Tuesday, December 22, 2015

How Important is an Atmosphere?

When we talk about looking for planets with aliens, the atmosphere is one potentially visible signature. Oxygen in large amounts, such as we have on Earth, is something that could be seen with the right observational equipment.

If we are talking about solo planets, ones where life originates, oxygen resulting from photosynthesis might be a sign that evolution took whatever chemotrophs that originated there into a higher energy plane, where they start absorbing photons. There is, in most situations, so much more photon energy from the nearby sun than there might be chemical energy, that the chlorophyll transition makes a tremendous difference in what life can become. Chemotrophs as we know them are very limited, extremely limited, compared to life which lives directly or indirectly on the solar fusion energy which arrives via photons.

In the series about interstellar nomads and especially the post about speciation, it was considered how alien genetic engineers might come up with a new species that did not need an atmosphere to survive. This would be much better for living in a spaceship, as the problems of maintaining an atmosphere disappear, as does the threat of depressurization due to impact or to age-related ruptures. In place of breathing, some source of oxidizer has to be provided, so this could be either a liquid that is ingested, or gas in a quantity that can last for hours between ‘feeding’. Instead of purely carbohydrates for intake, there would be both the carbohydrates going into one digestive pipeline and the oxidizers going into another digestive pipeline, or in the case of gas under pressure, into some organ that can withstand more than normal pressures. Since there would be no atmosphere, there is no standard by which pressure can be measured in an alien body of this type, but pressures could be larger than are present in our atmosphere and still not rupture a specially designed organ.

Once this design is completed, the genetic code for it optimized and turned into a set of chromosomes, and the problems of ontogeny worked out, there is a creature which is capable of living in a much wider variety of planetary situations than atmosphere-dependent ones. A small planet without any atmosphere would be suitable, provided there was some protection from solar UV. Even if there was solar UV, the creature could be designed to have skin and surface organs as immune to damaging effects as possible. A cave on such a planet would provide even more protection.

Temperature would be another problem for a small planet, as a creature on its surface would be exposed to the vacuum of outer space. The surface of the planet would be at the same temperature, so there would be heat loss both from conduction through surface contact and radiation into space. Obviously the solution would be for internal heating to compensate for this, and as much shielding, either part of the creature’s hide or as clothing, as possible would be necessary.

Another hazard would be high-energy radiation, particles of some sort, such as cosmic rays. Too much of this would lead to genetic damage, and, while genetic repair can be done, there must be limits to the rate at which repairs can be done, both from an operational standpoint and from an error-correction standpoint. Too high a rate of damage and the repair mechanism is overwhelmed. Too high an accumulation of damage and the repair mechanism itself becomes faulty.

These are the known, obvious problems that would face any genetic engineer seeking to design a sentient creature able to function on a planet without a satellite. Caves and thermal clothing would help and reduce the requirements on the design. The same design might be useful for satellites that have no atmosphere.

Gravity is another issue. On a nomad ship, if there was never much acceleration from propulsion, designing the organisms that live there for zero or small gravity would be ideal. This is a design problem for digestion to a small extent, and for locomotion for a large extent. Having adhesive pads on the end of limbs might be the most efficient way to move about, but then using tools might be affected by the constant stickiness present. Perhaps four limbs with adhesion and two without would be an option. For planets, gravity creates structural issues, both for simple standing and for the impact that jumping can cause. On the nomad ship there is no need for a strong bone skeleton, but on any sizable planet, there is.

The issue of how to design a biological organism that would be intelligent, mobile, dexterous and strong enough to handle heavy tools for any planet is an interesting one, and should amuse the engineers of an alien civilization as much as designing robots amuses our engineers. The functionality should have many similarities, but beyond that, not much in common. The issue of doing without an atmosphere is one challenge that seems to be solvable, but we are at such a primitive level of understanding of these engineering skills that almost nothing sensible can be said. It is like asking a medieval peasant to decide what kinds of robots might be created. He would simple have no background whatsoever to assess the potential of the technology.

What we can discuss, however, is the implication of being able to design species that can inhabit airless planets and satellites. When astronomers talk about habitable zones, they are thinking of planets where some sort of life, similar to what we know on Earth, might be able to live. There are extremephilles here, able to tolerate heat and cold, salinity, pH in both directions, and other conditions we have here. But conditions we do not have here might be able to support life as well, if the life that goes there is designed by intelligent technologists. Our search for life in the galaxy might have to have the assumed boundaries widened. If such technologists could create life able to survive on the moon, we need to even consider all possibiities for life. Since we are so far from understanding the ultimate limits of intelligently designed life, the only answer might be to simply look everywhere for it.

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