This visual and infrared mapping spectrometer image of Saturn's moon Enceladus in the 2 micron-wavelength shows the dark cracks at the south pole dubbed "tiger stripes" for their distinct stripe Tiger Stripes are Cubs. Atmosphere and Enceladus. This mosaic of images from NASA's Cassini spacecraft shows the trail of a great northern storm on Saturn raging in full force. The contrast in the images has been enhanced to make the turbulent par Northern Storm in Full Force.
In the Company of Dione. These two views of Saturn's moon Titan show the southern polar vortex, a huge, swirling cloud that was first observed by NASA's Cassini spacecraft in Spectral Map of Titan with Polar Vortex. A Shot in the Dark. The Sun's rays strike the terrains near the terminator on Tethys at low angles, throwing features there into sharp relief. The cluster of peaks at the center of the crater Odysseus kilometers, Rough Sphere of Tethys. With this false-color view, Cassini presents the closest look yet at Saturn's small moon Epimetheus epp-ee-MEE-thee-uss. The color of Epimetheus in this view appears to vary in a non-uniform wa Epimetheus: Up-Close and Colorful.
The two-toned surface of Saturn's moon Iapetus is demonstrated in the dark region of the moon visible on the top left and the bright crater in the lower right of this Cassini portrait. See PIA Yin Yang Iapetus. Saturn's moon Mimas has many large craters, but its Herschel crater dwarfs all the rest. This large crater kilometers wide 80 miles has a prominent central peak, seen here almost exactly on t Herschel Dead-On.
As for the possibilities of making ourselves extinct by our own actions, those could as easily be a consequence of a rush to colonize as averted by them, so what matters is not so much whether we colonize as how we do it. If we have protecting and cherishing Earth as our top priority, I think that will lead to a healthier approach to space settlement. The Moon is hardly explored by humans. So far we've only explored locations close to its equator, on the near side. Also we've only ever visited it in early morning of the lunar day - the safest time for humans to be there. The longest visit was for three days and only one party Apollo 17 had a geologist on board.
Every EVA there was dangerous, and we haven't been back there since the s. Since then, we have only shuttled back and forth between Earth and LEO for several decades. To take the next step, to last out on the surface of the Moon for an entire lunar month, through the heat of the two weeks long lunar day and the darkness and cold of the lunar night, is a bit like overwintering in Antarctica for the first explorers, after they proved that they can land on the continent and walk around for a day or two there.
The Moon is not at all well known on the surface at present and we can expect many surprises and difficulties to overcome. So the Moon is a more natural starting point, I'd love to see humans to Mars orbit, and if it is done carefully, this has no planetary protection issues, as we'll see in this booklet. But we should start closer to Earth first. The secret to success for Apollo 11 was a step by step approach, starting with orbital tests around Earth, the first orbit of the Moon with Apollo 8, and so on. A similar step by step approach ending in a mission to Mars orbit would start with two year missions closer to Earth, before we try the long mission to Mars without lifeboats.
We would then explore the surface from orbit via telepresence, just as we often explore the sea bed, ship wrecks, etc. There are places on Earth we don't go to because they are unsafe, e. We send expendable robots instead. There are other places tourists and explorers can't visit because we would harm what's there, e.
New discoveries of prehistoric cave art are immediately set off limit to all except a few scientific researcher.
The spacecraft instruments, in other words, are becoming more like collective sense organs for humankind. South America may be seen in the first frame top left , the great Pacific Ocean in the second bottom left , India at the top and Australia to the right in the third top right , and Africa in the fourth bottom right. A hilly and furrowed terrain is found antipodal to the Caloris basin, probably created by antipodal convergence of intense seismic waves generated by the Caloris impact. Argonne National Laboratory. This is perhaps the closest we have to planetary protection on Earth. Mercurian craters have the morphological elements of lunar craters—the smaller craters are bowl-shaped, and with increasing size, they develop scalloped rims, central peaks, and terraces on the inner walls.
This happened for instance for these recently discovered 14, year old cave etchings in Iberia. As soon as new cave art like this is discovered, the cave is made off limits to all except a few experts ,because humans can damage the paintings and etchings just by breathing inside the cave. And though they are rare on Earth, there are places here too that we don't go to, to avoid contaminating them with microbes. We haven't sent a submarine into Lake Vostok. Lake Vostok in Antarctica , a deep subsurface lake isolated from the surface for perhaps , years. The Russians drilled nearly all the way through but stopped.
