Opuntia fragilisfragilis"Brittle Cactus"Their habitat ranges from the south western states to Canada, and farther north than any other cacti in British Columbia. They have colonies into the eastern states as far as Michigan, and north all the way to the upper peninsula of Michigan. Their flowers are usually yellow, but maybe there are some rare magenta or white flowering plants too. The pads are small from half an inch to a few inches long, and depending on the colony visual spine texture varies slightly too. Plants form mounds from two to fifteen feet wide, and they remain close to the ground mounding few inches high. These cacti rarely produce seeds, and their main method of distributing themselves over a vast range of habitat is by stem propagation. Their pads are only slightly attached to one another and it's possible for pads to catch on passing wildlife then drop off in a new place. Pads will send down roots and generate a new plant allowing this plant to easily establish itself in new places without seeds. All cacti have the ability to grow new roots from their stems, and this species specializes in propagating itself this way. Some colonies thrive in areas with heavy rainfall and others require arid conditions. This is often considered to be the most cold tolerant cactus by any standard for survivors of extreme conditions.
Opuntia polyacanthapolyacantha"Starvation Cactus" or "Plains Prickly Pear"This species lives in wide spread locations of the western states, and has habitat as far north as Canada. They grow from lower plains to medium high elevations in sparsely treed habitat with some grasses and rocky ground. They tend to grow in dryer climates and it is unlikely to find colonies outside of arid and semi arid regions. Their general visual texture is highly variable making them a plant suitable for study by anyone who wants to specialize in one species of Opuntia. They sometimes have tuberous roots, but their most noted habit is the lack of fleshy mass inside of the fruit to accompany the seed at maturity. They grow low to the ground and pile up their pads to form clumps a few feet across, but sometimes colonies may spread out more than five feet across. The spines of these cacti vary in color, and appearance may vary in density from thick to showing no spines . The pad size may vary, but usually pads are small from less than two to five inches across. They have a wide variety of flower colors like white, pink, magenta, red, chartreuse, and colors in the yellows sometimes with red centers. Some flowers of this species have different colored edges of their peddles. Many colonies survive in extremely hot and dry conditions while others grow where winters are long, cold and the snow piles high. They are true survivors of extreme climates and will tolerate different climate conditions depending on the specifics of their habitat.
Pediocactus simpsonii var. minorsimpsonii"Mountain Cactus"These cacti specialize in high altitude conditions and have some of the most interesting survival strategies of any cold hardy plant. They are small globular cacti with plenty of spines. They are visually distinct in the way tubercles line up around the stem creating spiral channels. When seeds drop from the top of the stem they can fall down the sides of the plants beneath the spines falling in a spiral path. Many seeds collect at the base of these plants as they grow where they may stay without germinating for the life of the plant. They seem to have plain looking flowers in photos, but if you ever see their pink to white flowers in person they are very intense. Perhaps they are some of the most beautiful and mysterious plants in the world. They are similar to other cacti which survive in extremely cold conditions in that they shrink before winter, and some of them can become almost flat to the ground. They also have some unique and interesting chemistry that happens inside the stems of these plants which sets them apart from other extreme cold survivors. Beneath the winter snow they create their own snow caves by using some sort of chemical method to melt the snow near the stems. From all of the cacti who are survivors of extreme habitats this one is very unique.
You might even want BOTH systems in parallel to provide completely dissimilar redundancy and overlap. Probably want to grow potatoes, though, since they're so dang productive. Or at least have a plan to grow potatoes.
But is it realistically conceivable that vegetation could be engineered to grow in Mars-ambient conditions?If we can take all that we know about extremophiles, lichens, etc, and intensively breed them for Mars-ambient conditions, then could such a project succeed?
I've heard that a microorganism heavy diet could cause gout problems due to the high nucleic acid content, so it might *have* to be both types even before you factor in the psychological benefits of green plants and "real" food.
Everyone says that hydroponics will be the main way to grow food on Mars - but will it always be?
One thing to keep in mind is that the greenhouses do not necessarily have to be pressurized enough for humans. They only need to be pressurized enough for plants. So agricultural space is likely to be easier to build than living space. With that said, you could certainly have gardens/orchards in your living space as well.
What's the diffusion rate for a dome that doesn't have a bottom? That is, we dig a nice deep circular trench, put a half-dome of plastic or what have you over the top of the area, edges in the trench, anchor it down well, fill the trench up with some sort of concrete, and blow her up to maybe an armstrong limit or two? Then we continuously pump in a nice inert gas/CO2 mixture at the rate it leaks out. It ain't elegant, and you don't want people in there all the time, but it might be fast and to build, and give roots indefinite access downwards. Or is this what people are talking about when they say domes?
Nonsense! One of the key things that can't be automated entirely is growing food. Shirt-sleeve access to it will be essential at habitat pressure.Everything on automatic and apple trees in your apartment is a bit silly.The first people on Mars will be farmers and bloggers and reality tv stars...
Plus the bulk of calories will come from easily grown algae.
Well, if you use a crater, that then reminds me of what I said before - can you fill it with some heavy gas that won't easily dissipate? There's been plenty of discussion about sulfur hexafluoride (SF6) as a breathing gas for humans which is heavy enough that it could be used to fill up craters, etc. But if you're talking about a heavy gas that's meant to be tolerable to plants, then maybe you've got more choice on what kind of gas you can use?Does anybody know of any candidates? How about some heavy hydrocarbon gas?
What about in comparatively low-altitude depressions like Hellas Basin, where triple-point of water is believed to be possible?
Just looking at the general shape/structure of cactus plants, their typical globe shape seems to suit the pressure hull idea
Since plants must exchange gas with the atmosphere to get CO2 (and excrete O2) I don't think the pressure hull idea is very workable. They would have to somehow pump CO2 in through the stomata against a pressure gradient.