Prof. Miller's Astronomy 1 lecture notes on Venus and Mars's Geology

1. Geology of Venus
LACC §9.1, 9.2, 9.4
• Know Venus’s interior and evolution
• Know Venus’s surface features and age
• Understand Venus’s day
An attempt to answer the “big question”: what is out
there? Are we alone?
Tuesday, March 9, 2010 1

2. Terrestrial Planets: Interiors
http://www.star.le.ac.uk/edu/Solar_System.shtml
Earth and Moon to Scale
(which amounts to 30.1 Earth diameters)
http://hyperphysics.phy-astr.gsu.edu/hbase/solar/moonscale.html#c2
Tuesday, March 9, 2010 2

3. Terrestrial Planets: Orbits
The size of the
orbits of each planet
are to scale,
although the size of
the planets
themselves are
much too large.
http://www.schoolsobservatory.org.uk/astro/solsys/inner.shtml
Tuesday, March 9, 2010 3

4. Terrestrial Planets:
Surface Gravity
If you weigh 100 pounds on Earth...
(These worlds are not to scale.)
http://www.exploratorium.edu/ronh/weight/
Tuesday, March 9, 2010 4

5. Terrestrial Planets:
The Sun in the Sky
The sun is about 0.5° across as it appears from Eath
1.4° 0.7° 0.5° 0.35°
6.7x brighter 1.9x brighter* 1.0x brighter 0.4x brighter
(These worlds are not to scale.)
* But you can’t see the sun through the clouds
Tuesday, March 9, 2010 5

6. Venus
http://www.astrosurf.com/nunes/explor/explor_m10.htm
Tuesday, March 9, 2010 6

7. Venus: Surface Features
Impact craters indicate a surface age of 500
million years (15% as old as lunar maria and
between the age of Earth’s younger ocean
sea-floor and older continents); yet erosion
rates are very low.
Volcanoes on Venus are about as common as
on Earth, but Venus has “pancake” volcanoes
in addition to shield, volcanoes. Coronae
(circular bulges) are more common on Venus.
Tectonic activity does occur on Venus: ridges,
cracks, mountains, the coronae; but no plate
tectonics.
Tuesday, March 9, 2010 7

8. Venus: Pancakes & Crater
http://photojournal.jpl.nasa.gov/jpegMod/PIA00084_modest.jpg
Tuesday, March 9, 2010 8

9. Venus: Corona
http://photojournal.jpl.nasa.gov/jpeg/PIA00202.jpg
Tuesday, March 9, 2010 9

10. Venus: Oddities
Venus rotates backwards and slowly. A solar day on
Venus is 117 days, and the sun rises in the west and
sets in the east, not that you would ever see the sun
through the dense clouds.
Venus’s slow rotation (sidereal day: 243 days (longer
than its year: 225 days!)) results in low wind
velocities and low erosion rates on the surface.
Tuesday, March 9, 2010 10

11. Geology of Venus
LACC §9.1, 9.2, 9.4
• Know Venus’s interior (volcanically inactive?) and
evolution (resurfaced about 0.5 billion years ago)
• Know Venus’s surface features (coronae, pancake
lave domes, impact craters) and age (0.5 billion
years)
• Understand Venus’s day (orbits backwards--CW
when most planets are CCW, solar day is 117 days
(its sidereal day: 243 days, is longer than its year:
225 days)
An attempt to answer the “big question”: what is out
there? Are we alone?
Tuesday, March 9, 2010 11

12. LACC HW: Franknoi, Morrison, and Wolff,
Voyages Through the Universe, 3rd ed.
• Ch. 9, pp. 219-220: 10.
Due at the beginning of the next class period.
Be thinking about the Solar System Project.
Tuesday, March 9, 2010 12

13. Geology of Mars
LACC §9.1, 9.2, 9.4
• Know Mars’s interior and evolution
• Know Mars’s surface features and age
• Know Phobos and Deimos, Mars’s moons
An attempt to answer the “big question”: what is out
there? Are we alone?
Tuesday, March 9, 2010 13

14. Mars
http://rosetta.jpl.nasa.gov/dsp_images.cfm?buttonSel=gallery&buttonSelL2=images&category=mars
Tuesday, March 9, 2010 14

15. Mars: Surface Features
Impact craters indicate a surface age of 3 - 4
billion years (same as lunar maria) for the
Martian lowlands.
Olympus Mons, the largest volcano in the
solar system, maybe be intermittently active.
Tectonic activity does occur, but not as much
evidence for it as Earth or Venus.
Polar caps of H2O and CO2 ice.
Channels and gullies indicate liquid water
flowed, but over 3 billion years ago.
Wind erosion occurs.
Tuesday, March 9, 2010 15

16. Mars: Tharsis Bulge
http://www.britannica.com/eb/art/print?id=70956
Tuesday, March 9, 2010 16

17. Mars: Olympus Mons
http://www.nasm.edu/ceps/etp/mars/surface/canyons.html
Tuesday, March 9, 2010 17

18. Mars: Oddities
In a way, Mars is so much like the Earth, it’s odd:
• Mars’s day is only 42 min. longer than Earth’s
• Mars’s axial tilt is 25°; Earths is 23.5°.
• Mars’s diameter is about 0.53 Earth diameters,
which means Mars’s total surface area is about
the same as Earth’s land surface area.
Mars has two moons: Phobos and Deimos.
Mars had liquid water at some point in its past,
and may have had life.
Tuesday, March 9, 2010 18

19. Mars: Phobos and Deimos
• 28 x 23 x 20 km • 12 x 10 x 6 km
• 7h 39m 27s synod. • 30h 21m 16s synod.
• 5h 36m West to East • 66h East to West
http://apod.nasa.gov/apod/ap061203.html http://apod.nasa.gov/apod/ap951003.html
Tuesday, March 9, 2010 19

