HD 63433
Young Sun-like star with three transiting exoplanets.
HD 63433 (also designated TOI-1726 and V377 Geminorum) is a G-type main-sequence star located 73 light-years from Earth in the constellation Gemini. It is a young, Sun-like star, approximately 414 million years old, and hosts a system of three known exoplanets, including one Earth-sized planet and two mini-Neptunes. The star is notable as the third-brightest star with transiting exoplanets confirmed by the Transiting Exoplanet Survey Satellite (TESS) and is a key target for studying planetary system evolution in the first billion years.
- Type
- G-type main-sequence star (G5V)
- Distance
- 73 light-years
- Age
- 414 ± 23 million years
- Apparent magnitude
- 6.92
- Constellation
- Gemini
- Number of exoplanets
- 3
- Variable star designation
- V377 Geminorum
Lore & Background
The planetary system was discovered via the transit method using TESS. The first two planets, HD 63433 b and c, are mini-Neptunes announced in 2020. In 2024, a third planet, HD 63433 d, was identified after removing the transit signals of the known planets. HD 63433 d is Earth-sized, tidally locked, and has a dayside temperature estimated at 1,260 °C, likely covered in lava. The mini-Neptunes are thought to be composed mostly of silicate and water, with planet c losing its hydrogen atmosphere at a rate of 50 km/s.
Reader's Guide
The HD 63433 system is of high scientific importance because it offers a rare opportunity to study the early evolution of planetary systems. At roughly 400 million years old, it is only 9% as old as the Solar System, providing a snapshot of planetary development within the first billion years. The star's relative brightness (magnitude 6.9) and proximity (73 light-years) allow detailed atmospheric characterization of its planets using the Hubble and James Webb Space Telescopes. The system is particularly valuable for investigating atmospheric mass loss in young, close-in mini-Neptunes. HD 63433 d is the smallest known exoplanet less than 500 million years old, making it a unique laboratory for understanding the fate of hot, rocky worlds. The system's membership in the Ursa Major Moving Group also provides a well-constrained age, enhancing its utility as a benchmark for planetary evolution models.
Did You Know?
- HD 63433 is the third-brightest star with transiting exoplanets confirmed by TESS, after Pi Mensae and HR 858.
- The star is predicted to approach within 7.33 light-years of the Sun in 1.33 million years.
- The outermost planet, HD 63433 c, has an escaping hydrogen atmosphere forming a gas cocoon 12 times larger than the planet itself.
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