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Solar System analogues among exoplanetary systems

Lomaeva, Maria LU (2016) In Lund Observatory Examensarbeten ASTK02 20161
Department of Astronomy and Theoretical Physics
Lund Observatory
Abstract
Over the past two decades many discoveries of exoplanets have been made, which have drawn much attention to extrasolar planetary systems. In this work we study the composition of these systems and search for analogues of the Solar System.

We considered the planets in the database at exoplanet.eu. The search of solar-like systems required these planets to be classified. The classification was performed using k-means clustering algorithm and planets with measured masses and semi-major axes were divided into three clusters: hot Jupiters, gas giants and the third cluster with rocky and Neptunian planets.

Our first attempt to separate rocky and Neptunian planets by their density was performed by using k-means algorithm for planets with... (More)
Over the past two decades many discoveries of exoplanets have been made, which have drawn much attention to extrasolar planetary systems. In this work we study the composition of these systems and search for analogues of the Solar System.

We considered the planets in the database at exoplanet.eu. The search of solar-like systems required these planets to be classified. The classification was performed using k-means clustering algorithm and planets with measured masses and semi-major axes were divided into three clusters: hot Jupiters, gas giants and the third cluster with rocky and Neptunian planets.

Our first attempt to separate rocky and Neptunian planets by their density was performed by using k-means algorithm for planets with three measured parameters: mass, radius and semi-major axis. The results, however, were not satisfactory and a simple mass limit was chosen instead.

Our examination of the extrasolar systems showed that there are few Solar System analogues. This most probably depends on the selection effects of the present-day detection techniques. Two of them were studied more closely: the Doppler radial velocity and transit technique. The first one is more likely to detect massive planets in close orbits, while the latter is more preferable for planets that pass in front of their host stars and have large radii and short orbital periods. Low-mass Earth-like rocky planets are more likely to be detected by the transit technique. Overall, the distribution of planets in their classes has been shown to follow expectations and selection effects.

The systems that contain hot Jupiters were studied closely and the results suggest that there is a number of hot Jupiters that might likely be caught in the act of migration. Also, the number of transiting extrasolar Neptunes and Earths was compared to the results presented by Petigura et al. (2013). It revealed a discrepancy, which arose due to the correction of the occurrence rate of these planets made by the article’s authors.

Rocky planets that potentially can host life were another interesting subject in the search of Solar System analogues. According to our definition of the habitable zone, we found six super-Earths and one Earth-like planet that might be habitable. However, such conclusions need deeper examination of the planetary properties. (Less)
Popular Abstract (Swedish)
Människans intresse för rymden har alltid varit stort. Man har antagit att andra planetsystem, om de existerar, ser ut som vårt: med mindre stenplaneter i banor närmast stjärnan och gas-samt isjättar i de yttre banorna. Idag känner man till drygt 2 000 exoplaneter, d.v.s., planeter som kretsar kring andra stjärnor än solen. Man vet även att vissa av dem saknar motsvarighet i solsystemet, t. ex., heta jupitrar (gasjättar som har migrerat inåt och kretsar väldigt nära stjärnan) och superjordar (stenplaneter större än jorden). Därför blir frågan om hur unikt solsystemet är ännu mer intressant, vilket vi försöker ta reda på i det här projektet.

Det finns olika sätt att detektera exoplaneter på men två av dem har gett flest resultat:... (More)
Människans intresse för rymden har alltid varit stort. Man har antagit att andra planetsystem, om de existerar, ser ut som vårt: med mindre stenplaneter i banor närmast stjärnan och gas-samt isjättar i de yttre banorna. Idag känner man till drygt 2 000 exoplaneter, d.v.s., planeter som kretsar kring andra stjärnor än solen. Man vet även att vissa av dem saknar motsvarighet i solsystemet, t. ex., heta jupitrar (gasjättar som har migrerat inåt och kretsar väldigt nära stjärnan) och superjordar (stenplaneter större än jorden). Därför blir frågan om hur unikt solsystemet är ännu mer intressant, vilket vi försöker ta reda på i det här projektet.

