7.1 Earth as a Planet 7.2 Mercury and the Moon 7.3 Mars 7.4 Venus 7.5 Earth as a Living Planet

Transcription

1 Chapter 7: Earth and the Terrestrial Worlds 7.1 Earth as a Planet 7.2 Mercury and the Moon 7.3 Mars 7.4 Venus 7.5 Earth as a Living Planet All picture credits: 2015 Pearson Education, Inc unless stated otherwise. Fall 2015 PHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 1

2 7.2 Mercury and the Moon Our goals for learning: Was there ever geological activity on the Moon or Mercury? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 2

3 The Moon and Mercury are geologically inactive Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 3

4 Moon Some volcanic activity 3 billion years ago must have flooded lunar craters, creating lunar maria. The Moon is now geologically dead. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 4

5 Cratering of Mercury Mercury has a mixture of heavily cratered and smooth regions like the Moon. The smooth regions are likely ancient lava flows. Fall 2015 PHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 5

6 Cratering of Mercury The Caloris Basin is the largest impact crater on Mercury. Region opposite the Caloris Basin is jumbled from seismic energy of impact. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 6

7 Tectonics on Mercury Long cliffs indicate that Mercury shrank early in its history. Fall 2015 PHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 7

8 Recent Geology on Mercury Lighter areas (color enhanced) are thought to be "hollows" formed as easily vaporized minerals escape. Fall 2015 PHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 8

9 What have we learned? Was there ever geological activity on the Moon or Mercury? Early cratering on the Moon and Mercury is still present, indicating that activity ceased long ago. Lunar maria resulted from early volcanism. Tectonic features on Mercury indicate early shrinkage. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 9

10 Missions on Mercury Visited by two spacecrafts, Mariner 10 (NASA) flew by three times in 1974 and Only 45% of the surface was mapped Picture: NASA Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 10

11 Missions on Mercury MESSENGER (NASA) MErcurySurface, Space ENvironment, GEochemistry, and Ranging launched by NASA in 2004 Its flybys in 2008 and 2009 provided new high quality images most of the hemisphere not seen by Mariner 10 Entered an elliptical orbit around Mercury in 2011 after several flybys. Picture: NASA Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 11

12 Mercury's orbit Mercury's orbit is highly eccentric perihelion it is only 46 million km from the Sun aphelion it is 70 million. The position of the perihelion precessesaround the Sun at a very slow rate. Problem 19th century astronomers made very careful observations of Mercury's orbital parameters but could not adequately explain them using Newtonian mechanics. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 12

13 Mercury's orbit Solution Einstein's General Theory of Relativity The correct prediction of the motions of Mercury was an important factor in the early acceptance of the theory. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 13

14 Measuring Mercury s Rotation Period By measuring the wavelength shift of the reflected radiation, astronomers deduced how rapidly Mercury rotates and thus determined its rotation period: 1.5 per Mercury year. Mercury is not tidally-locked to the Sun. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 14

15 Water on Mercury The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102K. The icy regions may contains to 1o 15 kg of ice (the Antarctic sheet mass is kg) Origin: outgassing and comet impacts Picture: Nasa 15 PHYS 171: Introduction to Astronomy I Chapter 7 Part 1: Mercury

16 Mercury s interior Second densest major body in the solar system, after Earth gm/cm 3 Earth's density is due in part to gravitational compression; if not for this, Mercury would be denser than Earth. Mercury's interior is dominated by a large iron core whose radius is 1800 to 1900 km. Mercury therefore has only a relatively thin (500 to 600 km thick) silicate mantle and crust 16 PHYS 171: Introduction to Astronomy I Chapter 7 Part 1: Mercury

17 Formation of Mercury A collision theory explain Mercury s high iron content 17 PHYS 171: Introduction to Astronomy I Chapter 7 Part 1: Mercury

18 Mercury magnetosphere Large metallic liquid core + Slow rotation -> weak magnetic field 1% of Earth s magnetic field strength 18 PHYS 171: Introduction to Astronomy I Chapter 7 Part 1: Mercury

