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Summary of the Limits of the New Habitable Zone

posted Mar 23, 2013, 5:45 PM by Abel Mendez   [ updated Apr 8, 2013, 12:39 AM ]
The new habitable zone (Kopparapu et al., 2013) has a narrow and wide definition (Figure 1). The narrower 'conservative habitable zone' is bounded by the 'moist greenhouse' and 'maximum greenhouse' limits (Table 1). The wider 'optimistic habitable zone' is bounded by the 'current Venus' and 'early Mars' limits (Table 2). We recommend to use the wider definition since the current definition of the habitable zone does not include the potential widening effects of water and CO2 clouds. A habitable zone calculator is available here. More details about these boundaries are available here.


Figure 1. Habitable Zone of around main sequence FGKM stars. The warm 'habitable' zone is divided into a 'conservative habitable zone' (light green) and an 'optimistic habitable zone' (dark green). Earth is at the inner edge of the 'conservative habitable zone.'

Table 1. Limits of the 'Conservative Habitable Zone' for various planetary parameters, including some transiting properties.

 

 

 

 

 

Transit Properties

Star

Type

Distance (AU)

Stellar Flux (SU)

Eq. Temp. (K)

Period (days)

Depth

(ppm)

T. Prob. (%)

Max. T. Dur. (hrs)

inner

outer

inner

outer

inner

outer

inner

outer

Inner

outer

inner

outer

F

1.56

2.60

1.05

0.38

257

199

621

1341

43

0.41

0.25

19.7

25.5

G

0.99

1.69

1.01

0.35

255

196

361

801

83

0.47

0.28

13.1

17.0

K

0.64

1.13

0.95

0.31

251

189

216

507

119

0.61

0.35

10.2

13.6

M

0.12

0.22

0.87

0.25

246

179

26

68

939

1.19

0.63

2.5

3.4


Table 2. Limits of the 'Optimistic Habitable Zone' for various planetary parameters, including some transiting properties.


 

 

 

 

 

Transit Properties

Star

Type

Distance (AU)

Stellar Flux (SU)

Eq. Temp. (K)

Period (days)

Depth

(ppm)

T. Prob. (%)

Max. T. Dur. (hrs)

inner

outer

inner

outer

inner

outer

inner

outer

Inner

outer

inner

outer

F

1.18

2.84

1.84

0.32

296

191

408

1529

43

0.55

0.23

17.2

26.6

G

0.75

1.84

1.78

0.29

294

187

237

913

83

0.62

0.25

11.4

17.8

K

0.48

1.23

1.67

0.26

289

181

142

578

119

0.81

0.32

8.9

14.2

M

0.09

0.24

1.53

0.21

283

171

17

77

939

1.57

0.58

2.1

3.5


Table Notes:
  • Star Type: spectral type of the parent star. Some of the values in these tables were calculated for specific stars (check here Table 1 for a description of the stars).
  • Distance (AU): distance from the parent star in astronomical units (AU).
  • Stellar Flux (SU): stellar flux in solar units (SU).
  • Eq. Temp. (K): equilibrium temperature of a planet in kelvins (K) assuming a bond albedo of 0.3.
  • Period (days): orbital period of a planet in days. This values also depends on the actual mass of the star.
  • Depth (ppm): transit depth of an Earth-size planet in parts per million (ppm). This value also depends on the actual size of the star but does not depend on the habitable zone.
  • T. Prob. (%): transit probability of a planet in percent (%). This value also depends on the actual size of the star.
  • Max. T. Dur. (hrs): maximum transit duration in hours (hrs) for a planet. This value also depends on the actual size of the star.