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Size: 3339
Comment:
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Size: 3965
Comment:
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| Deletions are marked like this. | Additions are marked like this. |
| Line 8: | Line 8: |
| Stellar ||Class || Radius || Mass || Luminosity || Temperature || Examples || || || R/R☉ || M/M☉ || L/L☉ || K || || || F0 || 1.3 || 1.7 || 6 || 7,240 || Gamma Virginis || || F5 || 1.2 || 1.3 || 2.5 || 6,540 || Eta Arietis || || G0 || 1.05 || 1.10 || 1.26 || 5,920 || Beta Comae Berenices || || G2 || 1.00 || 1.00 || 1.00 || 5,780 || Sun || || G5 || 0.93 || 0.93 || 0.79 || 5,610 || Alpha Mensae || || K0 || 0.85 || 0.78 || 0.40 || 5,240 || 70 Ophiuchi A || || K5 || 0.74 || 0.69 || 0.16 || 4,410 || 61 Cygni A || |
Long Life Star
The heating Sun will make the (unmodified) Earth uninhabitable in less than a billion years. How long would a lower mass star last, and for a closer planet with the same illumination as earth, what would the system escape velocity be?
In the mass range near the suns ( 0.5 M⊙ < M < 2.0 M⊙), the luminosity is approximately L/L⊙ = (M/M⊙)⁴ . Assuming a 5 billion year lifetime for Earth, and an escape velocity of 30 km/s, what is the orbit radius in AU and the escape velocity for an "earthlike" planet?
NOTE the "lifetime" should be scaled (somehow) to the amount of photosynthesis-friendly red light compared to the amount of life-scrambling thermal infrared. Life decays with thermal energy, and builds from red photons (blue is used by terrestrial photosynthesis, but probably is not necessary). Stellar
Class |
Radius |
Mass |
Luminosity |
Temperature |
Examples |
|
R/R☉ |
M/M☉ |
L/L☉ |
K |
|
F0 |
1.3 |
1.7 |
6 |
7,240 |
Gamma Virginis |
F5 |
1.2 |
1.3 |
2.5 |
6,540 |
Eta Arietis |
G0 |
1.05 |
1.10 |
1.26 |
5,920 |
Beta Comae Berenices |
G2 |
1.00 |
1.00 |
1.00 |
5,780 |
Sun |
G5 |
0.93 |
0.93 |
0.79 |
5,610 |
Alpha Mensae |
K0 |
0.85 |
0.78 |
0.40 |
5,240 |
70 Ophiuchi A |
K5 |
0.74 |
0.69 |
0.16 |
4,410 |
61 Cygni A |
M |
L |
r |
life |
vesc |
Wp |
Temp |
B |
V |
G |
R |
H |
|
M⊙ |
L⊙ |
AU |
GY |
km/s |
mag |
K |
445 |
551 |
|
658 |
1630 |
|
0.50 |
0.0625 |
0.2500 |
40.0000 |
42.4264 |
M1V |
|
|
|
|
|
|
|
0.55 |
0.0915 |
0.3025 |
30.0526 |
40.4520 |
|
|
|
|
|
|
|
|
0.60 |
0.1296 |
0.3600 |
23.1481 |
38.7298 |
M0V |
|
|
|
|
|
|
|
0.65 |
0.1785 |
0.4225 |
18.2066 |
37.2104 |
|
|
|
|
|
|
|
|
0.70 |
0.2401 |
0.4900 |
14.5773 |
35.8569 |
K5V |
|
|
|
|
|
|
|
0.75 |
0.3164 |
0.5625 |
11.8519 |
34.6410 |
K3V |
|
|
|
|
|
|
|
0.80 |
0.4096 |
0.6400 |
9.7656 |
33.5410 |
K2V |
|
|
|
|
|
|
|
0.85 |
0.5220 |
0.7225 |
8.1417 |
32.5396 |
G9V |
|
|
|
|
|
|
|
0.90 |
0.6561 |
0.8100 |
6.8587 |
31.6228 |
G7V |
|
|
|
|
|
|
|
0.95 |
0.8145 |
0.9025 |
5.8318 |
30.7794 |
G6V |
|
|
|
|
|
|
|
1.00 |
1.0000 |
1.0000 |
5.0000 |
30.0000 |
G2V |
|
|
|
|
|
|
|
1.05 |
1.2155 |
1.1025 |
4.3192 |
29.2770 |
G3V |
|
|
|
|
|
|
|
1.10 |
1.4641 |
1.2100 |
3.7566 |
28.6039 |
G1V |
|
|
|
|
|
|
|
1.15 |
1.7490 |
1.3225 |
3.2876 |
27.9751 |
F9V |
6130 |
|
|
|
|
|
|
1.20 |
2.0736 |
1.4400 |
2.8935 |
27.3861 |
F7V |
|
|
|
|
|
|
|
1.25 |
2.4414 |
1.5625 |
2.5600 |
26.8328 |
F6V |
6520 |
|
|
|
|
|
25 Cancri |
1.30 |
2.8561 |
1.6900 |
2.2758 |
26.3117 |
F4V |
|
|
|
|
|
|
|
1.35 |
3.3215 |
1.8225 |
2.0322 |
25.8199 |
F3V |
6740 |
14.2 |
13.3 |
|
13.1 |
11.7 |
COROT-3 |
1.40 |
3.8416 |
1.9600 |
1.8222 |
25.3546 |
F1V |
|
|
|
|
|
|
Twice the escape energy for a star lasting 8 times as long. A "perfect" star system for star-faring life might be a K5, with 3 times the lifetime and 20% more escape velocity.