They then used a method of drilling that made sure that the water rushed upwards from the lake with no risk of contaminating it with surface life. This is perhaps the closest we have to planetary protection on Earth. Even robots are hard to sterilize sufficiently to explore it, so they haven't yet sent a robotic submarine into it either. They have only drilled in such a way as to cause a geyser which they sampled before it rapidly froze over, and there are questions about whether what they sampled adequately represents what is in the subsurface lake or is contaminated by surface life.
Visitors to Antarctica also have to clean their boots to avoid introducing novel microbes and microfauna and flora to the Antarctic soil. Sadly, cleaning our boots is not a sufficiently stringent measure to protect Mars from our microbes, as we will see. I suggest in this book that just as with lake Vostok in Antarctica, and with even stronger motivation, there are places in our solar system that should be similarly off limits to humans at least until we understand them better.
Mars, Europa and Enceladus are the three top places in the solar system with planetary protection issues. Once it is safe to travel on interplanetary missions, there are many other challenges solar system wide. There are no planetary protection issues for the Moon, Callisto probably , Mercury, Venus clouds probably , and most asteroids and the moons of Mars. Let's focus on those first. Let's not rush humans as quickly as possible to the one place in the inner solar system where their microbes can cause most damage.
On behalf of those who love science and think that new discoveries in biology have value for our future, please, let's look first before we "Leap to Mars"! This is a news story that broke recently, on the idea that Elon Musk's plans would violate the Outer Space Treaty. The articles I've read so far focus on property rights and the provisions in the OST that rule out ownership of territory.
But that can be fixed with future legislation, especially since it's not really the land but the habitats that are of most value, and ownership of those is already covered in the OST. So far none of them have mentioned by far the toughest legal and practical obstacle, which is planetary protection of Mars from Earth microbes to preserve its science value for the future of mankind. That can't be fixed by passing new laws. Elon Musk says the mission would be dangerous, with colonists risking death, especially the first ones.
The biggest danger is on landing, and a crash of a human occupied ship on Mars in a Challenger type accident would strew fragments of bodies, food, water, air, and spacecraft over the planet. That would be pretty much the end of any planetary protection of Mars. The planetary protection requirements are not just a result of decisions by fussy bureaucrats. The ones responsible are concerned astrobiologists, such as Carl Sagan and Joshua Lederberg nobel prize winning pioneer in microbial genetics , and built up in detail over many discussions by international groups of astrobiologists and other scientists in biannual meetings of COSPAR.
Nor is it a minor concern of detail. They are concerned that we could rob ourselves and future generations of discoveries in biology as fundamental as the discovery of the helical structure of DNA or the theory of evolution. So far every space faring country has taken care to sterilize their spacecraft if necessary and abide by the provisions of the OST as interpreted by the COSPAR meetings and guidelines. Most have signed and ratified the Outer Space Treaty and even the United Arabic Emirates, who haven't ratified it yet, say that they will take care to abide by its provisions if they succeed in their plan to send a mission to Mars.
It just makes sense to do so. Then, Curiosity's "seven minutes of terror" wasn't just hyperbole. There was a real risk that it would crash, especially with such novel technology, with many previous examples of crashes on Mars. This is especially tricky with the Mars atmosphere too thin for a conventional parachute to work by itself - but with the gravity too much for a lunar module type landing.
You need to refuel to get back to orbit again. Elon Musk's idea is to use supersonic retropropulsion. The rocket lands on the Mars surface in reverse. It has to use the atmosphere for aerobraking, and simultaneously fires its rockets to bring it to a standstill on the surface.
The atmosphere is only thick enough for this close to the surface, so it skims down to a landing within a few kilometers to the surface - so close that it can't land on mountainous areas of Mars because the air is so thin. There is no set out protocol yet, but in their preliminary discussions they suggest human missions confined to a particular area of the surface. They accept that this is an irreversible introduction of Earth microbes to Mars and just aim to limit and delay the impact. However they do these planetary protection assessments of human missions to Mars based on the assumption of a successful landing on Mars.
They don't consider the possibility of a crash as that's left to mission planners at a later stage. Yet, for robotic orbiters Mars is treated as a Category III mission and needs to be sterilized to levels that will make the mission safe in case the orbiter crashes on Mars! At some point someone has to consider what the effect would be of a human crash on Mars, and once you consider that, and if you assess the planetary protection issues for it, I don't see how anyone could either say that a crash won't happen, or that a crash would be anything short of a total end of protection of the planet.
