1. In 2020, a spacecraft lands on Europa and melts its way through the ice into the Europan ocean. It finds numerous strange, living microbes, along with a few larger organisms that feed on the microbes.
This is fantasy because the X-ray emission from Saturn has effectively sterilized all the moons around it.
This is fantasy because it would take more than 20 years for a spacecraft to reach Saturn with current technology.
This is possible because there is evidence for an ocean underneath the icy surface of Europa and water is a good place to look for life.
This is likely because molecules produced only by life were already detected on Europa by Voyager 2.
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2. 18.2 Life in the Solar System
Our goals for learning
Could there be life on Mars?
Could there be life on Europa or other jovian moons?

3. Could there be life on Mars?
Mars had liquid water in the distant past
Still has lots of subsurface ice; possibly subsurface water near sources of volcanic heat.
This photo shows the Opportunity panorama that appears as the opening photo for Ch. 6. Spend a couple minutes reviewing why Mars is a promising place for life: evidence of past water, evidence for subsurface ice today… You might wish to repeat some slides from Ch. 7 on Mars to show the evidence for past water from orbit.

4. In 2004, NASA Spirit and Opportunity Rovers sent home new mineral evidence of past liquid water on Mars.

5. Close-up view of round pebble apparently formed in water on Mars.
Optional additional slide (this is Figure 7.24).
Close-up view of round pebble apparently formed in water on Mars.

6. The Martian Meteorite debate
composition indicates origin on Mars.
1984: meteorite ALH84001 found in Antarctica
13,000 years ago: fell to Earth in Antarctica
16 million years ago: blasted from surface of Mars
4.5 billion years ago: rock formed on Mars
If you wish to discuss the martian meteorite debate, it’s good to start with a brief history of the meteorite as reconstructed from its geology and dating of various components.

7. Does the meteorite contain fossil evidence of life on Mars
Does the meteorite contain fossil evidence of life on Mars? (left: Mars; right: Earth)
These microscopic photos show structures with a fossil-like appearance, but they may also have been formed by non-biological processes. Bottom line: meteorite is intriguing, but certainly not definitive. We’ll need much more evidence to conclude that life ever existed on Mars.
Depending on level of coverage, you might wish to go into the pro and con debate in greater detail, as discussed in the text on p

8. Could there be life on Europa or other jovian moons?
Review evidence for liquid water ocean on Europa, in which case there might be undersea volcanoes. Artists conception of volcanic eruption temporarily disrupting surface ice.

9. Ganymede, Callisto also show some evidence for subsurface oceans.
Relatively little energy available for life
Nonetheless, intriguing prospect of THREE potential homes for life around Jupiter alone.
Ganymede
Callisto

10. Titan Surface too cold for liquid water (but deep underground?)
If you are teaching after the Huygens descent, you’ll certainly want to update this slide with new information/images…
Surface too cold for liquid water (but deep underground?)
Liquid ethane/methane in places on the surface
...but not at Huygens probe landing site, Jan. 2005
No evidence for surface life (if any, probably quite alien)

11. What have we learned? • Could there be life on Mars?
Mars once had conditions that may have been conducive to an origin of life. If life arose, it might still survive in pockets of liquid water underground.

12. What have we learned?
• Could there be life on Europa or other moons of Jupiter or Saturn?
Europa probably has a subsurface ocean of liquid water, and may have undersea volcanoes on its ocean floor. If so, it has conditions much like those in which life on Earth probably arose, making it a good candidate for life beyond Earth. Ganymede and Callisto might have oceans as well. Titan may have other liquids on its surface, though it is too cold for liquid water. Perhaps life can survive in these other liquids, or perhaps Titan has liquid water deep underground. Enceladus may have subsurface water, or it may just have slush.

13. What suggests there could be life on Mars?
A) Evidence of liquid water at or near the surface, and evidence there was more water in the past
B) Mars has the closest climate to Earth’s in the solar system. It is colder than Earth but was warmer in the past
C) Mars has an atmosphere
D) All of the above
E) A and C
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14. Should we send humans to Mars and search for life?
Yes, if we found evidence of life it would have important scientific implications
Yes, if we found evidence of life it would have major scientific, philosophical, and religious implications
No, it’s too expensive
No, at best we’re likely to find fossils, and they aren’t interesting enough
Of course there is or was life on Mars. We don’t have to actually go there to find out
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15. Activity 21, pages 75-78
We’ll do questions 1-3 and 7-8

16. 1. Which of the following is true for the moving point source in Figure 1?
Wavelength shortest to left and longest to right; star moving to right
Wavelength shortest to left and longest to right; star moving to left
Wavelength shortest to right and longest to left; star moving to left
Wavelength shortest to right and longest to left; star moving to right
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17. 2A. For the observer in Figure 2, which two velocity arrows will NOT produce a Doppler shift?
A and B
A and C
C and D
A and D
C and E
D and E
None of the above
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18. 2B. For which velocity arrows in Fig
2B. For which velocity arrows in Fig. 2 can the astronomer measure the total velocity, and for which only a component of the velocity?
Total for A and D, component for B, E and C
Total for B, E and C, component for A and D
Total for C and E; component for A, B and D
Total for A, B and D; component for C and E
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19. 3. The star in Figure 3 has a …
Blueshifted spectrum, so it’s moving away from us
Blueshifted spectrum, so it’s moving towards us
Redshifted spectrum, so it’s moving away from us
Redshifted spectrum, so it’s moving towards us
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20. 7. In Figure 4, which of the following is true for the smaller star moving in its circular orbit?
Redshift at A, blueshift at C, no shift at B and D
Redshift at B, blueshift at D, no shift at A and C
Redshift at C, blueshift at A, no shift at B and D
Redshift at D, blueshift at B, no shift at A and C
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21. 8. In Figure 5, when the radial velocity of the smaller star is plotted versus time, …
Velocity is zero at B and D, positive (farthest above the line) at A, negative (farthest below the line) at C
Velocity is zero at A and C, positive (farthest above the line) at D, negative (farthest below the line) at B
Velocity is zero at B and D, positive (farthest above the line) at C, negative (farthest below the line) at A
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