TOI-1227 b is one of the youngest transitingexoplanets discovered (as of September 2022), alongsideK2-33b andHIP 67522 b. The exoplanet TOI-1227 b is5–12 million years old^[2][a] and currently 9.6 R_🜨 large. It will become a 3-5 R_🜨 planet in about 1 billion years, because the planet is still contracting. TOI-1227 b orbits its host star every 27.36 days.^[1]

TOI-1227 b has a size that is 85% that ofJupiter, or 9.6 times that of Earth. No other Jupiter-sized planet was detected around mid- to lateM-dwarfs, despite the deep transits such a planet would create. The researchers find that the planet is still hot from its formation and this heat, combined with a hydrogen-dominatedprimary atmosphere makes the atmosphere of TOI-1227 b inflated. Evolutionary models suggest that TOI-1227 b will eventually evolve into asub-Neptune within the next billion years.^[1]

Radial velocity follow-up to determine themass of TOI-1227 b is not possible in theoptical, but might be possible in thenear-infrared. A less challenging follow-up would be the measurement of the Spin-Orbit-Alignment via theRossiter–McLaughlin effect.^[1]

TOI-1227 was first identified as apre-main-sequence star (PMS star) with theGaia satellite.^[5][6][7] Without this prior identification as a PMS star the exoplanet signal of TOI-1227 b would have been disregarded as aneclipsing binary due to the V-shape of the transit signal.^[1]

The star is located north of the globular clusterNGC 4372, but it is much closer to earth than this cluster of stars, at a distance of about 101parsecs (330light-years).^[1] NGC 4372 is 5,800 parsecs (19,000 ly) away.^[8]

The host star TOI-1227 is part of a subgroup of theLower Centaurus Crux OB association, sometimes called B,^[7] A0^[5] and called Musca group by the scientists that discovered TOI-1227 b. This group was called Musca after the constellationMusca in which most of its members are located.^[1]

TOI-1227 has a spectral type of M4.5V to M5V, a mass 17% of theSun and a radius 56% of the Sun. The host star is relative faint for a TOI with avisual magnitude of about 17.^[1] The right ascension of12^h 27^m 4.31^s and the declination −72° 27′ 6.5″ implies that it is located in the Musca constellation.^[3][c] The host star showsLithium in its atmosphere, which should be depleted within 10-200 million years for M-dwarfs.^[1]

• TESS Objects of Interest
• Transiting exoplanets
• Exoplanets discovered in 2022
• Protoplanets

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