1. Amount of Water to be Habitable
Takanori Sasaki (Tokyo Tech)

3. H.Z. for Ocean Planets
・Inner edge of habitable zone
runaway greenhouse limit: 0.84AU@present S.S.
[Kasting 1988; Nakajima et al. 1992]
・Outer edge of habitable zone !
Forming CO2 clouds: 1.37AU [Kasting 1993]
from Kasting et al. (1993) 436

4. 3 Types of Water Planets
“Land Planet” “Aqua Planet” “Ocean Planet”
unconnected lakes connected oceans an ocean
on a land and lands without lands

5. H.Z. for Land Planets
・Inner edge of habitable zone
Dry low latitude can emit above the “critical flux”
Runaway greenhouse limit of solar flux is larger
・Outer edge of habitable zone
Lower albedo by smaller area of ice and cloud
Freezing limit of solar flux is smaller
H.Z. is wider for “land planets” than “aqua planets”
[Abe et al. 2011]

6. C.H.Z. for Various Planets
= the region in which liquid water can exist over the lifetime of a host star
“Land Planet” “Aqua Planet” “Ocean Planet”
~0.73-1.3AU 0.9-1.1AU
[Abe et al. 2011] [e.g., Kasting et al. 1993]

7. - 初期海洋質量の影響 - 進化せ
時間 [Gyr]
時間 [Gyr]
4
4
・恒星：太陽質量 ・恒星からの距離：0.75AU
・惑星：地球質量 ・初期海洋質量：0.001 2海洋質量
Evolution of H.P.
habitable
1
6
6
[[Earth’s ocean mass]
runaway
現在の地球の海洋質量で規格化]
greenhouse 進化せず
進化
Initial ocean mass
初期海洋質量
0.15
進化せず
進化せず
0.1
進化
進化
進化
habitable
8
8
10-2
10-3
10
10
0 2 4 6 8 10 Earth-size
Time [Gyr]
時間 [Gyr] ＠0.75AU
[Kodama, Genda & Abe, in prep.]

8. Habitable Snowball Planets
Snowball planets could have an internal ocean with
IKA
geothermal heat flowVol. 680 the planetary interior
from
Fig. 3.—Limit of the planetary mass above which liquid water exists. (a)
[Tajika 2008]
Ice thickness as a function of planetary mass and distance from the central
star with the present luminosity of our Sun. Because of higher heat flow, ice
thickness is thinner for larger planets. (b) The water depth and the maximum

9. H.Z. for Snowball Planets
NOWBALL PLANETS L55
[Tajika 2008]
Fig. 4.—Limit of the distance from the central star for the existence of

10. High-pressure Ice
– 22 –
・High-pressure ices appear if the planet has larger
amount of water than the Earth
・High-pressure ices are denser than liquid water

11. S.P. w/ High-pressure Ice
Mwater = 5 x 0.023 wt.%
Habitable? Not Habitable?
Europa Ganymede
[Ueta & Sasaki, submitted to ApJ]
Fig. 6.— Conditions for a planet around a central

12. 期海洋質量の影響 -
期海洋質量の影響 -
・初期海洋質量：0.001 2海洋質量
・初期海洋質量：0.001 2海洋質量
・恒星からの距離：0.75AU
・恒星からの距離：0.75AU
結果 -
- 初期海洋質量の影響 - 進化せず
Summary
時間 [Gyr]
時間 [Gyr]
4
4
・恒星：太陽質量 ・恒星からの距離：0.75AU
・惑星：地球質量 ・初期海洋質量：0.001 2海洋質量
1
6
6
[現在の地球の海洋質量で規格化]
進化せず
進化
[Earth’s ocean mass]
Initial ocean mass
初期海洋質量
0.15
進化せず
進化せず
0.1
進化
進化
進化
8
8
10-2
10-3
0 2 4 6 8 10
10
10
時間 [Gyr]
Time [Gyr]
・Amount of water changes the range of H.Z.
Fig. 6.— Conditions for a planet ar
・Too much water could prevent the habitability.
(b) Msw /Msw0 = 2, (c) Msw /Msw0 =
・How much water do they 8
4 6 10question.
have? is a keythe central star; v
the distance from