An exoplanet discovered just 73 light-years away offers a glimpse of what baby Earth might look like if it were locked in a very tight orbit with its star. Earth has been named HD 63433 d, a newborn exoplanet only slightly larger than Earth that orbits a Sun-like star. This is the smallest planet we have found and is less than 500 million years old; It’s a rare window into the formation of planets that are similar to our Earth but not exactly like it.

Earth is the only world we know of that has life. Studying the different ways Earth-like planets form and evolve, especially around Sun-like stars, helps scientists understand the ingredients that allow life to emerge elsewhere in the universe.

HD 63433 d is both very Earth-like and very dis-Earth-like, which means it presents a huge opportunity. And it is different from Earth in many fascinating ways.

“This is a useful planet because it could be similar to early Earth,” said University of Wisconsin-Madison astrophysicist Melinda Soares-Furtado, who led the research with astronomer Benjamin Capistrant of the University of Florida.

“Although in a very close orbit, we can use further data to look for evidence of outgassing and atmospheric losses, which could be important constraints on the evolution of terrestrial worlds. But that’s where the similarities end, and they end dramatically.”

The Earth-sized world was discovered during a survey by exoplanet-hunting telescope TESS, which tracks stars for faint, steady dips in starlight that indicate the presence of an orbiting exoplanet. By measuring various effects of an exoplanet on starlight, astronomers can determine its size and mass.

HD 63433 is a yellow dwarf with a similar temperature profile and approximately the same size and mass as the Sun. But it is much, much younger, just over 400 million years old, compared to the Sun’s 4.5 billion years. HD 63433 is just a baby in star terms; and exoplanets orbiting it. Three exoplanets have been discovered so far: two mini-Neptunes and HD 63433 d, detected in 2020.

Transit data (these dips in starlight as it rotates) show that HD 63433 d’s radius is 1.1 times that of Earth. We don’t know its mass yet, but this physical size clearly points to a terrestrial structure, a rocky world like Earth, Mars or Venus.

The exoplanet orbits its star in an extremely tight orbit every 4.2 days. This means that it and its star are extremely close to each other; It’s so close that HD 63433 d is probably tidally locked, with one side always facing the star. Because this hemisphere always receives the full brunt of heat from the star, its surface is likely a permanent sea of ​​molten rock, with a daytime temperature of 1,570 Kelvin (1,297 Celsius, or 2,366 Fahrenheit), scientists say.

It’s basically a giant ocean of lava.

Earth has, of course, never been this close to the Sun, but it may have reached temperatures of up to 2,300 Kelvin after the impact that ripped apart much of the planet to form the Moon.

We still don’t know much about the HD 63433 d; The team hopes that further research will tell us a little more about it, including its mass; This will allow scientists to calculate its density, which can tell us why the exoplanet formed. We can even determine whether it has an atmosphere and what it contains.

“This is our sunny garden and it’s very exciting,” says Soares-Furtado. “What information can a star so close with such a crowded system around it provide? How will this help us as we search for planets among perhaps 100 similar stars in this young group of which it is a part? ?”