gas and dust in interstellar nebulae can form-
Nebula Most nebulae are of vast size, some are hundreds of light years in diameter.[3][not in citation given] A nebula that is barely visible to the human eye from Earth would appear larger, but no brighter, from close by.[4] The Orion Nebula, the brightest nebula in the sky that occupies a region twice the diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers.[5] Although denser than the space surrounding them, most nebulae are far less dense than any vacuum created on Earth â€“ a nebular cloud the size of the Earth would have a total mass of only a few kilograms. Many nebulae are visible due to fluorescence caused by embedded hot stars, while others are so diffuse they can only be detected with long exposures and special filters. Some nebulae are variably illuminated by T Tauri variable stars. Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions the formations of gas, dust, and other materials "clump" together to form denser regions, which attract further matter, and eventually will become dense enough to form stars. The remaining material is then believed to form planets and other planetary system objects.
Nebular hypothesis The birth of the modern widely accepted theory of planetary formation—the solar nebular disk model (SNDM)—can be traced to the Soviet astronomer Victor Safronov.[8] His 1969 book Evolution of the protoplanetary cloud and formation of the Earth and the planets,[9] which was translated to English in 1972, had a long-lasting effect on the way scientists think about the formation of the planets.[10] In this book almost all major problems of the planetary formation process were formulated and some of them solved. Safronov's ideas were further developed in the works of George Wetherill, who discovered runaway accretion.[2] While originally applied only to the Solar System, the SNDM was subsequently thought by theorists to be at work throughout the Universe; as of 8 September 2017 astronomers have discovered 3,667 extrasolar planets in our galaxy.[11]