ASTRONOMY 202 Spring 2007: Solar System Exploratio n

Instructor: Dr. David Alexander Web-site: w ww.ruf.rice.edu/~dalex/ASTR202_S07

Class 37: Life in the Universe [4/18/07]

� Announcements

� Habitability of other planets

� Intelligent Life – Drake Equation

Now Playing: Subterranean Homesick Alien – Radiohead

Chapter 24Chapter 24

Announcements

Homework

HW10 is online due Mon Apr 23

Extra-credit discussion paper is available due NOW

Test

Study Guide online

Review on Monday – send topics, requests, or suggestions via email

YOU WILL NEED A CALCULATOR!!!!

Observing

Open House tonight at Observatory for those interested

What’s the point?

FINAL NOTICE: the Earth will fall into Null Space.FINAL NOTICE: the Earth will fall into Null Space.FINAL NOTICE: the Earth will fall into Null Space.FINAL NOTICE: the Earth will fall into Null Space.

Which Stars make Good Suns?• Which stars are most likely to have planets harboring life?

• they must be old enough so that life could arise in a few x 108

years• this rules out the massive O & B main sequence stars

• they must allow for stable planetary orbits• this rules out binary and multiple star systems

• they must have relatively large habitable zones• region where large terrestrial planets could have surface temperature

that allow water to exist as a liquid

Properties of Other Planetary Systems

• planets appear to be Jovian• more massive than our system• planets are close to their stars• many more highly eccentric orbits than in our Solar System

Saturn-Mass Planet Transits

across HD 149026

Habitable exoplanets?

• In the near future, NASA plans to launch Terrestrial Planet Finder.• an interferometer in space

• take spectra and make crude images of Earth-sized extrasolar planets

• Spectrum of a planet can tell us if it is habitable.• look for absorption lines of ozone

and water

Astrobiology

Astrobiology is the study of life in the universe. Astrobiology is the study of life in the universe.

Recent HighlightsExoplanet plants may not be greenBy looking at the changes in star light through different atmospheres, researchers identified colors that would be most favorable for photosynthesis on other planets. This new research narrows the range of colors that scientists would expect to see when photosynthesis is occurring on extrasolar planets. Each planet will have different dominant colors for photosynthesis, based on the planet’s atmosphere where the most light reaches the planet’s surface. The dominant photosynthesis might even be in the infrared.

Data from the Hubble Space Telescope has helped astronomers identify water in the atmosphere of a giant planet far away from our Solar System.

Water in Extrasolar Planet's Atmosphere

Are Earth-like planets common?

YES

Our own solar system has three Earth-like planets so should be common.

Galactic Habitable ZoneInside – too many supernovae

Outside – not enough heavy elementsNO “Rare-Earth hypothesis”

- formation of life is a series of complex circumstances so life like us is unlikely.

- need a Jupiter to remove comets to “Oort cloud” which could otherwise bombard Earth

- plate tectonics is just lucky

- Large moon is lucky – stabilizes Earth tilt and therefore climate

Drake EquationAn equation that lays out the factors that play a r ole in determining

the number of communicating civilizations in our ga laxy.

Number of civilizations =Number of habitable planets

x fraction with life

xfraction

with civilization

xfraction

civilization now

NHP × flife tells us the number of life-bearing planets in the galaxy.

NHP × flife × fciv, we get the total number of planets upon which intelligent beings have evolved and developed a communicating civilization at some time in the galaxy’s history.

NHP × flife × fciv × fnow tells us how many civilizations we could potentially make contact with today.

The result of the Drake equation is the number of civilizations that we might hope to contact.

Intelligence

This graph shows how brain mass compares to body mass for some

mammals (including primates) and birds. The straight line represents an average of the ratio of brain mass to body mass, so that animals that fall

above the line are smarter than average and animals that fall below the line are less smart. Note that the

scale uses powers of 10 on both axes.

Humans lie significantly farther above the line tha n the data point for any other species. Thus, by this measure of intelligence, we are far s marter than any other species that has ever existed on Earth.

Is the human level of intelligence rare?

Epilogue

http://www.youtube.com/watch?v=9JSR_6qfXTg