The planet, called TOI-561b, is approximately 50 per cent larger than Earth, and it orbits around its star astonishingly quickly: in just one of our days, it has seen two years.
Despite the planet having a mass nearly three times as much as the Earth, its density is approximately the same – a fact that surprised scientists when they discovered it.
“This is surprising because you’d expect the density to be higher,” UC Riverside planetary astrophysicist and team member Stephen Kane said. “This is consistent with the notion that the planet is extremely old.”
The older a planet is, the less dense it usually is. This is because heavy elements are usually produced by fusion reactions when a star forms, but as time goes on and the stars break down, these elements are disposed and sent off into the universe.
“TOI-561b is one of the oldest rocky planets yet discovered,” said University of Hawaii postdoctoral fellow and team lead Lauren Weiss. “Its existence shows that the universe has been forming rocky planets almost since its inception 14 billion years ago.”
As well as the planet being extremely old, it is also extremely hot. Its average surface temperature is over 2,000 degrees Kelvin or 1726.85 degrees Celcius.
That’s approximately one-third as hot as the surface of the Sun, which is 5,505 degrees Celcius.
TOI-561b is also what is referred to as a galactic thick disk, which have distinct chemical compositions that include less iron and magnesium – elements associated with planets forming – than other stars.
Astronomers are currently trying to understand the relationship between the planet’s mass and its radius, as it could help scientists understand the conditions of other planets that are currently too distant to be properly studied.
“Information about a planet’s interior gives us a sense of whether the surface of the planet is habitable by life as we know it,” Kane said.
Discovery of planet TOI-561b, and the observations about its composition, will be published in the Astronomical Journal.