19 Mercury s atmosphere (exosphere) Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Mercury surface is hot => escape velocity is very low => atoms quickly escape into space. Mercury's atmosphere is constantly being replenished. 19 PHYS 171: Introduction to Astronomy I Chapter 7 Part 1: Mercury

20 Moon exploration Luna 2 (Soviet Union) made an impact on the surface of the Moon on September 14, The Cold War lead to a space race between the Soviet Union and the USA with a focus on the Moon NASA's Apollo program was the first, and to date only, mission to successfully land humans on the Moon. Moon rock samples were brought back to Earth by three Luna missions (Luna 16, 20, and 24) and the Apollo missions 11 through 17 Credit: NASA Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 20

21 July 20, 1969: One Giant Leap For Mankind Apollo 11: Firsthuman foot on another world Over the next three and a half years, 10 astronauts will follow. The Apollo program advanced many areas of technology incidental to rocketry and manned spaceflight, including avionics, telecommunications, and computers. Credit: NASA Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 21

22 7.3 Mars Our goals for learning: Missions on Mars What geological features tell us that water once flowed on Mars? Why did Mars change? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 22

23 Mars versus Earth 50% Earth's radius, 10% Earth's mass 1.5 AU from the Sun Axis tilt about the same as Earth Similar rotation period Thin CO 2 atmosphere: little greenhouse Main difference: Mars is smaller and further away from the Sun Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 23

24 Missions on Mars Successful missions Flybys Mariner 4 and Mariner 6-7, Rosetta Mission: take pictures of Mars Orbiters: Spacecraft in orbit around Mars for longer term, global studies. Mariner 9, Mars 2-3, Viking 1-2, Mars Global Surveyor, 2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, Mars Orbiter Mission Landers & Rovers Surface observations Viking 1-2, Pathfinder, Mars Exploration Rovers, Phoenix Low success rate of Mars mission (50%). 24 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

25 Martian Explorers Each Viking Lander is about 2 m tall A dish antenna is used for sending data to an orbiter, which in turn relayed the information back to Earth. View from the stationary part of Mars Pathfinder shows the rover Sojourner, deploying its X-ray spectrometer against a rock named Moe. 25 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

26 Spiritand Opportunity Ongoing robotic space mission that began in The mission was planned to last 90 days. Spirit mission lasted 6 years and 2 months. Opportunityis still active and have travelled over 40 km on Mars in 11 years. Objectives: Analyze rocks and soils to find evidence of past water activities on Mars. Perform calibration and validation of surface observations by orbiters. Characterize the rock geology. Assess if the environment was once conductive to life. 26 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

27 Spirit and Opportunity Watch the video Opportunity: 10 years on Mars at 27 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

28 Curiosity Landed on Mars on August 2012, still active Objectives Study of climate and geology Investigate biosignature Role of water and planet habitability (surface radiation) Instruments High resolution cameras (17) Laser-induced breakdown spectrometer Microscope and x-ray spectrometer Analytical laboratory for sample 28 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

29 Curiosity Laser-Induced Breakdown Spectroscopy in the ChemCam instrument aboard the Curiosity rover An irradiance threshold of 1 GW/cm 2 is needed to obtain a plasma representative of the target composition PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

30 Mars rovers Spirit and Opportunity (2004) sibling: 160 cm Curiosity (2012) prototype: 300 cm Sojourner (1997) prototype: 65 cm 30 PHYS 171: Introduction to Astronomy I Chapter7 Part 4: Mars

31 Future missions Airplanes & Balloons: soaring views from the Martian sky, atmospheric studies. Subsurface Explorers Geology of the planet The presence of water, Was Mars ever a habitat for life? Sample Returns: Bringing samples of Martian rocks, soils, and atmosphere back to Earth 31 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

32 The Martian canals The misunderstanding that convinced many that Mars was harboring an advanced civilization. In 1877, Giovanni Schiaparelli observe long straight lines on Mars that he called canali. The term was mistranslated as «canals». Improved astronomical observations revealed the "canals" were an optical illusion. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 32

