In A Propanal Molecule An Oxygen Atom Is Bonded With A Carbon Atom What Is The Total: Fill & Download for Free

Carboxylic acids contain a -COOH groupCarboxylic acids are compounds which contain a -COOH group. For the purposes of this page we shall just look at compounds where the -COOH group is attached either to a hydrogen atom or to an alkyl group.Note: There is no very significant reason for this. For simplicity, I am just trying to avoid making it look complicated by having either another active group present in the molecule as well as the -COOH, or the presence of a benzene ring.Benzoic acid (benzenecarboxylic acid) has the -COOH group attached to a benzene ring. Its physical and chemical properties are in line with those of any other carboxylic acid of a similar size, so I haven't felt it necessary to write about it separately.If you are interested in amino acids, you could follow this link to the amino acids and proteins menu.Examples of carboxylic acidsThe name counts the total number of carbon atoms in the longest chain - including the one in the -COOH group. If you have side groups attached to the chain, notice that you always count from the carbon atom in the -COOH group as being number 1.Note: If you aren't confident about naming organic compounds, then you might like to follow this link at some point.Use the BACK button on your browser if you want to return to this page.Salts of carboxylic acidsCarboxylic acids are acidic because of the hydrogen in the -COOH group. When the acids form salts, this is lost and replaced by a metal. Sodium ethanoate, for example, has the structure:Depending on whether or not you wanted to stress the ionic nature of the compound, this would be simplified to CH3COO- Na+ or just CH3COONa.Notice:The bond between the sodium and the ethanoate is ionic. Don't draw a line between the two (implying a covalent bond). That's absolutely wrong!Although the name is written with the sodium first, the formula is always written in one of the ways shown. This is something you just have to get used to.Note: We often write the formula of the ion showing the negative charge on one of the oxygen atoms (as above). This is OK for many purposes, but is technically wrong. In fact the negative charge is delocalised over the whole of the -COO end of the ion and the two carbon-oxygen bonds are identical - not one single and one double.Physical properties of carboxylic acidsThe physical properties (for example, boiling point and solubility) of the carboxylic acids are governed by their ability to form hydrogen bonds.Boiling pointsBefore we look at carboxylic acids, a reminder about alcohols:The boiling points of alcohols are higher than those of alkanes of similar size because the alcohols can form hydrogen bonds with each other as well as van der Waals dispersion forces and dipole-dipole interactions.Note: Hydrogen bonding in alcohols is discussed in detail in the introduction to alcohols. If you aren't confident about hydrogen bonding and other intermolecular forces and their relationship to physical properties it would be a good idea to read this before you go on. It is all done in more detail than I have used on this present page.Use the BACK button on your browser to return to this page.The boiling points of carboxylic acids of similar size are higher still.For example:propan-1-ol CH3CH2CH2OH 97.2°Cethanoic acid CH3COOH 118°CThese are chosen for comparison because they have identical relative molecular masses and almost the same number of electrons (which affects van der Waals dispersion forces).The higher boiling points of the carboxylic acids are still caused by hydrogen bonding, but operating in a different way.In a pure carboxylic acid, hydrogen bonding can occur between two molecules of acid to produce a dimer.This immediately doubles the size of the molecule and so increases the van der Waals dispersion forces between one of these dimers and its neighbours - resulting in a high boiling point.Solubility in waterIn the presence of water, the carboxylic acids don't dimerise. Instead, hydrogen bonds are formed between water molecules and individual molecules of acid.The carboxylic acids with up to four carbon atoms will mix with water in any proportion. When you mix the two together, the energy released when the new hydrogen bonds form is much the same as is needed to break the hydrogen bonds in the pure liquids.The solubility of the bigger acids decreases very rapidly with size. This is because the longer hydrocarbon "tails" of the molecules get between water molecules and break hydrogen bonds. In this case, these broken hydrogen bonds are only replaced by much weaker van der Waals dispersion.The energetics of dissolving carboxylic acids in water is made more complicated because some of the acid molecules actually react with the water rather than just dissolving in it.

