Water for the plants in the lobby, and the large aquaculture ponds elsewhere within the base, was harvested from the Moon itself. Using purpose built spacecraft, assembled on site, mining teams were sent to the Moon’s nearby north pole region. There, in the perpetually dark shadows of a raft of small craters, lay water ice. From prior orbital surveys, NASA estimated there could be 600 million metric tons or more of water ice in the depths of the craters, lying in sheets up to two meters thick. Large blocks of ice were cut and transported to the surface above the base, where warmth from the Sun was used to melt the ice and separate water from grit.
Near the top of the water use list was the pool in the polar bear quarters, since their physical, hygienic and psychological well being were all greatly improved by being able to swim in icy cold water. A load of sea salt was even brought from Earth to give the faux Arctic waters the right taste. Once the drinking water, hydroponic gardens, and aquaculture tanks were filled, plans called for building an Olympic sized swimming pool for the base’s human residents.
Elena and Sally crossed the main lobby atrium, its artificial sun shining brightly on the mass of tropical plants. Simulated breezes rustled the foliage and the soothing babble of falling water could be heard through the trees. All the interior decorating seemed an extravagance to Dr. Li and she said so. “This area is quite beautiful but shouldn’t more practical things be constructed first? Don’t get me wrong, as a botanist I love the sight of green things growing, but I understand that the first hydroponic crops are just now starting to come in. Surely food is more important than a decorative garden, no matter how pretty.”
“It is not my area of expertise, but according to some of the psychologists and medical personnel the addition of green plants and natural surroundings improves people’s performance and mental health,” replied Elena. “And according to Melissa Scott Hamilton, the Peggy Sue’s horticulturalist, the crops take time to establish and really could not be made to grow faster. The fish, shrimp and crustaceans in the aquaculture tanks will take even longer.”
“No land animals? I like seafood, but without an occasional hamburger I get cranky—another result of attending grad school in the US.”
“Evidently the usable food yield from aquaculture is greater than from terrestrial farm animals. Plus, aquatic animals seem to acclimate to the lower gravity more rapidly. I understand that there are plans to raise cattle, pigs and chickens eventually. Until then, occasional shuttle runs will have to supply our carnivorous longings.” As they ascended a curving stairway to an elevated terrace a voice spoke: “Warning. You are entering the base administrative area, all offices are kept at full Earth gravity.”
“That’s another thing,” Dr. Li said. “Keeping these areas under heavy gravity must use a lot of power.”
“Not as much as you would think, and it is good for our health to remain under Earth gravity as much as possible, at least that is what Ludmilla says. The Marines in particular, need to stay in good physical condition. They might even find themselves having to fight under heavier gravity than Earth’s.”
“Yes, that makes sense. I am really interested in seeing how the plants in the atrium fair under reduced gravity. After all, plant circulatory systems developed under the same conditions as terrestrial animals.”
“You may well get to observed plant development at different evolutionary stages, assuming we find life on other planets,” Elena said to her new friend. “That is if life on other worlds is anything like Earth life, and we even find any planets in the systems we visit.”
“I thought that you were the expert in finding habitable planets around other stars?” asked Sally.
“Oh, I am as much of an expert as one can be without ever having a chance to actually test one’s theories. The Peggy Sue has just changed that forever. That is why I have no choice, I have to go on this mission—it is that or find another field of research.”
“In China we have an old saying: be careful what you wish for, you might get it.”
“We Italians have the same saying and it is undoubtedly based on long experience,” Elena said, smiling. The duo found themselves in front of the double glass doors of the conference room. “Looks like we are here,” she said, opening one of the doors, “after you, Dr. Li.”
Well,
Elena thought,
this is my chance to either make my reputation or to destroy it.
