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 hardly take the place of hydrogen in very many cases. Such an atmosphere would obviously be a rarer phenomenon than a fluorine atmosphere.”
“And possible only on very hot planets,” Tey Eron said, turning over the pages of the manual. “A sulphur ocean would be liquid only at a temperature of one hundred to four hundred degrees.”
“I think Afra is right,” Moot Ang said. “All these atmospheres we have been talking about are far less likely than our standard type of atmosphere consisting of the most common elements in the Universe. That it is made up of these elements is no chance phenomenon.”
“I agree with you there,” put in Yas Tin. “But the element of chance occurs often enough in the infinity of the Universe. Take our ‘standardized’ Earth, for instance. Both it and its neighbours the Moon, Mars and Venus have a great deal of aluminium which is rare enough elsewhere in the Universe.”
“And yet it can take tens if not hundreds of thousands of years to run across repetitions of these chance phenomena,” Moot Ang said gloomily. “Even with warp ships. If the people of the other ship have been looking for another planet like theirs for a long time, I can understand what they felt like on meeting us.”
“It’s a good thing our atmosphere consists of the most common elements in the Universe,” Afra said. “At least we can look forward to finding a great many planets like ours.”
“And yet our first encounter was with one of a different order,” Tey remarked.
Afra had a retort ready but the ship’s chemist came in just then to report that the transparent screen was finished.
“But we can enter their ship in space suits, can’t we?” Yas Tin asked.
“Of course we can. And so can they visit ours. We’ll probably have many such exchanges of visits, but it’s better to get acquainted from a distance,” replied the captain.
The Earthmen mounted the transparent sheet of plastic at the outer end of the gallery, and the others did the same in theirs. Then the members of both crews met in space where they worked together to connect the two galleries. Pats on the sleeve or shoulder were exchanged as a token of friendship equally understandable to both sides.
Thrusting the horn-like protuberances of their helmets forward, the strangers tried to peer through the Earthmen’s space helmets, which afforded a much better view of the faces inside than the strangers’ helmets whose slightly convex fronts revealed nothing of their owners’ features. Yet the Earthmen instinctively felt that the curious eyes examining them were friendly.
When invited to board the Tellur the figures in white gestured their refusal. One of them touched his helmet and then flung his arms outward as if scattering something. Tey understood this to mean that the stranger was afraicf for his helmet in an oxygen atmosphere.
“They obviously have the same idea as we have and want to meet us in the gallery first,” Moot Ang said.
The two space ships now hung motionless in the infinity of space, joined together by the communication gallery. The Tellur turned on its powerful heating units, which made it possible for the crew to enter the gallery in the close-fitting blue artificial wool overalls they always wore at work on shipboard.
A pale blue light like the crystalline radiance on mountain tops on Earth appeared on the other side of the partition. The difference in the lighting on either side of the transparent wall tinted it aquamarine as if it were made of petrified pure sea-water.
A silence set in broken only by the Earthlings’ quickened breathing. Tey Eron’s elbow touched Afra. He felt the young woman trembling with excitement. He drew her close and she flashed him a quick look of gratitude.
A group of eight from the other ship appeared in the far end of the gallery. A gasp of astonishment escaped the Earthmen. They could hardly believe their eyes. In his heart of hearts each had expected something extraordinary, something supernatural. Because of this, the close resemblance of the strangers to themselves struck them as a miracle. But that was only at first glance, for the closer they examined them the more points of difference they noticed in all that was not concealed by the short loose jackets and long wide trousers the strangers wore, which, incidentally, were very much like the clothes worn on Earth in ancient times.