What is a planet and how is it classified?
The definition of a planet has evolved over time, but generally speaking, a planet is a celestial body that orbits a star and has enough mass to form a spherical shape due to its own gravity. In 2006, the International Astronomical Union (IAU) defined a planet as a celestial body that:
- Is in orbit around the Sun.
- Has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
- Has “cleared the neighborhood” around its orbit.
However, this definition has been controversial and there is ongoing debate among astronomers about how to classify celestial bodies that do not meet all three criteria, such as dwarf planets and exoplanets. As of now, there are eight planets recognized in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
How many planets have been discovered in our own solar system?
As mentioned earlier, there are currently eight planets recognized in our solar system. The discovery of these planets dates back to ancient times when the five visible planets (Mercury, Venus, Mars, Jupiter, and Saturn) were identified and named by astronomers. Uranus was discovered in 1781 and Neptune in 1846, while Pluto was discovered in 1930 and classified as a planet until 2006 when it was reclassified as a dwarf planet.
In addition to these eight planets, there are also numerous other celestial bodies in our solar system, such as dwarf planets, moons, asteroids, and comets. The total number of these objects is constantly changing as new discoveries are made through advances in technology and astronomy. However, as of now, there are five recognized dwarf planets in our solar system: Ceres, Pluto, Haumea, Makemake, and Eris.
Beyond our solar system: How many exoplanets have been found?
An exoplanet, or extrasolar planet, is a planet that orbits a star other than our Sun. The discovery of exoplanets is a relatively new field in astronomy, with the first confirmed detection in 1992. Since then, the number of known exoplanets has been steadily increasing as new detection methods and technologies are developed.
As of March 2021, over 4,000 exoplanets have been confirmed by astronomers. These planets vary greatly in size, composition, and distance from their host star. Some are rocky planets like Earth, while others are gas giants like Jupiter. Many exoplanets are located in their star’s habitable zone, where conditions may be suitable for liquid water and potentially even life.
The search for exoplanets is ongoing and it is likely that many more will be discovered in the future. The ultimate goal is to find an exoplanet that is similar to Earth and has the potential to support life.
The search for habitable planets: Are there other Earth-like planets out there?
The search for habitable planets, or “Goldilocks” planets, is a major focus in exoplanet research. A habitable planet is one that is located in its star’s habitable zone, where conditions may be suitable for liquid water to exist on the planet’s surface.
So far, several potentially habitable exoplanets have been discovered, including Proxima Centauri b, TRAPPIST-1e, and LHS 1140b. These planets have similar sizes and compositions to Earth, and are located within the habitable zones of their respective stars.
However, simply being located in the habitable zone does not guarantee that a planet is habitable. Other factors, such as the planet’s atmosphere and the presence of a magnetic field, also play important roles in determining a planet’s habitability.
The search for habitable planets is expected to continue in the coming years as new telescopes and technologies are developed, including the James Webb Space Telescope, which is set to launch in 2021.
The limits of our current technology: How many planets may remain undiscovered?
Despite the increasing number of exoplanets being discovered, it is estimated that the total number of planets in our galaxy alone could be in the billions or even trillions. However, our current technology is only capable of detecting a small fraction of these planets.
The most common method of exoplanet detection is the transit method, which detects a planet as it passes in front of its host star and causes a slight dip in the star’s brightness. Other methods include the radial velocity method, which detects a planet’s gravitational influence on its host star, and direct imaging, which captures an image of the planet itself.
Each detection method has its own limitations and biases, and there are likely many planets that remain undetected due to these limitations. For example, smaller planets are more difficult to detect than larger ones, and planets that are located close to their host stars are more likely to be detected than those that are farther away.
As technology continues to improve, it is expected that the number of detected exoplanets will increase. However, it is also likely that many planets will remain undiscovered due to the limitations of our current technology.