Inflated hot Neptune TOI-2195 A b likely formed from a massive gas giant

Star system: TOI-2195 A | Distance from the Sun: 572 light years

A newly identified planet, TOI-2195 A b, has been found orbiting an orange dwarf star. Classified as an inflated hot Neptune, this planet completes an orbit around its host star every 4.16 days. The discovery offers a new perspective on how such planets form, suggesting they may have once been much larger gas giants that lost a significant portion of their mass.

Researchers analyzed the system using the Rossiter-McLaughlin effect, which measures the change in light as a planet transits a rotating star. This technique revealed that the planet follows a near-polar orbit, meaning it circles the star over its poles rather than its equator. The planet's large size compared to its mass, referred to as inflation, is attributed to tidal heating generated by its proximity to the host star.

The findings suggest the planet began as a distant, cold Jovian-sized gas giant. Through gravitational interactions with a companion star—a process called the Eccentric Kozai-Lidov mechanism—the planet was pushed into a highly elliptical, or elongated, orbit. As it swung close to its host, it lost up to 90 percent of its mass through a process where the star's gravity stripped away the planet's outer layers. This mass loss allowed the planet to migrate into a tight, circular orbit.

Key findings
- TOI-2195 A b is a hot Neptune with a 4.16-day orbital period.
- The planet exhibits a near-polar orbital path relative to its host star.
- High-eccentricity migration and mass loss are the likely origins of this inflated planet.
- Tidal heating from the host star contributes to the observed expansion of the planet's radius.

Scientific study

Discovery of an Inflated Hot Neptune and Its Formation from Jovian Mass Loss (external link)