Mars s atmosphere. continued. Dust devil on as seen by rover Spirit 3/27/07

Transcription

1 Mars continued Mars s atmosphere Dust devil on as seen by rover Spirit

2 Announcements Reading Assignment for 1 st lecture after the exam Chapter 14 All previous assignments have been graded and handed back please pick up all of your material since I will be clearing out the boxes later this week Uncollected assignments will be in my office Exam #2 on Thursday Brief review after today s lecture Next study-group session is tomorrow (3/28) from 10:30AM-12:00Noon in room 330. Public lecture tonight at 7:30PM in 308 of Kuiper (this room). Prof. Bob Brown, Saturn seen through infrared eyes Look for PTYS/ASTR206 sign-up sheet (our class!) Note Prof. Brown will conduct a limited number of special 10-minute tours of the VIMS Operations Center; these tours will originate in the Atrium at 6PM early arrival is recommended!

3 Today Mars s red color Mars s Atmosphere Water on Mars Moons Life on Mars later in the course For now, suffice it to say that we have NOT detected any life on Mars. This is covered in Chapter 13. But, we will discuss it further in a few weeks.

4 Mars s red color Mars is red because it s surface contains a lot of iron which is oxidized by its atmosphere Iron is abundant in the lowlands Iron easily loses 2 or 3 of its electrons when coming into contact with, for example, Oxygen (which mostly exists in the form of CO 2 in Mars s atmosphere) This oxidizes the iron and makes it red Dark regions on Mars can change shape with the Martian season (due to dust storms) and have a different composition than the brighter areas Note that Moon also contains iron in the Mare, but because it has no atmosphere, it is just dark gray, and not red

5 The Atmosphere of Mars very tenuous! the surface air pressure is only about 0.75% of the average on Earth The air pressure on Earth at about 40km in altitude (about 5 times higher than Mt. Everest) is about the same as at the surface of Mars Discovered by noting cloud formations Difficult to determine chemical composition from spectroscopy Very weak greenhouse effect raises the surface temperature by only 5 o C

6 Mars s Atmospheric Composition Mostly CO 2 (95%) with only a trace of O 2 and H 2 0. Small amount of Methane is intriguing discovered in 2003 by Earth-based telescopes, confirmed by Mars Express Orbiter). Unstable gas sunlight would destroy it in about 100 years What is it origin? Life? Volcanic vents? Comet impact?

7 The Mars Sky is Yellowish Dust particles in the atmosphere scatter all wavelengths nearly the same This should make the sky white Because of the presence of magnetite in the dust, blue light is absorbed Leaving a yellowish sky

8 Martian Dustdevils Common features on Mars In some wide-field views, can see several at one time A Mars rover owes its extended mission to one Much larger than on Earth Formed as the air right above the ground is heated and moves through cooler air above it, becoming elongated conservation of angular momentum leads to rapid rotation

9 Comparison of Sizes

10 Dust Storms Mars seen by Hubble Space Telescope just over 2 months apart showing how global Martian dust storms can be

11 Sand Dunes on Mars Twice as large as on Earth Because of Mars s smaller gravity Dune formation (1) Piling up of sand on wind-side of dune (2) Avalanche of sand on lee-side of dune

12 Seasons on Mars Reason for seasons is that same as that on Earth. However, Mars has a highly eccentric orbit (the most eccentric of the 8 planets Pluto s is larger) Thus, the seasonal variation is much more extreme The polar caps, which are continually bathed in sunlight during their respective summers, are known to shrink considerably

13 More Martian Seasonal Variations: Atmospheric Pressure In the southern winter (northern summer) CO 2 condenses out of the atmosphere, reducing atmospheric pressure of the planet. Mars is farthest from the Sun at this time Creating flakes that cover the surface Enlarges the southern polar cap In southern summer (northern winter) CO 2 is released back into the atmosphere, increasing the pressure. Mars is closest to the Sun at PTYS/ASTR this time 206

14 The Evolution of the Martian Atmosphere: A runaway icehouse effect Mars may have once had a thick atmosphere which provided enough pressure for liquid water to exist on its surface. If it did, it must have undergone a runaway icehouse effect Colder temps more H 2 O condenses to rain, brings more CO 2 with it lessens the greenhouse effect gets colder etc. No plate tectonics or volcanic activity to recycle the CO 2 and other greenhouse gasses. Much of the water molecules were disassociated by solar UV the H and O were lost to space making the atmosphere thinner the rest of the H 2 0 became frozen underneath the surface

15 The two Martian moons resemble asteroids Mars has two small, irregularshaped satellites that move in orbits close to the surface of the planet Discovered in 1877 by Asaph Hall (US Naval Observatory) Probably captured asteroids Highly eccentric orbits They look like asteroids Deimos (lower left) Phobos (lower right) (asteroid Gaspra is also shown at the top)

16 Phobos The larger and closest to Mars As seen from Mars it rises in the west and sets in the east Slowly Spiraling in to Mars Near the Roche limit the point where tidal forces will tear the moon apart Will take about 40 million years to reach the Roche limit may form a ring around Mars may impact the surface

17 Deimos Much smaller than Phobos Much fewer surface features Why so featureless? Also has a large impact crater From Mars, it rises in the east but takes nearly 3 days to set!

