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Chapter 7: Problem 18

What is a protoplanetary disk? What are two reasons that the inner part of the disk is hotter than the outer part?

Short Answer

Expert verified
A protoplanetary disk is a disk of gas and dust around a new star. The inner part is hotter due to proximity to the star and accretion heating.

Step by step solution

01

Understanding Protoplanetary Disks

A protoplanetary disk is a rotating circumstellar disk of dense gas and dust surrounding a newly formed star. It is the region where planets are formed.
02

Reason 1 - Proximity to the Star

The inner part of the protoplanetary disk is hotter because it is closer to the central star. The star emits significant amounts of radiation and heat, causing nearby materials to become much hotter.
03

Reason 2 - Accretion Heating

The inner parts of the disk experience more intense accretion processes. As materials spiral inward due to gravitational forces, they collide and release kinetic energy as heat, further increasing the temperature of the inner region.

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Key Concepts

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

Circumstellar Disk
A circumstellar disk, also known as a protoplanetary disk, surrounds a newly formed star. This disk is made of dense gas and dust, which forms a flat, rotating structure.
It is significant because it's the birthplace of planets.
The materials in the circumstellar disk come from remnants of gas and dust left over from the star formation process. Over time, these materials clump together to form larger bodies.
In essence, the circumstellar disk is crucial in understanding how planetary systems emerge and evolve.
Planet Formation
Planet formation takes place within the protoplanetary disk. This process begins with small dust particles sticking together through electrostatic forces.
As they grow in size, gravity helps clump more materials together, forming planetesimals and eventually protoplanets.
There are two main methods of planet formation:
  • Core Accretion: This is the dominant theory for forming terrestrial planets like Earth. It involves the gradual buildup of solid materials.
  • Disk Instability: This method may form gas giants quickly by the disk's gas forming dense clumps, collapsing under its gravity.
Understanding planet formation gives insights into the diversity of planetary systems observed throughout the galaxy.
Accretion Heating
Accretion heating happens when materials in a protoplanetary disk collide and stick together. This process often takes place in the disk's inner regions.
As materials spiral inward toward the star, they move faster due to gravity. These high-speed collisions release kinetic energy, turning it into heat.
This heat contributes significantly to the increased temperature of the inner disk.
Accretion heating effects can be observed because the inner parts of the disk glow brightly in certain wavelengths, indicating high energy and temperature.
Stellar Radiation
Stellar radiation refers to the energy emitted by a star in the form of light and heat. This energy has a profound effect on the protoplanetary disk.
The inner part of the disk receives more stellar radiation due to proximity to the star. As a result, the material there becomes much hotter than that in the outer regions.
Stellar radiation also influences the disk's chemistry, which can affect planet formation.
Additionally, radiation pressure from the star can push away smaller particles, helping to clear out the disk over time.
Understanding stellar radiation allows us to grasp how proto-planets can survive and evolve under different energy regimes.

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Most popular questions from this chapter

Space missions: a. Go to the website for the Kepler Mission (http://kepler . nasa.gov). How many confirmed planets has Kepler discovered? Mouse over "confirmed planets": How many planet candidates are there? What kinds of follow-up observations are being done to verify whether the candidates are planets? What is new? b. Search for the latest version of the "Kepler Orrery," an animation that shows multiplanet systems discovered by Kepler. Do most of these systems look like our own? c. Go to the website for the European Space Agency (ESA) mission Gaia (http://sci.esa.int/gaia). This mission was launched in \(2013 .\) Click on the "Exoplanets" link on the left-hand side. What method(s) will GAIA use to look for planets? What are the science goals? Have some planets been found?

Jupiter has a mass equal to 318 times Earth's mass, an orbital radius of \(5.2 \mathrm{AU}\), and an orbital velocity of \(13.1 \mathrm{km} / \mathrm{s}\). Earth's orbital velocity is \(29.8 \mathrm{km} / \mathrm{s}\). What is the ratio of Jupiter's orbital angular momentum to that of Earth?

The transit method preferentially detects a. large planets close to the central star. b. small planets close to the central star. c. large planets far from the central star. d. small planets far from the central star. e. the method detects all of these equally well

A planet in the "habitable zone" a. is close to the central star. b. is far from the central star. c. is the same distance from its star as Earth is from the Sun. d. is at a distance where liquid water can exist on the surface.

One of the planets orbiting the star Kepler-11 with an orbital radius of radius 1.1 solar radii, or \(R_{\text {sun }}\) has a radius of 4.5 Earth radii \(\left(R_{\text {Earth }}\right) .\) By how much does the brightness of Kepler-11 decrease when this planet transits the star?
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