4. The Moon.pdf

Lesson 4 The Moon What is the Moon? ▪A natural satellite ▪One of more than 181 moons in our Solar System ▪The only moon of the planet Earth Location, location, location! ▪About 384,000 km (240,000 miles) from Earth ▪3,468 km (2,155 miles) in diameter (about ¼ the size of Earth) Movements...

Lesson 4 The Moon What is the Moon? ▪A natural satellite ▪One of more than 181 moons in our Solar System ▪The only moon of the planet Earth Location, location, location! ▪About 384,000 km (240,000 miles) from Earth ▪3,468 km (2,155 miles) in diameter (about ¼ the size of Earth) Movements of the Moon ▪ Revolution – Moon orbits the Earth every 27 1/3 days (sidereal month) ▪ The moon rises in the east and sets in the west ▪ The moon rises 50 minutes later each day due to the difference in the orbit of the moon and earth (sets 50 minutes) ▪ Rotation – Moon turns on its axis every 27 1/3 days ▪ Same side of Moon always faces Earth Our Nearest Neighbor: The Moon ▪ ▪ ▪ ▪ Our nearest neighbor is the Moon. It’s the only other Solar System object humans have landed on. Only the near side is visible (left). The far side was photographed first in 1959 by the Russian built, Luna 3 (right). First time this side was seen. ▪ Understanding of the Moon took a great leap forward in the 1960s, when unmanned space probes and later, Apollo spacecraft orbited the moon ▪ In 1966, an unmanned Soviet space probe made the first successful landing on the Moon. Then, between 1969 and 1972, the United States landed six manned spacecraft on the moon bringing back 381 kg of Moon rocks Figure 22.6 The Moon’s Surface ▪No atmosphere ▪No liquid water ▪Extreme temperatures • Daytime = 120C • Nighttime = -175C ▪1/6 Earth’s gravity Far Side of the Moon ▪First seen by Luna 3 Russian space probe in 1959 ▪Surface features different from near side • More craters • Very few maria • Thicker crust Russia’s quest to the Moon The exploration and ‘conquest’ of the Moon is commonly attributed to the Americans and their Apollo programme. Nevertheless, many consider the Russians to be the true pioneers of our satellite. In 1959: LUNA 1 first manmade object to escape the Earth’s gravity and approach the Moon LUNA 2 first manmade object to impact on the Moon LUNA 3 first photographs of the “far side” of the Moon Indeed, no-one before 1959 knew what the hidden side of the Moon looked like. It was a surprise: few dark areas of note (maria), but a monotonous light-coloured surface scarred by countless impacts. The Russians persevered through their exploration programme while the Americans were busy developing the most ambitious space programme ever: landing the first men on the Moon. In 1966, the Russian programme continued: LUNA 9 first successful soft landing LUNA 10 first lunar orbiting satellite (followed by Luna 11 and 12) Luna 1 Here comes the cavalry… But the Americans responded with a breathtaking performance including: Apollo 8 Apollo 11 Apollo 14 first manned lunar orbit first man landing on the Moon first colour images of the Moon 1968 1969 1971 January Apollo 15 Apollo 16 Apollo 17 first use of lunar rover (~28 km) first mission to the highlands first mission with a scientist on board This was also the last manned mission beyond low Earth orbit. 1971 July 1972 1972 In total the Apollo missions returned 381.7 kg of rocks and other surface materials. © NASA S a t u r n V r o c k e t Characteristics of the Moon ▪ The near side of the Moon hosts most of the maria (mare is singular), which lie at relatively low elevations and are mainly basaltic in composition (left). Mare is Latin for sea, composed of basalt lava flows and have low albedo (reflectivity) ▪ The far side of the Moon consists almost entirely of heavily cratered, rugged highlands, higher elevation, made mostly of anorthosites largely consisting of the mineral plagioclase (right). ▪ Because so much of the Moon consists of anorthosite, a relatively low density rock, the Moon has a lower average density than the Earth (3.4 g/cm3 for the moon vs 5.5 g/cm3 for the Earth) and due to its smaller size, the Moon has 1/80 the mass of the Earth and therefore has weaker gravity ▪ The Moon has no Volcanos to supply gases, has no atmosphere, and therefore, no oceans, rivers, glaciers, or life ▪ Without an atmosphere or ocean to hold and redistribute heat, ground temperatures undergo violent swings ranging from over 120oC on the sunlit lunar equator to -175oC on the Moon’s dark side Figure 22.6 Moon Rock Figure 22.6 Lunar Features - Craters ▪ Up to 2500 km (1,553 miles) across ▪ Most formed by meteorite impact on the Moon ▪ Some formed by volcanic action inside the Moon Lunar Features - Maria ▪ Originally thought to be “seas” by early astronomers ▪ Darkest parts of lunar landscape ▪ Filled by lava