TLDR: mo’ reactions, mo’ problems.table from Wikipedia: Heat of Combustion.It’s reasonable that this is confusing. In the table above, burning one mole of methane liberates 889 KJ. Ethane can be seen as two methane molecules minus a hydrogen molecule. (889 x 2) - 286 = 1492, rather than 1560, so there must be a hidden “something” present in ethane that is not present in methane that is released. Continuing: Propane can be seen as an ethane plus a methane minus a hydrogen, so (1560 + 889 -286) = 2163. Butane can be seen as two ethane minus hydrogen, so (1560 x 2) - 286 = 2834. Pentane can be seen as an propane and an ethane minus a hydrogen, so (2220 + 1560 - 286) = 3494. From just the thermodynamics, it seems they are all tremendously similar reactions, with slight differences, so from a thermodynamic standpoint, we might naively expect that all of these are equally flammable.In all of these cases, the heat of combustion of a hydrocarbon is a slight excess to the combustion of its parts, which is to be expected- there is greater bonding energy in ethane, steric strain, potential energy. That’s the missing something, but it doesn’t explain the differences in flammabilitySo what does that mean for flammability? Combustion is, in fact, a kinetic act, and not only must overcome (or release) potential energy, but also requires activation energy, and a bit of luck with mixing. The combustion from a thermodynamic standpoint looks likefrom Combustion: elmhurst.edubut from a kinetic standpoint, there are in fact (more than) 19 different reactions taking place when methane and oxygen are combined and burned.from Wikipedia: MethaneNote the existence of intermediate molecules, simply referred to as M or M*. These are any molecules, in fact, any matter containing potential or kinetic energy present- methane, oxygen, other molecules, water vapor, smoke, the walls of the container, cosmic rays, neutrinos, etc. Furthermore, although the net complete (thermodynamic) reaction seems to form carbon dioxide and water, in reality we know this not to be true: carbon monoxide and hydrogen are formed in significant quantities, enough that they can be spectroscopically observed during combustion, while other molecules, including ethane and methanol, are also able to be formed, though they are not seen in significant quantities and typically ignored. It all happens very quickly, but there are dozens of ways to slow it down- add helium to the mixture and lower the total (partial) pressure, say, and you will see these side products forming in much greater quantities as the reaction is slowed because more energy is lost to M + hν -> M* as M increases.Now, let’s talk about the non-gas hydrocarbons, starting with hexane. Hexane is not as nearly flammable as any of the gases, because in order to react with oxygen it needs to mix with oxygen. Since the total partial pressures are much lower at room temperature, very little hexane is present in the gas phase and therefore reactions really only take place at the surface of the hexane. There’s a simple way that I tend to visualize this, a mnemonic lie, so that it makes sense: all combustion occurs in the gas phase, and so combustion is a subset of oxidation where the oxidation happens in the gas phase.When you look at a piece of wood burning, or a marshmallow burning, you will see little jets of fire streaming out of the sides of the combustible object, and blue or yellow light. The heat released not only breaks down the wood, the cellulose, the sugars, etc., but also volatilizes smaller bits and pieces. The smell of wood burning is distinctive because the wood tannins break down into pyrogallol (and dozens of other chemicals, too, but the etymology of the scientific name for this compound, pyrogallol, pyro- “fire” + gall- “Oak apple” + -ol “alcohol” is telling ) but if you took some pure pyrogallol and smelled it, you would begin to believe why burning wood smells like it does.Where does the blue light, the yellow light, come from? In part, as hydrocarbons burn they form carbon monoxide, which is combusted further into carbon dioxide. It is this reaction which imparts a blue glow to the flame. Also, there are sodium ions present in wood or marshmallow, and the strong emission of yellow light as Na(energized ion) -> Na + hν(yellow light). In this case, the M in the reactions above is sodium ions.Pyrogallol is a solid at room temperature, so the heat is actually causing decomposition product pyrogallol (and billions of other molecules) to sublime, since they have a partial pressure even below their evaporation temperature.The kinetic combustion of hydrocarbons, in fact, forms some amount of carbon atoms, rather than just carbon dioxide and