen was replaced by a black spot in a greyish annular cloud — evidently the nucleus of an atom surrounded by electrons in orbit. Moot Ang’s throat contracted. He wanted to cry out in amazement, but he couldn’t utter a sound. For now there were four figures on the screen — two, one above the other — in the centre with a thick white connecting line in between, and one on each side with black arrows pointing to them.
With fast-beating hearts, Moot Ang and his companions counted the electrons. The bottom figure probably represented the principal element in the unknown world’s oceans; it showed one electron spinning around the nucleus — hydrogen. The uppermost was by the same token the principal element of their atmosphere — nine electrons in orbit around the nucleus meant fluorine!
“Fluorine!” Afra cried out in despair.
“Keep on counting!” snapped Moot Ang. “Top left — six electrons, that means carbon. Right — seven, meaning nitrogen. Couldn’t be clearer. Pass on the word to draw up a similar table of our atmosphere and metabolism. It’ll be the same as theirs except for the top centre figure, which will be oxygen with its eight electrons instead of fluorine. What a pity!”
When the table was displayed, the astronauts on the observation platform of the Tellur saw the foremost of the white figures on the other space ship start and raise his hand to his helmet in a gesture that made it clear he was no less, if not more, disappointed than the Earthmen.
Bending over the railing of the platform, the captain of the ship from the unknown planet made a sharp movement with his arm as if severing some invisible bond. The spines on his helmet seemed to bristle menacingly at the Tellur, which was then several metres below the level of his ship. Then he raised his arms and brought them down as if trying to indicate two parallel planes.
Moot Ang repeated the gesture, whereupon the other raised one arm high in wordless greeting, turned round and disappeared into the black maw behind him. His companions followed him.
“Let us go down too,” Moot Ang said, pressing the descent lever.
The hatch closed over them before Afra had had more than a fleeting glimpse of the magnificent sight of the stars blazing in all their brilliance in the black void — a sight that never failed to delight her. The lights went on in the airlock and there was a faint hissing of the pumps — the first indication that the air pressure had reached that at the Earth’s surface.
“Shall we set up a dividing wall before joining the galleries?” Yas Tin asked as soo nas he had got his helmet off.
“Yes,” Moot Ang replied. “That’s what the captain of the other ship was trying to tell us. It’s a tragedy that they can’t exist without fluorine, which happens to be deadly to us. Oxygen would be just as lethal for them. Besides, many of our materials, paints and metals which are durable enough in an oxygen atmosphere would corrode from their breathing. Instead of water they have hydrofluoric acid which eats away into glass and attacks all silicates. We will have to put up a transparent partition that is not affected by oxygen while they will have to make another of some substance resistant to fluorine. But we must hurry. We can talk things over while the partition is being made.”
The quenching chamber which separated the crew’s quarters from the engine room of the Tellur was turned into a chemical laboratory. Here a heavy plate of crystallike transparent plastic was cast of ready components brought from Earth and left to set.
In the meantime the white space ship showed no signs of life although it was kept under constant observation.
In the library of the Tellur work was in full swing. The members of the expedition were busy selecting stereofilms and magnetic recordings of photographs of the Earth and its finest works of art. Diagrams and drawings illustrating mathematical functions and the crystal structure of the most common substances on Earth, other planets of our solar system and the Sun were being hurriedly prepared. A large stereoscopic screen was being adjusted and an overtone sound unit which reproduced the sound of the human voice without the slightest distortion was being encased in a fluorine-proof jacket.
During the brief intervals for food and rest, the crew of the Tellur discussed the unusual atmosphere of the planet from which the others had come.
The processes on the unknown planet set in motion by the energy radiated by its sun which made it possible for life to exist and accumulate energy to offset the dissipation of energy, must follow a general pattern similar to that on Earth. A free active gas — oxygen, fluorine or any other — could accumulate in the atmosphere only as a result of the vital functions of plants. Under all circumstances animal life, human beings included, must use up this gas, combining it with carbon, the basic component of both animals and plants.
The oceans of the planet must consist of hydrofluoric acid, which the plants broke up with the aid of the radiation energy of the system’s luminary as plants on Earth break up water (hydrogen oxide), accumulating carbohydrates and releasing free fluorine. The fluorine mixed with nitrogen was breathed by humans and animals, who obtained energy from the combustion of the carbohydrates in fluorine, and must exhale carbon fluoride and hydrogen fluoride.
This type of metabolism would give one and a half times as much energy as oxygen metabolism. It could very well serve as the foundation for the development of the highest forms of life. But the greater degree of activity of fluorine would require more intensive solar radiation. To produce enough energy to break up the molecules of hydrogen fluoride by photosynthesis, what is needed is not radiation in the yellow-green region, which will do for water, but the more powerful blue and violet radiation. Evidently the luminary of the unknown planet was a very hot blue star.
“There’s a contradiction there,” said Tey Eron, who had just returned from the workshop. “Hydrogen fluoride readily turns into a gas.”
“Quite so. At plus twenty degrees,” Kari replied after a glance into a manual.
“What’s the freezing point?”
“Minus eighty.”
“That would make the planet rather cold. How does that theory go with the hot blue star hypothesis?”
“No discrepancy at all,” said Yas Tin. “Its orbit may be a distant one. And the oceans may be located in the moderate or polar zones. Or…”
“There may be a great many reasons,” Moot Ang said. “Whatever it is, we have run across a space ship from a fluorine planet and soon we’ll learn all about it. What’s more important at the moment is this: fluorine is not very common in the Universe in general. Although recent discoveries have raised it from fortieth place to the eighteenth as regards prevalence, oxygen still remains the third most common element, after hydrogen and helium, and followed by nitrogen and carbon. Other estimates show that there is two hundred thousand times more oxygen in nature than fluorine. This is a clear indication that there are very few planets in the Universe which are rich in fluorine, and a still smaller number of planets with a fluorine atmosphere — that is, planets that have a vegetation that has released free fluorine into the atmosphere. The latter must be very rare indeed.”
“Now I can understand the gesture of despair their captain made,” Afra Devi said. “They are searching for other human beings like themselves. That’s why we are such a disappointment for them.”
“That would suggest they’ve been searching for a long time and had already found other thinking beings.”
“Yes, oxygen-breathing beings like ourselves!” cried Afra.
“There may be other kinds of atmosphere,” objected Tey Eron. “Chlorine, for instance, or sulphur, or hydrogen sulphide.”
“They wouldn’t be able to support the highest forms of life,” exclaimed Afra triumphantly. “They all produce in the living organism anything from one-third to one-tenth the energy oxygen yields!”
“That doesn’t apply to sulphur,” put in Yas Tin.
“It’s the equivalent of oxygen.”
“You mean an atmosphere of sulphuric anhydride and an ocean of liquid sulphur?” Moot Aug asked the engineer. Yas Tin nodded.
“But in that case the sulphur would be taking the place of hydrogen, not oxygen, if we compare with the Earth,” Afra said. “And hydrogen is the most common element in the Universe. Sulphur in view of its rarity can
