The discovery of a colossal gas river in the Orion constellation has astronomers rethinking their understanding of planet formation. This river, stretching over 1 trillion miles long, has tipped the orbits of planets in the GW Orionis triple-star system, a rare find in itself. The system, located 1,300 light-years away, is a triple-star system with three pre-main sequence stars, meaning they are still in the process of forming and have not yet ignited fusion reactions. The stars are part of the Lambda Orionis star-forming molecular ring in the constellation of Orion, the Hunter. The planet-forming disk around GW Orionis is composed of three rings, with the outer ring being the most noticeably misaligned. Initially, an unseen gas giant planet was thought to be perturbing the outer ring, but new ALMA observations have revealed a different culprit: an enormous finger of gas reaching in from the surrounding molecular cloud. This gas river, mostly composed of molecular hydrogen, is believed to be how stars grow, delivering mass onto nascent suns. The streamer is astonishingly long, stretching 0.2 light years, or 12,600 astronomical units, and is composed of carbon monoxide molecules, which are invisible at radio wavelengths. The angle at which the streamer impacts the disk is closely aligned with the outer ring, and it is thought that the streamer has already done most of the work in tipping over the outer ring. The discovery of this gas river might explain why astronomers keep finding planets with orbits that are drastically misaligned with the rotational axes of their stars. In our solar system, all planets orbit around the sun in the ecliptic plane, but exoplanets can have highly inclined or even retrograde orbits. The GW Orionis streamer could be the force that creates these wonky planets. However, the team recognizes that this conclusion is based on just one discovery and plans to find more planet-forming disks influenced by similar streamers to confirm their theory. The findings were published in The Astronomical Journal, and the discovery raises a deeper question about the role of gas rivers in shaping planetary systems.
