Similar to Kepler-10 b, as depicted above, the exoplanet HD 63433 d belongs to the category of small, rocky planets with a compact orbit around its star. Standing out for its youth, HD 63433 d holds the distinction of being the smallest confirmed exoplanet under 500 million years old. Notably, it also holds the title of the closest Earth-sized planet discovered at this youthful age, with an estimated age of around 400 million years.
In the HD 63433 planetary system, initially known for two planets, astronomers made a groundbreaking discovery – the presence of a new entity traversing the Sun-sized star. Upon investigation, this object unveiled itself as an additional planet, characterized by its compact size and scorching temperatures akin to Earth. Named HD 63433 d, this Earth-sized exoplanet orbits the star HD 63433 (TOI 1726).
Notably, HD 63433 d boasts the status of being the smallest confirmed exoplanet younger than 500 million years, and it holds the distinction of being the nearest Earth-sized planet identified at approximately 400 million years old. One unique aspect of this newfound celestial body is its tidal locking, where one side is perpetually illuminated by the star, while the other remains in constant darkness.
The revelation of HD 63433 d unfolded through a meticulous analysis by a team of astronomers, leveraging NASA’s TESS (Transiting Exoplanet Survey Satellite). Initially recognized as a system hosting two planets, the researchers delved into the TESS data, strategically filtering out signals from the known planets to uncover additional celestial phenomena. This led to the identification of a third, smaller planet exhibiting recurring transits every 4.2 days. HD 63433 d, characterized by tidal locking, is approximately 1.1 times the diameter of Earth and encircles a G-type star similar in size to our Sun. However, this newfound exoplanet orbits its star much more closely, completing a diminutive “year” in just 4.2 days and experiencing scorching temperatures on its illuminated side.
Facts about HD 63433 d:
Youthful Origin: HD 63433 d and its star are part of a planetary system that is about 10 times younger than our solar system. The exoplanet, at 400 million years old, is considered relatively youthful compared to Earth’s 4.5-billion-year age.
Proximity to Its Star: HD 63433 d orbits its star at a distance approximately 8 times closer than Mercury does to the Sun. The close proximity results in scorching temperatures, with the dayside reaching about 2,294 Fahrenheit (1,257 Celsius).
Potential Lava Hemisphere: Due to its small size, young age, and intense heat, researchers speculate that the dayside of HD 63433 d could resemble a “lava hemisphere,” lacking a substantial atmosphere.
Comparison to Other Worlds: The planet’s extreme temperatures are akin to other lava worlds like CoRoT-7 b and Kepler-10 b. Its unique characteristics make it an intriguing subject for further exploration and study.
The discovery, part of the “TESS Hunt for Young and Maturing Exoplanets (THYME) XI,” will be presented at the 2024 American Astronomical Society Meeting. The study is titled “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.”