# How is the chemical composition of water on other planets different from our own? **URL:** \ **Category:** Factual Questions\ **Created:** [June 12, 2014, 10:05am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614 "2014-06-12T10:05:05Z")\ **Posts on this page:** 15\ **Page:** 3
**Author:** ![davidmich](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@davidmich](https://boards.straightdope.com/u/davidmich)\ **Post date:** [November 12, 2014, 7:46am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/41 "2014-11-12T07:46:55Z")
I just heard a project scientist talking about the Rosetta mission to land a probe on a comet. He is interested to find out if the water on the comet is similar to water on earth. Does that mean that the composition of water is possibly different or is he referring to impurities? davidmich ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [November 12, 2014, 8:06am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/42 "2014-11-12T08:06:27Z")
Ah. Vox has an article on that probe: " If water ice is present on this comet, as scientists hope, Philae will calculate **the ratio of different sorts of hydrogen isotopes** present in it…" Emphasis added. So while water is water, hydrogen can take a number of forms. > **[Philae is about to become the first spacecraft ever to land on a comet](https://www.vox.com/2014/11/11/7185827/philae-rosetta-comet)** > > We've landed on six celestial bodies ever. The tiny spacecraft is about to make it seven. ---
**Author:** ![dofe](https://avatars.discourse-cdn.com/v4/letter/d/7ba0ec/32.png) [@dofe](https://boards.straightdope.com/u/dofe)\ **Post date:** [November 12, 2014, 8:14am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/43 "2014-11-12T08:14:16Z")
Like [heavy water](http://en.wikipedia.org/wiki/Heavy_water) – which means that water is fundamentally still H20, regardless of where it’s found. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [November 12, 2014, 9:16am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/44 "2014-11-12T09:16:41Z")
There isn’t much water on Venus, and what little there is exists in the form of a thinly spread vapour; but if we has a sample of that water in the lab, it would be possible to tell that it is different from Earth water. Because of the slightly lower escape velocity on that planet, deuterium is retained more easily than ordinary hydrogen, so the water there has more ‘heavy water’ in it. Maybe as much as 160 times as much, depending in altitude. This is a physical difference, not a chemical difference- but heavy water does have some minor chemical differences to normal Earth water, so the answer to the OP is ‘there is a slight difference’. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [November 12, 2014, 9:57am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/45 "2014-11-12T09:57:22Z")
> [@davidmich](#): > > I just heard a project scientist talking about the Rosetta mission to land a probe on a comet. He is interested to find out if the water on the comet is similar to water on earth. Does that mean that the composition of water is possibly different or is he referring to impurities? > davidmich Did you follow the link I posted, Lo! these 5 months ago? This one: [http://haroldconnolly.com/EES%20716%20Fall%2009%20Reading/Lecture%201/Background%20reading/1.06%20%20Oxygen%20Isotopes%20in%20Meteorites.pdf](http://haroldconnolly.com/EES%20716%20Fall%2009%20Reading/Lecture%201/Background%20reading/1.06%20%20Oxygen%20Isotopes%20in%20Meteorites.pdf) ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [November 12, 2014, 4:04pm UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/46 "2014-11-12T16:04:13Z")
The only difference that actually fits the OP that I could think of would be the isotopes of H and O present. And that could be used to determine if it is from a known water source on earth, but since not all are know it would be hard to say it was from another planet, or even harder to know if it was from a specific place. But going further, the definition of water usually, normally includes water + it’s dissolved substances and also suspended substances. That may give a very different answer. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [November 12, 2014, 5:00pm UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/47 "2014-11-12T17:00:30Z")