water, along with the hundreds of other combustion products. How it is burned matters more than a simple balanced reaction, and knowing the simple, high-school-chemistry thermodynamic view is not all you need to know to understand fire. This is why most hydrocarbons produce soot- atoms of carbon left behind in the kinetic combustion of hydrocarbons. While if the complete combustion of a hydrocarbon is summed up, all of those millions of intermediates convert into carbon dioxide and water, the net thermodynamic energy will be exactly equal to the total observed energy. This is why I could do the math I performed at the top of the page- the heats of combustion are equal to the heats of formation of the reactants minus the heats of formation of the products. The “leftover” is the difference in the heats of formation, showing that there is residual bonding energy in the more complicated molecules.So, the answer is as follows:more complicated molecules need to have energy added to move into the gas phase, where they can mix with oxygen to combustmore complicated molecules have orders of magnitude more reactions going on in the gas phase: mo’ reactions, mo’ problems.and the relative concentrations of these intermediates determines how fast the reaction can proceedThe faster the mixing and rise in temperature to provide the activation energy, the faster it will burn.Flammability is a kinetic, not a thermodynamic, governed behavior.

Actually some have suggested that we do. First we need to be sure that it is okay to do so, that there are no planetary protection issues. One of the big issues with Mars is that it is one of the few places in our solar system where present day life may exist, perhaps independently evolved from Earth life. It may also have habitats where Earth microbes could survive, and we simply don’t know if Earth and Mars microbes would play nicely together. It could be, for instance, that Mars has early life that has not evolved as far as it has on Earth, predating all the complexity of DNA.We don’t have any early life on Earth with a big gap between the first chemicals life must have evolved from and present day life which is so intricate with its DNA, messenger RNA, huge molecules and a million different chemicals taking part in a complex dance in every cell. So what happened to the early life here? Maybe DNA life made it extinct on Earth. But Mars has hardly changed for billions of years and there are traces that just possibly might be tiny cells, too small for all the cell machinery of modern life in the Mars meteorite ALH84001. That suggests that - just possibly as one of many possibilities - Mars may still have this early life on it. Such life might be incredibly vulnerable to Earth microbes.The best place to start for planetary protection reasons is the Moon. We can do a lot there. It’s closest and safeest and it is known to have water ice, ammonia, carbon dioxide etc in the cold traps at its poles, millions of tons possibly, though we don’t yet know how easy it is to extract.There are many other places we can visit with no planetary protection issues, including Jupiter’s outer most moon Callisto, the moons of Mars, Mercury (which is thought to have ice at its poles) and probably the upper clouds of Venus. But amongst them also is Titan.Titan is very unusual here because there is a possibility of life there, native life, but if so, it’s likely to be so different that Earth and Titan life can’t live in the same habitats.(There is a chance of this for Mars also, if its native life is hydrogen peroxide and perchlorate based which may only be able to survive in perchlorate and hydrogen peroxide based salty brines too cold for Earth life, and also not survive warming up to Earth microbe friendly conditions - but though it is possible for Mars, it’s a bit of a stretch at present. For Titan it is perhaps even the most likely situation).And, Titan is surprisingly habitable. Nowhere on Mars is a patch on Earth of course. But Titan could come a close second best, despite the cold temperatures there.(Note - I have expanded this answer to a new article on my Science 2.0 blog which goes into a lot more detail (and also covers Callisto too): Value Of Titan As Base For Humans In Saturn System - Surprisingly - Once There - Easier For Settlement Than Mars Or The Moon)So - a bit of a review of Titan first:WHAT IS TITAN LIKE?Saturn's moon Titan is, so far, the only known place in the solar system with liquid on its surface apart from Earth. Most of the lakes are around the north pole, with one lake, lake Ontario, at the south pole. But the lakes are of ethane and methane instead of water.Glint of sunlight on the lake region around the northern pole of Titan.Titan Methane Lakes Cassini Flyover 2013 NASA-JPL Animation from Saturn