20. Mars: Phobos and Deimos
• Average Distance from Mars: 9,378 km (Phobos),
23,459 km (Deimos)
• Orbital Period: 7h 39m (Phobos), 30h 18m (Deimos)
• Eccentricity of Orbit: 0.015 (Phobos), 0.0005
(Deimos)
• Rotation Period: 7h 39m (Phobos), 30h 18m (Deimos),
i.e. both moons are tide locked to Mars
• Density: 2 gm/cm3 (Phobos), 1.7 gm/cm3 (Deimos)
• Atmosphere: n/a
• Surface Temperature:
25°F Max, -170°F Min (Phobos)
http://www.solarspace.co.uk/Mars/phobosdeimos.php
Tuesday, March 9, 2010 20

21. Mars: “Months”
Since Mars rotates a bit faster than the revolution period of Deimos, we would indeed see it rise in
the east, but it would then appear to move across the Martian sky at a very slow pace. In fact, it
would take about 33 hours to reach that point directly overhead (or very nearly so). It would then
take yet another 33 hours to descend the sky before we would see it finally set in the west.
And then, we would have to wait another 66 hours before it again reappears above the eastern
horizon.
In contrast, Phobos, takes only 7 hours and 39 minutes to rotate around Mars. So it has the
distinction of being the only natural satellite in the solar system revolving about its planet in a time
shorter than the planetary "day," running three laps around Mars each day.
As seen from the Martian equator, Phobos appears to move far more rapidly than the sluggish
Deimos. In fact, just 2 hours and 48 minutes after Phobos has risen, it is already overhead. And after
another 2 hours and 48 minutes it is setting; an astronaut on Mars could witness it rising twice
during a single Martian night.
And since Phobos west-to-east motion is much faster than Mars rotation period, it would appear to
rise in the west and set in the east.
Furthermore, about every 10 hours and 18 minutes, Phobos appears to rapidly race closely past
Deimos as they trek in opposite directions. Phobos, in fact, probably even appears to briefly eclipse
Deimos for some parts of Mars on each pass.
Try picturing this: during the 66-hours that Deimos moves ponderously in the sky toward the west,
Phobos appears to whiz rapidly in the opposite direction more than six times!
http://www.space.com/spacewatch/mars_moons_040116.html
Tuesday, March 9, 2010 21

22. Mars: Moon Phases
Phobos goes through its entire cycle of phases in the short time it takes to go
once around Mars.
If, for example, it were rising in the west just as the Sun were setting, it would be
at its "New" phase. A little over four hours later, it will already have moved well
past the overhead point to a position roughly halfway up in the east and would
appear "Full." When it sets in the east about an hour and half later, it will have
waned to its Last Quarter phase.
As for Deimos, because the Sun appears to move across the sky more than twice
as fast, this moon would appear to go through a full set of phases more than twice
during the 66 hours that it is continuously above the horizon.
Unfortunately, because of the very small size of both satellites, we should not
expect to see the same kind of sight that we're accustomed to seeing with our
own Moon. Deimos, for example, would appear only about 1/19 the apparent
width of our Moon. It would shine at its very best when at its "Full" phase, but
because of its very small size it would probably look more like an oversized
version of Venus to the unaided eye.
http://www.space.com/spacewatch/mars_moons_040116.html
Tuesday, March 9, 2010 22

23. Mars: Phobos and Deimos
http://www.nasaimages.org/luna/servlet/detail/nasaNAS~4~4~11828~113853:The-Night-Sky-on-Mars
Tuesday, March 9, 2010 23

24. Mars: Phobos and Deimos
Apparent size of the Moon as seen from Earth: 0.5°
Apparent size of the Phobos as seen from Mars: 0.18°
Apparent size of Sun as seen from Earth: 0.5°
Apparent size of Sun as seen from Mars: 0.35°
Apparent size of Earth as seen from the moon: 1.9°
Apparent size of Mars as seen from Phobos: 42°
http://www.johnstonsarchive.net/astro/phobos.html
Tuesday, March 9, 2010 24

25. Mars: Terraformed Mars
from Phobos
Book cover by Hardy for Carl Sagan's 'Pale Blue Dot'.
We see Mars at an advanced stage of terraforming
with the Tharsis volcanoes, a flooded Mariner Valley
and the Boreal Ocean.
http://www.users.globalnet.co.uk/~mfogg/gallery.htm
Tuesday, March 9, 2010 25

26. Geology of Mars
LACC §9.1, 9.2, 9.4
• Know Mars’s interior (volcanically inactive?) and
evolution (some meteorites came from Mars, water
once flowed on surface)
• Know Mars’s surface features (poles of H2O and CO2
ice, Valles Marineris, Tharsis Bulge, Olympus Mons--
largest volcano) and age (3 to 4 billion years)
• Know Phobos (larger, orbits in less than a day) and
Deimos (small, takes 66 hours to cross the sky),
Mars’s moons (captured asteroids)
An attempt to answer the “big question”: what is out
there? Are we alone?
Tuesday, March 9, 2010 26

27. LACC HW: Franknoi, Morrison, and Wolff,
Voyages Through the Universe, 3rd ed.
• Ch. 9, pp. 219-220: 15.
• Ch 9: Tutorial Quiz accessible from:
www.brookscole.com/cgi-brookscole/course_products_bc.pl?
http://
fid=M20b&product_isbn_issn=9780495017899&discipline_number=19
Must Know: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18
Important: 1, 12, 19, 20
Due at the beginning of the next class period.
Be thinking about the Solar System Project.
Tuesday, March 9, 2010 27