But someone has to do it. I think that an orbiter mission for humans on Mars also needs assessment for the possibility of a crash on Mars just as for robotic orbiters. There could be ways to make it safe enough so that the possibility of a crash is for practical purposes non existent.
First, I think flyby missions like Robert Zubrin's Double Athena Flyby could be made sufficiently safe for planetary protection. This is an interesting mission that does two flybys of Mars and in between orbits almost parallel with Mars for half an orbit or one Earth year. The crew are close enough to the surface of Mars for telepresence style telerobotics for of order of hours, for both flybys, and are within close range of the planet for days.
Flybys can be done accurately, we've done multiple flybys with Cassini and other spacecraft. We haven't yet had a crash during a flyby mission. You'd use trajectory biasing, so that the final stage misses Mars, and so that if something goes wrong the human occupied spacecraft also misses Mars, and then do gentle nudges to keep it on target, and months during which you can refine the orbit and make sure you are on target. I think that an orbital insertion maneuver though could go wrong and lead to humans crashing on Mars as has already happened, with the Mars climate orbiter.
Another type of transfer though is very safe - that's ballistic capture. In this approach, the spacecraft is launched to arrive in a distant orbit around Mars, at just the right speed so that it is captured by Mars as a temporary distant extra minimoon with no need for an insertion burn. The crew then can use ion thrusters to slowly modify their orbit to get close to Earth for telepresence during part of the orbit. Ion thrusters change orbit so slowly, that there's not really any significant risk of them accidentally impacting on Mars.
So it's much safer for the crew also, and I think probably has no significant planetary protection risks. This would need to be looked at carefully, and you need to consider also whether any waste material ejected from the spacecraft could hit Mars, but it does seem you could have human missions to Mars that don't need to be sterilized to the levels needed for robotic orbiters to date, without compromising on planetary protection. Extremophiles that also live in human habitats and found in spacecraft clean rooms can survive in the suggested habitats on Mars if they exist and many have hardy spores and other dormant states that could be carried in the global dust storms throughout Mars.
Humans are not the problem, the microbes that inevitably come with them are. After that, any searches for present day life on Mars would need to have as the default hypothesis that what they find was brought to Mars on that crashed human mission, an enormous impact on scientific exploration of Mars. It would not be "easy to distinguish" as Zubrin suggests with the analogy of anthrax, as only , of one trillion microbe species, 0. It's not at all practical to have an "inventory" of every single microbial species on the spaceship.
Also archaea swap DNA fragments very readily via horizontal gene transfer so could do that with life on Mars, if related, by an ancient mechanism that goes back billions of years. If related, even if the common ancestor came from lifeforms that seeded our solar system from another planet around another star at birth via panspermia, then the DNA could get mixed up to the extent it is hard to tell what came from Mars and what from Earth. But most vulnerable would be some early form of life.
There's the shadow biosphere hypothesis for Earth that there might be tiny RNA lifeforms here with no DNA or proteins, so having much smaller cells. None have been found, and if that was what came before modern life, it is probably extinct here, as also all other suggestions for life precursors. They may perhaps still survive on Mars.
If so then modern life could make them extinct on Mars just as it did on Earth. Or the life on Mars could, some or all of it, have followed a different direction that makes it vulnerable to Earth life. That juts needs Earth life to have a slightly more efficient metabolism, or to be slightly better at photosynthesis, say, and it could over time take over from Mars life completely. It could of course also work the other way that Mars life is slightly better than Earth life and takes over from Earth microbes in the soil water etc.
Zubrin and a few others have argued that we don't need to protect Mars because of the exchange of materials between Earth and Mars. This argument does work for samples returned from comets or asteroids because we have a natural flux of those materials anyway. But in the case of Mars, it happens rarely. We can only contaminate Mars, and vice versa , after meteorite impacts large enough to send material all the way to the other planet, and the material takes from a century to millions of years to do the transit, in the deep cold of interplanetary space, vacuum conditions, has to withstand the shock of ejection and re-entry.
The material sent into space comes from some meters under the ground in the spreading crater, and it has to be able to survive when it gets there, and find a suitable habitat. Compare that with landing on the surface of Mars immediately from a crashed human ship and it is clear that many lifeforms could get to Mars in the ship that couldn't get there by any other way. It's also a matter of probabilities, a human mission would introduce trillions of microbes in one go, compared with a few in a few species, over millions of years.
