Can we harvest H & O from space to make water? (Intermediate)

I read that mountain ranges were most likely formed by continents crashing into each other. I am wondering if elements on the periodical table formed in a similar way, i.e. by crashing together at tremendous speeds long ago. Of the elements we know, do we know, or hypothesize, about how their original bonds were set?

Can humans make water by combining H and O? If not, why not? If yes, why are we so worried about water shortages? Couldn't, in theory, water be harvested from space? Are people working on that prospect?

I am just a mom, trying to answer some of my son's questions. He is in middle school. We live in Korea, so it is tough to find appropriate materials in English for his level.

There are a few reasons why we cannot make water by harvesting hydrogen and oxygen from space. First, you CAN make water by combining H and O, but the reaction is really slow at "normal" temperatures. You need some sort of catalyst (like lighting the H and O with a match) to get things going. Thus you could only get the water at the price of some energy. A second problem is that when the reaction does get sparked, it creates a HUGE blast. (Have you heard of the Hindenburg zeppelin that exploded in 1937 in New Jersey? These explosions can be very dangerous!) Assuming that we found a way to get around all of these issues, we would still have trouble bringing the hydrogen and oxygen to Earth from space. The amounts we would require would be very heavy and thus the fuel required for such missions would be quite costly. Not to mention the safety issues of transporting a flammable gas!

As for the other part of your question, not all the elements on the periodic table were formed the same way. Hydrogen, helium, and trace amounts of lithium (the three lightest elements) were formed during the Big Bang at the creation of the universe.

So where do all the other elements come from? There is a popular quote by astronomer Carl Sagan: "We are all made of star stuff." Any of the elements heavier than lithium were produced through nuclear reactions in the cores of stars. For instance, after our Sun is finished burning through all of the hydrogen in its core (something that won't happen for another 5 billion years or so), it will begin to burn helium to form carbon by way of something called the triple alpha process. The sun is a relatively low-mass star, so the burning process ends there, but in more massive stars, oxygen can then be formed by fusing carbon and helium. The more massive a star, the heavier elements it can create. Stars cannot form elements heavier than iron, however, because such reactions require energy rather than create it. The whole reason for undergoing nuclear fusion is to create energy to help the star support itself against gravitational collapse.

The heaviest elements (i.e. heavier than iron) are formed when particles are thrown together at high speeds during a supernova explosion. (See our page on supernovae for more details on these spectacular events.)

Page last updated on June 22, 2015.

About the Author

Sabrina Stierwalt

Sabrina Stierwalt

Sabrina was a graduate student at Cornell until 2009 when she moved to Los Angeles to become a researcher at Caltech. She now studies galaxy mergers at the University of Virginia and the National Radio Astronomy Observatory in Charlottesville. You can also find her answering science questions in her weekly podcast as Everyday Einstein.

 Twitter: @galaxygirlguru

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