In recent years, astronomers have made various important discoveries regarding the existence of new planets in the solar system. This discovery not only attracted the attention of scientists, but also the general public, who are always curious about what might exist outside the earth. With advanced technology, such as space telescopes and ground observatories, the discovery process has become increasingly detailed. Newly discovered planets are often referred to as “external planets” or “mini-planets” beyond the orbit of Neptune. These planets come from objects of varying sizes, ranging from small planets to larger ones. The discovery of new planets is generally made through direct observation, measuring the movement of stars, or monitoring the effects of gravity on nearby objects. One of the latest discoveries is Planet Nine, which is thought to be far beyond the orbit of Neptune. Although there is no visual confirmation of the existence of this planet, statistical data suggests the existence of a massive object that influences the orbits of small objects in the Kuiper Belt. Mathematical models suggest that Planet Nine may have 5-10 times the mass of Earth and be located 20 times the distance from Earth to the Sun. However, planets are not the only focus. Scientists also face the challenge of identifying exoplanets—planets that reside outside our solar system. Using the transit method, in which the light of a monitored star decreases as a planet passes in front of the star, astronomers have detected thousands of exoplanets. This discovery paves the way for a deeper understanding of the diversity of planets in the universe. The planets discovered often have unique characteristics. For example, some of them were found to be in the habitable zone, which allows for the possibility of liquid water. Likewise, planets with the composition of gas giants or terrestrial planets provide new insights into how planets form and develop. Looking to the future, AI-based technology is expected to provide further understanding and identify previously overlooked objects. In observations, artificial intelligence-based software can analyze astronomical data and recognize patterns that may indicate the presence of new planets. As this research continues, many experts believe that the discovery of new planets in and outside the solar system will continue to increase. This not only challenges the limits of our knowledge of astronomy but also increases curiosity about the possibility of life beyond our planet. Each discovery adds a new layer to our cosmic map, broadening our knowledge of the vast universe.