One method used to assess whether missions need planetary protection is to look at the "natural contamination standard". We get material all the time from comets or asteroids so it is not considered hazardous to Earth life to return those materials to Earth. But there is no similar natural process corresponding to a human spaceship crashing on Mars. And in addition, the scientific experiments would look for the most sensitive of traces. Detecting life by chirality of amino acids, or by metabolic activity. Those exquisitely sensitive instruments would be useless if there is Earth life there already introduced by a human crash on Mars.
As for how long it would take to do a biological survey of Mars, Carl Sagan took a figure of 60 landers, 57 of those successful, and 30 orbiters, all devoted to biological exploration like Viking, as a starting point. So that's as good an estimate as any. The ability to explore from orbit would help hugely. It's just a preliminary survey, there are a dozen different types of habitat to explore, and you have an area the size of Earth's land mass, so it is like landing eight rovers on each of the seven continents on Earth.
You would get a first rough idea. But you wouldn't find some rare lifeform in some unexpected location. I don't think we should say in advance what counts as a completed survey - as we would find out things as we go that would help us understand how complete it is, which we can't know in advance.
But exploration from orbit by telerobotics, and sending lots of small robots to Mars would speed it up a lot. For more on this, see How many years are needed to do a biological survey of Mars? I've actually worked for some time on an alternative vision, based on exploring the Moon first, as the gateway to the entire solar system. Not in the sense of a "pit stop" but a place of great interest in its own right and also resource rich, which happens to be just next door to us.
The Moon in this vision is a gateway to the solar system , a place to develop new techniques and explore a celestial body that is proving much more interesting than expected. Along the way, we are bound to get human outposts in space, and colonization may happen also. However, settlement in space doesn't need to be the driving force, any more than it is the driving force behind the study and exploration of Antarctica. If we try to turn Mars and other places in space into the closest possible imitations of Earth as quickly as possible, this may close off other futures, like the discovery of vulnerable early life on Mars, or better future ways to transform Mars.
Once we develop the ability to live in space for years at a time, the whole solar system will open out to us. While keeping future options open on Mars we can explore Venus, Mercury, asteroids, Jupiter's Callisto and further afield, and Mars itself via telepresence. We also have many experiments in human settlement to try closer to hand on the Moon. This can be an exciting future, with humans working together with robots for remote exploration, as our mobile sense organs and hands in the solar system and galaxy.
However it doesn't mean we can never send humans to the surface ever. For instance if we find that:. Then, after enough study to make sure we understand the situation well and the consequences of introducing Earth life to Mars, we might get to a point where we decide we know enough to say it is safe to send humans there, much as we have already done for the Moon. We haven't done a thorough study of the Moon at all. Only know it from the ground in a few locations, and rather sketchy orbital surveys too, compared with Mars.
Yet astrobiologists are confident that humans on the Moon don't need to take special planetary protection measures. It is possible that at some point we know enough to make the same decision about Mars. However we don't know enough to make such a decision quite yet, I'd say. So we should leave open for now the other options such as for instance:. There are many possible futures here. The main thing for now is to keep these options open, for as long as we don't know enough to make such decisions, which would be binding not just on us but our descendants and all future civilizations on Earth.
To follow this up further, you may be interested in the sections of my "Case for Moon First" starting with This approach doesn't mean that humans can never land on Mars ever.
Here is my executive summary of the vision which I did before my most recent appearance on David Livingston's The Space Show. The Outer Space Treaty says clearly that you own your own habitats that you construct in space, and since nowhere in space is worth living except in habitats, that deals with most of the ownership issues for space colonies. The case for ownership of minerals mined in space is far less clear. The US act mainly clarifies the US government's own domestic position - they made it illegal for anyone to sell moon rocks returned by Apollo, but have now made it clear that they will support their citizens if they try to sell materials mined from space.
However they also say throughout the treaty that they will comply with all international obligations and treaties. What those will be is not known yet. So it's not clear what the situation is there. However future law will surely somehow or other make it legal to return resources from space. There are many ideas for how to make it legal suggested by lawyers. The main sticking point here is that many say that the laws should somehow recognize that we go into space for the benefit of all humanity, as stated in the Outer Space Treaty, so the laws must be made fair for all countries, with many ideas about how that could be done.
