Marshmallow Gas Giant Found at Red Dwarf Star

An exoplanet found orbiting a red dwarf star turns out to have the density of a marshmallow, surprising researchers who didn’t expect a planet with an atmosphere that close to an active star.

IMAGE: A gas giant exoplanet [right] with the density of a marshmallow has been detected in orbit around a cool red dwarf star [left] by the NASA-funded NEID radial-velocity instrument on the 3.5-meter WIYN Telescope at Kitt Peak National Observatory, a Program of NSF’s NOIRLab. The planet, named TOI-3757 b, is the fluffiest gas giant planet ever discovered around this type of star. CREDIT: NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani

Astronomers at Kitt Peak have discovered a Jupiter-ish planet orbiting a red dwarf. Now, you know we only bring you exoplanet stories when there is something unusual, and as always, this release is no exception. This planet, TOI-3757 b, has the density of a marshmallow, making this the lowest-density planet ever detected, coming in at a mere 0.27 grams per cubic centimeter. That’s less than half the density of our own planet Saturn.

This strange exoplanet was found in data taken by NASA’s TESS spacecraft, which uses the transition method of detection — measuring the change of the star’s light as the planet passes between the star and the spacecraft. From those measurements, researchers calculated the gas giant has a diameter of 150,000 kilometers. For reference, Jupiter is slightly smaller.

As a follow-up to the space observations, the research team took measurements with two different instruments — NEID and NESSI — at the WIYN 3.5-meter Telescope, as well as with the Habitable-zone Planet Finder (HPF)…