1DPHBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 'DWH BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 0$5635(/$% 8VLQJ\RXUOHFWXUHWH[WERRNDQGRUDQ\RWKHUDFFHSWDEOHVRXUFHRILQIRUPDWLRQDQVZHUHDFKTXHVWLRQ LQFRPSOHWHVHQWHQFHV%HVXUHWRGHÀQHDQ\UHOHYDQWWHUPV ([SODLQWKHIROORZLQJWHUPVUHODWLQJWR0DUWLDQJHRORJLFVXUIDFHIHDWXUHV D&DOGHUD E7HFWRQLFIDXOWVIUDFWXUHV F/DQGVOLGH G&UDWHU'HQVLW\ 'HVFULEHWKHQDWXUHRIWKHIHDWXUHVRQ0DUV·VXUIDFHZLWKWKHIROORZLQJQDPHV D2O\PSXV0RQV E9DOOHV0DULQHULV ([SODLQWKHIROORZLQJWHUPVUHODWHGWRÁRZRIZDWHURURWKHUOLTXLGVRQDVXUIDFH D%UDQFKLQJ E0LGVWUHDP7HDUGURS,VODQGV ² Name: ________________________________ Partners: _______________________________ Date: _________________________________ _______________________________ _______________________________ MARS LAB EXERCISE FEATURES To complete this lab, you will use a web-page which you can reach from the Elementary Astronomy Laboratory homepage. Your instructor will show you the location of this page. From the homepage, click on “MARS” to start the lab. Scroll down until you see a star-filled screen with a few boxes and buttons above it. Eventually we will use this to do a general survey of the surface of Mars. First however, let’s familiarize ourselves with the types of features we find on the Martian surface. Above the star-filled screen, the second box from the right gives access to a menu of images of Martian features. (It usually contains the word’‘Volcanoes’ when the page is first loaded.) By clicking on the small M you open a menu which displays a list of images of Mars from which you will choose. Every time you need a new image, just open this menu again and click the feature you want. Start by opening up ‘Olympus Mons’. This is a picture of the Olympus Mons (Mount Olympus). As we tour Mars, the size of the field of view will change. In this case the size of the image is 700x700km. The irregular crater at the summit of the volcano is called a caldera. It is approximately 70km across. Atlanta and the perimeter (I-285) would fit very easily inside the caldera. The resolution (the size of the smallest feature you can distinguish) will change also. However, resolution depends on many factors, (the resolution of the camera, how the picture is stored in the computer, etc.), so we cannot list that information. In general the resolution is a kilometer or so. We will now take a short tour of a few of the many types of features, which we have discovered, on Mars. In many cases they are similar to geological features we see on Earth, but Mars certainly has created its own features in its own way. For example, your picture of Olympus Mons shows the largest volcano in the solar system. It is a shield volcano formed over eons by hot lava flowing out onto the surface of Mars. Notice the large central caldera at the top and the solidified lava down the side. To look at another shield volcano open ‘Volcanoes’ from the menu. Again we see the lava flows down the slope from the caldera. Both of these volcanoes are evidence of vulcanism on Mars. Vulcanism is one of the four major processes that form Martian surface features. The four major surface-modifying processes include: • Vulcanism includes lava flows and volcanoes, • Impact features, include a large variety of impact craters, • Tectonic features consist of large cracks in the surface caused by large scale crustal shifts and • Water features. 11–5 Before we move on to features other than vulcanism, look at the surface around the volcano. 1. How many craters do you see? ____________________ This is a region about 600x600 km or 360,000 square km. 2. Thus the crater density in this region is about _______________ craters/square km Now look at ‘Large Crater’ from the menu. This impact crater is about 120km in diameter. Notice the dark patch in the center of the crater, which is lava that has filled the crater floor after the impact. In the box below, sketch a rough picture of the crater walls. Larger craters and some of the smaller ones (see the crater to the right of the large one, near the edge of the picture) also show the ejecta thrown out by the impact. If the impact took place where there was enough subsurface water you may see that the ejecta look like a splash in a mud puddle. 3. Sketch in the ejecta of the large crater. Large Crater Smaller craters may not have as much ejecta. Furthermore, since their impacts are less energetic they may not experience a ‘rebound’ during the formation of the crater. This rebound often fills the floor of the larger craters and so they have flat floors. In the same picture you should be able to see several craters with bowl-shaped floors. (They show darker shadows in the crater floors because they are deeper.) 