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Astronomers have long been fascinated by the unusual behavior of objects orbiting the Sun in the Kuiper Belt, a scattered disc of minor planets beyond the orbit of Neptune.<\/p>\n
Many of these frozen objects appear to be affected by the gravitational influence of much more massive ones, with some astronomers controversially<\/a> arguing that the region could be home to a hidden ninth major planet<\/a> in the solar system.<\/p>\n However, the region\u2019s extreme distance from the Sun makes it incredibly difficult to study, shrouding the nature of \u201ctrans-Neptunian objects\u201d (TNOs) in enduring mystery.<\/p>\n Now, a team of astronomers in Japan says it\u2019s spotted only the second TNO to have an atmosphere after the dwarf planet<\/a> Pluto, the largest known TNO by volume. As detailed in a paper<\/a> published in the journal Nature Astronomy this week, the researchers say they\u2019ve identified a minor planet only about 311 miles across \u2014 roughly a fifth of Pluto\u2019s diameter \u2014 that\u2019s wrapped in an extremely thin envelope of gases.<\/p>\n If confirmed, the research could force us to reconsider how atmospheres can form around small objects, and what other mysterious neighbors we might expect to find in the Kuiper Belt.<\/p>\n The team of astronomers, led by National Astronomical Observatory of Japan associate professor and senior lecturer Ko Arimatsu, observed the TNO, dubbed 2002 XV93, as it passed in front of a bright star \u2014 rare events known as stellar occultations \u2014 in January 2024.<\/p>\n As its name suggests, the object was first discovered in 2002, and is located several billion miles away from Earth. But thanks to its diminutive size, typical for the Kuiper Belt, researchers expected it to closely resemble other similarly-sized TNOs.<\/p>\n However, as it passed in front of the distant background star, Arimatsu and his colleagues saw the starlight gradually fade away, suggesting the presence of an atmosphere since if it didn\u2019t have one, the light would be cut off far more abruptly. <\/p>\n \u201cThe observation data showed a smooth change of the star\u2019s brightness near the edge of the shadow, lasting about 1.5 seconds,\u201d he told CNN<\/a>. \u201cThis kind of smooth brightness change is naturally explained if the starlight was bent by a very thin atmosphere around the object.\u201d<\/p>\n It\u2019s certainly not nearly as thick as the Earth\u2019s atmosphere, and is anywhere from five million to ten million times thinner.<\/p>\n In their paper, the researchers suggest that \u201ccryovolcanic activity\u201d \u2014 the eruption of water, ammonia or methane instead of molten rock on the surface of icy moons or dwarf planets \u2014 or the \u201crecent impact of a small icy object\u201d could help explain the thin atmosphere around 2002 XV93.<\/p>\n In case of the latter, Arimatsu said the atmosphere could dissipate within hundreds of years. In case of the former, such a thin atmosphere could stick around for much longer.<\/p>\n The researchers are now excited to have another chance to observe the intriguing TNO using NASA\u2019s James Webb Space Telescope, which could reveal the presence of other gases, including methane or carbon monoxide.<\/p>\n \u201cThat is why future monitoring is so important,\u201d Arimatsu told NBC News<\/a>. \u201cIf the atmosphere fades over the next several years, that would support an impact origin. If it persists, or varies seasonally, that would point more toward ongoing internal gas supply\u201d from cryovolcanic activity.<\/p>\n