Hydrogen is the most abundant element in the cosmos. The reason is simple. Its nucleus was already made a second after the Big Bang, when the early Universe was filled with a hot soup of protons and neutrons. Composite nuclei like helium or heavier elements required synthesis of multiple protons and neutrons, a fusion process which took longer than the age of the Universe when the matter density and temperatures were suitable. During the first few minutes of cosmic history, only 8 helium nuclei were made per 100 free protons. About 400,000 years later, the Universe cooled below 3,000 degrees Kelvin and free electrons combined with these protons to make neutral hydrogen atoms. A billion years later, most of these hydrogen atoms were broken (ionized) back to their constituent electrons and protons by the ultraviolet radiation from the first generation of stars and galaxies. This process of re-ionization was pedagogically explained in my two textbooks “How Did the First Stars and Galaxies Form?” and “The First Galaxies in the Universe”.
The abundant cosmic hydrogen from the early Universe was contained in the gas cloud that made the Sun and the planets around it. Indeed, three quarters of the mass of the Sun is hydrogen, as discovered by Cecilia Payne-Gopaschkin in the course of the first PhD thesis in Astronomy at Radcliffe-Harvard in 1925. Since hydrogen is lightweight, it easily escapes from the Earth’s atmosphere. Particles in the high-speed tail of the thermal distribution exceeded the escape speed from Earth’s gravity and rapidly depleted hydrogen on Earth, except for the hydrogen trapped in molecular bonds to heavier elements, such as oxygen in water (H2O), carbon in methane (CH4), or nitrogen in ammonia (NH3).
Some molecular hydrogen, H2, is currently being produced out of molecular deposits by subsurface geological processes on Earth. A new paper, just published in the journal Science Advances by Geoffrey Ellis and Sarah Gelman from the U.S. Geological Survey, argues for a large uncertainty in the mass of the natural hydrogen reservoir on Earth, ranging between a billion to ten quadrillion tons, with the most likely value being about 5.6 trillion tons.
Geologic hydrogen could be a primary energy resource with a low carbon footprint for fueling our future economy. Therefore, the actual magnitude of Earth’s subsurface reservoir could be of great financial value. The new paper combines knowledge on the occurrence and behavior of natural hydrogen on Earth with geochemical information to construct a model that predicts the available mass of the hydrogen fuel reservoir. The authors conclude that even just two percent of the most likely reservoir mass would have major economic implications.
For example, a hundred billion tons would supply the hydrogen needed to reach net-zero carbon emissions for two centuries. This amount of hydrogen fuel carries nearly twice the total energy contained in natural gas reserves on Earth — which is 8 sextillion Joules. This much energy can supply the global energy consumption of humans today for about two decades. Gladly, there is much more energy available from nuclear, solar and wind sources.
Mining geologic hydrogen resources could be profitable to a nation which identifies an abundant reservoir within its territory. So far, geologic hydrogen has been discovered only in a few places, including Albania, France and Mali. Extracting geologic hydrogen is a low-carbon process, but Mali is currently the only country where this is being done. Mining hydrogen at scale requires a major global initiative that could take a long time, since hydrogen deposits were so far ignored by the oil and gas industry.
Finding large reservoirs of geologic hydrogen could disrupt geopolitics. Currently, there is modest investment of nations billions of dollars in making hydrogen by breaking water molecules. This limited production of hydrogen fuel is used as a substitute for fossil fuels in steelmaking, fertilizer production or heavy transportation. Extracting hydrogen from naturally occurring subsurface deposits could be cheaper for sufficiently large reservoirs.
Because of its escape from the early Earth, the most abundant element in the cosmos is an expensive fuel for humanity. However, spacecraft that leave the solar system and venture into interstellar space can harvest the abundant cosmic hydrogen there. Fueling of spacecraft may be particularly easy in giant molecular clouds, each of which is known to contain about a million solar masses of molecular hydrogen, enough to fuel our current economy for a million times longer than the age of the Universe.
To fuel its grandest ambitions, humanity should aspire to become an interstellar species. Finding the technological products of another interstellar civilization could inspire us to do so. This is what I argued last night in an uplifting meeting with a Book Club in Maine, whose members read my books “Extraterrestrial” and “Interstellar” cover-to-cover. The event organizer, Eric Dinnerstein, kindly remarked: “When we find the evidence of superior intelligence, you will be the one remembered who made it happen.” Independently, I was humbled to receive an email from a European who watched a preview of the Netflix documentary about my research and wrote: “Thank you for daring to be the pioneer and trailblazer in your field, so that generations upon generations can benefit from your work long after you have left this earth (hopefully not any time soon though).” Hydrogen offers the best rocket fuel in terms of energy released per mass taken for the ride. Personally, I would love to leave this Earth on a hydrogen-fueled rocket.
Earlier in the day, I explained on Sky News and ABC News that the mysterious New-Jersey drones are likely terrestrial in origin. It takes much more fuel to cross interstellar distances than to reach New-Jersey. This is simple rocket science. And in addition to refueling opportunities, the travel to a giant molecular-hydrogen cloud offers far more exciting views than New-Jersey, like the Pillars of Creation in the Eagle Nebula — 6,500 light-years away from Earth.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
