Advanced

The Formation of Giant Planets

Lambrechts, Michiel LU (2015)
Abstract (Swedish)
Popular Abstract in Swedish

Jätteplaneterna, Jupiter, Saturnus, Uranus och Neptunus, är de största planeterna i solsystemet. De ligger långt från solen och har alla betydande gasatmosfärer, upp emot hundra gånger mer massiva än hela jorden.



Tack vare de tjocka gashöljena, med en sammansättning som liknar solens, kan man förstå att jätteplaneterna bildades i en gasskiva. Denna skiva kallas för solnebulosan och existerade under några miljoner år runt den unga solen. Studier av jätteplaneternas inre struktur visar att de också innehåller en stor mängd fast material, motsvarande tio gånger jordens massa i is och sten.



I tidigare studier har man därför argumenterat att jätteplaneterna... (More)
Popular Abstract in Swedish

Jätteplaneterna, Jupiter, Saturnus, Uranus och Neptunus, är de största planeterna i solsystemet. De ligger långt från solen och har alla betydande gasatmosfärer, upp emot hundra gånger mer massiva än hela jorden.



Tack vare de tjocka gashöljena, med en sammansättning som liknar solens, kan man förstå att jätteplaneterna bildades i en gasskiva. Denna skiva kallas för solnebulosan och existerade under några miljoner år runt den unga solen. Studier av jätteplaneternas inre struktur visar att de också innehåller en stor mängd fast material, motsvarande tio gånger jordens massa i is och sten.



I tidigare studier har man därför argumenterat att jätteplaneterna attraherade sina gashöljen efter att först ha bildat en fast kärna, ungefär tio gånger mer massiv än jorden. Denna process är fokus för denna avhandling.



Vi föreslår att små is- och stenpartiklar, runt centimeter-storlek, är ansvariga för den fasta kärnans tillväxt. Detta påstående grundas på numeriska och analytiska beräkningar som visar att friktionen från den omgivande gasen på is- och stenpartiklarna är en kritisk faktor för kärnornas tillväxt.



Tidigare trodde man att det fasta material som attraherades av kärnorna framförallt var i form av asteroidliknande kilometerstora, eller ännu större,kroppar. Vi visar att detta inte är sannolikt, då sådana stora kroppar inte

påverkas av den omgivande gasen på samma sätt som de mindre partiklarna, och därför inte hinner bygga upp planeternas kärnor under solnebulosans livstid.



Popular Abstract in English

The giant planets, Jupiter, Saturn, Uranus, and Neptune, are the most massive planets in the Solar System.They are located far from the Sun and they all have significant gaseous atmospheres, up to hundreds of times more massive than the Earth.



Because of the presence of envelopes of gas similar to that of which the Sun is composed, it is understood that the giant planets formed in a disc of gas. This disc is called the Solar Nebula and existed for a few million years around a young Sun. Studies of the interior of these planets also show that a lot of solid material

is present deep inside the giants. In total, this amounts to ten times the mass of the Earth in rocky/icy material.



Therefore, previous studies argued that the giant planets attracted the gaseous envelopes after first forming a solid core approximately ten times as massive as the Earth. This process is the focus of this thesis.



We propose that small icy/rocky pebbles, particles around a centimetre in size, are responsible for the growth of the cores. This claim is supported by numerical and analytical calculations that show gas drag on the pebbles to be

critical in order for cores to attract solid material.



Previously it was believed that the most commonly accreted solid was a kilometre or larger in size, more resembling asteroid-like bodies. We show that this is likely not the case, because material of that size does not benefit from gas drag and therefore the growth can not be completed within the lifetime of the Solar Nebula. (Less)
Abstract
Giant planets form embedded in a protoplanetary disc around a young star. Close to the midplane a large fraction of the available mass in solids is found in particles of cm to dm in size, which drift towards the star due to friction with the surrounding gas.

In paper I, II, III we describe a novel theory that explains how embryos, planetesimals larger than ~1000 km, grow efficiently by sweeping up the surrounding pebbles. The accretion radius of the embryo is large because gas drag aids the settling of passing pebbles to the core. In this way, the formation of large cores of 10 Earth masses is possible even in wide orbits (beyond the current Jupiter orbit), which previously could not be achieved when only considering the accretion... (More)
Giant planets form embedded in a protoplanetary disc around a young star. Close to the midplane a large fraction of the available mass in solids is found in particles of cm to dm in size, which drift towards the star due to friction with the surrounding gas.

In paper I, II, III we describe a novel theory that explains how embryos, planetesimals larger than ~1000 km, grow efficiently by sweeping up the surrounding pebbles. The accretion radius of the embryo is large because gas drag aids the settling of passing pebbles to the core. In this way, the formation of large cores of 10 Earth masses is possible even in wide orbits (beyond the current Jupiter orbit), which previously could not be achieved when only considering the accretion of building blocks with sizes larger than km in size. Such high core masses are necessary for the attraction of massive gaseous envelopes, like the ones around the giant planets Jupiter and Saturn.



The above model relies on large planetesimal seeds to form and particles to settle to the midplane.

In paper IV, we study the previously unexplored sedimentation of particles in fluids with high dust-to-gas ratio and detect spontaneous clumping which could aid the sedimentation and formation of a midplane of pebbles in the outer disc. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr. Rafikov, Roman, Princeton University
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Planet formation, Solar System, Exoplanets, Giant planets, Hydrodynamics
pages
114 pages
publisher
Department of Astronomy and Theoretical Physics, Lund University
defense location
Lundmarksalen (Department of Astronomy and Theoretical Physics)
defense date
2015-03-09 09:00
external identifiers
  • Scopus:84934288234
ISBN
978-91-7623-269-9
language
English
LU publication?
yes
id
9ebcdc34-0848-42d9-a21c-a75bb1e9ddca (old id 5154501)
date added to LUP
2015-03-23 09:50:07
date last changed
2016-10-13 04:38:52
@misc{9ebcdc34-0848-42d9-a21c-a75bb1e9ddca,
  abstract     = {Giant planets form embedded in a protoplanetary disc around a young star. Close to the midplane a large fraction of the available mass in solids is found in particles of cm to dm in size, which drift towards the star due to friction with the surrounding gas.<br/><br>
In paper I, II, III we describe a novel theory that explains how embryos, planetesimals larger than ~1000 km, grow efficiently by sweeping up the surrounding pebbles. The accretion radius of the embryo is large because gas drag aids the settling of passing pebbles to the core. In this way, the formation of large cores of 10 Earth masses is possible even in wide orbits (beyond the current Jupiter orbit), which previously could not be achieved when only considering the accretion of building blocks with sizes larger than km in size. Such high core masses are necessary for the attraction of massive gaseous envelopes, like the ones around the giant planets Jupiter and Saturn.<br/><br>
<br/><br>
The above model relies on large planetesimal seeds to form and particles to settle to the midplane.<br/><br>
In paper IV, we study the previously unexplored sedimentation of particles in fluids with high dust-to-gas ratio and detect spontaneous clumping which could aid the sedimentation and formation of a midplane of pebbles in the outer disc.},
  author       = {Lambrechts, Michiel},
  isbn         = {978-91-7623-269-9},
  keyword      = {Planet formation,Solar System,Exoplanets,Giant planets,Hydrodynamics},
  language     = {eng},
  pages        = {114},
  publisher    = {ARRAY(0x852bc08)},
  title        = {The Formation of Giant Planets},
  year         = {2015},
}