The first Ultra-Hot Neptune Planet has discovered orbiting the star LTT 9779 (260 light-years away from the Earth) by an international team of astronomers. If you are a layman, then the classification ‘Ultra-Hot Neptune Planet’ might sound a little strange to you, but it is pretty much exactly what it sounds like; the planet is similar in density and elemental composition to our own Neptune (though it is twice as massive and has more volume), but its proximity to its star causes it to have a very high temperature. It takes only 19 hours to complete an orbit around its star (even Mercury takes around 88 days), which gives it a temperature of over 1700 degrees Celsius.
The ‘improbable’ part comes in when you consider that it is estimated to be around 2 billion years old, which makes scientists wonder how exactly it managed to keep its atmosphere for that long. It should have been affected by a phenomenon known as photoevaporation, where intense radiation from the parent star (generally in the form of X-Rays and UV-rays) heats the upper layers of a nearby gas giant’s atmosphere, causing these layers to be expelled into space. The planet should either have been a bare-rock or a traditional gas giant, but it is neither.
It is composed of a metal-rich core (especially iron) that weighs as much as 28 Earths, and a large atmosphere that makes up for 9% of its planetary mass (our own atmosphere accounts for 0.0005% of our planetary mass). Even its atmosphere is iron-rich, as it contains twice as much iron in its atmosphere than even our Sun. These elevated levels of iron point towards the theory that maybe the planet used to be a part of an even larger gas giant, which expelled its atmosphere over the years, possibly even into its star, while the heavy Iron plasma sunk lower into the atmosphere. This phenomenon is known as Roche Lobe Overflow, wherein a planet comes so close to its star than the star’s gravity pulls the outer layers of the planet into itself.
Another theory is that the planet, LTT 9779b, arrived at its current orbit more recently due to collisions or gravity interactions with other planets in the system or other heavenly bodies like passing stars. Though this doesn’t necessarily explain the high levels of iron, it does explain why it still has such a significant atmosphere despite the considerable age of the system.
The discovery is very scientifically significant, displaying a plethora of rare phenomena occurring on the same planet, making it a ‘laboratory’ of sorts for us. According to the team leader, Chilean Prof. James Jenkins, “The planet is very hot, which motivates a search for elements heavier than Hydrogen and Helium, along with ionized atomic nuclei. It’s sobering to think that this ‘improbable planet’ is likely so rare that we won’t find another laboratory quite like it to study the nature of Ultra Hot Neptunes in detail. Therefore, we must extract every ounce of knowledge that we can from this diamond in the rough, observing it with both space-based and ground-based instruments over the coming years.”