NATS1311 From the Cosmos to Earth

NATS1311 From the Cosmos to Earth

Mercury

Property Earth Mercury

Equatorial Diameter 1 0.4

Density (gm/cm3) 5.5 5.4

Avg. Distance from Sun (AU) 1 0.4

Orbital Period (days) 365 88

Sidereal Rotation Period (days) 1 59

Inclination of axis to orbital plane 23.5° 7°

Inclination of orbit to ecliptic plane 0° 7°

Maximum angle from sun ~ 28°

Surface temperature ~ Day: 800°F

~ Night: -280°F

Atmosphere - pressure 1 atmosphere 10-15 atmosphere

Atmosphere - composition N2, O2 Helium, sodium, potassium, oxygen


The orbit of Mercury

At an average distance of only 58 million kilometers (36 million miles) from the sun, mercury takes a mere 88 days to go around its orbit.

As viewed from earth, mercury can be seen only near times of greatest eastern or western elongation.

At greatest western elongation (when the planet is farthest west of the sun in the sky), mercury rises about 1 1/2 hours before sunrise.

At greatest eastern elongation (when the planet is farthest east of the sun in the sky), mercury sets about 1 1/2 hours after sunset.


Differences between the Moon and Mercury

1. Areas between craters on Mercury smoother than on Moon.

2. Secondary impact craters don't scatter as much on Mercury.

3. Gravitational acceleration on Mercury twice that of moon.

4. Mercury has scarps - lines of cliffs- caused by shrinkage of its surface.

5. Mercury's atmosphere consists of sodium and potassium (sputtered form surface by the solar wind), helium and oxygen.

6. Atmospheric pressure about the same as on the Moon.

NATS 1311 From the Cosmos to Earth

NATS 1311 From the Cosmos to Earth Fig.8.2

Figure 8.2 Surface views of the terrestrial worlds. No spacecraft have landed on Mercury, so an artist's conception is shown; all other images are photos.


Atmosphere of EarthBlanket of Gases Surrounding Earth Contains a Mixture of Gases

Composition of Dry AirNitrogen 78%

Oxygen 21%

Argon 0.93%

Carbon Dioxide

0.035%

Water Vapor < 1%

•Pressure on a surface is weight of air above that surface•Pressure of 1 atmosphere at Earth’s surface at sea level:

•14.7 Lb. per Square Inch•76 Cm of Mercury (30 inches of Mercury)•1034 Grams per Square Centimeter

•Pressure decreases as altitude above Earth’s surface increases


Regions of the Atmosphere

Region Upper Boundary Feature

Names Altitude

Troposphere Tropopause 10 Miles Meteorological interestTemperature decreasing

Stratosphere Stratopause 30 Miles Temperature increasing

Mesosphere Mesopause 50 Miles Temperature decreasing

Thermosphere - 300 Miles

Temperature increasing

Exosphere - - Gas molecules can

escape from atmosphere

NATS 1311 From the Cosmos to Earth Fig. 8.12

Figure 8.12 The structure of a generic planetary atmosphere: Solar X rays are absorbed in the thermosphere, ultraviolet light is absorbed in the stratosphere, and visible light reaches the ground. Planets that lack ultraviolet-absorbing molecules will lack a stratosphere, and planets with very little gas will have only an exosphere.


Thermal structure of the atmosphere.

Atmospheric temperature plotted as a function of altitude from ground level to 110 kilometers.


Figure 8.13 Atmospheric gases scatter blue light more than they scatter red light. During most of the day, you therefore see blue photons coming from most directions in the sky, making the sky look blue. But only the red photons reach your eyes at sunrise or sunset, when the light must travel a longer path through the atmosphere to reach you.


Figure 8.14 The greenhouse effect: The troposphere becomes warmer than it would be if it had no greenhouse gases.


Figure 8.16 A planet's magnetosphere acts like a protective bubble that shields the surface from charged particles coming from the solar wind. Among the terrestrial planets, only the Earth has a strong enough magnetic field to create a magnetosphere. The Earth's magnetosphere allows charged particles to strike the atmosphere only near the poles, thereby creating the phenomena of the aurora borealis and aurora australis.


Comparison of Venus and Earth

Parameter Venus Earth

• Distance from Sun (AU) .72 1.00 (million KM) 108

150

• Sidereal Period (year) (earth days) 225 365

• Rotation Period (day) (earth days) -243 1.00

• Direction of rotation Retrograde Direct

• Equatorial Diameter 0.96 1.00

• Escape velocity (km/Sec.) 10.3 11.2

• Inclination of axis 3 23.5• Seasons No Yes

VENUS


Comparison of Venus and Earth• Parameter Venus Earth

• Surface Temperature 480C (900F) 15C (60F)

• Surface atmospheric pressure 90 1

(atmospheres)

• Atmospheric gases CO2 N2, O2

• Cloud cover Total Partial

• Surface Solid 3/4 water

• Number of satellites 0 1

VENUS


• Venus clouds:

3 layers 49 to 65 km in altitude

haze down to 30 km

clear below 30km

composition:

H2so4 droplets and sulfur particles

• Venus surface:

Rock strewn surface• Temperature: 480c (900f)

VENUS


VENUSSurface: Venus:

No plate tectonics - (movement of surface) Radioactive heating Vocanoes are scattered over the surface of Venus Crustal material is denser than the underlying magma Every 500 million years, the crust breaks up and

sinks, forming a new crust Earth:

1 0 plates - volcanoes found on plate boundaries


Atmosphere Formation

Original atmospheres were swept away from the terrestrial planets early in their life.

Present day terrestrial atmospheres are secondary atmospheres:

Venus:

Formed by outgassing (volcanoes and gas seepage)

from beneath the surface.

Surface too warm for water to condense as a liquid -

water dissociated into hydrogen and oxygen.