OrbiterTitan is the only place in the outer solar system which we have sent a lander to, the Huygens probe.Hi-res narrated video of Huygens probe landingSometime maybe we will send some more probes there to explore it further. This was a recent idea for a submarine to explore Titan:Titan Submarine: Exploring the Depths of Kraken MareAnd this is an idea for an aerostat to explore it's atmosphere, VAMPThe Northrup group's VAMP aerostat could also be used for Titan.See also Life on Titan (wikipedia).This is such an extreme habitat, at temperatures of -180 °C, that it seems impossible that Earth originated life could grow there naturally, except in cryovolcanoes or ice temporarily melted by impacts. The limit for microbes to complete their life cycle is usually given as around - 20 °C (the usual temperature for freezers), around -10 °C for lichens, and around -2 °C for higher lifeforms such as insects, though there can be some metabolic activity down to -26 °C for microbes and down to -50 °C or lower for some cold hardy multicellular life.Details, lowest temperatures for Earth life: The lowest temperatures that microbes can grow, i.e. complete their lifecycle and reproduce, is usually said to be around - 20 °C in salty brines, for instance, there have been no examples of spoilage of food in freezers kept below that temperature. When cold loving (psychrophile) microbes are cooled, they produce a kind of antifreeze that prevents formation of the ice crystals which normally damage cells as the ice expands. Instead their cells gradually turn into a kind of glass as they cool down (vitrify). As they do this, they can can still do some metabolic activity until they are completely vitrified and it stops completely at - 26 °C which seems to be the limit for any activity at all.Some invertebrates may continue to have some metabolic activity down to much lower temperatures, below - 50 °C. Insects may not just have metabolic activity but even remain active at low temperatures, for instance a Himalayan insect which is still active down to −16°C. But even these cold tolerant multicellular lifeforms typically need temperatures of around -2 °C to complete their life cycle.Many microbes and multicellular life also, if the cooling is slow, will revive after vitrification when restored to normal temperatures. More details here: A Low Temperature Limit for Life on Earth, and The thermal limits to life on Earth, for details of how low temperature life is possible, see Psychrophilic microorganisms: challenges for life , also see more cites in wikipedia article PsychrophileAlso there is no liquid water, instead, ethane and methane, which makes it exceptionally interesting for exobiology, if there is life there. There is no way it can be similar to Earth life.Even the cell walls can't be the same. There are some microbes on Earth that can live in hydrocarbons, by having an extra layer to protect themselves from the oil, including a report of one strain of Pseudomonas able to tolerate up to 90% of a hydrocarbon alpha-pinene. They don't metabolize the hydrocarbons but usually have an outer membrane modified to let them tolerate them. See page 38 of this PhD thesis by Lucy Norman. However Titan life would have to live in 100% hydrocarbons. The cell membrane structure of Earth life would not work in those conditions as it depends on hydrophilic molecules that are attracted to water to retain its structure. There is water inside and outside the membrane, and then the membrane itself consists of long chain molecules with one end hydrophobic and the other hydrophilic. Then they join together back to back to form a membrane with the hydrophilic heads pointing both outwards and inwards and the hydrophobic tails touching each other in the middle of the membrane.This shows how it works:Figure 7 of Lucy Norman's PhD thesis on spontaneous self assembly of reverse vesicles suitable for Titan in hydrocarbon fluids. She credits it as: "Illustration of the reverse vesicle structure taken from Norman & Fortes"Normally it's the other way around on Earth with the hydrophobic tails inwards and heads outwardsYellow polar heads separate the grey hydrophobic tails from the surrounding water and the interior fluid of the cell itself. Diagram by Jerome Walker (https://en.wikipedia.org/wiki/Cell_membrane#/media/File:Fluid_Mosaic.svg).Lucy Norman looks at many ways that reverse vesicles can spontaneously self assemble, from her experimental results. It's very technical. But she has a summary in her chapter 9 which looks at the applications for astrobiology.I will paraphrase what she says there in the first few paragraphs of her chapter 9 (as it uses rather technical language):It's unlikely that these reverse vesicles would be used only for cell walls. The hydrocarbon lakes of