18 Photos of Solar eclipses as seen from the Surface of Mars Solar Transits of Phobos (left) and Diemos (right) seen by Mars Rover Opportunity

19 Water on Mars Artist s conception of a water filled Gusev crater What is the evidence that liquid water once existed on the surface Mars What is the evidence that water currently exists on Mars (in the form of ice underneath the surface)?

20 Visual Evidence: Ancient river flows and channels Ancient flood plains NOT canals as Percival Lowell thought!!!

21 Gullies in Crater Walls Probably there is a layer of ice underneath the surface. Upon a crater impact, this water is then released to flow, creating large gullies along the crater walls.

22

23 In what form can water exist on Mars?

24 Where is the water today? Frozen beneath the surface Like the Alaskan Tundra (shown at the right) There is not enough pressure in Mars s atmosphere today to have liquid water, but perhaps it did in the past There is also a lot of water ice underneath carbon-dioxide ice in the polar caps.

25 Water Ice underneath CO 2 ice As the season turned to summer in the Northern hemisphere on Mars, the CO 2 sublimates (solid vapor) revealing water ice underneath! This was also seen at the Southern polar cap by Mars Global Surveyor and Mars Odyssey

26 The Discovery of Water on Mars The GRS (Gamma-Ray Spectrometer) on Mars Odyssey was used to discover water on Mars LPL-led team (PI: B. Boynton) It used a different form of spectroscopy measuring spikes in the gamma-ray spectrum The gamma rays are produced when cosmic rays collide with material in the Martian topsoil

27 Gamma rays and neutrons are produced by cosmic rays striking the Martian surface

28

29 Can Mars be terraformed to be suitable for human life? Carl Sagan proposed the idea of blackening the polar ice caps. This would cause them to melt and release water vapor into the atmosphere Terraforming Mars Plants which grow on ice have been proposed as the blackening agent Would take ,000 years Not on NASA s roadmap. Private enterprise?

30 Second Exam Format: 5 short-answer questions (5 pts each) 30 multiple choice questions (2 ½ pts each) To be answered on the scantron sheets BRING A #2 PENCIL! Closed book, closed notes, no electronic devices (including a calculator!) The allotted time will be 75 minutes

31 Second Exam What will it cover? Mostly material discussed in the lectures (75%) All lectures since the first exam Reading (25 %) Chapters 9-13 and 18 Note: some lecture topics are discussed more deeply in the reading How much does it count towards the final grade? Either 20% or 10% of your overall grade depending on how you did on the first exam (the best score of the 2 is 20%, the worst is 10%)

32 Second Exam What should you study? Go over guiding questions at the beginning of each chapter Go over key ideas and review questions at the end of each chapter Go over the lecture slides! Review activities, homework, and quizzes Solutions are posted on the website Practice exam is on the website now

33 Second Exam: A Brief Review Terrestrial planet surfaces and interiors (Lecture 11 and part of Lecture 12) interiors Formation of terrestrial planets Sources of heat, and cooling processes Methods of probing the interior Planetary magnetic fields and their origin (dynamo) surfaces volcanism Aeolian processes Impact cratering Evidence for impacts due to bombardment by solar-system debris Effects of an impact Chixculub crater, the KT boundary, and the extinction of the dinosaurs

34 Second Exam: A Brief Review Planetary Atmospheres (Lecture 12) Definition Which planets have them and why Evolution of Earth s atmosphere What atmospheres do Atmospheric pressure hydrostatic equilibrium Atmospheric scale height

35 Second Exam: A Brief Review Chapter 9 Earth as a planet Ways that Earth is unique in the solar system Earth s interior Plate tectonics and continental drift Basic process Different rock types Atmospheric structure Greenhouse effect!! Layers of the atmosphere Atmospheric circulation patterns Coriolis force Earth s magnetosphere Origin of aurora Van-Allen radiation belts

36 Second Exam: A Brief Review Chapter 18 The Sun Source of energy Thermonuclear fusion Solar neutrinos Basic internal structure (3 main regions) Atmospheric structure Photosphere, chromosphere, corona Visible characteristics in each region, and what wavelength is best to see it Sunspots, magnetic fields Solar Cycle and Sun-Earth Connection (Lecture 15) 11-year sunspot cycle Solar maximum and solar minimum Coronal mass ejections and solar flares Geomagnetic storms Space radiation environment Solar-energetic particles PTYS/ASTR Galactic 206 cosmic rays Threats to astronauts

37 Second Exam: A Brief Review Chapter 10 The Moon Tidal forces 1:1 synchronous rotation Surface characteristics Lunar highlands Maria Regolith lunar rocks and their origin Possibility of water ice in deep craters near the lunar poles Theories for lunar origin Chapter 11 Mercury Orbit, rotation, appearance from Earth Surface features (craters, scarps, inter-crater plains, etc.) Interior, Magnetic field, and iron content

38 Second Exam: A Brief Review Chapter 12 Venus Orbit, Rotation, and appearance from Earth Atmosphere (runaway greenhouse effect, clouds, composition, etc.) Surface (volcanoes, craters, etc.) and interior Chapter 13 Mars History, orbit, and appearance from Earth, spacecraft exploration Surface, Geology, and Atmosphere Its two moons (Deimos and Phobos) Water on Mars