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August 28, 2025—Adult humans can grow new neurons, why scientists remain hopeful in the search for alien life, and succulents that glow. —Andrea Gawrylewski, Chief Newsletter Editor | | Researchers gave these succulents in the Echevaria genus a glow-up by injecting them with luminescent particles. Liu et al./Matter | | A consensus is growing among neuroscientists that the brains of adult humans can create brand-new nerve cells, or neurons, at least in some regions and under some circumstances. This neurogenesis has been revealed primarily in the hippocampus, which plays a role in memory and learning. Researchers also are figuring out how to repair damage to neurons and to peripheral nerves, those that connect the brain to the rest of the body. In some cases surgeons can reroute a branch of a nearby nerve to do the work of a damaged one, restoring function to the muscle or other tissue it controls. The backstory: For centuries, physicians thought that humans could not regenerate neurons and that nerve damage was irreversible. But in the first half of the 20th century, doctors successfully grafted pieces of nerves into gaps in wounded soldiers' broken nerves. Over time, doctors found it was easier to restore function in tissue closer to a damaged nerve than tissue farther away. In the early 1980s, neuroscientists demonstrated that grafting segments of peripheral nerves could enable the regrowth of neurons of the spinal cord and brain stem, opening the door to neurogenesis and repairing damage to the central nervous system. Why this matters: Scientists now are trying to figure out how to control the processes surrounding neurogenesis in humans. Such insights could lead to treatments for Alzheimer's disease, other neurodegenerative conditions, and possibly even for PTSD and other psychiatric conditions. —Robin Lloyd, contributing editor | | Astronomers now know that most, if not all, stars harbor planets, and that microbial life can live in "profoundly inhospitable conditions," writes journalist Sarah Scoles. And the latest sky surveys are clarifying the proportion of habitable planets among all those exoplanets. Add it up like astronomer Frank Drake did in 1961: Scientists remain hopeful that life exists beyond Earth, despite failure, thus far, to find it. The backstory: In the early 20th century, American astronomer Percival Lowell interpreted observed markings on Mars as water infrastructure made by a local civilization of beings. His alien life ideas came during an era of optimism about the possibility of life on Mars. In 1965, Mariner 4 spacecraft images of Mars's dry, desolate surface diminished some of that hope for the Red Planet. Fortunately, findings in the past three decades are narrowing down two of the once highly uncertain variables in the Drake equation, the astronomer's famous probabilistic formula meant to direct discussions about detecting radio communication from extraterrestrial intelligent beings. Why this is interesting: After all this back and forth, it's now clear that science will have an easier time finding potential microbial life beyond Earth than any intelligent aliens. But we might discover that primitive life relatively close to home, in icy oceans on Jupiter's moon Europa, in geysers at Saturn's moon Enceladus or even in ponds of Martian meltwater under the planet's ice caps. —Robin Lloyd, contributing editor
The Top Stories today are part of our 180th anniversary package, which is all about reversals in scientific thinking (180-degree turns. Get it?). Check out the rest of them here. This week, our Science Quickly podcast explores some of the wildest U-turns in science. Listen here. | | | | |
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- It's been 20 years since Hurricane Katrina flooded New Orleans and killed more than 1,400 people. In the decades since, officials have been working to reinforce the city, which well-withstood Hurricanes Isaac in 2012 and Ida in 2021. But New Orleans is still sinking, and the surrounding protective wetlands need to be restored, writes senior editor Mark Fischetti. In July, Louisiana canceled funding for the largest restoration project, confounding and disappointing local experts. "Twenty years after disaster, perhaps the harsh lessons of Katrina are fading and politics are resurging," Fischetti says. "As this year's hurricane season plays out, Louisiana must remember the power of water." | 7 min read
| | Astronautical engineer Loren Chang, a scientist at the Center for Astronautical Physics and Engineering at the National Central University in Taoyuan City, Taiwan, designs satellites and other scientific machinery to explore the environment of space. "We can communicate with spacecraft in Earth's orbit only when they are in our direct field of view; the rest of the time, the Earth blocks the signal," he says. "We have only two windows a day for direct communication, and each is typically less than ten minutes." That means the team must build space systems that can work autonomously the rest of the time. Nature | 3 min read | | As Sarah Scoles writes, the only constant in the centuries-long search for extraterrestrial life is hope. That life is out there is almost certain, given the sheer size of the universe, but, as Christopher K. Walker, an astronomer at the University of Arizona, wrote earlier this year, scientists must manage their expectations of what is possible to be found given, again, the sheer size of the universe. If we ever do encounter intelligent beings, we must "prepare for a long and lonely voyage through space and time before meeting them, either virtually or physically," he says. | | I'm glad we've found each other in this neck of the universe. Let me know how I'm doing with this newsletter: newsletters@sciam.com. And I'll see you tomorrow. —Andrea Gawrylewski, Chief Newsletter Editor
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