Titan are likely to contain more than one alkane liquid, with methane-ethane-propane in equilibrium with the atmosphere. The vesicles could be used to create a cell with a "cytoplasm" that differs from its medium, and also, pockets of unique solutions for specific purposes within the cell.These pockets then could be used to create the equivalent of the organelles of Earth microbes, which could also trap different alkanes to help with whatever process that organelle is devoted to facilitating. Multiple vesicles joined together then have the potential to carry out long chemical processes with different chemical environments for each step.Some of them could also trap ammonia water in bilayers which could decrease its freezing temperature to the point where perhaps it could be used for nano-reaction centeres for bological processes that depend on polar solvents. Then there could be nano-channels of liquid ammonia water to transport these throughout the cell. The microbes on Titan could get the water from short lived liquid water from cryovolcanoes (cryolava) or maybe from the icy bed of the hydrocarbon lakes using antifreeze proteins.They could be used as reservoirs for polar solutes (like the ammonia rich water) and to transport proteins and enzymes.(paraphrase of the first few paras of Chapter 9, page 331 of Lucy Norman's 2015 thesis)Here is Chris McKay talking about prospects of life in the Titan lakesSaturns Moon Titan: A World with Rivers,Lakes, and Possibly Even LifeHe mentions there that Huygens made provisional observations of hydrogen and acetylene and ethane depletion near the surface of Titan, which they'd predicted as a possible sign of life on Titan. Also he mentions that oxygen would be in short supply, in a hydrocarbon ocean without water, and need to be extracted from water ice "rock" by microbes.This is related, a possible way that life on Titan could make cell membranes without use of oxygen atoms in an environment like Titan where it is in short supply.Possible oxygen free cell structure made of organic nitrogen compounds that could function at the low temperatures of Titan's ocean.Such oxygen free cell walls are exotic biochemistry but still carbon based.Titan's ethane / methane ocean is also ideal for William Bains' silicon based biochemistry (with silicon's weak bonds permitting much faster chemical reactions in such cold conditions). See page 160 of this paper and earlier pages.You can read about Chris McKay's ideas about Titan in detail in his 2016 paper Titan as the abode of life.Amongst other evidence, the photochemical models predict a layer of ethane enough to cover the surface to a depth of many meters, but Cassini didn't find it. The Huygens lander didn't find any acetylene in the gases released from the surface. And models suggest that hydrogen is being transported towards the surface suggesting something there is removing hydrogen from the atmosphere.Also, there is more hydrogen above 50˝N than the global average. Could this be because the southern hemisphere, with more ethane, is more hospitable to life than the northern hemisphere dominated by methane?He suggests four possible conclusions (see page 11)The result about a strong flux of hydrogen onto the surface may be mistakenThere is some physical process leading hydrogen to fall towards the ground maybe absorbed onto organic haze particles. But this would just be a hydrogen flow, and it wouldn't take hydrogen out of the atmosphereThat there is some chemical catalyst that causes a hydrogenation reaction at 95 K - which would be quite interesting and a startling find, if not as startling as lifeThat it's due to a liquid methane based life form.Titan as potentially the easiest place for humans to live outside EarthIf that's right, then we may be able to land humans on the surface of Titan with no planetary protection issues, at least in the forward direction from Earth to Titan. That is, unless there is any cryovolcanism or other connection with its subsurface ocean. But if there is no such connection, then there would be no way to contaminate its deep subsurface ocean from the surface. You'd also have to consider whether there is a chance that Earth biochemistry could give native Titan life "new ideas" I suppose.If Titan does turn out to be okay for planetary protection, then in some ways it might be one of the easiest places for us to live outside of Earth, as suggested by Charles Wohlforth and Amanda Hendrix, authors of Beyond Earth: Our Path to a New Home in the Planets. Their idea is described in brief in Let's Colonize Titan in the Scientific American. Some of the advantages are:Atmosphere at the same pressure as our Earth's atmosphere. Your spacesuits wouldn't need to be pressurized. They would of course have to be insulated from the cold, but