ESA Satellite Discovers 'Inside-Out' Planetary System Defying Formation Theories

A New Discovery in the Universe

Astronomers have made a groundbreaking discovery of a distant planetary system where planets are arranged in an unexpected order, challenging existing theories about how planets form. In our own Solar System, the four planets closest to the Sun are small and rocky, while the four farther away are large gas giants. For many years, scientists believed this pattern — rocky planets near the star and gaseous planets farther out — was common throughout the universe.

However, a star named LHS 1903, located in the Milky Way's thick disc, appears to contradict this belief. This red dwarf star is cooler and dimmer than our Sun. Researchers from across Europe, analyzing data from several telescopes, had already identified three planets orbiting LHS 1903. The closest planet to the star was rocky, followed by two gas giants, which aligns with what scientists typically expect.

But further observations using the European Space Agency’s (ESA) Cheops space telescope revealed a fourth planet that is even farther from the star. Surprisingly, this outermost planet also appears to be rocky.

"That makes this an inside-out system, with a planet order of rocky-gaseous-gaseous-and then rocky again," said Thomas Wilson, the lead author of the study and a planetary astrophysicist from the University of Warwick in the United Kingdom, in a statement with ESA. "Rocky planets don't usually form so far away from their home star," Wilson added.

How Planets Form

Inner planets are expected to be small and rocky because intense radiation from the nearby star blasts most of the gas away from their rocky core. However, in the colder regions farther from the star, a thick atmosphere can form around cores, creating gas giants.

To explain the unusual LHS 1903 system, researchers tested several possibilities before proposing a new idea: the planets may have formed one after another rather than all at once. According to the currently most widely accepted theory, planets form simultaneously in a massive ring of gas and dust called a protoplanetary disc. This process involves tiny dust grains clumping together, then snowballing into cores that eventually evolve into mighty planets.

But in this system, scientists believe LHS 1903 may have formed after most of the gas had already disappeared. "Yet here is a small, rocky world, defying expectations," Wilson said. "It seems that we have found the first evidence for a planet which formed in what we call a gas-depleted environment," he added.

Expanding Our Understanding of Exoplanets

Since the 1990s, astronomers have discovered more than 6,000 planets outside our Solar System, known as exoplanets. These discoveries have mostly been made by observing slight changes in brightness as the planets pass in front of their star.

"Historically, our planet formation theories are based on what we see and know about our Solar System," said Isabel Rebollido, a planetary disc researcher at ESA. "As we are seeing more and more different exoplanet systems, we are starting to revisit these theories."

This new discovery challenges long-held assumptions and opens up exciting possibilities for future research. By studying systems like LHS 1903, scientists can gain deeper insights into the processes that shape planetary systems across the universe. The findings highlight the importance of continuing to explore and question our understanding of how planets form and evolve.

As technology advances, more such discoveries are likely to emerge, reshaping our knowledge of the cosmos and the diverse ways in which planets can come into existence.