The Search for Life in the Universe

Criteria Defining Life

1. Made up of one or more cells2. Organized3. Grows & develops4. Reproduces 5. Responds to stimuli6. Requires energy7. Maintains homeostasis8. Adapts and evolves over time

Building Blocks of Life

(1) Basic elements: – Carbon– Nitrogen– Hydrogen– Oxygen

Where did the elements come from?

The Elements: Forged in Stars

* The elements alone do not form life. They need to combine to form amino acids.

(2) Amino acids – proteins that make DNA

(3) Water – necessary for chemical reactions of life to take place.

Meteorites

• Carbonaceous chondrites – type of meteor that may contain small amounts of carbon, amino acids, & water

• Scientists witnessed the Comet Shoemaker-Levy crashing into Jupiter in 1994

• “Seed” Theory – Did life come to Earth from a meteor??

Miller-Urey Experiment

• Stanley Miller and Harold Urey, University of Chicago, 1952.

• Experiment: They combined methane, hydrogen, ammonia, and water and shocked the mixture with electrical currents . They created an enviornment similar to Earth’s early atmosphere which would have been exposed to lightning and high-energy UV rays.

H2O

N

NH3

CO2

CO

CH4

H2

The result was that amino acids, but not life itself, were created.

This is exciting!

From meteorites, we know that the ingredients for life are abundant in our universe, and our universe is so vast that the chances that life

evolved elsewhere is likely!

Ideal Conditions for Life

• Amino acids must be present• Liquid water must be present; the

environment cannot be too hot or too cold • Can’t rule out unlikely environments.

Extremophiles are organisms that thrive in very harsh environments (ex. bacteria in Yellowstone’s Mammoth Springs)

Mammoth Springs, Yellowstone NP

The search for life within our

own solar system...

Mars

• Past: Volcanic & impact heat reacting with water similar to conditions of hot springs

• Present: Evidence for liquid water (dry river beds, canyons)

• Frozen water located at the poles and in the ground.

• 1996 – discovery of fossil bacteria?

Europa

• One of Jupiter’s Moons• Surrounded by a thick, frozen ocean (up to

100 miles deep!)

• Liquid water may surface where there are cracks from tidal forces

Titan

• One of Saturn’s Moons• Has a very dense hydrogen atmosphere• The hydrogen “rain” disappears at the

surface- indication of life in an unexpected environment?

Viking Mission

• Launched beginning in 1976 to study Mars

Cassini Mission

• Launched in 1997 to study the outer planets, especially Saturn.

The search for life beyond our solar

system...

Exoplanets

• Exoplanets – planets orbiting stars other than our Sun

• They are detected by changes in visible light – transit – “eclipses” of the planet that dim the light in a cyclic manner.

Four Ways to Find a Planet

(1)Radial Velocity(2)Astrometry(3)Transit Method(4)Optical Detection

History of Exoplanet Exploration

Radial Velocity

• The Doppler Spectroscopy shows the star moving away and toward the Earth. This technique can detect the orbital period and mass of the planet.

Radial Velocity

Doppler Effect

Astrometry

• Stars can be measured in relation to their distance to other stationary stars using a “ruler”

Transit Method

• Instruments can detect changes in brightness of a star that would be caused by a planet crossing in front of that star

Problems with Transit Method

• Planets must be edge-on• Some planets may be too small to detect• Long periods of revolution?

Optical Detection

• “Nulling”- Light can be canceled out by aligning crests of one wave to troughs of another. This will block out a star’s light and expose the hidden planet

• The light from a star can be blocked so that only the “corona” shines through. This may expose a hidden planet!

Habitable Zones

• “Goldilocks” zone where ideal environments for life on exoplanets exist.

• Based on size of the star that an exoplanet ortbis and the distance of the exoplanet to that star.

NASA Mission

• Kepler – launched in March 2009 to search for exoplanets in a very small region of the Milky Way galaxy.

What are the chances??

• Billions of stars in our own galaxy and billions of galaxies in the universe!

• As of February 2012, there have been 2,321 exoplanets discovered!!