A visual representation of a loud and unusual sound, dubbed a Bloop, captured by deep sea microphones in 1997. Although Bloops are some of the loudest sounds of any type ever recorded in Earth's oceans, their origin remains unknown. The Bloop sound was placed as occurring several times off the southern coast of South America and was audible 5,000 kilometers away. Although the sound has similarities to those vocalized by living organisms, not even a blue whale is large enough to croon this loud. The sounds point to the intriguing hypothesis that even larger life forms lurk in the unexplored darkness of Earth's deep oceans.

FINAL EXAM: Wednesday, May 5, 5:00 – 7:00 pm.

Review session:Monday, May 3, 7:15 until ?, Swain West 007

Exam questions will mostly cover material presented since last exam, but some LARGE CONCEPT questions

may be asked.

Europa• metallic core, rocky mantle, &

a crust made of H2O ice• fractured surface -> tectonics.

• few impact craters seen• double-ridged cracks • jumbled icebergs

• (evidence of a subsurface

• ocean).

• Europa has a magnetic field.• implies liquid salt water beneath

the icy crust

• Where liquid water exists, there could be life!

Ganymede• largest moon in the Solar System

• Two types of terrain:• heavily cratered, implies old• long grooves, few craters, implies

young like Europa

• It also has a magnetic field.

• Could it have subsurface ocean?• case not as strong as Europa’s• tidal heating would be weaker• would need additional heating from

radioactive decay

• It has an old surface.• heavily cratered, dirty ice• cratering reveals clean, white ice• no evidence of tectonics

• Its interior did not differentiate.• rock mixed with ice

• It does not experience tidal heating.

• Yet it has a magnetic field.

• Could it have a subsurface ocean anyway?

Callisto

• largest of Saturn’s moons

• Huygens landed in January 2005

• has a thick atmosphere.• Nitrogen (from dissociated NH3; 90%),

Argon, methane, ethane• methane, ethane are greenhouse gases:

surface is warmer than it should be• Ethane/methane may condense to form

clouds and rain

• Atmosphere blocks view of surface• may have oceans of ethane/methane• erosion may be important

Titan

http://saturn.jpl.nasa.gov

Liquid Lakes on Titan:

Some regions on Titan reflect very little radar. The leading explanation for this is that these regions are lakes, possibly composed of liquid methane.

This image is a false-color radar map of a northern region of Titan taken by the Cassini spacecraft. On this map, which spans about 150 kilometers across, dark regions reflect relatively little of the broadcast radar signal. Titan is the only body in the Solar System, other than the Earth, known to possess liquids on its surface.

Cold, windy, surface like wet clay, ice “rocks”

Enceladus

Enceladus

Regardless of how it is accomplished, it is generally agreed that if civilization continues on Earth, we are likely to travel to the stars

and possibly populate the Galaxy.

But this leads to a problem…

Fermi Paradox Our planet is not special

If even one civilization had originated before us then it should have already colonized the entire galaxy

“So where is everybody?” (Enrico Fermi, 1950)

The Fermi Paradox:

Voices the apparent contradiction between high estimates of the probability of the

existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such

civilizations.

With foreseeable technology, we can achieve speeds of 10% of the speed of light

We can travel 10 light years in 100 years

We can reach the nearest star in 43 years

Allow each new colony 5000 years to duplicate the technology

Colonies could spread out about 50 light years every 25,000 years

How long to colonize the Galaxy?

Assume 100,000 yearsper 20 parsec hop

Total time to cover theGalaxy:

1500 hops x 100,000 years

= 150,000,000 years

30,000 pc

Fermi ParadoxFermi Paradox

Our Galaxy is ~ 14 billion years old so ...Our Galaxy is ~ 14 billion years old so ...

Time to populate the Galaxy: 150 Million Years

Drake Equation: 200 ET Civilizations

Extraterrestrial Life?Where are they?

Don’t Overlook the Obvious!

Fox Network

Since 1947 We’ve had 33 U.S.

Saucer Crashes!

(~1 Every 2 years)

04-Jul-47 Roswell, NEW MEXICO (4 Bodies)

13-Feb-48 Aztec, NEW MEXICO (2 Bodies)

07-Jul-48 MEXICO So.of LAREDO TX (1 Body)

08-Aug-49 Roswell, NEW MEXICO (2 Bodies)

10-Sep-50 Albuquerque, NEW MEXICO (3 Bodies)

14-Aug-52 Ely, NEVADA (16 Bodies)

….

Since 1965 We’ve Had 14 Boeing

700 SeriesU.S. Airline Crashes

(~1 Every 3 Years)

Boeing Jets (1 crash every 3 years) vs

ET (1 crash every 2 years)

Don’t Get on Flying Saucer (They’re Death Traps)

Earth is the O’Hare International Airport of the Galaxy

– This morning, violence broke out in an up-til-now quiet region of Iraq, in the southern town of Rajaf. Four US soldiers were killed.

– With great effort, I can fly short distances (10-20 ft) using the power of my mind.

Which (if either) do you believe? Why?

“Extraordinary claims require extraordinary evidence”Carl Sagan .

Possible solutions to Fermi Paradox

We are alone.

There is life, but no advanced civilizations

Civilizations are common, but no one has colonized the Galaxy.

They Are/Were Here

They Are Us

Zoo/Interdiction Scenario

Stay tuned…