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ESS9 – Our Solar System – Lab # ___
Determining Surface Ages from Cratering
Date of Lab:
Due Date:
Name_______________________________ id#____________ SEC#___________
Summary: The crater density (i.e., number of craters per unit area) is the primary "remote"
method used to estimate the ages of planetary surfaces: the older a surface is, the more craters it
has. In this lab you will use this technique to estimate ages for the surfaces of the Moon,
Mercury, Venus, Earth, Mars, and the four large moons of Jupiter. While doing this you will also
gain familiarity with some of the surface features of these planets, which reveal clues about their
history. By the end of the lab you should be able to roughly estimate the age of a planet's surface
just by looking at it!
The first part of the exercise involves using an interactive computer module to simulate cratering
and estimate quantitative ages; the second part involves looking at images of the planets and
answering interpretive questions.
Part 1: Age determination by cratering simulation
Instructions: there are 10 planetary surfaces to date. You will look at the planetary surface image
in the left window and try to estimate the age by recreating a similar cratering density in the right
window. For each surface:
1.
2.
3.
4.
5.
6.
7.
8.
Select the planetary surface image in the left window
Estimate the age and set the slider accordingly
Press 'fire'. The simulation will last for ~20 seconds and you will hear a 'click' at the end.
Compare the amount of cratering with the picture.
If the cratering doesn't match, set the slider to a different age and try again
Keep trying until you get a reasonable match. It will never be perfect, of course.
Do a couple more simulations at this age to check (there are random variations)
Enter the age in the table below and go to the next planetary surface
Body
Moon - highlands
Moon - maria
Mercury - highlands
Mercury - plains
Size of image (km)
Estimated age
(billion years)
2
Venus
Mars - highlands
Mars - plains
Callisto
Ganymede
Part 2: Interpretation of Images
In all parts, fill in the blanks or select the correct answer from underlined alternatives.
The Moon
Look at the global picture of the Moon (http://oro.ess.ucla.edu/ess9/images/moon1sm.gif) and
the close-up picture of the Moon (http://oro.ess.ucla.edu/ess9/images/moon_closeup_w3.jpg)
and fill in the blanks or select the correct answer for the underlined words:
The light highland areas have a high/low crater density. The dark maria areas have a
higher/lower crater density than the highlands. Thus, the maria are older/younger than the
highland regions.
Scientists have dated rock samples brought back from the Moon. To date Moon rocks they used
the technique of ___________________ (discussed in Ch. 7). Using these absolute ages they
were able to deduce the rate of crater formation (i.e., number of craters forming per time
interval) at various times in the Moon's history. Look at
http://oro.ess.ucla.edu/ess9/images/craterrate_www.gif which shows this schematically.
Early in solar system history the cratering rate was higher/lower than at present. Try to explain
why this is the case according to what you have learnt.
______________________________________________________________________________
Mercury
Look at the picture of Mercury (at http://oro.ess.ucla.edu/ess9/images/mercuryglobe1.jpg)
The crater density on Mercury is much higher/ similar/much lower than that of the lunar
highlands. Thus, the surface of Mercury is older/ similar in age/younger than the lunar
highlands.
Look at the closeup view of Mercury's surface (http://oro.ess.ucla.edu/ess9/images/caloris.jpg)
Does the crater density vary from place to place? Yes/No.
Suggest a reason for this (hint: think of what happened on the Moon).
______________________________________________________________________________
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Venus
Look at the global picture of Venus at http://oro.ess.ucla.edu/ess9/images/venus.gif (obtained
using Magellan radar). Does it look heavily cratered? yes/no
The surface age of Venus is probably older/similar/younger than the surface age of the lunar
highlands.
Interpretation of possible crater-like features is difficult at this scale because some of them are
volcanoes. Now Compare feature1 (http://oro.ess.ucla.edu/ess9/images/golubnew.gif) and
feature2 (http://oro.ess.ucla.edu/ess9/images/sapas.jpg). One of them is a volcano and one is a
crater. Which is which?
Feature 1 is a __________________. Feature 2 is a _________________.
Why do you think so?
_____________________________________________________________________________
There are about 1000 craters having diameters>30 km on the surface of Venus. Suggest a reason
why don't you get small craters on Venus (hint: Venus has a dense atmosphere, unlike the Moon
and Mercury):
Earth
Earth has 28 impact craters having diameters >30 km on its continents (area about 150 million
km2). Look at the picture (http://oro.ess.ucla.edu/ess9/images/manicgn.gif) of one of them, the
100-km diameter Manicouagan crater in Canada. It is quite weathered, despite having been
protected by sediments for a large fraction of its lifetime.
Earth and Venus are almost the same size, but Earth has 28 impact craters compared to Venus'
1000 (on an area of 460 million km2). Therefore, Earth's surface must be much younger / about
the same age / much older than Venus' surface.
Mars
Look at the two pictures of Mars's surface, from the southern highlands
(http://oro.ess.ucla.edu/ess9/images/mars_high.jpg) and the northern plains
(http://oro.ess.ucla.edu/ess9/images/mars_plain.jpg) (Mars has a crustal dichotomy, with the
northern part quite different from the southern part).
The age of the southern highlands is probably higher/similar/lower than that of the lunar
highlands.
The age of the northern plains is probably higher/similar/lower than that of the lunar highlands.
Compared to the Moon, the northern plains look most similar to the highlands/maria.
Callisto
Callisto is the outermost of Jupiter's 4 large moons, and is larger than Earth's moon. Look at the
picture of Callisto (http://oro.ess.ucla.edu/ess9/images/callistom.jpg)
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Callisto is heavily/lightly cratered. Its age is probably most similar to the lunar
highlands/maria.
There are 2 big differences between Callisto's craters and craters on the moon. One is related to
the color, and the other is related to the size distribution:
Callisto's craters are often white/black/purple.
Does Callisto have any very large craters (e.g., ones as large as those that made the lunar basins
that the mare basalts flowed into)? Yes/No.
Both of these differences occur because Callisto's surface is made of ice.
Ganymede
Ganymede is the next outermost of Jupiter's large moons. Look at the picture
(http://oro.ess.ucla.edu/ess9/images/ganymede.gif).
On the whole, is Ganymede as more heavily / less heavily / similarly cratered as Callisto.
Its surface cratering shows more / less / similar variability than Callisto's surfacing.
Europa
Europa, Jupiter's 2nd innermost large moon, looks quite different from anything we have seen so
far. Look at the picture (http://oro.ess.ucla.edu/ess9/images/europa_globe.jpg). It is slightly
smaller than Earth's moon, and made largely of ice. Count the number of craters you see. Write
the number below.
I see ______ crater(s) on Europa.
This implies that the surface of Europa is very young / slightly younger / about the same age /
older than the lunar maria.
Io
Io, Jupiter's innermost large moon, is unique in the solar system. Look at the picture
(http://oro.ess.ucla.edu/ess9/images/io5m.jpg).
Do you see things that might be craters? yes/no
If you knew that Io is the most volcanically-active body in the solar system, that volcanoes are
continually resurfacing it, giving it the youngest surface age of anything we have looked at
today, would this change your interpretation? yes/no
Last Updated: Oct 15, 2007