I don't think more needs to be said at this point. By the time Elon Musk or anyone else wants to set up colonies in space, I expect the legal issues will have got sorted out. However planetary protection can't be dealt with in the same way. It's not just a legal issue. It is to do with whether or not one group of humans by sending microbes to Mars can rob the rest of humanity of the knowledge they could gain from a Mars without those microbes introduced to it. It's a conflict of freedoms we have here. The problem is that it is irreversible, and would change Mars for all future time.
Why not hold off from Mars surface for a while? Explore from orbit instead. And send humans to the Moon first, the obvious first place to test out our closed system habitats, safety systems, close to Earth. It may even have an economic case through tourism and through supply of volatiles to Low Earth Orbit, maybe even supply of precious metals to the Earth's surface eventually. And you can get back to Earth within two days in an emergency, can keep "lifeboats" attached to your habitats at all times, just as they do with the ISS, enough for all the crew to evacuate and return to Earth in an emergency, with provisions in the lifeboats sufficient to last the short two day journey back to Earth.
You can also resupply with emergency equipment and provisions from Earth within two days - something that our space stations have had to do on many occasions in the past, emergency oxygen, and fixes for various equipment failures. We may be able to get the transport costs from the Moon to LEO and back again down to almost zero by using Hoyt's cislunar transport system.
This can be made with present day materials and weighs only 27 times the payload mass. It works by exploiting the position of the Moon higher in the Earth's gravitational well than LEO to power the transport of material back and forth, so long as more material is returned from the Moon to LEO than is sent there. It needs only minimal power to control the flow of the material from the surface see Exporting materials from the Moon. It would be very hard to compete with that from Mars or almost anywhere else though you can do similar tricks with spinning asteroids, spinning them down slowly meanwhile using the angular momentum to supply materials to Earth via a tether system.
There are many ways the Moon could be commercially viable, potentially, in the near future. I don't know if it is, but if anywhere in space can be, then the Moon seems our best bet. I haven't listed exports of Helium 3 for fusion here. Although it gets a lot of publicity, it's based on technology we don't have, and some experts think we will never have. Also, Crawford calculates page 25 that manufacturing a square meter of solar panels on the lunar surface - which you can do by melting the indigenous silicon and using the high grade lunar vacuum to form panels in situ - would create as much power through solar power in seven years as you'd get from mining the same region for Helium 3 to a depth of three meters.
So, if mining for helium 3 is viable, this suggests that beaming solar power from the Moon back to Earth or to spacecraft in LEO would also be viable and a better business case than Helium 3. It may however be a useful byproduct of other mining operations on the Moon, for cryogenics, neutron detection, and MRI scanners , and possibly for fusion in the future.
For details, see Case for Moon First - Helium 3. Also, I don't think colonization is the way to begin. That's like the early Antarctic explorers saying:. Space is so hostile for us and so dangerous and such a hard place to live, that it's far more inhospitable than Antarctica. Nowhere in space is nearly as suitable for colonization as Antarctica or the coldest driest deserts on Earth. You can breathe the air anywhere on Earth for starters, and it is hard to beat that. I think the way ahead that's most likely to succeed is not colonization, but rather, settlement with industry, tourism, explorers, scientific bases like the ones in Antarctica.
Take Antarctica as the model but with addition of permitted commercial exploitation of the resources which you can't do in Antarctica. Also the ESA idea of a lunar village is a good one - space is so much more dangerous than Antarctica, where at the least you can take breathable air for granted wherever you go. So I think we need the different space agencies to work together to start with, to have the habitats close together in one village rather than scattered over the surface, so that they can support each other, use common equipment and do this as an international venture.
And see where that leads us. Mars is not even needed long term if you have a vision of millions of people in space. The Moon has enough volatiles probably for a city of a million, enough water so each of those million people could have all the water in an entire lane of an Olympic swimming pool, maybe more.
Huge caves that in the low Lunar gravity may be as large inside as an O'Neil colony, able to house millions of people in a single cave, so large that the city of Philadelphia could fit easily within the cave. We have radar data suggesting these caves exist, and can only find out for sure on the ground. Then longer term, the asteroid belt alone has enough materials to build habitats for a trillion people, total land area a thousand times that of Earth. Here I'm not talking about hollowed out asteroids or covering asteroids and dwarf planets with a shell, but using asteroid materials to make new habitats in space.
The mass requirements and the technology requirements are just about identical to those for Mars, except for the regolith shielding - which you need on Mars as well, using bulldozers - in space colonies you'd use them too with mass drivers. But space colonies have the advantage you can set up any gravitational level inside, through spinning the habitat, any amount of illumination using mirrors, and can position them anywhere you like in the solar system too.
