A grand summary of this course

Life in Other Worlds• What is life?

– A process of systems that are capable of extracting energy and reproducing

– It could be much more general, and very different, than we know or think

• What is the physical base for life?– A physical mechanism capable of supporting extraction and

utilization of energy– In our case: carbon-based substrate

• Where can we look for life as we know it?– Easy answer: in places like our own Earth– What we need is water, carbon, oxygen, silicon, calcium,

phosphorus and temperature condition not too extreme – Caution: it took Earth 4.5 billion years to develop intelligent life– We have been a “communication civilization for about 100 years– Is this typical?

Can life form in other worlds?

The Habitable Zone(only for life like ours)

Potential candidates in the Solar System

Atmospheric spectraonly Earth conducive to

life

But Mars could have had life in the past

Mars Exploration

Looking for Martian fossils(none found)

Martian Meteorites

Is this evidence of life on Mars?

Life or mineral forms?

Mineral formation or fossile life?

Cosmos (our own Galaxy, in fact) too big for travel

• Enormous problems of storage/production of energy– Travel for small-size sip to nearest star at 1/3 c

needs 40,000 times the whole yearly US energy production

• Full size exploration way longer than human life span. Need colonies: will we remain what we are after 100 years in space?

• Communication seems more doable– SETI– Arecibo message– Voyager message

Radio telescopesRadio is best for distant

communication (best of all: water hole)

The Arecibo Telescope

The Arecibo MessageCoded in binary numbers

Numbers 1 to 10

Atomic numbers of H, C N, O and Ph

Chemical formulas for sugars and proteins

DNA molecular structureNumber of units in DNA

Height of human in wavelengths (12.3 cm)

Human figure

Population of Earth Solar system schematic

Arecibo transmitting antenna (telescope) Diameter of telescope in

wavelength

The Voyager Message

The message on the spacecraft

Drake Equation:The number of “cummunication capable”

civilazations in out Galaxy

• NC = N* x fp x nLZ x fL x fI x FS

• N*: number of stars per galaxy, ~ 1011

• fp: fraction of stars with planets, 0.01 to 0.5

• nLZ: planets per star in life zone over 4 Gyr, 0.01 to 1

• fL: fraction of suitable planets where life begins, 0.01 to 1

• fI: faction of life forms that develop intelligence, 0.01 to 1

• FS: fraction of star’s life with communicative intelligence, 10-8 to 10-4

• 2x10-5 < NC < 107

Drake Equation visualized