asteroids and comets

Astronomers were able to incorporate the new idea of the evolution of asteroids and comets into their larger picture of how the solar system formed. This larger model is based on the solar nebula notion, which was first proposed in the eighteenth century by German philosopher Immanuel Kant and French mathematician Pierre-Simon Laplace. (A nebula is a gaseous cloud.)

According to current understanding, the solar system formed 4.5 to 5 billion years ago from a vast cloud of gases and particles traveling through space. These materials took time to thicken and become more homogeneous. While all matter is subject to gravitational attraction, the gas and dust particles converged over time.

The core of the nebula became increasingly dense as material sank toward it. According to astronomer John Davies, as this core became more compact, it gained mass and so generated a stronger gravitational field. This sucked in additional material, rapidly expanding the core’s mass. Friction [particles grinding against one another] slowed the flow of material, releasing its energy as heat and warming the core.

As the cloud grew denser, it became increasingly difficult for heat to escape, causing the temperature at its core to rapidly rise. The conditions for nuclear reactions to begin eventually were favorable, and the sun was born—the flattened disk of material that had formed around the young Sun continued to circle it. From this sphere of material, planets, comets, and asteroids formed. Disk regions further from the burning star began to cool and form into little pebbles and ice particles. Meanwhile, gravity caused the smaller particles to gather and remain together, culminating in the formation of larger ones. Long-term,

Asteroids and Comets: Their Origins

As a result of this process, massive clusters began to form, some measuring several miles across or even several thousand feet in diameter. Astronomers refer to these huge collections as planetesimals, which loosely translates as “planetary building components.” Numerous planetesimals grew in size over time.

According to Curtis Peebles:

Using planetesimals to collect debris was a great idea. Planetesimals resembled dustballs on Earth in their loose, granular form. An object could not rebound off of them because it would absorb the energy. The dustball would enclose the object. The rate of expansion of a planetesimal would be accelerated if a few of its constituents grew larger than the rest.

The gravitational attraction would attract dust into their field of vision, and the mass gained would enable them to increase their range. This mechanism has the potential to affect a wide variety of objects, from dust grains to tennis balls to kilometer-sized planetesimals. These colossal planetesimals would be composed of numerous smaller objects of varying composition that would be grouped in loose aggregates [collections].

There are numerous varieties of planetesimals, with some clumping together to create planets and their moons, while others, including numerous smaller planetesimals, form asteroids and comets.

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