It is theoretically possible to have another planet similar to Earth in our solar system. However, the chances of such a planet existing within our solar system are extremely low based on our current knowledge. Our understanding of the formation and evolution of planetary systems suggests that each system typically has only one habitable planet within the so-called "habitable zone," where conditions are suitable for the presence of liquid water.
If, by some rare occurrence, a planet similar to Earth were to exist in our solar system, its fate would depend on various factors such as its initial conditions, interactions with other celestial bodies, and the stability of its orbit. Here are a few possibilities:
Stability: The new Earth-like planet could settle into a stable orbit, allowing it to persist in a habitable state for a significant period. It could potentially develop its own biosphere and undergo geological processes similar to Earth.
Orbital Instability: Depending on the planet's initial conditions and interactions with other planets or large objects in the solar system, its orbit could become unstable over time. This instability could lead to collisions or ejections from the solar system, rendering the planet uninhabitable or causing its eventual destruction.
Environmental Changes: Over time, even a habitable planet can experience changes in its environment. Factors such as variations in the host star's activity, changes in the planet's atmosphere, or long-term geological processes could affect its habitability. These changes could either make the planet less hospitable for life or potentially lead to its extinction.
Interactions with Earth: If a second Earth-like planet were to exist in our solar system, its gravitational influence could have complex effects on Earth and the other planets. Over time, these gravitational interactions could lead to perturbations in the orbits of planets, affecting their stability and potentially altering the long-term habitability of both planets.
It's important to note that our understanding of planetary formation and dynamics is still evolving, and new discoveries may provide further insights into the possibilities of Earth-like planets within our solar system. As of now, however, there is no evidence or indication of such a planet existing in our immediate cosmic neighborhood.