Conference Room, Farside Base
After discovering that the Peggy Sue was capable of traveling to other star systems by transiting alter-space, the project team was faced with a significant problem—where to go next? With more than 100 billion stars in the Milky Way galaxy, it was definitely a nontrivial question. Most of the science section, the ship’s officers and TK Parker were convened in the large conference room in the base’s administrative area. Their task: a first attempt at charting the next voyage of Earth’s only working starship.
“I believe you all know why we are here,” the Captain began. “While the Peggy Sue is in dry dock for refitting, we have a couple of months to decide on a course of action. Included in that plan must be a list of star systems to be visited when we venture forth to perform a reconnaissance of our stellar neighborhood.”
This statement brought murmurs and nods from those assembled. Having set the topic for the meeting, Jack continued. “The process of selecting the destinations for Peggy Sue’s next cruise is proving more complicated than I expected. Basically, we are hoping to find life on other worlds. Life that can give us information about the hostile aliens we encountered on the Moon and at Beta Comae. The fundamental question is, where do we look?”
Many of the scientists began to speak at once, but Sally Li won the floor. “That depends on the characteristics of the lifeforms you are looking for, Captain.”
“Yes,” added Olaf Gunderson, “life in the wider Universe may take on forms much different than the ones we are familiar with. Don’t expect aliens to look like people with blue skin or strange protuberances on their foreheads.”
“Continue, Dr. Gunderson,” Jack prompted.
“All the life we are familiar with is based on a common chemistry: the primary compounds are based on carbon and the universal solvent is water, liquid H
2
O. But there are other biochemistries possible, from a strictly chemical perspective. Speculative work on alternative biological systems has been done by Steven Benner, a member of the NASA Astrobiology Institute and a founder of several research institutions. The Benner group worked to identify “bio-signatures”, molecular structures likely to be universal features of living systems whether Earth-like or “weird” life forms.”
“That’s right,” added Sally. “And in the late 1980s, the astrobiological committee chaired by John Baross also investigated ways to generate molecules that reproduce the complex behavior of living systems using chemical synthesis. Their work included ammonia, sulfuric acid, methanamide, and various hydrocarbons. They even speculated about life based on liquid nitrogen or supercritical hydrogen fluid.”
“You are correct, Dr. Li,” said Olaf, recapturing control of the conversation. “Ammonia, NH
3
, is perhaps the most commonly proposed alternative. Numerous chemical reactions are possible in an ammonia solution, and liquid ammonia has several chemical similarities with water. For instance, ammonia can dissolve most organic molecules at least as well as water does, and in addition it is capable of dissolving many elemental metals.
“However, an ecology based on ammonia would likely exist at temperatures or atmospheric pressures that are unusual for terrestrial life. This means that casting a wide net to include “weird” lifeforms will greatly expand the number of candidate planets we need to survey.”
“I see,” said the Captain. “What is the alternative to searching for all these non-terrestrial forms of life?”
“We could be carbon/water chauvinists, as Carl Sagan called himself,” responded Dieter Schmitt, the project’s lead chemist. “That would winnow the field of prospective planets considerably, ja?”
“Yes, that does narrow the field,” said Elena. After all, this was her area of expertise. “I think we need a little background on the size of the problem, before we start making simplifying assumptions. Yuki, you are our lead astrophysicist—explain where the local stars came from.”
With a nod of encouragement from the Captain, Dr. Saito took the podium. The soft-spoken Japanese astrophysicist cleared his throat and began what could have been a University symposium lecture.
“Over the past century, astronomy’s greatest success has been the theory of stellar evolution: the way stars are born from clouds of interstellar gas, live out their lives, burning hydrogen into helium and producing heavier elements such as carbon, nitrogen, and oxygen. We know that big heavy stars burn brightest and emit higher average frequencies of electromagnetic radiation.
“The life of one star, the Sun, holds particular importance for us, as it provides practically all the energy for life on Earth. Fortunately, our star is remarkably stable and long-lived. The geological evidence from within the solar system indicates that the Sun has been burning for around 4.5 billion years. Astronomers are now confident that the Sun will burn for another 5 billion years before expanding into a red giant, ending all life on Earth.
