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Using NASA's Transiting Exoplanet Survey Satellite (TESS), astronomers have discovered two new exoplanets around a young sun-like star known as TOI-6109. The newfound alien worlds are slightly larger than Neptune and orbit their host in less than 10 days. The finding was presented in a paper September 18 on the arXiv pre-print server.

TESS is continuing its survey of about 200,000 of the brightest stars nearby, looking for transiting exoplanets. To date, it has identified about 7,700 candidate exoplanets (TESS Objects of Interest, or TOI), of which 693 have been confirmed so far—ranging from small rocky worlds to gaseous giants.

TOI-6109, also known as TIC 384984325, is one of the stars that was observed with TESS. It is a young sun-like star of spectral type G3 located some 484 light years away in the Alpha Persei cluster. TESS observations have identified transit signals in the light curve of this star and follow-up observations conducted by a team of astronomers led by Anne Dattilo of the Pennsylvania State University have confirmed the planetary nature of these signals.

"We report the discovery of a planetary system around TOI-6109, a young, 75 Myr-old sun-like star in the Alpha Persei cluster," the researchers write.

The planet closer to the host star, which received designation TOI-6109 b, has a radius of about 4.87 Earth radii. It orbits the star every 5.69 days, at a distance of approximately 0.06 AU.

The second newly found alien world around TOI-6109, designated TOI-6109 c, is comparable in size to TOI-6109 b as its radius was measured to be 4.83 Earth radii. The planet has an orbital period of 8.54 days, and is located at a distance of some 0.078 AU from the host.

The astronomers underline that TOI-6109 b and TOI-6109 c orbit just outside a 3:2 mean motion resonance. They add that this near-resonant configuration enables the determination of the mass of these planets via transit timing variations (TTV) measurements and to bypass difficult radial velocity measurements.

When it comes to the properties of the host star TOI-6109, it is similar in size and mass to the sun. The star has an effective temperature of 5,660 K and a luminosity of around 0.88 solar luminosities.

Summing up the results, the authors of the paper recommend further investigation of TOI-6109 due to its unique properties.

"The system's youth and near-resonant state make it a prime candidate for further investigation. Continued transit monitoring of TOI-6109 will refine the TTV-derived masses and enable detailed studies of its dynamical interactions. These efforts will contribute to our broader understanding of how planets form, migrate, and settle into their final configurations," the scientists conclude.