This Week in Astronomy: New skepticism surrounds the potential biosignatures detected on exoplanet K2-18b, as revised analyses question the strength and interpretation of the chemical evidence. Meanwhile, theorists explore the idea that primordial black holes—stabilized by a “memory burden” effect—could be the true nature of dark matter, with future gravitational wave observatories poised to test this. Separately, new findings suggest that a massive ancient impact may have triggered the Moon’s now-lost magnetic field.