The outermost regions of the Solar System are an undiscovered frontier. Past Neptune, the Kuiper Belt contains icy rocks and dwarf planets, while the theoretical Oort Cloud houses long-period comets and potentially additional rocky planets, challenging the traditional belief in only four terrestrial planets close to the sun. Now, recent research hints at the presence of up to five more rocky planets at the outer limits of the Solar System.
Rogue Planets: The Sun's Early Attraction to Celestial Wanderers
Free-floating planets (FFPs), also known as rogue planets, are celestial bodies of planet size that lack a stellar orbit. They form independently from gas clumps or originate near stars but get ejected from their orbits.
The James Webb Space Telescope (JWST) has detected numerous rogue planets, including pairs of Jupiter-sized ones in the Orion constellation, while Simulations indicate most FFPs are likely as large as Mars.
Although some rogue planets are expelled by stars, the latter can also capture these wandering objects with their gravity, making them permanent members of a solar system.
In a study, titled "Are There Terrestrial Planets Lurking in the Outer Solar System?" published in the Astrophysical Journal Letters, Princeton University astrophysics doctoral candidate Amir Siraj suggests that the Sun, in its early stages, may have attracted rocky FFPs.
Using models based on FFP observations, Siraj conducted 100 million simulations, proposing that the Sun might have trapped two Mars-sized or three to five Mercury-sized rogue planets approximately 1,400 astronomical units away.
These captured planets would likely reside in the Oort Cloud, a theoretical region enveloping the solar system with billions of icy objects. Unlike the hypothetical Planet X, a Neptune-like world predicted to be around 43 astronomical units from the Sun, the proposed planets originate from other star systems.
Even though their habitability remains uncertain due to faint sunlight, future space missions exploring exoplanets may target them. Identifying these distant planets poses a challenge, with the Vera C Rubin Observatory expected to commence operations in 2025 offering a potential solution, particularly in the Southern sky and proximity to a high albedo.
The Rich Diversity of Terrestrial Planets in the Solar System
Terrestrial planets, characterized by rocky or metallic compositions and hard surfaces, typically possess molten heavy-metal cores and distinct topographical features like valleys, volcanoes, and craters.
In the solar system, the four terrestrial planets closest to the Sun are Mercury, Venus, Earth, and Mars. While it is believed that there were more terrestrial planetoids during the solar system's formation, they likely merged or were destroyed.
NASA's Kepler space observatory, active until 2018, identified over 2,300 confirmed alien planets, with thousands more potential discoveries. The telescope's data suggested the existence of billions of Earth-like planets in the Milky Way galaxy.
In 2017, the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) found a system called TRAPPIST-1, located over 39 light-years away, hosting seven Earth-like planets, four of which are super-Earth sized. A 2021 study indicates that these planets share similar densities, suggesting consistent material ratios like iron, silicon, and oxygen commonly found on rocky planets.
Three planets in the TRAPPIST-1 system-TRAPPIST-1 e, f, and g-reside in the habitable zone around their central star. This zone is conducive to liquid water on the planet's surface, making these planets potentially habitable for life.
The TESS (Transiting Exoplanet Survey Satellite), launched in 2018 as Kepler's successor, aims to detect Earth-size planets within a few light-years from our planet, facilitating swift observations by other Earth-based telescopes.
RELATED ARTICLE: Mars-Sized Planet Might Be Lurking in Trans-Neptunian Space of the Solar System as Hinted by Computer Simulations
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