INTERSTELLAR CLOUD AND PROTOSUN

When clouds of dust and gas are sufficiently cold and dense, they can collapse under the force of gravity to form a protostar. Surrounding each star is a rotating disk of leftover material, the wherewithal for making planets....[More]

INTERSTELLAR CLOUD AND PROTOSUN

When clouds of dust and gas are sufficiently cold and dense, they can collapse under the force of gravity to form a protostar. Surrounding each star is a rotating disk of leftover material, the wherewithal for making planets. In their hot, dense inner regions, dust grains are vaporized; in the cool, tenuous outer parts, the dust particles survive and grow as vapor condenses onto them.  [Less] [Link to this slide]

Illustrations by Don Dixon

DUST GRAINS AND GAS

Dust grains in the protoplanetary disk are stirred by nearby gas and collide with one another. The grains intercept starlight and reemit lower-wavelength infrared light, ensuring that heat reaches even the darkest regions of the disk’s interior....[More]

DUST GRAINS AND GAS

Dust grains in the protoplanetary disk are stirred by nearby gas and collide with one another. The grains intercept starlight and reemit lower-wavelength infrared light, ensuring that heat reaches even the darkest regions of the disk’s interior. The temperature, density and pressure of the gas generally decrease with distance from the star.  [Less] [Link to this slide]

Illustrations by Don Dixon

COSMIC DUST BUNNIES

Even the mightiest planets have humble roots: as micron-size dust grains embedded in a swirling disk of gas. These dust grains collide, clump and grow in size. The temperature of the protosun’s disk falls with distance from the newborn star, defining a “snow line” beyond which water stays frozen....[More]

COSMIC DUST BUNNIES

Even the mightiest planets have humble roots: as micron-size dust grains embedded in a swirling disk of gas. These dust grains collide, clump and grow in size. The temperature of the protosun’s disk falls with distance from the newborn star, defining a “snow line” beyond which water stays frozen. In our solar system, the snow line marks the boundary between the inner rocky planets and outer gas giants.  [Less] [Link to this slide]

Illustrations by Don Dixon

PLANETESIMALS

As the crammed-together dust grains continue to collide and grow, some break through the snow line and continue to migrate inward. But in the process they become coated with slush and complex molecules, which makes them stickier....[More]

PLANETESIMALS

As the crammed-together dust grains continue to collide and grow, some break through the snow line and continue to migrate inward. But in the process they become coated with slush and complex molecules, which makes them stickier. Some regions are so thick with dust that the grains’ collective gravitational attraction also accelerates their growth. In these ways, the dust grains pack themselves into kilometer-size bodies called planetesimals.  [Less] [Link to this slide]

Illustrations by Don Dixon

LARGE PLANETESIMALS

In the beginning the growth of a body is self-reinforcing. The larger a planetesimal becomes, the stronger the gravity it exerts, and the faster it sweeps up its less massive partners....[More]

LARGE PLANETESIMALS

In the beginning the growth of a body is self-reinforcing. The larger a planetesimal becomes, the stronger the gravity it exerts, and the faster it sweeps up its less massive partners. When they attain masses comparable to our moon, however, bodies exert such strong gravity that they stir up surrounding solid material and divert most of it before they can collide with it. In this way, they limit their own growth. Thus, an “oligarchy” arises—that is, a population of planetary embryos with similar masses that compete with one another for the residual planetesimals.  [Less] [Link to this slide]

Illustrations by Don Dixon

FREE-FLOATING PLANETS

Occasionally during the process of planetesimal formation, bodies are ejected until the system reaches an equilibrium configuration. Astronomers have observed free-floating planets in young stellar clusters....[More]

FREE-FLOATING PLANETS

Occasionally during the process of planetesimal formation, bodies are ejected until the system reaches an equilibrium configuration. Astronomers have observed free-floating planets in young stellar clusters.  [Less] [Link to this slide]

Illustrations by Don Dixon

BIRTH OF GAS GIANT

The formation of a gas giant such as Jupiter is the defining moment in the history of a planetary system; if such a planet forms, it shapes the rest of the system....[More]

BIRTH OF GAS GIANT

The formation of a gas giant such as Jupiter is the defining moment in the history of a planetary system; if such a planet forms, it shapes the rest of the system. But for that to happen, the embryo’s gravity must draw in gas. But the gas cannot settle down until it cools off. The planet may well spiral toward the star before that happens. Embryo growth, embryo migration and gas depletion all occur at roughly the same rate. Which wins depends on the luck of the draw.  [Less] [Link to this slide]

Illustrations by Don Dixon

GAS GIANT SATELLITES

The process for the development of moons of gas giants is not well understood but could be similar to that of the development of the rocky inner planets of our solar system....[More]

GAS GIANT SATELLITES

The process for the development of moons of gas giants is not well understood but could be similar to that of the development of the rocky inner planets of our solar system. In that instance, the gas giant would serve as a protosun. Gas giants like Jupiter and Saturn, with their numerous and diverse moons, are like mini solar systems.  [Less] [Link to this slide]

Illustrations by Don Dixon