Water is expected to exist in the liquid form under the ice of Europa, Enceladus and a number of other moons. What solutes might be expected in these ice-covered oceans? Europa appears to have magnesium sulphate in its oceans, as shown by the residues observed on its frozen surface. An ocean of Epsom salts would be exotic, and probably undrinkable depending on the concentration, but not utterly alien. What would be alien would be the ethane lakes and seas on Titan, which aren’t water at all. > **[Lakes of Titan](https://en.wikipedia.org/wiki/Lakes_of_Titan#Chemical_composition_of_the_lakes)** > > Lakes of liquid ethane and methane exist on the surface of Titan, Saturn's largest moon. This was confirmed by the Cassini–Huygens space probe, as had been suspected since the 1980s. The large bodies of liquid are known as maria (seas) and the small ones as lacūs (lakes). > The possibility that there are seas on Titan was first suggested based on data from the Voyager 1 and 2 space probes, which flew past Titan in 1980. The data showed Titan to have a thick atmosphere of approximately the correct ... > [@](#): > > According to a computer model developed by Daniel Cordier of the University of Rennes,[24] three-quarters of an average polar lake is ethane, with 10 per cent methane, 7 per cent propane and smaller amounts of hydrogen cyanide, butane, nitrogen and argon. Benzene is expected to fall like snow and quickly dissolve into the lakes, although the lakes may become saturated just as the Dead Sea on Earth is packed with salt. The lack of waves suggests that these lakes are viscous, something like tar. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [November 12, 2014, 5:24pm UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/48 "2014-11-12T17:24:22Z")
What about the water that Philae (which has recently landed, as I write) might find on the comet? Well, the isotope ratio is most important here, since this will be different according to where the comet was located when it first formed. Objects that were formed in the inner Solar System will have a similar isotope ratio to the water in Earth’s oceans, unless there has been some sorting process in action (as demonstrated on Venus). However objects that formed in the outer reaches of the system will have very different isotope ratios, with at least twice as much deuterium as water on Earth. So Philae should be able to tell if this is an inner system or an outer system object, just by analysing the water with its cromatograph. ---
**Author:** ![davidmich](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@davidmich](https://boards.straightdope.com/u/davidmich)\ **Post date:** [November 13, 2014, 10:14am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/49 "2014-11-13T10:14:24Z")
Thank you all. Very helpful. davidmich ---
**Author:** ![davidmich](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@davidmich](https://boards.straightdope.com/u/davidmich)\ **Post date:** [April 16, 2015, 2:09pm UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/50 "2015-04-16T14:09:07Z")
I read somewhere that GJ 1214b has different varieties of water. Does anyone know which kinds. I’ve been trying to find an article listing them, but can’t locate one. > **[New Type of Alien Planet Is a Steamy 'Waterworld'](https://www.space.com/14634-alien-planet-steamy-waterworld-gj1214b.html)** > > Astronomers using the Hubble Space Telescope have discovered a new class of alien planets, so-called steamy waterworlds. The discovery is based on the planet GJ 1214b, which appears hot, wet and is la GJ 1214b thus appears to have much more water than Earth does, and much less rock. The alien planet’s interior structure is likely quite different from that of our world. “The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water,’ substances that are completely alien to our everyday experience,” Berta said. > **[Weird Water on GJ1214b](https://www.smithsonianmag.com/air-space-magazine/weird-water-on-gj1214b-106950597/)** > > Astronomers learn more about a hot, watery, exotic "super-Earth" Materials “like ‘hot ice’ or ‘superfluid water’ – substances that are completely alien to our everyday experience” would form, according to Berta. We emailed Berta to ask if he could explain these strange materials further. Frankly, it’s difficult for me to imagine what these exotic forms of water would be like – we have very little experience with them here on Earth. They’re simply how the molecule H2O acts when it is in high pressure and temperature environments … Our closest point of comparison is that the outer atmosphere might be something like a hot, steamy oven that you would use to bake bread with nice crust. But as you go deeper into the planet, you would encounter these exotic forms of water. I should add, however, that there’s still an enormous uncertainty about the composition of the planet overall. Yes, the observations point to a planet that is rich in water, but what is it mixed with, and in what proportions? Really visualizing the “surface” of this planet (if there is one!) will require us figuring those things out! But whatever the case, the temperatures are too high for liquid water as we know it to exist on GJ1214b. ---