Det finns olika sätt att detektera exoplaneter på men två av dem har gett flest resultat: transitmetoden och dopplerspektroskopin. Med transitmetoden mäter man minskningen av en stjärnas ljus när en planet passerar framför den. Den metoden passar bäst för stora planeter med små omloppsbanor. Dopplerspektroskopin använder sig av Doppler effekten som innebär att ljuset utsänt från en stjärna verkar blåare respektive rödare när en stjärna förflyttar sig fram och tillbaka från observatören. Denna rörelse avslöjar att det finns en planet som kretsar kring stjärnan och påverkar den med sin gravitation. Dopplerspektroskopin är lämpligast för massiva planeter med små omloppsbanor.

Under projektets gång har vi inte bara letat efter solsystemets motsvarigheter utan även studerat planetsystem som är annorlunda. Vi har hittat tecken på att vissa av heta jupitrar fortfarande kan hålla på och migrera inåt vilket kan leda till att mindre planeter i dessa system blir utkastade.

En annan fråga som dyker upp i detta sammanhang är om det finns liv på andra planeter än jorden. Vi har funnit några kandidater som skulle kunna ha samma uppbyggnad som jorden har. Man kan även definiera gränserna för en så kallad beboelig zon, d.v.s., det avstånd från stjärnan på vilket en planet får lagom med stjärnljus och kan ha vatten i flytande form på sin yta. En planet inom denna zon skulle då, rent teoretiskt, kunna vara bebodd. Bland planeter som vi betraktat fanns det sju sådana. Uppkomsten av ett liv är dock väldigt komplex och beror inte enbart på avstånd från stjärnan. Därför kan man tyvärr inte garantera att det finns ett utomjordiskt liv på dessa planeter.

Solsystemets motsvarigheter är fortfarande väldigt svåra att detektera med dagens teknologier. Därför förblir frågan om deras existens obesvarad. Man behöver uppfinna mer känsliga teleskop som kommer att kunna detektera små stenplaneter samt planeter med stora omloppsbanor. Det återstår att se vad morgondagens upptäckter kommer att visa. (Less)
Please use this url to cite or link to this publication:
author
Lomaeva, Maria LU
supervisor
organization
course
ASTK02 20161
year
type
M2 - Bachelor Degree
subject
publication/series
Lund Observatory Examensarbeten
report number
2016-EXA105
language
English
id
8889110
date added to LUP
2016-08-29 16:33:16
date last changed
2016-11-15 13:46:54
@misc{8889110,
  abstract     = {Over the past two decades many discoveries of exoplanets have been made, which have drawn much attention to extrasolar planetary systems. In this work we study the composition of these systems and search for analogues of the Solar System.

We considered the planets in the database at exoplanet.eu. The search of solar-like systems required these planets to be classified. The classification was performed using k-means clustering algorithm and planets with measured masses and semi-major axes were divided into three clusters: hot Jupiters, gas giants and the third cluster with rocky and Neptunian planets.

Our first attempt to separate rocky and Neptunian planets by their density was performed by using k-means algorithm for planets with three measured parameters: mass, radius and semi-major axis. The results, however, were not satisfactory and a simple mass limit was chosen instead.

Our examination of the extrasolar systems showed that there are few Solar System analogues. This most probably depends on the selection effects of the present-day detection techniques. Two of them were studied more closely: the Doppler radial velocity and transit technique. The first one is more likely to detect massive planets in close orbits, while the latter is more preferable for planets that pass in front of their host stars and have large radii and short orbital periods. Low-mass Earth-like rocky planets are more likely to be detected by the transit technique. Overall, the distribution of planets in their classes has been shown to follow expectations and selection effects.

The systems that contain hot Jupiters were studied closely and the results suggest that there is a number of hot Jupiters that might likely be caught in the act of migration. Also, the number of transiting extrasolar Neptunes and Earths was compared to the results presented by Petigura et al. (2013). It revealed a discrepancy, which arose due to the correction of the occurrence rate of these planets made by the article’s authors.

Rocky planets that potentially can host life were another interesting subject in the search of Solar System analogues. According to our definition of the habitable zone, we found six super-Earths and one Earth-like planet that might be habitable. However, such conclusions need deeper examination of the planetary properties.},
  author       = {Lomaeva, Maria},
  language     = {eng},
  note         = {Student Paper},
  series       = {Lund Observatory Examensarbeten},
  title        = {Solar System analogues among exoplanetary systems},
  year         = {2016},
}