Mapping Surface of a Planet (1)

LAB: Mapping the Surface of a Planet Written and Developed by: Keith Watt, M.A., M.S. Assistant Director ASU Mars Education Program Edited by: Paige Valderrama, M.A. Assistant Director ASU Mars Education Program Sheri Klug, M.S. Director ASU Mars Education Program (C) 2002 ASU Mars Education Program. All rights re-served. This document may be freely distributed for non- commercial use only.

MAPPING THE SURFACE OF A PLANET Identifying Surface Features The National Aeronautics and Space Administration (NASA) has been returning pictures of Mars back to Earth since 1965, when the Mariner 4 spacecraft flew past Mars and sent back twenty-one images. Science and technology have progressed greatly since the early mission days. The Mars Global Surveyor spacecraft has sent back over 100,000 pictures of the Martian surface. These pictures have helped scientists determine what types of geological activity have occurred to make the planet appear as it does today. Impact craters, volcanoes, layering, and riverbeds look much the same on Mars as they do on Earth. Scientists can, therefore, use Earth's features as a comparison for Mars. In these activities you are a mission scientist trying to figure out what is happening on the surface of Mars. Geological features on Mars are easy to identify if you know what you are looking for. The following is a description of some of the most common geological features on Mars. Becoming familiar with these features will assist you in completing the activities that follow. Impact Craters Impact craters on Mars, the Moon, or any other planetary body are formed when meteorites slam into its surface displacing rock and soil, creating a bowl-shaped hole or crater.  Impact craters on Mars vary in size from less than 1 km (0.6 miles) to 2,100 km (1,300 miles) in diameter. o The picture on the following page is of a crater in a region called Arabia Terra on Mars. It has a morphology typical of many of the Martian craters.  An impact crater usually has five parts, although not all of these parts are visible in all craters. o The rim : the raised area around the edge of the crater is material that was thrown upward by the violence of the impact that created the crater. o Ejecta: Some of the material that was in the crater was thrown high into the air and landed outside the crater in a blanket called ejecta. o Rays: One type of ejecta is long, outward pointing streaks called rays . These rays are particularly visible on the Moon. o Walls of the crater slope down to the floor , which is often remarkably flat. o The central uplift: If the impact was violent enough to melt the rock which became the floor of the crater, a central uplift or peak will often form, a result of a rebound action (like a water

drop hitting a pool of water). Floor Ejecta Rim Walls Central Uplif

MAPPING THE SURFACE OF A PLANET Volcanoes On both Earth and Mars, volcanoes are hills or mountains made from built-up layers of lava (hot, molten rock) ejected from cracks or vents in the planet's crust.  There are five major types of volcanoes (see following figures): o Shield volcanoes are domes much wider than they are high (shaped like a shield) and have very s h a l l o w slopes. They are formed from hot, freely flowing lava (usually silica-poor basalt) centered atop magma plumes, or “hot spots,” as well as along divergent tectonic zones.  The largest volcano on Earth is a shield volcano called Mauna Loa , which rises over 9 km (5.4 miles) from the sea floor.  The largest volcano in the Solar System, Olympus Mons, Mars, is a shield-like volcano, rising 27 km (17 miles) high, and measuring 700 km (430 miles) across! o Composite volcanoes, also known as stratovolcanoes . These are the most common volcano type on Earth, associated with subduction zones related to Earth’s plate tectonic activity, and the most violent as they can erupt with a powerful explosive force, the result of trapped gasses escaping the silica-rich viscous magma.  A classic composite volcano is conical with a concave shape that is steeper near the top. Composite cones are large volcanoes (many thousands of feet or meters tall) generally composed of lava flows, pyroclastic deposits, and mudflow (lahar) deposits, as well as lava domes .  Mount St. Helens , which last erupted on May 18, 1980, is an example of this type of volcano. o Volcanic dome (lava dome) : Domes form from the slow extrusion of highly viscous silicic lava, too thick to spread out into a lava flow. Most domes are small, and many do not have a summit crater. Domes can form volcanic edifices in their own right such as Lassen Peak in Lassen Volcanic National Park or extruded in the summit craters of composite volcanoes as part of a post-caldera eruptive phase, such as at Redoubt Volcanoes in Lake Clark National Park .  This type of volcano is usually small, rising not more than a few thousand meters above the surface. o Spatter cones: S patter cones formed as hot lumps of lava were thrown a short distance into the air only to fall back to earth around a small central vent. As the still-molten blobs landed on top of each other, they cooled and adhered to nearby pieces to form the walls of what could be considered a mini-volcano. o Cinder cones are formed from volcanic ash and coarse materials exploding from the vent. The most famous cinder cone appeared in a Mexican farmer's cornfield in 1943, Mt. Paricutin growing to over 400 meters (1300 feet) in nine years.

 At the top of the volcano is a roughly circular depression. This depression is called a caldera if it is larger than one mile (0.6 km) in diameter or, confusingly enough, a crater if it is smaller than one mile (0.6 km) in diameter. Schematic diagram of a composite volcano (left). (Credit: Modified from USGS illustration). Eruption of Mt. St. Helens, WA, 1980 (right) Schematic diagram of a shield volcano (top). (Credit: Modified from USGS illustration). Mauna Loa volcano, HI (bottom)