A group of astronomers discovered a giant planet near the star LTT 9779. The newly discovered celestial body was called ‘ultra-hot Neptune’, and its orbit around its star is ‘ultrashort’.
The planet is similar to Neptune, but it weighs twice as much as the icy giant and probably has a solid core surrounded by an atmosphere of hydrogen and helium, according to the study published in the journal Nature Astronomy. Compared to Earth, the new world is about 4.7 times its diameter and 29 times its mass.
Previous research found that about one in 200 sun-like stars has a planet that surrounds its star in less than one Earth day. Astronomers call these worlds ‘ultrashort period planets’.
Ultrahot Neptune, located 260 light-years from Earth, is one of these ultrashort worlds. It orbits so close to its star (60 times closer than Earth to the Sun) that its year lasts only 19 hours.
A “unique laboratory” to study the chemistry of the planets
The nickname of ultra-hot comes from the stellar radiation that heats the planet to more than 1,700 degrees, while a normal hot Neptune could only heat up to about 1,225. At these temperatures, heavy elements like iron can ionize in the atmosphere and separate molecules. Therefore, scientists are puzzled how this Neptune retained its hydrogen-helium atmosphere for so long given the intense stellar radiation.
The system itself is about half the age of the Sun – 2 billion years – and, given the intense exposure to radiation, a Neptune-like planet cannot be expected to maintain its atmosphere for that long being this close to its star. So this is another mystery of how such an incredible system was born.
Scientists assume that for some time the planet was far from its star and that it was relatively recently (by cosmic standards) close to it.
According to the researchers, the unique characteristics of the newly discovered ultrahot Neptune make it a “unique laboratory” for studying the chemistry of planets outside our solar system.