Astroblog

Left image: The Kepler-20 solar system, simulated in Celestia. Right image: Simulation of the view from orbit around Kepler-20e, with Kepler-20b visible in the sky. Click on an image to embiggen.

The Kepler-20 system made a bit of a splash back in December, when it was announced that the system, previously known to have three Neptune sized worlds in it, had two Earth-sized worlds in it.

And this time Earth-Sized actually Means Earth-Sized, with the planets Kepler-20e being 0.87 times the radius of Earth and Kepler-20f being 1.03 times the radius of Earth. The previously smallest world was 1.42 times Earth’s radius, and most of the "Super Earths" are much larger.

This report was an important demonstration that earth-sized worlds can be picked up by Kepler. Kepler 20 is a G8 star very similar to the Sun, but its solar system is crammed into a space inside Mercury's orbit. Kepler-20e would have a surface temperature hotter than 1000 degrees C, and Kepler-20f would be more Venus like.

The interesting thing is that these are almost certainly rocky worlds. Many exoplanetary systems have gas giants very close to the parent star, and the current thinking is that the Gas giant form far out in the developing solar system, then migrate inwards. This should expel any rocky worlds closer to the star. The fact the Kepler-20e and f have survived suggests that we may still find terrestrial worlds in some of these systems (Kepler-20e could have been an ice-world that migrated in and had its ocean boiled off, leaving a rocky core, but Kepler-20f is too far out to be a boiled down ice-world).

You can read the NASA press release here, and thoughtful commentary by the Bad Astronomer and Emily Lakdawalla. The paper just came out in the print copy of nature, so I've used this as an excuse to make Celestia files for the system. One for the star (which isn't in the default files) and one for the planet.

As usual, copy the data here to plain text files (Kepler-20.stc and Kepler-20-planets.ssc), copy both of the files to the Celestia extras folder. The star is around 950 lightyears away in Lyra, so in the Celestia star browser, you will have to show around 500 stars to see Kepler-20 in the list.
I'll have to update my Celestia Exoplanet Tour as well.

===============Kepler-20.stc======================================
#Kepler survey

"Kepler-20"
{
RA 287.7000
Dec 49.3386
Distance 945.9 # light years from published data
SpectralType "G8"
AppMag 12.423
}
==============================================================================

==================Keper-20_Planets.ssc=================================
"b" "Kepler-20"

# Neptune like world
# All data from original papers

{
Texture "exo-class4.*"
NightTexture "exo-class4night.*"


Mass 8.7 # M.sin(i) = 8.7 Earth
Radius 12181.98 # 1.91 Earth radi, from paper

#InfoURL "http://en.wikipedia.org/wiki/Kepler-20b"

EllipticalOrbit {
Period 0.0101
SemiMajorAxis 0.04537
Eccentricity 0.32
ArgOfPericenter 267 #guess
Inclination 86.50
#MeanAnomaly 271
}

# likely to be in captured synchronous rotation
}

AltSurface "limit of knowledge" "Kepler-20/b"
{
Texture "extrasolar-lok.*"

}

"c" "Kepler-20"

# Neptune like world

{
Texture "exo-class4.*"
NightTexture "exo-class4night.*"


Mass 16.1 # M.sin(i) = 16.1 Earth
Radius 19580.46 # 3.07 Earth radi, from paper

#InfoURL "http://en.wikipedia.org/wiki/Kepler-20b"

EllipticalOrbit {
Period 0.0297
SemiMajorAxis 0.0930
Eccentricity 0.4
ArgOfPericenter 267 #guess
Inclination 88.39
#MeanAnomaly 271
}

# likely to be in captured synchronous rotation
}

AltSurface "limit of knowledge" "Kepler-20/c"
{
Texture "extrasolar-lok.*"
}

"d" "Kepler-20"

# Neptune like world

{
Texture "exo-class4.*"
NightTexture "exo-class4night.*"


Mass 20.17 # M.sin(i) = 20.1 Earth
Radius 17539.5 # 2.75 Earth radi, from paper

#InfoURL "http://en.wikipedia.org/wiki/Kepler-20d"

EllipticalOrbit {
Period 0.21249
SemiMajorAxis 0.3453
Eccentricity 0.6
ArgOfPericenter 267 #guess
Inclination 89.570
#MeanAnomaly 271
}

# likely to be in captured synchronous rotation
}

AltSurface "limit of knowledge" "Kepler-20/d"
{
Texture "extrasolar-lok.*"
}

"e" "Kepler-20"

# earth like world

{
Texture "venussurface.*"
# Using venus although it may be a magma world


Mass 1.67 # M.sin(i) = 1.67 Earth, upper limit of theoretical range
Radius 3844.5167 # 0.868 Earth radi, from paper

#InfoURL "http://en.wikipedia.org/wiki/Kepler-20e"

EllipticalOrbit {
Period 0.0167
SemiMajorAxis 0.05073
Eccentricity 0.28
ArgOfPericenter 267 #guess
Inclination 87.50
#MeanAnomaly 271
}

# likely to be in captured synchronous rotation
}

AltSurface "limit of knowledge" "Kepler-20/e"
{
Texture "venussurface.*"
OverlayTexture "ganymede-lok-mask.png"
}

"f" "Kepler-20"

# earth like world

{
Texture "ganymede.*"
# Using Ganymede as it may be giant ice world
# NightTexture "gasgiantnight.jpg"


Mass 3.04 # M.sin(i) = 3.04 Earth theoretical maximum
Radius 6569.34 # 1.03 Earth radi, from paper

#InfoURL "http://en.wikipedia.org/wiki/Kepler-20f"

EllipticalOrbit {
Period 0.0536
SemiMajorAxis 0.11038
Eccentricity 0.32
ArgOfPericenter 267 #guess
Inclination 88.68
#MeanAnomaly 271
}

# likely to be in captured synchronous rotation
}

AltSurface "limit of knowledge" "Kepler-20/f"
{
Texture "ganymede.*"
OverlayTexture "ganymede-lok-mask.png"
}


==============================================================================

Labels: celestia, exoplanet, extrasolar planet