Hydrogen escaped - oxygen combined with surface

materials.


Atmosphere Formation

Carbon dioxide and nitrogen accumulated in the

atmosphere.

CO2 96%

N2 3-4%

"Runaway" greenhouse effect.

Earth:Water condensed into liquid formCO2 dissolved into the water - formed limestone rocks

Nitrogen accumulated in the atmosphereOxygen accumulated after life formed in the oceans


Differences between Venus and earth

1. Venus rotation rate is very slow and in retrograde direction.

2. Venus surface consists of 1 plate; earth has 9 plates.

3. Venus has little or no magnetic field.

4. Venus' atmosphere pressure is 90 times that of earth.

5. Dominant gas in the Venus atmosphere is carbon dioxide.

6. Venus' surface temperature is 900° F.

7. Venus has very little water vapor in its atmosphere.

8 Venus has a very strong greenhouse effect.

9. There is no water on Venus' surface.

10. Venus has a very dense cloud cover.


Figure 8.26 The surface of Venus is covered with

abundant lava flows and tectonic features, along with a few

large impact craters. Because these images were taken by

the Magellan spacecraft radar, dark and light areas

correspond to how well radio waves are reflected, not

visible light. Nonetheless, geological features stand out

well. In (b), the data have been converted to a three-

dimensional perspective view; heights are magnified by a

factor of more than 20, so the volcano is not actually as

steep-sided as it appears.


Figure 8.26

(a) Two of Venus's relatively rare impact craters.

(b) Shield volcanoes like this one are common on Venus. (Height exaggerated to show detail.)

(c) Tectonic forces have fractured and twisted the crust in the region.

(d) The circular cracks and volcanic bumps make up a corona, probably caused by the pressure of a mantle plume below.


MarsComparison of Venus, Earth and Mars

•Parameter Venus Earth Mars

•Distance from Sun (AU) .72 1.00 1.52 (million KM) 108 150 228

•Sidereal Period (year) (earth days) 225 365 687

•Rotation Period (day) (earth days) -243 1.00 1.03

•Direction of rotation Retrograde Direct Direct

•Equatorial Diameter 0.96 1.00 0.53

•Escape velocity (km/Sec.) 10.3 11.2 5.0

•Inclination of axis 3 23.5 25.2•Seasons No Yes Yes


MarsComparison of Venus, Earth and Mars

•Parameter Venus Earth Mars

•Surface Temperature 480C (900F) 15C(60F) -60C(-76F)

•Surface atmospheric pressure 90 1 1/200

(atmospheres)

•Atmospheric gases CO2 N2, O2 CO2

•Cloud cover Total Partial Rare

•Surface Solid 3/4 water Solid

•Number of satellites 0 1 2


Viking Life Detection Experiments on Mars

Living organisms alter their environment - they breathe, eat, grow, and produce waste

Three experiments were designed to detect signs of living organisms by treating soil samples in a closed environment (a container):



Gas exchange -

Looked for changes in the atmosphere

caused by metabolism of organisms in the soil.

Soil sample fed nutrient in a carbon dioxide (co2)

atmosphere.

Organisms eat nutrients and release gases like CO2,

methane, oxygen and hydrogen into the container.

Some gases were found but were thought to be due to

chemical reactions between the nutrient water and

the soil.



Labeled release -

Looked for co2 breathed into the atmosphereSoil sample fed radioactive nutrientOrganisms released radioactive CO2 into the

containerSome gases were found but were thought to be

due to the chemical reactions between the nutrient and the soil



Pyrolytic release - Looked for radioactive carbon in soil sampleSoil sample in radioactive CO2 atmosphere

illuminated by ultraviolet light to simulate sunlight

Soil sample then heated to 650°C to decomposeany growth material in the soil

Soil contained some radioactive carbon - did notrepresent life

Conclusion:Some positive results found in each experiment.However, not sufficient to confirm life as we know it Explanation - unusual chemical activity


METEORITES FROM MARS

Meteorites found on antarctic ice

Concentrated in place where ice flows are impeded and the ice is ablated

Well preserved:Not exposed to water erosionNot exposed to industrial contaminants


METEORITES FROM MARS

Twelve antarctic meteorites came from Mars:Called SNC meteoritesAge: 4.5 billion yearsEjected from Mars by collision of some large

object (asteroid?) with MarsSpent several million years in orbit, then

landed on earthDiscovered within the last 20 yearsWhy from Mars?

Trapped gases in voids in the meteorites match martian atmosphere


ALH 84001 METEORITE

Formed 4.5 billion years agoEjected from Mars 1 6 million years agoArrived on earth 13,000 years agoFound in 1993Contains carbonate globules formed 3.6 billion years ago

Found along fractures in meteorite -

not of earth origin

Formed from CO2 in martian atmosphere


ANALYSIS OF GLOBULES:Laser desorption mass spectrometerShowed presence of polycyclic aromatic

hydrocarbons (PAM) unlike any on earthThese molecules contain many rings of carbon

atoms

APPEARANCE OF GLOBULES:Transmission electron microscope images

Orange colorFlattened circular disksIron rich materials characteristic of fossil

remains


Scanning electron microscope imagesTubular shaped bodesDimensions - less than 100 nanometers

(1000 times smaller than the diameter of a human hair)

Carbonate globules are the key to biogenic activity on Mars Globules formed in fractures of rock Globules are younger than the rock Globular features resemble earth microorganisms,

earth biogenic carbonate structures and microfossils

Globules contain PAH's


CONCLUSION:Alternative explanations exist for each globular

phenomenon taken individually

Collectively, they are evidence for primitive life on

Mars

NATS 1311 From the Cosmos to Earth FIG. 11.16

NATS1311 From the Cosmos to Earth

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