they would be much more flexible, without the enormous outwards pressure of tons per square meter needed in vacuum conditions.You could build conventional houses too, equal pressure inside and out. They would only need to be air tight.Protection from cosmic radiation by the atmospherePlenty of ice for water.Earth life would probably have no impact on any Titan lifeAbundant resources for making plastic which could be used to make housing. Habitats would be so easy to construct, with just a thin covering to keep out its atmosphere, equal pressure inside and out. This means like the Venus cloud colonies, you could have huge internal spaces filled with oxygen and nitrogen for very little by way of massTerminal velocity a tenth that on Earth so if you fall out of a plane in the Titan atmosphere, no problem. You would gently fall to the surface, at most a few bruisesHuman powered flight - could fly in the light gravityThe gravity levels are lower even than for the Moon. Would humans be healthy at such low levels of gravity? Well, if not, we may be able to augment it with artificial gravity. Considerations are similar to the Moon. See my sections in Case for Moon First:What about gravity - isn't that a big advantage for Mars over the Moon?Artificial gravity on the Moon to augment lunar gravityYou have to be design the habitats to be well insulated and they have to be airtight to prevent the methane in the atmosphere mixing with the oxygen rich atmosphere of the habitat. On the plus side, it doesn't have the risk of rapid decompression of a normal space habitat, and any leaks will be very slow.The main remaining issue would be power, as Saturn gets very little sunlight and Titan with its nearly opaque atmosphere, even less. We need it for heat, or some way to generate heat. We also need electricity etc. Perhaps by then we have fusion power, or we use a conventional nuclear reactor with imported fuel. But it has native sources of power too, from this paper Energy Options for Future Humans on TitanHydropower - just as on Earth if it has any lakes at higher altitudes they could produce power by cutting a channel to a lower level. Sadly the seas discovered so far seem to occupy the lowest levels in the landscape, at the lunar poles. Still, the topography isn’t very high resolution and there is plenty of scope for finding lower levels close to the seas. It would only take 145 meters of difference to generate a very useful 9 MW assuming flow rates typical of hydropower installations on Earth adjusted to Titan conditions. The Kraken ocean could supply power at these levels for thousands of years - and it could be replenished too by natural processes refilling the seas just as happens for hydropower on Earth. However this depends on more detailed topography for Titan.Wind power - with such a dense atmosphere then wind power is feasible (unlike the case for Mars) - but surface winds are slow so you could use tethered blimp or balloon mounted windmills at a height of 3 km where the speed is 2 meters per second (4.4 miles per hour) or even better at 40 km where the wind speeds are 20 meters per second (44 miles per hour). These could generate hundreds of terrawattsSolar power. Surprisingly, with modern efficient solar cells, covering 10% of the surface would give you enough power for the population of the US (which has a surface area 10.8% that of Titan). I.e. at typical population densities of the US you’d need roughly equal areas for the solar panels and for the human populations.Chemical - for instance hydrogen and acetelyne can be extracted from its atmosphere and react together to produce energy. There are several other reactions including hydrogenation of nitrogen to produce ammonia using chemicals in its atmosphere which is quite a bit out of chemical equilibrium.Nuclear power - likely to be useful for early misisons there using RTGs as a source of heat and power. Mining for it locally may be hard as radioactive materials are likely to be deep below the surface, under hundreds of kilometers thickness of ice, so these materials would probably be imported.The solar power calculation there may surprise you, so here is the relevant part of their paper where they explain the assumptions they use that lead to this conclusion:"We estimate the amount of solar energy available at Titan’s surface by scaling down from Earth. At the top of Earth’s atmosphere, the average solar energy is 1400 J/m2 -s. At the top of Titan’s atmosphere, this scales to 14-17 J/m2 -s. Titan’s atmospheric transmission depends on wavelength: the red and nearinfrared are transmitted (minus methane absorption) whereas blue light is absorbed; here we assume that 10% of the solar flux makes it to Titan’s surface. In reviewing the response function of various photovoltaic