“Since Earth is the only planet we know of that harbors life, any search for alien lifeforms starts with a search for other stars like our own. The type of star a planet circles has all sorts of implications for the possible development of life. For example, large hot stars, similar to those in the night sky that appear blue white, emit high levels of ultraviolet light. So much radiation that it could prevent life from forming.” This brought a node from Olaf Gunderson.
“Moreover, such large stars do not last long. They burn through their hydrogen in a matter of millions of years, not the billions taken by stars like the Sun. The deaths of such stars are spectacular explosions that can outshine entire galaxies for a brief period. The short lives of such stars are thought to be too brief for life to develop.”
“That is true, Yuki,” commented Olaf. “While there are indications that primitive, single cell organisms arose on Earth in about 500 million years, more complex life took another three and a half billion years to evolve. While this observation is based on only one example, it is thought that anything less than several billion years is too short a span for intelligent life to develop.”
“Thank you for that observation, Dr. Gunderson.” Yuki took a sip of water and then continued with his narrative. “There are problems on the other end of the spectrum as well.” This remark brought a few snickers from the other physicists—nothing like a physics pun to liven up a lecture.
Yuki smiled at his audience and explained. “Small stars, those much less massive than our star, are thought to be very long lived. Astrophysicists expect them to live several times longer than the current age of the Universe. When viewed through a telescope they appear as dim red colored objects—astronomers call them red dwarfs and they can be as small as 10% the size of the Sun. Most of their light is emitted in the infrared, which may be too feeble for life to develop under.”
“Yes, Earth plant life absorbs light in the visible part of the spectrum,” said Dr. Li. “Photons of infrared light may not be energetic enough to power any form of photosynthesis.”
“And a lack of any ionizing radiation may lead to a mutation rate too low for effective evolution,” added Olaf.
“Indeed,” replied Yuki. “Plus there are other problems with red dwarfs that Dr. Piscopia will no doubt comment on during her presentation. But let us finish the background information. Compared to the general stellar population, the Sun is big, in the 80
th
percentile by mass, and metal-rich. With apologies to Dieter, when astronomers talk about metals they mean anything higher on the periodic table than hydrogen and helium.”
This brought a good natured scowl from the German chemist, along with mumbled comments about those who could not appreciate the true complexity of the physical Universe.
“High metal content is associated with an increased likelihood of terrestrial planet formation. This is because a star’s planets are formed from the same cloud of material that went into making the star itself. A lot of metals in a star is an indication of a lot of material available to form terrestrial planets. Astronomers use our Sun to set the standard for chemical abundances in other stars, termed metallicity. The Sun’s metallicity is defined to be zero. In our neighborhood, the median metallicity for all exoplanet host stars is +0.10, while the typical value for G type dwarfs is -0.20.”
“What is a G type dwarf, Doctor?” asked Ludmilla, knowing others in the room were thinking the same question but too shy or intimidated to ask.
“Good question, Dr. Tropsha. Astronomers classify stars by their spectral characteristics, basically color, and size. Most stars are classified using the letters O, B, A, F, G, K, and M, where O stars are the hottest and the letter sequence indicates successively cooler stars. Class G stars like the Sun are yellow. Other Sun like stars are class F, yellow-white, and class K, orange.
“The designation as a dwarf star is a bit misleading. There are much larger types of stars—giant stars are between 10 and 100 times as wide as the Sun—but such stars are quite rare. Most main sequence stars are classified as dwarfs. Our middle-aged Sun qualifies as a G2 dwarf star, even though it is more massive than 80% of the stars in the galaxy.” Yuki paused for further questions, but there were none.
“To recap, we are looking for stars that are likely to have planets, that have been around for several billion years, and are not likely to either irradiate or starve carbon based life. Those general criteria were used to select the initial list of 33 stars. At this point, I would like to turn things over to Dr. Piscopia.”