Rogue planets, also known as free-floating planets, are planetary-mass objects that do not orbit around a star. Instead, they drift through space without being gravitationally bound to any particular star or stellar system. These planets are thought to form through various mechanisms, such as gravitational interactions during the early stages of planetary system formation or through ejection from their original star systems due to gravitational disturbances.
Rogue planets can vary in size, ranging from Earth-sized bodies to gas giants similar to Jupiter or even larger. They are expected to have a diverse range of compositions, similar to planets found within star systems. Some rogue planets may retain atmospheres and have solid surfaces, while others could be entirely composed of gas.
Observing rogue planets directly is challenging because they do not emit their own light and are not illuminated by a nearby star. However, scientists have detected some rogue planets indirectly using methods such as gravitational microlensing and infrared observations.
As for the possibility of planets surviving without the protection of a star system, rogue planets are the prime examples. They don't rely on a star's energy for warmth or light. Instead, they can retain heat from their initial formation or generate internal heat through processes like radioactive decay. This means that even without a nearby star, rogue planets could potentially support environments that sustain some forms of life, such as subsurface oceans warmed by internal heat sources.
Estimating the exact number of rogue planets in the galaxy is challenging due to their elusive nature and difficulties in detection. However, based on current understanding, it is believed that there could be a large number of rogue planets in the Milky Way. Some estimates suggest that there could be billions of rogue planets for every star in the galaxy, while others propose a more conservative estimate of around one rogue planet per star. The true number is uncertain and requires further observational evidence to refine our understanding.