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September 19, 2025—Deep-sea desalination could solve the world's water problems. Plus, the number of exoplanets discovered passes 6,000 and a new AI tool can predict what disease you might get. —Andrea Gawrylewski, Chief Newsletter Editor | | Artist's concept shows exoplanets range in size and composition, although scientists have not seen most of them directly. NASA's Goddard Space Flight Center | | Plans are underway for the world's first large-scale deep-sea desalination plant off the coast of Norway. The high pressure of the ocean depths will force seawater through filters. On land, it's extremely costly to pressurize water through reverse osmosis. One company developing the technology says it uses 40 to 50 percent less energy than conventional desalination plants—and it can be built with modular systems that can be deployed to many deep-sea locations without bespoke engineering. How it works: Reverse osmosis pods are submerged to depths of around 500 meters (1,600 feet), where immense hydrostatic pressure does the hard work of separating water from salt. Purified water is then pumped back to shore. Operating on the seafloor has other benefits, too. This region harbors fewer bacteria and other microorganisms compared with shallower water, and there is little local variation in temperature or pressure. Multiple prototypes of such systems are already at work. The challenges: Though it may be more efficient than surface desalinators, deep-sea plants are still more expensive than surface ones–the filtered water needs to be pumped back up to the surface. Most seaside cities and towns are surrounded by continental shelves where the water is not deep enough for the process, so the plants must be placed near communities adjacent to continental drop-offs. What the experts say: Subsea desalination could go mainstream and supply water to entire cities, says Nidal Hilal, founding director of New York University's Water Research Center in Abu Dhabi. But "reaching true city scale will take time, conceivably a decade or more." | | NASA announced that the current tally of exoplanets observed outside our solar system is 6,007. The first exoplanets were found mostly by the gravitational pull they exert on their host stars: that pull causes a star to wobble, and this movement can be detected visibly or (far more often) via a change in the wavelength of stellar light. With the Kepler mission's launch in 2009, more and more exoplanets were discovered via the so-called transit method: a regular flicker in a star's light that occurs when its planet happens to pass between it and a watching telescope. Methods of discovering exoplanets have grown since then. Experts predict that the exoplanet tally will surpass 10,000 in a few years. | | Amanda Montañez; Source: NASA Exoplanet Archive (data) | | | | |
- If you read Scientific American this week you should ace today's science quiz! And be sure to check out today's Spellements puzzle, and send any words missing from the puzzle to games@sciam.com. This week reader Ryszard C. spotted the word halothane, which is a strong inhaled anesthetic. Good eye!
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| | Planets that rain iron.
Planets whose surface is entirely ocean. Planets with one side always in darkness. The Milky Way is awash with a diversity of planetary bodies that surpasses science fiction. In cataloguing these fantastical worlds, astronomers hope they might encounter life out there in the galaxy, yes. But the study of this vast array of exoplanets promises to revolutionize our basic understanding of how the cosmos formed. And perhaps refresh our gratitude that conditions here on Earth were just right for human life to arise. | | Thanks for reading Today in Science this week. Send your ideas and suggestions to: newsletters@sciam.com. Have a lovely weekend. —Andrea Gawrylewski, Chief Newsletter Editor
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