Astronomers Discover "Inside-Out" Planetary System With Rocky World Beyond Gas Planets, Challenging Formation Theories

Astronomers have discovered a strange planetary system that is making scientists rethink how planets form. In this system, a rocky planet is located beyond two gas planets, something that current theories say should not normally happen, reported Reuters.

The discovery was made using the European Space Agency's Cheops space telescope. This system consists of four planets, two rocky and two gaseous,all orbiting a small, dimly luminous red dwarf star. This star is located approximately 117 light-years from Earth, in the direction of the Lynx constellation. A light-year is the distance light travels in one year, which is approximately 5.9 trillion miles (9.5 trillion kilometers).

This star is called LHS 1903. It has about half the mass of our Sun and is only 5 percent as luminous.

The arrangement of the planets surprised scientists. The planet closest to the star is rocky. The two next to it are gaseous. But the outermost, fourth planet is rocky again, despite current theories suggesting it should be gaseous.

Why This Contradicts Existing Theory

Thomas Wilson, an astronomer at the University of Warwick in England and lead author of the study, published in the journal Science, explained that according to the theory of planet formation, planets formed near stars are typically small and solid, with very little gas or ice. He argues that the region near the star is extremely hot, so gas or ice cannot persist for long, and any atmosphere that forms can be destroyed by the star's radiation.

He also noted that regions farther from the star are cooler, with greater amounts of gas and ice. In such an environment, gaseous planets with dense atmospheres are more likely to form. However, in this system, a rocky planet exists outside the gaseous planets, challenging this theory.

Wilson described this system as evolving from the inside out.

Comparison With Our Solar System

In our solar system, the four inner planets are solid, while the outer four larger planets are made of gas. Small dwarf rocky planets like Pluto orbit the gas giants, but their size is much smaller than the primary planets.

Since the 1990s, scientists have discovered approximately 6,100 planets outside our solar system, called exoplanets.

All four planets in this new system orbit very close to their star. They are closer than Mercury orbits the Sun. The outermost planet covers only 40 percent of the distance between Mercury and the Sun. This is common around red dwarf stars, which emit much less energy than the Sun.

Two of these rocky planets are classified as super-Earths, meaning they are Earth-like in composition but have two to ten times Earth's mass. The two gaseous planets are called mini-Neptunes, which are smaller than Neptune but larger than Earth.

How Did This Happen?

Researchers believe that these four planets may not have formed simultaneously. It's possible that these planets formed at different times rather than all at once from a large cloud of gas and dust surrounding the star.

According to Wilson, the fourth planet likely formed last, when there was very little gas left in the surrounding atmosphere. Therefore, there wasn't enough material available for its formation.

Another possibility is that it initially had a dense gaseous atmosphere, but a major event destroyed it, leaving only its solid core.

Astronomer Andrew Cameron of the University of St. Andrews in Scotland, co-author of the study, said that the planet may have formed when the system was nearly depleted of gas, or that its atmosphere was stripped away by a collision with another celestial body. He also stated that scientists believe the Earth and Moon originated as a result of similar collisions.

Is Life Possible There

The fourth planet is particularly important because it may have conditions conducive to life. Its mass is approximately 5.8 times that of Earth and its temperature is approximately 140 degrees Fahrenheit, or 60 degrees Celsius.

Wilson said that 60 degrees Celsius is very close to the maximum temperature ever recorded on Earth, 57 degrees Celsius. He said the possibility of life being possible there cannot be ruled out. He also said that future studies by the James Webb Space Telescope could provide more information about the planet's atmosphere and clarify whether it is truly habitable.