You'd start off making them using materials from the Moon and from asteroids that do close flybys of Earth with low delta v needed for capture of the materials in the Earth Moon system - simultaneously eliminating the risk of them ever hitting Earth by mining them away to nothing, and making a habitat that is within easy reach of Earth, perhaps located in cislunar space.
Mars is not the only place to go to. As well as the Moon and the asteroid belt there's Callisto as well, outermost of the large moons of Jupiter, and the only one of them outside its lethal radiation belts, is within two years journey of Earth via type II Hohmann transfer. It's an icy body, and preliminary study suggests that though there is a global ocean below the surface, it is completely insulated from the surface.
This needs to be checked with robotic missions first, but it probably has no planetary protection issues. Venus cloud colonies also have a lot to recommend them, surprisingly, with protection from the acid using teflon and other plastics far easier than protection that has to hold in atmosphere against a vacuum with outwards pressure of tons per square meter. There are advocates for Mercury colonization too. Our imaginations can soar indeed with ideas like that. I was so glad that Elon Musk chose to include these wider visions and not just focus on Mars. His technology can be of great benefit for human and robotic exploration of the entire solar system.
But let's leave the places of most interest to the search for life - Mars, Europa, Enceladus and perhaps Ceres and Vesta - for exploration via robots and telerobotics for now, and leave consideration of whether to send humans to the surface of these places to a later date once we know enough to make a properly informed decision. You may have heard that the Moon is hopeless for gardening and for growing crops, and that Mars is the "go to" place for a prospective astronaut gardener.
But is it? As it turns out, the Moon has some advantages over Mars, especially if you can plant your garden in a habitat or greenhouse on its summits of sunlight at the poles. This is a frame from a charming Russian movie about the Moon made in , before humans landed there. Looking out on the lunar surface from inside a Moon city, in a frame from the Russian film Luna. You can also watch The full movie, in restored colour , with machine translation subtitles for part of it.
The ESA now wants to go back to the Moon in collaboration with Russia and many other international partners, and build a base at one of the summits of sunlight - the "peaks of almost eternal light". Lunar gardening could make a major difference on the Moon, reduce the amount of food they need to import, and generate their oxygen too.
You might think that Mars is far better for gardening than the Moon. We are surely going to do our best shot at gardening on the Moon whatever, but it may be encouraging to compare it with Mars. Actually the Moon isn't that bad a place for gardening as deep space locations go. It may be better than Mars in many ways. The main thing Mars has going for it is its day just short of 24 hours 40 minutes , similar to Earth, while the Moon's night is two weeks long.
Here is a photo showing progression of a dust storm as seen by Opportunity. These storms often continue for weeks on end, and the dust storm season happens every two Earth years. In dust storms like this, artificial light is needed to grow plants, much as it is during the lunar night. Mars is also further from the sun, with only half the levels of sunlight Earth receives.
Its nights get so cold, below You might think that the thin carbon dioxide atmosphere of Mars is an advantage, but plants only need trace amounts in the atmosphere we have less than 0. A habitat will have only a few kilograms of carbon dioxide total in its atmosphere. Actually, if an astronaut gardener can grow enough crops to eat, the people eating the crops exhale enough carbon dioxide for the next generation of crops. While if they don't grow all their own food, the carbon dioxide builds up and needs to be scrubbed. So carbon dioxide is not likely to be much of an asset for greenhouse construction.
It's far more likely to be a problem gas to scrub from the atmosphere of a space habitat, and indeed that's been the situation in all the spacecraft and space stations built to date. Also the atmospheric pressure from the thin Mars atmosphere makes almost no difference to greenhouse construction. It still has to withstand nearly a ton of outwards pressure per square meter on the walls of the greenhouse, not much different from the situation on the Moon. So, greenhouses on both Mars or the Moon are likely to be dome shaped to hold in the immense outwards pressure of the atmosphere inside.
For more on this, with the calculations, see Greenhouse construction - comparison of the Moon and Mars in Case for Moon First. Detail of lunar colony showing a greenhouse inside a base. Detail from image from NASA, This was for the Lunar Oasis proposal for a ten year program to establish a self sufficient science outpost on the Moon to act as a test bed for space settlements. If you build a greenhouse on the Moon or on Mars it has to withstand getting on for a ton per square meter of outwards pressure even at a tenth of an atmosphere.
