Formation of terrestrial planets
Download
1 / 11

Formation of Terrestrial Planets - PowerPoint PPT Presentation


  • 106 Views
  • Updated On :

Formation of Terrestrial Planets. Roman Rafikov (Institute for Advanced Study). More than 150 extrasolar planets are known at present. Most of them have masses typical of gas giants , i.e. Only planets around pulsar PSR B1257+12 (neutron star) resemble terrestrial planets.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Formation of Terrestrial Planets' - casey


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Formation of terrestrial planets l.jpg

Formation of Terrestrial Planets

Roman Rafikov

(Institute for Advanced Study)


Slide2 l.jpg

  • More than 150 extrasolar planets are known at present.

  • Most of them have masses typical of gas giants, i.e.

  • Only planets around pulsar PSR B1257+12 (neutron star) resemble terrestrial planets

gas giants

ice giants

terrestrial planets

The most likely scenario of the giant planet formation is a rapid gas accretion onto a preexisting massive solid core.

Solar System

Extrasolar planets

8 major planets:

exoplanets.org

nineplanets.org

Formation of the Earth-like planets have likely been an important stage of the giant planet genesis.


Slide3 l.jpg

Planetary diversity

Lissauer 2004

Currently known to us are

  • terrestrial planets – consist mainly of solid refractory materials – silicates and iron

  • gas giants – mostly gas , with solid cores

  • ice giants – large ice + rock cores , covered with thick atmospheres composed of mainly H and He


Initial conditions for planet formation l.jpg

Pictoris

Mouillet et al’97

Initial conditions for planet formation

Planets form in protoplanetary disks

  • Gaseous disks in differential rotation around parent stars

  • Dust (about 1% by mass) is a material for planet building

  • Sizes range from 100 to 1000 AU (AU – distance between Sun and Earth )

  • Disks live for 1 to 10 million years

  • Cold (hundreds of K) and geometrically thin


Stages of terrestrial planet formation l.jpg
Stagesof Terrestrial Planet Formation

  • From dust to km-size planetesimals

  • Myriads of microscopic dust particles merging together. Motion of solid objects is coupled to gas.

  • From planetesimals to Moon-sized objects (embryos)

  • Large number of gravitationally interacting objects.

  • Gravity is the major player. Planetesimal collisions and mergers lead to formation of bigger objects.

  • From embryos to terrestrial planets and cores of giants

  • Small number of massive, spatially isolated bodies.

  • Weak gravitational perturbations between them cause their orbits to cross leading to giant impacts.

  • Possible accretion of gas and transition to gas giants


Slide6 l.jpg

From dust to planetesimals

Very poorly understood!Potential planetesimal formation mechanisms:

  • Gravitational instability(Goldreich & Ward 1973; Youdin & Shu 2002)

  • Dust sediments towards midplane, forms dense layer, becomes gravitationally unstable. 1-10 km size bodies form on dynamical (about 100 yr) timescale.

  • ???Can dust really sediment? What is the role of turbulence in the disk?

  • Coagulation of dust particles(Weidenschilling & Cuzzi 1993)

  • Dust particles collide with each other and stick ensuring growth. 1 m bodies grow in less than 10,000 yr if 100% sticking probability.

  • ???Sticking mechanism is very unclear. Collisions may occur at high velocities leading to dust fission rather than fusion.

  • “Exotic” mechanisms: vortices, turbulent concentration, etc.

  • ???Do these work at all?

Interdisciplinary connections: dust sticking (chemistry, surface science), dust destruction (solid state physics), physics of turbulence, etc. Need many realistic, controlled lab experiments!


Slide7 l.jpg

From planetesimals to embryos

  • Features of this evolutionary stage:

  • Many planetesimals ( within 1 AU); orbits overlap.

  • Mutual gravitational perturbations excite their eccentricities and inclinations -energy gets pumped from circular orbital motion into random motion.

  • Low-velocity collisions lead to mergers and planetesimal grows, high velocity collisions cause erosion and fragmentation

  • System evolves under simultaneous action of all these processes

planetesimals

embryo

Because of the huge number of bodies involved, kinetic theory should be employed to study planetesimal agglomeration, including both mass and velocity evolution.

Direct N-body simulations can also probe spatial evolution but they are very limited.

Particle-in-a-box simulations (modeling disk as a “gas” of gravitating particles) demonstrate growth up to g in yr at 1 AU – Moon-size embryos in the terrestrial region.

(Kenyon & Luu 1998)

From planetesimals to Moon-size “embryos”


Slide8 l.jpg

From planetesimals to embryos

???Planet formation timescale exceeds age of the Universe in the outer Solar System. How do Uranus and Neptune form?

We have interesting clues on this one!

- After some coagulation has proceeded, growing embryos cause rapid dynamical evolution of surrounding planetesimals, increase their speeds dramatically

- As a result, when planetesimals collide with each other they fragment into smaller pieces

- Fragments are subject to strong gas drag and mutual inelastic collisions, this decreases their random velocities

- Dynamically “cold” fragments are accreted by embryos much more efficiently than the original planetesimal material

Embryos grind their food for better digestion!

???Details of planetesimal fragmentation? Internal strengths of planetesimals?

Interdisciplinary connections: cratering, physics of impacts, crack propagation, granular flows (“rubble piles”)


Slide9 l.jpg

150 Moon-size bodies

Moon-forming impact (Canup 2004)

Chambers 2001

From Moon-size embryos to fully-grown planets

  • Evidence:

  • Earth-Moon system: giant impact about 30 million yrs after Earth formed.

  • Planetary obliquities

???Final dynamical state?

Interdisciplinary connections: geology, equation of state at high T and P (shock experiments), numerical hydrodynamics


Conclusions l.jpg
Conclusions each other into

  • Formation of terrestrial planets provides clues to the genesis of giant planets

  • Growth of terrestrial planet consists of three important stages:

  • - Formation of planetesimals (very poorly understood) - strong coupling of dust to gas.

  • - Coagulation of planetesimals (general picture is within our grasp but details are often not clear) – “gas” of gravitating and merging particles, with important contribution of dissipative processes.

  • - Stage of giant impacts (numerical studies give reasonable picture although not without questions) – catastrophic collisions of massive protoplanetary cores.

  • Plenty of room for interdisciplinary studies in a wide variety of fields – chemistry, geology, physics, atmospheric sciences, etc. – both on theoretical and experimental sides. Without them progress will be stalled.


Slide11 l.jpg

Planetary diversity each other into

Lissauer 2004

Currently known to us are

  • terrestrial planets – consist mainly of solid refractory materials – silicates and iron

  • gas giants – mostly gas , with solid cores

  • ice giants – large ice + rock cores , covered with thick atmospheres composed of mainly H and He


ad