The Chamberlin–Moulton planetesimal hypothesis was proposed in 1905 by geologist

Thomas Chrowder Chamberlin Thomas Chrowder Chamberlin (; September 25, 1843 – November 15, 1928) was an American geologist and educator. In 1893 he founded the ''Journal of Geology'', of which he was editor for many years. Biography Chamberlin was born September 25, 184 ...

and astronomer

Forest Ray Moulton Forest Ray Moulton (April 29, 1872 – December 7, 1952) was an American astronomer. He was the brother of Harold G. Moulton, a noted economist. Biography He was born in Le Roy, Michigan, and was educated at Albion College. After graduatin ...

to describe the formation of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. It was proposed as a replacement for the

Laplacian In mathematics, the Laplace operator or Laplacian is a differential operator given by the divergence of the gradient of a scalar function on Euclidean space. It is usually denoted by the symbols \nabla\cdot\nabla, \nabla^2 (where \nabla is th ...

version of the

nebular hypothesis The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System (as well as other planetary systems). It suggests the Solar System is formed from gas and dust orbiting t ...

that had prevailed since the 19th century. The hypothesis was based on the idea that a star passed close enough to the sun early in its life to cause tidal bulges to form on its surface, which along with the internal process that leads to

solar prominence In solar physics, a prominence, sometimes referred to as a filament, is a large Plasma (physics), plasma and magnetic field structure extending outward from the Sun's surface, often in a loop shape. Prominences are anchored to the Sun's surface ...

s, caused material to be ejected repeatedly from the sun. Due to the gravitational effects of the passing star, two spiral-like arms would have extended from the sun, and while most of the material would have fallen back, part of it would remain in orbit. This orbiting material would cool and condense into numerous small bodies that they termed

planetesimal Planetesimals () are solid objects thought to exist in protoplanetary disks and debris disks. Believed to have formed in the Solar System about 4.6 billion years ago, they aid study of its formation. Formation A widely accepted theory of pla ...

s and a few larger

protoplanet A protoplanet is a large planetary embryo that originated within a protoplanetary disk and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimals that gravitatio ...

s. Their theory proposed that as these objects collided over time, the planets and their moons were built up, with

comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...

s and

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

s being the leftover debris. The "spiral nebulae" photographed at

Lick Observatory The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton (California), Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The ...

were thought to possibly be views of other suns undergoing this process. These nebulae are now known to be

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...

rather than developing solar systems. In 1917, James Hopwood Jeans argued that only a very close approach of a second star was necessary to eject material, instead of requiring solar prominences. In 1939, Lyman Spitzer showed that a column of material drawn out from the sun would dissipate rather than condense. By this time the theory had mostly fallen out of favor, and in the 1940s, the work of Henry Norris Russell showed that if the solar material had been pulled away from the sun with the force necessary to account for the angular momentum of Jupiter, the material would have continued out of the solar system entirely. Though the Chamberlin–Moulton hypothesis is no longer accepted, the idea of planetesimals remains in modern theory.

References

Lankford, John (1997). ''History of Astronomy, an Encyclopedia''. Garland Publishing, Inc. {{more categories, date=April 2025 Planetary science