{"id":610565,"date":"2026-09-24T18:46:15","date_gmt":"2026-09-24T18:46:15","guid":{"rendered":"https:\/\/www.newsbeep.com\/nz\/610565\/"},"modified":"2026-09-24T18:46:15","modified_gmt":"2026-09-24T18:46:15","slug":"astronomers-found-a-planet-orbiting-backwards-around-a-red-dwarf-and-the-usual-culprit-is-missing","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/nz\/610565\/","title":{"rendered":"Astronomers Found a Planet Orbiting Backwards Around a Red Dwarf and the Usual Culprit Is Missing"},"content":{"rendered":"

\"-3\"<\/a>Up to now, it was expected that exoplanets would all orbit in the same plane and that they would move along their orbits in the same direction as the star\u2019s rotation as they do in the Solar System. Credit: ESO\/L. Cal\u00e7ada<\/p>\n

Planets usually keep the direction they were given at birth. A star forms from a collapsing cloud of gas, and the leftover material settles into a spinning disk. Planets grow in that disk and generally orbit in the same direction their star rotates.<\/p>\n

GJ 3090 b<\/a> has other ideas. The planet circles a small red dwarf approximately 72 light-years from Earth on a sharply tilted path, traveling opposite to its star\u2019s rotation. Astronomers have seen planets do this before. What makes this one puzzling is that they cannot find the massive companion that might have pushed it onto such an orbit.<\/p>\n

\u201cMeasuring the angle Psi (the small angle between their orbital planes and the star\u2019s equatorial plane) provides clues about the formation and evolution of planetary systems. It is therefore natural for us to try to measure it for other planetary systems,\u201d said Yann Carteret, a doctoral student in the Department of Astronomy at the University of Geneva\u2019s Faculty of Science and first author of the study. <\/p>\n

\u201cTo our great surprise, not only is the planet GJ 3090 b on a highly misaligned orbit, but it also orbits retrogradely, in the opposite direction to the rotation of its star.\u201d<\/p>\n

GJ 3090 b is a sub-Neptune<\/a> exoplanet, approximately 2.2 times Earth\u2019s radius and 4.5 times its mass. It completes a trip around its star every 2.85 days. The planet was already known since it regularly passes in front of the star from Earth\u2019s viewpoint, briefly dimming its light. Those crossings gave researchers a way to investigate its orbit.<\/p>\n

The international team observed six of the crossings using the Near-InfraRed Planet Searcher (NIRPS<\/a>), an infrared spectrograph installed on the European Southern Observatory\u2019s 3.6-meter telescope at the La Silla Observatory<\/a>on a telescope in Chile, along with observations from the European Space Agency\u2019s 3.6-meter telescope High Accuracy Radial velocity Planet Searcher (HARPS<\/a>).<\/p>\n

As the planet passed across the rotating star, it blocked light from different parts of its surface. By tracking slight changes in that light, the team determined how the planet\u2019s orbit is oriented relative to the star\u2019s spin.<\/p>\n

\"\"<\/a>Illustration of the exoplanet GJ 3090 b. Credit: NASA.<\/p>\n

The answer was an angle of about 136 degrees between the star\u2019s spin axis and the planet\u2019s orbital axis. An angle greater than 90 degrees means the planet is on a retrograde orbit: it travels against the direction of the star\u2019s rotation.<\/p>\n

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\u201cTo our great surprise,\u201d Carteret said, \u201cit also orbits retrogradely, in the opposite direction to the rotation of its star.\u201d<\/p>\n

According to the researchers, GJ 3090 b is the first planet found on a retrograde orbit around a red dwarf. Their findings were published in Astronomy & Astrophysics<\/a>.<\/p>\n

Where\u2019s the bully?<\/p>\n

Backwards planets aren\u2019t unheard of. But in the few cases known, there\u2019s usually a suspect: a heavy planet or companion star whose gravity, over millions of years, has tugged a neighbor\u2019s orbit out of line.<\/p>\n

Only five other multi-planet systems are known to host a planet tilted more than 70 degrees from its star\u2019s equator. In those cases, astronomers can point to a massive object nearby. At GJ 3090, they\u2019ve found no such thing.<\/p>\n

So the team is looking at other possibilities. One idea, suggested by co-author Vincent Bourrier, a senior lecturer and researcher at UNIGE, is that the problem started before the planets existed. The young star may have gathered up a second disk of material, one that was tilted and spinning backwards compared to the star itself. If the planets formed inside that rogue disk, they\u2019d have been born on backwards orbits, with no need for a later gravitational shove.<\/p>\n

It\u2019s a neat idea, but it\u2019s still a hypothesis. It also hints at something unsettling: our tidy picture of star-and-disk formation may be too simple, especially around small stars like GJ 3090.<\/p>\n

A gravitational shove from another large object can explain some severely tilted planetary orbits. GJ 3090 has at least one other confirmed planet, but the team found no evidence of a massive outer planet or companion star capable of explaining GJ 3090 b\u2019s path. Their observations narrow the possibilities considerably, although they cannot rule out every unseen object.<\/p>\n

\u201cThe absence of a massive companion to explain this unusual orbit will lead us to explore other hypotheses,\u201d Bourrier said.<\/p>\n

One possibility is that the star acquired fresh gas after its initial formation. If that gas arrived from a different direction, it could have formed a second disk spinning out of step with the star. Planets born in that disk would have inherited its unusual orientation.<\/p>\n

The second disk remains a proposed explanation, not something the researchers observed. The study establishes GJ 3090 b\u2019s unusual present-day orbit, while leaving the events that produced it open to further investigation. Measurements of the other planets\u2019 orbital orientations could help test whether they, too, formed from a misaligned disk.<\/p>\n

For now, this small planet poses an important question: Was its orbit overturned after it formed, or was the material that made it already moving the other way?<\/p>\n


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