Using NASA’s Transiting Exoplanet Survey Satellite (TESS), astronomers have spotted an Earth-sized planet transiting the young Sun-like star HD 63433.
HD 63433d sits close to its parent star, HD 63433, while two neighboring, mini-Neptune-sized planets, HD 63433b and HD 63433c, orbit farther out. Image credit: Alyssa Jankowski.
HD 63433 is a G5V-type star located approximately 73 light-years away in the constellation of Gemini.
Otherwise known as TOI-1726, the star is a member of the 414-million-year-old Ursa Major moving group of stars.
The newly-discovered exoplanet, HD 63433d, is the third planet detected in this multiplanet system.
The discovery of the other two planets — HD 63433b and HD 63433c, both mini Neptunes — was reported by astronomers in 2020.
HD 63433d is tidally locked, meaning there is a dayside which always faces its star and a side that is constantly in darkness.
The planet has an orbital period of 4.2 days and extremely high temperatures (1,257 degrees Celsius, or 2,294 degrees Fahrenheit) on its dayside.
“These scorching temperatures are comparable to lava worlds like CoRoT-7b and Kepler-10b, and we think that the planet’s dayside could be a ‘lava hemisphere’,” said University of Florida astronomer Benjamin Capistrant and his colleagues.
HD 63433d is the smallest confirmed exoplanet younger than 500 million years old.
It’s also the closest discovered Earth-sized exoplanet this young.
“HD 63433d is the closest planet to our Solar System with an Earth-like radius orbiting a young star,” the astronomers said.
“Therefore, this is an appealing target for follow-up observations, offering an opportunity to reveal insights into the physics of exoplanet atmospheric mass loss.”
“Between HD 63433d and the two previously known larger planets, the HD 63433 system is poised to play an important role in our understanding of planetary system evolution in the first billion years after formation.”
The discovery of HD 63433d is reported in a paper in the Astronomical Journal.
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Benjamin K. Capistrant et al. 2024. TESS Hunt for Young and Maturing Exoplanets (THYME). XI. An Earth-sized Planet Orbiting a Nearby, Solar-like Host in the 400 Myr Ursa Major Moving Group. AJ 167, 54; doi: 10.3847/1538-3881/ad1039