Free Astronomy Magazine November-December 2025

NOVEMBER-DECEMBER 2025 M any telescopes contribute to the search for and study of exo- planets, including some in space (artists concepts shown here) and on the ground. Doing the work are or- ganizations around the world, includ- ing ESA (European Space Agency), CSA (Canadian Space Agency), and NSF (National Science Foundation). [NASA/JPL-Caltech] searching for life in the universe. “This milestone represents decades of cosmic exploration driven by NASA space telescopes — explo- ration that has completely changed the way humanity views the night sky,” said Shawn Domagal-Gold- man, acting director, Astrophysics Division, NASA Headquarters in Washington. “Step by step, from discovery to characterization, NASA missions have built the foundation to answering a fundamental ques- tion: Are we alone? With the Nancy Grace Roman Space Telescope and the Habitable Worlds Observatory, America will lead the next giant leap — studying worlds like our own around stars like our Sun. This is American ingenuity, and a prom- ise of discovery that unites us all.” The milestone comes 30 years after the first exoplanet was discovered around a star similar to our Sun, in 1995. (Prior to that, a few planets had been identified around stars that had burned all their fuel and collapsed.) Although researchers think there are billions of planets in the Milky Way galaxy, finding them remains a challenge. In addition to discovering many individual planets with fascinating characteristics as the total number of known exo- planets climbs, scientists are able to see how the general planet popula- tion compares to the planets of our own solar system. For example, while our solar system hosts an equal number of rocky and giant planets, rocky planets appear to be more common in the universe. Re- searchers have also found a range of planets entirely different from those in our solar system. There are Jupiter-size planets that orbit closer to their parent star than Mercury or- bits the Sun; planets that orbit two stars, no stars, and dead stars; plan- ets covered in lava; some with the density of Styrofoam; and others with clouds made of gemstones. “Each of the different types of plan- ets we discover gives us information about the conditions under which planets can form and, ultimately, how common planets like Earth might be, and where we should be looking for them,” said Dawn Gelino, head of NASA’s Exoplanet Exploration Program (ExEP), located at the agency’s Jet Propulsion Labo- ratory in Southern California. “If we want to find out if we’re alone in the universe, all of this knowledge is essential.” Fewer than 100 exo- planets have been directly imaged, because most planets are so faint they get lost in the light from their parent star. The other four methods of planet detection are indirect. With the transit method, for in- stance, astronomers look for a star to dim for a short period as an or- biting planet passes in front of it. To account for the possibility that something other than an exoplanet is responsible for a particular signal, most exoplanet candidates must be