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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:
- 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 / Size of image (km) / Estimated age (billion years)
Moon - highlands
Moon - maria
Mercury - highlands
Mercury - plains
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 pictureof the Moon () and the close-up picture of the Moon () 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 which shows this schematically.
Early in solar system history the cratering rate washigher/lowerthan at present. Try to explain why this is the case according to what you have learnt. ______
Mercury
Look at the picture of Mercury (at )
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 ()
Does the crater density vary from place to place? Yes/No.
Suggest a reason for this (hint: think of what happened on the Moon). ______
Venus
Look at the global picture of Venusat (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( and feature2 (). 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 () 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( and the northern plains() (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/lowerthan 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 ()
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 ().
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 (). 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 ().
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