Astronomers have discovered a new Earth-sized exoplanet that is not only the closest of its kind to our solar system, but also the youngest. The planet, named HD 63433 d, orbits a Sun-like star in a system that is only 400 million years old, about 10 times younger than our own.
A Lava Hemisphere
HD 63433 d is a scorching world that is tidally locked to its star, meaning it has a permanent day side and a permanent night side. The day side of the planet can reach temperatures of about 2,294 Fahrenheit (1,257 Celsius), hot enough to melt rock and create a lava hemisphere. The night side, on the other hand, is likely much cooler and darker.
The planet is also very close to its star, completing one orbit in just 4.2 days. It is eight times closer to its star than Mercury is to the Sun. Because of this proximity, the planet probably has a very thin or nonexistent atmosphere, making it unlikely to host life as we know it.
A Young Star System
HD 63433 d was detected by NASA’s Transiting Exoplanet Survey Satellite (TESS), which observes stars for periodic dips in brightness caused by planets passing in front of them. The planet’s host star, HD 63433 (also known as TOI 1726), is a G-type star that is slightly smaller and less massive than the Sun. It is located about 200 light-years away from Earth in the constellation of Aquarius.
The star system also contains two other known planets, HD 63433 b and c, which are both larger than Earth and orbit closer to the star than HD 63433 d. The system is estimated to be about 400 million years old, based on its low level of magnetic activity and fast rotation. For comparison, our solar system is about 4.5 billion years old.
A Significant Discovery
HD 63433 d is the smallest confirmed exoplanet younger than 500 million years old, and the closest discovered Earth-sized planet this young. It is also one of the few Earth-sized planets found around Sun-like stars by TESS, which mostly detects larger planets around smaller stars.
The discovery of HD 63433 d is significant for several reasons. First, it provides a rare opportunity to study a young rocky planet and how it evolves over time. Second, it helps us understand how common or rare Earth-sized planets are around Sun-like stars in our galaxy. Third, it demonstrates the power and potential of TESS to find new worlds beyond our solar system.