**Author:** ![davidmich](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@davidmich](https://boards.straightdope.com/u/davidmich)\ **Post date:** [April 16, 2015, 2:25pm UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/51 "2015-04-16T14:25:20Z")
> **[Cloudy Weather Discovered on Super-Earth GJ1214b](https://guardianlv.com/2014/01/cloudy-weather-discovered-on-super-earth-gj1214b/)** > > A group of scientists have recently harnessed the power of NASA’s Hubble Space Telescope to establish the weather conditions of an alien planet. The scientists, led by researchers in the Department of Astronomy and Astrophysics at the University of... In their latest study, the scientists found no “chemical fingerprints” in the planet’s atmosphere, eliminating the possibility that the super-Earth has cloud-free atmospheres that are comprised of carbon dioxide, carbon monoxide, methane, nitrogen or water vapor. In explaining these findings, the group offer a new explanation; GJ1214b possesses high-altitude clouds in its atmosphere with unknown compositions. However, models of super-Earth atmospheres have predicted the clouds could be made from potassium chloride or zinc sulfide, which could exist at the extreme temperatures of 450 degrees Fahrenheit found on the planet. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 16, 2015, 2:35pm UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/52 "2015-04-16T14:35:46Z")
Here’s the phase diagram for normal and exotic forms of H2O: [Water (data page) - Wikipedia](http://en.wikipedia.org/wiki/Water_(data_page)#Phase_diagram) As you can see, there’s really only one type of liquid and vapor phase. As such the gross physical properties of the liquid phase are gonna be familiar everywhere; it’ll just seem strange to measure unusually hot liquid water under unusually high pressure. Conversely, the solid phases come in a bunch of interesting varieties with differing properties independent of the conditions they’re embedded in. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [April 16, 2015, 9:59pm UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/53 "2015-04-16T21:59:52Z")
Don’t forget the suoercritical phase of water, which may be common on hot, water-rich worlds. This phase of water would be very different to anything we are familiar with. It’s the dark green area on this diagram. [![](https://i549.photobucket.com/albums/ii398/she-who-chatters/water-phase-diagram.gif) ](https://i549.photobucket.com/albums/ii398/she-who-chatters/water-phase-diagram.gif) > **[Supercritical fluid](https://en.wikipedia.org/wiki/Supercritical_fluid)** > > A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. It can effuse through porous solids like a gas, overcoming the mass transfer limitations that slow liquid transport through such materials. SCF are much superior to gases in their ability to dissolve materials like liquids or solids. Also, near the critical point, small changes in pre Su... Of course, like water ice, supercritical water is still H[SUB]2[/SUB]O. ---
**Author:** ![Carl\_Pham](https://avatars.discourse-cdn.com/v4/letter/c/e9a140/32.png) [@Carl\_Pham](https://boards.straightdope.com/u/Carl_Pham)\ **Post date:** [April 17, 2015, 12:37am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/54 "2015-04-17T00:37:32Z")
Water has the same chemical composition everywhere, but it can indeed have a different isotopic composition, meaning different proportions of deuterium instead of protium atoms, or even oxygen-18 instead of oxygen-16. This is one way to examine the cosmic origins of water, since various high-energy processes tend to favor some isotopes over others, and give a “signature” of the origin to the water. That’s the point of the Philae experiment. Interestingly, isotopically-varying water can indeed be considered an entirely different substance from certain points of view. Pure D2O, for example, has nontrivially different properties than pure H2O. It does not boil or freeze at the same temperatures, and its chemical reactivity is slightly different. In fact, it is actually technically poisonous: you cannot survive drinking only D2O. The chemical reactivity is sufficiently different from regular H2O that it does not sustain life. One wonders whether a detective story has yet been written in which a victim was knocked off by substituting D2O for his regular bottled water. ---
**Author:** ![davidmich](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@davidmich](https://boards.straightdope.com/u/davidmich)\ **Post date:** [April 17, 2015, 7:34am UTC](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614/55 "2015-04-17T07:34:52Z")
The bottom line is “Water has the same chemical composition everywhere, but it can indeed have a different isotopic composition”. Thank you all for clarifying this. davidmich [Previous page](https://boards.straightdope.com/t/how-is-the-chemical-composition-of-water-on-other-planets-different-from-our-own/690614.md?page=2)