PTYS/ASTR 206Mars (cont.) 3/27/07 Mars … continued Mars’s atmosphere Dust devil on as seen by rover Spirit

PTYS/ASTR 206 Mars (cont.)3/27/07

Mars … continued

Mars’s atmosphere

Dust devil on as seen by rover Spirit


Announcements

• Reading Assignment for 1st 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!


• 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.


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 CO2 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


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

5oC


Mars’s Atmospheric Composition

• Mostly CO2 (95%) with only a trace of O2 and H20.

• 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?


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


• 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

Martian Dustdevils


Comparison of Sizes


Dust Storms

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


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


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


More Martian Seasonal Variations:

Atmospheric Pressure

• In the southern winter (northern summer) CO2 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) CO2 is released back into the atmosphere, increasing the pressure. – Mars is closest to the Sun at

this time


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 H2O condenses to rain, brings more CO2

with it lessens the greenhouse effect gets colder … etc.– No plate tectonics or volcanic activity to recycle the CO2 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 H20 became frozen underneath the surface


The two Martian moons resemble asteroids

• Mars has two small, irregular-shaped 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)


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


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 !


Photos of Solar eclipses as seen from the Surface of Mars

Solar Transits of Phobos (left) and Diemos (right) seen by Mars Rover Opportunity


• 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)?

Water on Mars

Artist’s conception of a water filled Gusev crater


• Visual Evidence:– Ancient river flows and

channels– Ancient flood plains– NOT “canals” as Percival

Lowell thought !!!


• 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.

Gullies in Crater Walls



In what form can water exist on Mars ?


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.


• Water Ice underneath CO2

ice– As the season turned to

summer in the Northern hemisphere on Mars, the CO2 sublimates (solid vapor) revealing water ice underneath!

• This was also seen at the Southern polar cap by Mars Global Surveyor and Mars Odyssey


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


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



Terraforming Mars

• 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

• Plants which grow on ice have been proposed as the “blackening” agent

• Would take 100-10,000 years

• Not on NASA’s roadmap. Private enterprise?


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


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%)


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


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



• 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



• 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



• 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• Galactic cosmic rays• Threats to astronauts



• 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



• 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

Documents

PTYS/ASTR 206Mars (cont.) 3/27/07 Mars … continued Mars’s atmosphere Dust devil on as seen by rover Spirit