materials, we estimate that Titan’s transmitted spectrum is best matched by the response of amorphous silicon or perhaps cadmium telluride (CdTe) photovoltaic material. Нe efficiency of these material is in the ~13-20% range but the performance at Titan temperatures is unknown. To be conservative in this initial, simplified exercise, we estimate the efficiency at 10%. We also consider that for any low-mid latitude location on the surface, the sun is up for ~1/3 of the day. (This does not consider seasonal variations or eclipses by Saturn.)" It still needs more in situ research first though, I think, to establish that there are no planetary protection issues at all.Could Earth life harm Titan life?Even if there are no habitats for Earth life there, as seems likely except for the possibility of cryovolcanism - you still need to think about molecules from Earth life such as RNA and DNA. Could they somehow be incorporated by Titan life? Also, if any of the life forms there exist in small quantities, hard to study, could organics from a human occupied habitat confuse the search for life in the region close to the habitat?Could Titan life harm Earth life?Also, what about contamination in the backwards direction from Titan to Earth. We can show by studying Earth life that it is impossible for Earth life to survive there in its natural conditions.But we need to have a reasonable understanding of Titan life (if it exists) how can we be sure the other way around, that Titan life can't survive on Earth or in human occupied habitats?It may seems unlikely that life adjusted to those habitats could survive here. But you can make a plausibility argument for it even so.Here is how it could happen.What if the Titan life evolved from previous life that first originated in its deep subsurface oceans? That's one suggestion for how it could have originated. Is there any chance it could retain capabilities that would let it survive as spores, and then maybe reproduce in oil deposits or in some other way survive in the much hotter conditions of Earth?Or indeed, is there any chance that there could be a lifeform that on Titan can survive not just on the surface but also in occasional cryovolcanoes, or lakes formed from meteorite impacts? I.e. a life that has already evolved the capability to live in both those radically different environments? It seems unlikely, but can we rule it out before we know what is there?Both directions - cryovolcanismAlso, as a planetary protection issue in both directions: Titan probably has a subsurface ocean. If so, if there is communication between the subsurface and the surface, e.g. cryovolcanoes with liquid water in place of lava, then that's an obvious contamination issue for the subsurface oceans.Titan is currently categorized as "Provisional category II" with "only a remote chance that contamination from Earth could jeopardize future exploration". There category II is the same as our Moon. But it is provisional because they say that more research is needed. Other places categorized as provisional category II are Ganymede, Triton, the Pluto Charon system, Ceres and the larger Kepler belt objects (down to half the size of Pluto).Likely to know a lot about it before humans get thereTitan would surely be studied robotically first. There are no serious proposals to send humans there right away, unlike Mars.So, unless there is some drive to send humans there quickly, we'd probably answer all those planetary protection questions already before we land humans there, just in the natural course of solar system exploration. If so, and if the results turn out favourable, it may well turn out to be one of the best place for a human colony outside of Earth. It would be a fun place to live in some ways, with the human-powered flight, for instance, and the intriguing seas. And it might potentially be a biologists paradise if there is indeed native Titan life to study.On the other hand, it’s not such a great place for astronomy, at least, naked-eye astronomy. Despite its spectacular location close to Saturn, you’d have to go into orbit or use wavelengths able to penetrate its atmosphere to spot Saturn or indeed, stars or planets at all. But it might well be a base for astronomers and exobiologists studying Enceladus and the Saturnian rings, etc. - with their work done outside of Titan, maybe some of it robotically - but their main base on Titan itself.See alsoColonization of Titan - WikipediaBeyond Earth: Our Path to a New Home in the Planets. Summarized in Let's Colonize Titan in the Scientific American.This is based on a couple of sections from my Touch Mars? bookLife in the oceans of ethane and methane on TitanTitan as potentially the easiest place for humans to live outside EarthWHEN CAN WE DO IT?It’s not as far as you’d