It might be easiest to just put it inside your habitat as shown here. It could be illuminated with efficient modern LED lights which require little by way of electricity and don't have problems of excess heat to get rid of. You could also pipe the light from the sun into the habitat using optical fibres connected to solar collectors.
The Moon is a major challenge for gardeners too, it's no paradise. I'm not saying it is going to be easy there. It has no atmosphere at all, and apart from the polar regions, it has huge swings of temperature, and those two week long nights. But perhaps it can be made into a place to grow food more readily than Mars, especially if you can set up your garden in a habitat or greenhouse on the sunlit summits of the peaks of almost eternal sunlight at its poles.
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The lunar caves also work out well compared to Mars, as we'll see. Again, at those temperatures, it would be easy to warm up a lunar cave habitat or greenhouse enough for plants, if it is well insulated, as it would be. The night time darkness is the main problem with the caves, but as it turns out, its two weeks long night is not nearly as problematic for plants as you might think.
That's the result of some rather surprising experiments with wheat, beet etc done by the Russians, and advances in LED technology. We now know that the moon has water ice and other volatiles at the poles,. It is in darkness, and so can't be photographed from orbit, and the two main ways of detecting it from orbit radar and reduced levels of neutron emissions come up with different answers.
We don't know for sure where it came from either though comet impacts might be a good guess. But some think it is up to two meters thick layers of ice, and if so it may be easy to extract, with possibly hundreds of millions of tons, or a billion tons of them enough water for everyone in a city of a million to have the equivalent of an Olympic swimming lane filled with water.
The Moon is very different from Earth with its month long "day". But it has another difference which makes all the difference to the polar regions. Unlike Earth and Mars which have an axial tilt of over twenty degrees, the Moon has a tilt of only a bit over 1 degree 1. It's remarkable that the Moon's axis is so vertical.
Diagram from NASA. With the Moon's orbit tilted by 5. This remarkable coincidence is the reason the Moon's poles are so habitable. Earth has seasons because of its axial tilt of around As a result, the Moon has no seasons, and you get points at the poles in almost constant sunlight, the peaks of eternal night.
Habitats in those sunny spots can be kept warm just using solar collectors. Right next to them are permanently shaded craters that haven't seen sunlight for billions of years. There's indirect evidence that they may trap millions of tons of water, ammonia and carbon dioxide, possibly the results of comet impacts on the Moon. Hamiwari sun tracking solar collector - the light is collected, focused and sent through fiber optics to the interior of the spacecraft or habitat, where it can be used as a light source for algae or growing crops, or to help keep it warm.
For details of how this would work for spacecraft, see page of Peter Eckart's book: Spacecraft Life Support and Biospherics.
Solar collectors like this could be used to pipe sunlight into a polar base, or into cave habitats or greenhouses. See peaks of almost eternal light in the online NASA astrobiology magazine. When you are at the lunar poles, it's like a perpetual Arctic or Antarctic equinox, with the sun skimming the horizon, seeming to circle around you once every 28 days. This makes it easy to mount solar photovoltaic panels and solar collectors, to follow the sun and get maximum solar power.
They just need to be mounted vertically, and turned slowly once a month. Opposition occurs next July 27th, when Mars can finally strut its stuff at magnitude —2. Take that, Venus. Thursday's event takes place in Leo, the Lion, a hotbed of conjunction madness for weeks now.
Mercury, Venus, Mars, Regulus, and the waning crescent Moon have been mixing it up here since mid-September. Venus will move on to join Jupiter for an equally close and even more spectacular conjunction on November 13th at dawn in Virgo. Simple facts often lead to profound consequences. Stars dumbly cook helium to make carbon, the element essential to life. Gravity unwittingly attracts whatever it can get its hands on or alters the fabric of spacetime, take your pick to fashion everything from comets to black holes.
Dusty disks form planets, leading to the inadvertent beauty of conjunctions. We have the easy part: partake of and share the wonder. Talk about clooooose. They kissed at dawn for sure! Fantastic, Graham! Love your humor as always. Hope to get a photo, too. Seen through binoculars, Venus passed right between Mars and sigma Leonis. FOV is 2.
Down here in the Antipodes, Mars, Venus, and Sigma Leonis were almost right on my local Eastern horizon as dawn was about to break … which looks out across South Dunedin to the Pacific shoreline. You must be logged in to post a comment.