4. Draw circles with ‘B’ (for bowl-shape) on your sketch where a few of them are located. Anywhere on the surface where there have been crustal shifts the surface can develop tectonic fractures or faults. The largest of these is the Valles Marineris, which extends nearly 4000 km across the Martian surface near the equator. A piece of it is shown in ‘Water Feature.’ (This picture is approximately 300x300km and has been named ‘Water Feature’ only because it shows some water flow in the bottom of Valles Marineris. Valles Marineris was NOT created by water erosion, but by crustal uplift and cracking.) First note the smooth regions in the upper left and lower right corners of the picture. This is the original surface, which cracked open when the ground was pushed up from below. You can see the scalloped edges of this large crustal split, as well as a central piece of the original surface. The cliffs, sculpted by wind erosion, are several km high. In some parts of the floor of Valles Marineris, such as this one, we can see landslides, which have been caused by material falling away from the cliff and piling up on the floor of the valley. Wind erosion is also evident in the many mounds in the floor of the Valles. 11–6 One of the exciting surprises astronomers found on Mars was the presence of water features. Sometimes these features seem to be formed by sub-surface water gushing out onto the surfaces producing flash floods. Other times the water seems to have been in the form of precipitation during a period when the Martian atmosphere was much denser. ‘Crater Chain’ (300x300km) shows one such feature. Unlike rilles formed by flowing lava or tectonic faults, water features: are usually winding, have deposits on the outside edges of bends or in tear dropped-shaped ‘midstream islands’, and often show branching into smaller streambeds. In the upper left of this picture there is a crater with its southern wall cut by an incoming stream. You can follow that stream south to see a great number of smaller tributaries feeding it. Evidently, rain falling in that area flowed through this stream system and collected in the crater. Right near the top edge there is a small crater with a very faint tail of material extending upward and to the right. Craters in flood plains sometimes show these teardrop islands extending downstream behind them. Water must have flowed past this crater from the lower left leaving material deposited behind it. Contrast all these water features with the tectonic features just to the right of them. Look for straight intersecting cracks in the smooth area in the top middle of the picture. 5. In the box below, draw the streams, the crater they run into, the material deposited downstream from the small crater and the tectonic features. Label each feature. Crater Chain HISTORY One way to learn about past stages in the evolution of the Earth is to investigate the Moon, Mercury and Mars. Their surfaces preserve many of the phenomena that happened some 3 to 4 billion years ago and that have long vanished on the Earth. Ideally, we would like to date craters, volcanoes, etc., absolutely; that is, we would like to determine how many years ago these features were formed. For instance, radioactive dating of lunar samples returned to Earth enabled scientists to determine the approximate time when lava flowed on the Moon (about 4 billion years ago). In practice we have been able to do this only for the Earth and for a very few samples from the Moon. More generally, photography and mapping of planets and their features can tell us relative ages; that is, they help determine whether a canyon or volcano was made before or after some craters on the same planet. 11–7 SUPERPOSITION The method of superposition is one way of determining relative ages of surfaces. Whatever is on top of or partially obliterates another feature is the younger. Display ‘Cratered Region’ (300x300km). You will see many craters and their ejecta. A few of the craters have been numbered 1 though 5 on the image. The most obvious superposition is crater 2 on crater 1 and a very small crater next to 2 on crater 1. Further there is a small crater inside 2. This means crater 1 is older than 2 and it is also older than either of the smaller craters. The small crater inside 2 is younger than crater 2, itself. The relative ages of crater 2 and the small crater next to it cannot be determined unless we could see ejecta from one top of the other. Another example is craters 4 and 5. As 5 has broken the rim of 4, it had to be formed more recently. More difficult to decide is whether Crater 1 or 3 is older. If crater 3 had more overlap with 1 it might be easier to tell. As it is, we might have to hope for a picture with higher resolution to solve the problem. Remember if there is no superposition of one feature on another, nothing can be said about the relative ages.