2. Searching for Earths
Are there any planets where life may exist?
(Question) What are the conditions for life to exist?
3. Searching for Earths
Are there any planets where life may exist?
(Question) What are the conditions for life to exist?
(Answer) Existence of water in the form of liquid
4. Searching for Earths
•If the temperature of the planets is high….
Water evaporates（⽔蒸发）
•If the temperature of the planets is low….
Water freezes（⽔结冰）
For the existence of liquid water, the temperature of
planets should be not too hot and not too cold.
The region of the orbit of planets where life can exist is called the habitable
zone（宜居带）
5. Habitable zone
•In the case of our solar system, the habitable zone is between 0.97 AU and 1.4 AU from the sun.
Cold
Hot
6. Habitable zone
•If the main stars are different, the habitable zone is
also different (e.g., The sun's surface temperature (G
type) is roughly 5700K).
•The larger mass stars have a higher temperature.
The habitable zone depends on the mass of the
main stars.
The region of the orbit of planets where liquid water can exist is called the
habitable zone（宜居带）
7. Habitable zone
•The larger mass stars have a higher temperature.
The habitable zone of the exoplanets
orbiting high-mass stars is far from main
stars.
High-mass
main stars
Far from
main stars
8. For finding life in the universe
•We have already discovered more than 4000
exoplanets.
•~65-75 % of stellar stars have exoplanets
whose periods are less than 10 years!
Mayor et al (2009)
9. For finding life in the universe
•We have discovered more than 4000
exoplanets in the Milky Way.
(Question)
How many exoplanets are located in the
habitable?
1. ~50
2. ~100
3. ~1000
4. >1000
Discover exoplanets that are located in the habitable zone is the
first step to finding life in the universe!
10. For finding life in the universe
•We have discovered more than 4000
exoplanets in the Milky Way.
(Question)
How many exoplanets are located in the
habitable?
1. ~50
2. ~100
3. ~1000
4. >1000
Discover exoplanets that are located in the habitable zone is the
first step to finding life in the universe!
11. Summary
• Our solar system is not the only planetary system. We
have already discovered more than 4000 exoplanets.
• Life may exist on the planets where water can keep the
form of liquid.
• Those planets are located in the habitable zone.
• We have already discovered ~50 exoplanets which are
located in the habitable zones.
13. Before I start the life in the universe, I would like to ask a question.
If the history of the universe is 1 year, when do you think life and human
being came into being? (如果宇宙的历史是⼀年，你认为⽣命和⼈类是何
时出现的？)
37. Before I start the life in the universe, I would like to ask a question.
If the history of the universe is 1 year, when do you think life and human
being came into being? (如果宇宙的历史是⼀年，你认为⽣命和⼈类是何
时出现的？)
(Answer)
9/21: First life emerged.
12/5: First multicellular life(多细胞⽣命).
12/25:Dinosaurs（恐⻰🦕）.
12/31 6:05 :Apes（类⼈猿）.
12/31 23:52: Modern humans evolve.
Human history began last 1 minute on 12/31.
After the summer holidays,
the solar system formed!