after crash of huge meteorites on lunar surface 3-4 billion years ago ▪ Mostly basalt rock (igneous rock formed from volcanic activity) Lunar Features - Highlands ▪Mountains up to 7500 m (25,000 ft) tall ▪Rilles (trenchlike valleys) The Lunar Surface ▪ ▪ ▪ ▪ ▪ ▪ ▪ ▪ Galileo first discovered the craters on the moon. There are no volcanos on the Moon. It was initially believed that Volcanos created the craters, In 1892, G.K. Gilbert showed experimentally by dropping clay balls onto wet sand that the craters produced were from meteorite impacts Craters pockmark the surface of the Moon as the result of meteorite impacts. Lunar maps suggest that there are over 100,000 craters with a diameter of 1 km or more (left). Why do we see more craters on the Moon than the Earth? The types of crater depend on the speed and size on the impacting object; smaller simple craters tend to be smooth-floored bowls, larger complex craters have a central uplift and may be surrounded by concentric ridges (see picture below) Lunar regolith –dust and debris made of fragmented rock blasted out of the craters and glass droplets as rock melted by impacts of micrometeorites (2 mm)—regolith—covering the Moon, right and astronaut footprint Space weathering occurs as micrometeorites and cosmic rays (high-energy atomic nuclei from space) blunt and smooth out older craters while newer ones have sharper features Figure 22.7 Crater formation The boundary between the illuminated part of the Moon's disc and the dark part is called the terminator. ... The circular edge of the disc itself is called the limb, and the points where the limb and terminator join (roughly at the lunar poles) are the cusps. The origin of lunar rays is generally ascribed to ejecta material that was hurled out when particles of rock crashed into the lunar surface, forming the craters Galileo Galilei The astronomical (orbital) understanding of the Moon was already advanced centuries before the Birth of Christ; indeed, there is evidence that at least the Greeks, Chinese, and several South American civilisations could already forecast lunar and solar eclipses with a high degree of accuracy. But for the physical planetary study of this celestial body we really Annular solar eclipse need to wait until the development of observational astronomy, starting with Galileo Galilei’s first lunar studies in the year 1609, outlined in his book Sidereus Nuncius (Starry Messenger). ©2009 Stefan Seip Lunar eclipse ©2009 Cornell University Galileo’s sketches of the Moon A violent past… ▪ Analysis and observations from the Apollo and Luna missions did it become apparent that volcanism, or least as we know it on Earth, played a very minor role in shaping the lunar surface. • Instead, the lunar surface bears witness of a violent past and relentless bombardment of interplanetary objects from the macroscale (meteors and comets) down to the microscale (micrometeorites, cosmic and solar particles), which continues to this day. © NASA Lunar basalt from the Apollo 12 site. Pitted by micrometeorite bombardment Impact-saturated lunar farside © NASA Formation of the Moon ▪ The currently most widely accept model of the formation of the Moon suggests that it may have formed after an immense impact on the Earth by a Mars-sized protoplanet named Theia that blasted debris into orbit. ▪ Material blasted free formed a ring around Earth and later coalesced into the Moon. ▪ This happened 4.53 Ga, shortly after the interior of the earth had undergone differentiation (different layers, core, mantle etc). ▪ When the Moon first formed, its surface was probably a magma sea, as the moon cooled, denser mafic minerals formed and sank, while less dense felsic minerals such as plagioclase rose, the less dense rock solidified into an anorthosite crust, exposed in the lunar highlands today. ▪ The formation of the Mare is not fully understood ▪ From these rocks, it has been determined by Geologists, that the age of the moon is between 4.36 Ga and 3.16 Ga Figure 22.8 Homework 1. Why doesn't the Moon have an atmosphere? 2. The Moon is littered with craters, but the Earth (which is right next door) is not. Explain why this is the case. 3. The Moon has no surface tectonic activity – but it does have week 'moonquakes.' Explain the favored theory for the origin of these events. 4. The lunar maria are thought to be younger than the rest of the Moon's surface (the highlands). What makes us suspect this? Is there a way to verify this? 5. When and how did the Moon form? List some of the evidence that supports this model. 6. Is there economic incentive to harvest raw materials from the Moon for use on Earth? Can you think of another object in the solar system that might be a better target for exploration, if this is our motivation?