33 Seasons on Mars Seasons on Mars are more extreme in the southern hemisphere because of its elliptical orbit. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 33

34 Storms on Mars Seasonal winds on Mars can drive huge dust storms. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 34

35 Water on Mars Geological features show that water once flowed on Mars The surface of Mars appears to have ancient riverbeds. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 35

36 Craters and resurfacing Eroded crater New crater The condition of craters indicates surface history. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 36

37 Volcanism Volcanoes as recent as 180 million years ago Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 37

38 Volcanism Past tectonic activity Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 38

39 Breaking news NASA, revealed evidence of seasonal salty water still flows on the Red Planet. The dark streaks visible in this photo, released on Sept. 28, 2015, are caused by flowing water. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 39

40 The search for water on Mars In 1971, Mariner 9 became the first spacecraft to enter orbit around Mars. Drainage Channels from Mariner 9. Credit: NASA Mariner 9 View of Nirgal Vallis. Credit: NASA Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 40

41 The search for water on Mars Today, most water lies frozen underground (blue regions). Snowpack melts carve gullies even today. Fall 2015 PHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 41

42 The search for water on Mars Mars Express (European space Agency) saw its first water in 2004 The right band represents the visible image. The middle band represents the CO2 (carbon dioxide) ice The left band represents the H2O (water) ice. Credit: ESA Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 42

43 The search for water on Mars Ice water in a crater 13% of Mars remaining water is locked in the polar caps Image obtained from orbit with a ground resolution of approximate15 metres per pixel Credit: Mars Express (ESA) Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 43

44 The search for water on Mars 2004 Opportunityrover provided strong evidence for abundant liquid water on Mars in the distant past. How could Mars have been warmer and wetter in the past? Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 44

45 The search for water on Mars Clumps of rounded pebbles discovered by the Curiosity rover compared with similar formations in Earth streambeds Fall 2015 PHYS271: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 45

46 The search for water on Mars Microscopic imager on the Mars Exploration Rover Opportunity Area: 1.3 centimeters across Spherules may originate from accretion under water Credit: NASA/JPL/US Geological Survey Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 46

47 Ancient Mars Mars as it may have look like billions of years ago Why did Mars change? Artistic impression based on MOLA data Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 47

48 Climate Change on Mars Mars has not had widespread surface water for 3 billion years. The greenhouse effect probably kept the surface warmer before that. Mars lost most of its atmosphere. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 48

49 Climate Change on Mars Mars has a lower mass => It cannot retain as much gas as the Earth. Magnetic field has strongly decreased when the planet interior cooled down =>The solar wind have further stripped the atmosphere after field decreased because of interior cooling. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 49

50 Reduced Greenhouse effect 50 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

51 Carbon dioxide phase diagram Deposition/sublimation: elements transit between solid and vapor phases without becoming liquid. Sublimation Deposition 51 PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

52 Martian meteorites Meteorites ejected from the surface of Mars by large impacts. The 34 Mars known meteorites are called the SNC group (25 Shergottites, 7 Nakhlites, and 2 Chassignites). How do we know? The SNC meteorites possess the same chemical, isotopic, and petrologic features than Mars surface. The air bubbles trapped inside the rock match perfectly the chemical composition of the Martian atmosphere. Possible evidence for life? 52 Picture: NASA PHYS 171: Introduction to Astronomy I Chapter 7 Part 4: Mars

53 What have we learned? What geological features tell us that water once flowed on Mars? Dry riverbeds, eroded craters, and rock-strewn floodplains all show that water once flowed on Mars. Mars today has ice, underground water ice, and perhaps pockets of underground liquid water. Why did Mars change? Mars's atmosphere must have once been much thicker for its greenhouse effect to allow liquid water on the surface. Mars lost most of its atmosphere because of its lower mass and a declining magnetic field. Fall 2015 PHYS 171: Introduction to Astronomy I Chapter 7: Earth and the Terrestrial Worlds 53