About HD 63433d:

• It is an Earth-like exoplanet that orbits a sun-like star called HD 63433 (also known as TOI 1726).
  • The star is about 73 light years away from the sun and is part of the group of stars moving together that make up the constellation Ursa Major.
  • The star HD 63433 shares similarities with our sun in size and type but is significantly younger, at roughly 400 million years old.
• It is the smallest confirmed exoplanet, younger than 500 million years old. 
• It’s also the closest Earth-sized planet discovered so far, and it’s about 400 million years old.
  • For comparison, Earth and the rest of our solar system are around 4.5 billion years old, meaning HD 63433 d appears to be just around 10% of the age of our planet.
• It’s the third planet found in orbit around its star. This planet is eight times closer to its star than Mercury is to the Sun.
• Because of its proximity to its star, which has 99% the mass of our sun, the planet is tidally locked, just like the moon is to Earth.
  • This means that one side of the planet, its dayside, constantly faces the star and is permanently blasted with stellar radiation, while the cooler nightside perpetually faces out into space.
  • This pushes surface temperatures on the planet’s dayside up around 2,300 degrees Fahrenheit (1,260 degrees Celsius).
• Its orbit is remarkably short, completing a full revolution around its star every 4.2 days.
• Being so hot, so close to its star, and so small, this planet likely lacks a substantial atmosphere.