Asteroids
Module 13 Laboratory (edit) (2).docx
ASTEROIDS AND CRATERS
Asteroids are small rocky objects that orbit the Sun. For the most part, asteroids are located in a region between the orbits of Mars and Jupiter called the asteroid belt. However, the orbits of some asteroids bring them closer to the Sun and some of these cross the Earth’s orbit. The possibility exists for these Near Earth Asteroids (NEA; sometimes listed as NEO for Near Earth Objects) to collide with the Earth. If you go out to a field in the country, away from the city lights, you can see the effects of smaller asteroids (called meteors) slamming into the Earth’s atmosphere and burning up. These are called shooting stars, even though they have nothing to do with stars. Larger asteroids have survived their encounter with the atmosphere and have struck the ground. When they hit the ground, they are called meteorites, and they leave large impact craters where they land. If the asteroid is large enough, the damage can be enormous. Fortunately, the Earth does not suffer such impacts regularly. However, it has happened in the past and it will probably happen again in the future, but when?
After witnessing the impact of the Shoemaker-Levi 9 comet with Jupiter (which produced explosions larger than our entire planet), many scientists, astronomers, amateurs, and NASA officials became interested in searching for NEA’s that might threaten the Earth. The exercise today will take you through the process that professional astronomers use to find asteroids. Amateur astronomers can also find asteroids using relatively inexpensive equipment. The software you are using today can be used to really find asteroids! In Activity I, you will estimate ages from crater counts on the moon.
Lunar Lowlands
Activity I
In this Activity you will determine the age of the lunar surface by counting craters of a particular size. The craters were made by asteroid impacts, and asteroids have bombarded the entire lunar surface equally. However, in the distant past, lowland areas (maria) were filled in by ancient lava flows, erasing the older craters and clearing the landscape for new bombardments.
These lava flows did not reach the highland areas (mountains), so they remained pristine. Therefore, the number of craters in a given area can be used to determine how old the surface is.
Important: Make sure that you use a high-quality printer when you print out these photos!
Lunar Highlands
The pictures of the lunar surface on this and the previous page should be very close to 6 ½ inches on a side. The diameter of the craters that we are interested in are between 4 and 10 kilometers. On this scale, this corresponds to between 1 and 2 of the tick marks on the ‘inches’ side of the lab ruler (between 1/16 and 2/16 inches). Count the number of craters in each image with the correct size (yes, there should be a lot of them!) Suggested technique: place the ruler on the bottom of the image with the ‘inches’ side up. Look across the top of the ruler for any candidate craters of the proper side. Measure rim to rim. If the diameter is between 1 and 2 tick marks, then it counts. Slowly move the ruler up the image, scanning all the way to the edges for candidate craters. You should work on one image at a time very carefully highlighting all craters within this size range.. *Hint: the ‘Lunar Highlands’ picture should take longer to complete. When you have finished, record the total number of craters in each image on the worksheet.
Crater Counting Graph
Crater Counts:
Lunar Lowlands
1st Count____________________
2nd Count____________________
Average____________________
Lunar Highlands
1st Count____________________
2nd Count____________________
Average____________________
1. The y-axis on the above plot is calibrated for a lunar surface area of 106 km2 The area we used was smaller than this: about 1.9 × 105 km2 So we need to find the scale factor: Divide 106 km2 by 1.9 × 105 km2. The scale factor is _______________ .
2. Multiply the Average values from each average count by the scale factor from 1:
Lunar Lowlands __________Lunar Highlands __________
3. Look at the y-axis on the plot above. If your values from 2 are NOT between 100 and 600, please try counting again. If they are, draw two horizontal lines (use the ruler), one at the y-axis value for Lunar Lowlands from 2, the second at the y-axis value for Lunar Highlands from 2.
4. Draw two vertical lines (use a ruler) where each of your horizontal lines intersects the solid line – the data for the moon. (Ignore the dashed line – it’s for Mars). Your vertical lines will intersect the x-axis, which is time in years ago. For example, if your line intersected at –2, then the surface would be 2 billion years old. Estimate the ages from your lines:
Lunar Lowlands __________Lunar Highlands __________
Activity II
1. For ”= 271.385 arcseconds, find the following distance to an asteroid:
Distance = 206,265* ⦘ if the baseline is 5000 km.
_______________________________________________
2. Compare this distance the average Earth – Moon distance by dividing your
Answer in the above calculation by the Earth – Moon distance (384,400 km)
_______________________________________________
3. Using your answer to number 2 would you classify this asteroid as a Near Earth Asteroid? Why or why not? Consider the fact that Mars, when it is closest to Earth is about 203.7 Moon distances away.
_______________________________________________
1.1 ASTEROIDS QUESTIONS
1. Assume that your crater count for Activity I was 150. Use the plot on page 7 to determine
The age of the lunar surface ______________ years
The age of the Martian surface ______________ years
2. How would these ages change if your crater count was 425?
The age of the lunar surface ______________ years
The age of the Martian surface ______________ years
3. If the parallax angle for an asteroid viewed in Activity II was π”= 457.657 arcseconds, find the distance to the asteroid in kilometers. Show work.
4. For a time of 36 hrs, 27 min, 36.54 sec, calculate the total number of seconds in this interval.
5. For an asteroid moving with a velocity of 12 km/hr, how far (in km) would it travel in a time of 48 hours? Show work.
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