1. Martin Crow Crayford Manor House Astronomical Society

2. So is there life in the universe? What do you think?

3. Martin Crow Crayford Manor House Astronomical Society Time line for life on Earth. 4,567 million years – Formation of Earth. 4,200 – 3,800 million years – late heavy bombardment. 3,800 million years – evidence for life on Earth. 3,000 million years – Oxygen in atmosphere. 1,100 million years – multi-cellular life. 580 - 500 million years – Cambrian explosion. 360 million years – Earth begins to be recognisable. 170 million years – Mammals appear. 2 million years – Genus Homo appears. 0.2 million years - Anatomically modern humans appear in Africa.

4. Martin Crow Crayford Manor House Astronomical Society

5. Where might life be found? This question does depend on what type of life is being considered. Certain places in the universe are likely to be inhospitable to life. In regions where stars are densely packed like in the central parts of galaxies and in globular clusters. The large amounts of radiation would be damaging to carbon based life. For instance: In areas that are metal poor like in the early universe and globular clusters. In systems with massive stars.These are too short lived for life to really get going. In galaxies undergoing collision / interaction?

6. Martin Crow Crayford Manor House Astronomical Society It is thought that there is are galactic habitable zones where conditions would be favourable for life. In the Milky Way galaxy, the GHZ is currently believed to be a slowly expanding region approximately 25,000 l.y. from the galactic core and some 6,000 l.y. in width containing stars roughly 4 billion to 8 billion years old. The are estimated to be 500 x 10⁶ stars in the habitable zone. The GHZ will not be the same for all galaxies. This does, however, assume that all life has similar requirements.

7. Martin Crow Crayford Manor House Astronomical Society There will be a habitable zone around any given star where the temperature would allow water in the liquid phase. This is also called the “Goldilocks” zone, being neither too hot or too cold but just right. Again this all assumes that life needs similar requirements to here on Earth.

8. Martin Crow Crayford Manor House Astronomical Society However, there are probably other stable and durable environments that will support the development of life. It looks increasingly likely that the Icy Moons around the Gas Giants, Jupiter and Saturn have salty liquid oceans beneath their surfaces (Europa and Enceladus). Europa Enceladus

9. Martin Crow Crayford Manor House Astronomical Society Although they are both well outside the habitable zone their interiors are kept warm by tidal squeezing as they orbit the Giant planets. These environments are protected from the radiation of space and impacts by their icy crusts and are probably stable for millions of years. A black smoker in the Atlantic Ocean driven by geothermal energy

10. Martin Crow Crayford Manor House Astronomical Society It is possible that these sub-surface oceans will turn out to be the most common environment for life in the universe.

11. Martin Crow Crayford Manor House Astronomical Society It is also possible that there is life that does not rely on water for its solvent. Titan

12. Martin Crow Crayford Manor House Astronomical Society Titan has a methane cycle. On Titan it rains liquid methane

13. Martin Crow Crayford Manor House Astronomical Society Cassini radar image of titan’s surface showing evidence for lakes / seas and rivers of hydrocarbons.

14. Martin Crow Crayford Manor House Astronomical Society It has been suggested that life could exist in the lakes of liquid methane on Titan, just as organisms on Earth live in water. Such creatures would inhale H 2 in place of O 2, react it with acetylene instead of glucose, and exhale methane instead of carbon dioxide.

15. Martin Crow Crayford Manor House Astronomical Society Exoplanets Currently 474 stars are known to have planets orbiting them. A total of 564 planets have been discovered – non are Earth like. However, this is a bias caused by the way we are currently able to detect them. Greater sensitivity and more time will reveal earth like planets around other stars. Our presence will only be known out to around 90 l.y. as this is as far as our earliest radio signals will have got to.

16. Martin Crow Crayford Manor House Astronomical Society Amateur astronomers can detect exoplanets with their equipment.

17. Martin Crow Crayford Manor House Astronomical Society The Drake Equation First devised by Frank Drake in 1961 it is an equation used to estimate the number of detectable extraterrestrial civilizations in the Milky Way galaxy. The Drake equation states that: N = N*. f p. n e. f ℓ. f i. f c. L where: N = the number of civilizations in our galaxy with which communication might be possible. N * = represents the number of stars in the Milky Way Galaxy. f p = the fraction of those stars that have planets. n e = is the number of planets per star that are capable of sustaining life. f ℓ = the fraction of the above that actually go on to develop life at some point. f i = the fraction of the above that actually go on to develop intelligent life. f c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space. L = is fraction of the planet's life during which the communicating civilizations live.

18. Martin Crow Crayford Manor House Astronomical Society