Discovery of an Earth-Sized Planet with a "Lava Hemisphere" and a "Year" of Only 4.2 Days

A newly discovered Earth-sized exoplanet, HD 63433 d, has been found in the HD 63433 planetary system, with discovery credited to data from NASA’s TESS. This unique planet is less than 500 million years old and is the closest and youngest Earth-sized exoplanet to be discovered. The planet orbits extremely close to a star similar to our Sun, resulting in extreme temperatures and providing intriguing concepts for further research. Credit: SciTechDaily.com

The astronomers utilized TESS to discover the newly formed exoplanet HD 63433 d. This Earth-sized planet is remarkably young and orbits close to a Sun-like star which results in extremely high temperatures and unique opportunities for research.

In a system that originally contained two known planets, the astronomers identified a new entity, a small object traversing across the Sun-sized star, this object was confirmed to be a new planet, which happens to be extremely hot and the size of Earth.

This recently identified planet, HD 63433 d, is tidally locked, meaning there is one side in perpetual daylight and another in constant darkness. The exoplanet orbits the star HD 63433 (TOI 1726) situated in the HD 63433 planetary system. This extremely hot planet holds the title of the smallest confirmed exoplanet that is younger than 500 million years and is also the closest Earth-sized planet of this age, being approximately 400 million years old.

This exoplanet HD 63433 d, is comparable to Kepler-10 b, as both are small, rocky planets in close orbit with their respective stars. The planet is also the closest and smallest confirmed exoplanet under 500 million years old and orbits approximately 400 million years from Earth. Credit: NASA/Ames/JPL-Caltech/T. Pyle

The astronomers studying the system utilized data from NASA’s TESS, capable of identifying “transits,” instances where planets pass in front of their stars during orbit thereby blocking a small portion of starlight. There were two already known planets in this system, but after removing their signals, the team was able to discover an additional transit reoccurring every 4.2 days. This was further investigated and validated as an entirely new, smaller planet.

This tidally locked planet is very similar in size to Earth, around 1.1 times the diameter of our planet. Besides, it orbits around a star approximately 91% the size and 99% the mass of our Sun.

The star in this system is a G-type star, identical to our Sun. Compared to our orbit, HD 63433 d orbits closer to its star, with a year that lasts only 4.2 days and faces extremely high temperatures.

Despite the similarities of our own planet and Sun to HD 63433 d and its star, HD 63433 d exhibits prominent differences from Earth.

This planet is extremely young within a young celestial system, which is about 10 times younger than our planetary system. The age of this planet is considerably less than ours, with the former being 400 million years old and the latter 4.5 billion years old.

Furthermore, its proximity to its star is much closer than Earth’s proximity to the Sun, with it being 8 times closer to its star than Mercury is to our Sun. This close proximity results in the perpetual side of the tidally-locked planet facing temperatures reaching 2,294 Fahrenheit (1,257 Celsius). Due to the extreme temperatures, small size, and being close to its star, the planet probably lacks a considerable atmosphere.

These extreme temperatures are comparable to the lava worlds like CoRoT-7 b and Kepler-10 b, and the team who made the discovery believes that the planet’s dayside could resemble a “lava hemisphere.”

Due to its small size, youthful age, and proximity to its star, this planet is a prime candidate for more exploration. A follow-up study could verify the outcomes of this study and possibly reveal more details regarding the planet’s “dark side,” and the potential existence of an atmosphere. This study points out the importance of Young terrestrial worlds for testing existing theories of planetary formation and evolution.

The Discovery Team

This discovery is outlined in a new study published in the Astronomical Journal, 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." The study was led by Benjamin Capistrant and Melinda Soares-Furtado, and was also discussed at the 2024 American Astronomical Society Meeting.

Further details on this study can be found under the title "Earth-Sized Planet Discovered in “Our Solar Backyard.”