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Chapter 7: Problem 28

What is a protoplanetary disk? There are two reasons why the inner part of the disk is hotter than the outer part. What are they?

Short Answer

Expert verified
A protoplanetary disk is a rotating disk of gas and dust around a new star. The inner part is hotter due to proximity to the star and frequent particle collisions.

Step by step solution

01

Definition of Protoplanetary Disk

A protoplanetary disk is a rotating disk of dense gas and dust surrounding a newly formed star. It is the region where planet formation takes place. This disk is the early stage in the formation of a planetary system.
02

Reason 1 for Inner Disk Being Hotter

The inner part of the disk is hotter than the outer part because it is closer to the central star. The intense energy and radiation from the star heats up the inner regions of the disk more significantly than the outer regions.
03

Reason 2 for Inner Disk Being Hotter

Another reason is that within the inner regions of the disk, collisions between particles are more frequent and energetic due to higher densities. These collisions generate additional heat, contributing to the higher temperatures in the inner part of the disk.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

planet formation
Planet formation is a fascinating process that takes place within a protoplanetary disk. This disk consists of gas and dust surrounding a newborn star. Over time, these particles collide and stick together to form larger bodies, known as planetesimals.
These planetesimals, through further collisions and gravitational interactions, grow into protoplanets. As they continue to accumulate mass, they can eventually become full-fledged planets.
The process of planet formation can be divided into a few main stages:
  • Dust grain accumulation: Small dust particles and ice grains stick together due to static and chemical forces.
  • Formation of planetesimals: Collisions and coagulation of dust grains form kilometer-sized bodies.
  • Growth into protoplanets: Planetesimals collide and merge, growing larger through accretion.
  • Planetary differentiation: Protoplanets differentiate into core, mantle, and crust due to internal heating and melting.
Understanding planet formation helps us learn about the origins of our own solar system and other planetary systems in the universe.
stellar radiation
Stellar radiation plays a vital role in the heating of the protoplanetary disk. The central star emits immense energy in the form of light and other radiation.
As this radiation travels through the disk, it heats up the surrounding gas and dust. This heating effect is more intense near the star, which is why the inner part of the disk is hotter than the outer regions.
The radiation from the star includes:
  • Visible light: This is the light we can see and contributes significantly to the heating of the protoplanetary disk.
  • Ultraviolet (UV) radiation: UV radiation is highly energetic and can ionize gases, leading to increased heating and chemical reactions.
  • Infrared (IR) radiation: IR radiation, emitted by the star and re-radiated by the dust, also plays a role in heating the disk.
Understanding the effects of stellar radiation helps us comprehend the thermal structure of protoplanetary disks and the conditions under which planets form.
particle collisions
Particle collisions are another critical factor in the heating and evolution of the protoplanetary disk. The density of gas and dust is higher in the inner regions of the disk, leading to more frequent and energetic collisions between particles.
When particles collide, they convert kinetic energy into heat, raising the temperature of the surrounding material.
These collisions can:
  • Generate heat: The kinetic energy from collisions is converted into thermal energy, increasing the temperature of the disk.
  • Cause coagulation: Particles can stick together upon collision, forming larger bodies like planetesimals.
  • Promote differentiation: Energetic collisions can lead to the melting and differentiation of larger bodies into core, mantle, and crust.
By understanding the role of particle collisions, we can gain insights into the dynamic processes that shape the formation and evolution of planetary systems.

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Most popular questions from this chapter

Go to the "Extrasolar Planets Global Searches" Web page (http://exoplanet.eu/searches.php) of the Extrasolar Planets Encyclopaedia, which lists many of the current and future projects looking for planets. Click on one ongoing project under "Ground" and one ongoing project under "Space." What method is used to detect planets in each case? Has the selected project found any planets, and if so, what type are they? Now click on one of the future projects. When will the one you chose be ready to begin? What will be the method of detection?

Look under your bed for "dust bunnies." If there aren't any, look under your roommate's bed, the refrigerator, or any similar place that might have some. Once you find them, blow one toward another. Watch carefully and describe what happens as they meet. What happens if you repeat this action with additional dust bunnies? Will these dust bunnies ever have enough gravity to begin pulling themselves together? If they were in space instead of on the floor, might that happen? What force prevents their mutual gravity from drawing them together into a "bunny-tesimal" under your bed?

Place the following events in the order they occur during the formation of a planetary system. a. Gravity collapses a cloud of interstellar gas. b. A rotating disk forms. c. Small bodies collide to form larger bodies. d. A stellar wind "turns on" and sweeps away gas and dust. e. Primary atmospheres form. f. Primary atmospheres are lost. g. Secondary atmospheres form. h. Dust grains stick together by static electricity.

Planetary systems in the Milky Way Galaxy are probably a. universal (every star has planets). b. common (many stars have planets). c. rare (few stars have planets). d. exceedingly rare (only one star has planets).

T/F: The Solar System formed from a giant cloud of dust and gas that collapsed under gravity.
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