think, especially to Jupiter. To go as far as Mars and return, you already need to be able to survive several years without resupply from Earth. This is my summary in one of the linked to articles:—————It would take several years of travel to get there [Saturn], probably seven years though it could be shorter. Voyager I got there in just three years and two months with a Jupiter gravity assist flyby. And New Horizons on a fast trajectory doing just the one flyby of Saturn on the way to Pluto took only two years and four months to get there, but leaving Earth with much more delta v than is normal for an interplanetary spacecraft. Cassini did several flybys of Venus and Earth to increase its delta v from Earth, but from its final flyby of Earth to Saturn it took just under five years, from 18 August 1999 to 1st July 2004. That was a rendezvous with Saturn. For more on this see "How long does it take to get to Saturn" (Universe Today). It's hard to predict what our rockets will be able to do by the time this becomes a feasible proposition, to go to Titan. For instance if they are capable of continuous acceleration, even by only a small amount that can make a big difference.I think it's important to be clear that we do not have the technology to send a human to Titan at present. Mind you, even in the mid 1960s we did not have the technology to send a human to the Moon. And we don't have the technology to send a human to Mars either at present. For that matter we don't currently have the technology to send humans to the Moon, though we should regain that soon. To go to Mars or Venus is a far harder journey than to the Moon, to Jupiter is another step up, and to Titan is a step up again over any of those. However, if you are optimistic and we look forward to a decade or two into the future when we have more heavy lift capacity than we do today, and importantly - a fair bit of experience in sustainable living in habitats (perhaps on the Moon) to let us travel in spaceships for years on end without resupply from Earth - after that it might be within our reach.Elon Musk envisions his BFR traveling as far as the Jupiter and Saturn systems. If Elon Musk is right in his claims that his BFR can be fully re-usable and the cost per flight less than for the Falcon Heavy - I make it that he could send around 20 people to Titan for a cost of less than $100 million for a round trip with enough payload for fully sustainable agriculture to feed them and keep them supplied with oxygen throughout. It does however also mean outlay of the cost of three BFR's, two of which would be left in orbit around Titan- that could however be used as orbiting habitats for Titan or they could descend to the surface as instant skyscrapers on Titan. One of them returns to Earth with any that wish to return plus extra payload. Of course many breakthroughs are needed before that happens. If you are optimistic, I'd venture as a guess, 20 to 40 years before we can do that. If pessimistic, who knows, generations rather than decades, it may be a flight for our grandchildren.See:Value Of Titan As Base For Humans In Saturn System - Surprisingly - Once There - Easier For Settlement Than Mars Or The MoonHOW PRACTICAL IS IT?If he succeeds, Elon Musk’s BFR could make it possible to send humans out to Saturn. I work out it has enough interior space to sustain 20 people with food using the BIOD-3 system which needs minimal resupply from Earth(It’s more than 20 if you add extra agricultural external modules to the BFR and deflate them or detach them at the destination but 20 seems a good amount to be comfortable for a very long duration mission with loads of extra mass to take along to start a settlement).Once we can do things like that, of course worked out on the Moon and close to Earth first, then we can send humans to anywhere in the solar system, right out to Pluto, for not much more outlay than a mission to Mars except that it ties up a BFR for a decade or two. He thinks a BFR will eventually cost $200 million. Add the need to refuel at the destination to return and send that fuel out from Earth on other BFRs, and you are still talking about total cost including launch from Earth of under a billion dollars.2 years to Titan is very fast - it might be possible, but safer to assume say 5 years as for Cassini for its last leg from Earth to Saturn.This expanded version of this answer explains it in more detail, and includes that attempt at a first rough costing using BFRsValue Of Titan As Base For Humans In Saturn System - Surprisingly - Once There - Easier For Settlement Than Mars Or The MoonSee also Let's Make Sure Astronauts Won't Extinguish Native Mars Life - To Jupiter's Callisto, Saturn's Titan And BeyondFACEBOOK GROUPHumans to Jupiter's Callisto, Saturn's Titan and Beyond