Venus, Earth and Mars Lecture 14. Telescope Observing lab following class Maps are available at the...
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Transcript of Venus, Earth and Mars Lecture 14. Telescope Observing lab following class Maps are available at the...
Venus, Earth and Mars
Lecture 14
•Telescope Observing lab following class
•Maps are available at the front of the classroom
•You may want to stop for a snack on the way, we probably won’t do a lot of observing before about 7:30 due to sunlight (although we may look at the Sun if we get set up early enough).
• If weather (ie, clouds) prevents us from seeing enough tonight, we will likely try again later in the semester.
Announcements
•Comparative Planetology is the study of planets as groups, comparing their similarities and differences. We will take this approach to studying the solar system, starting with the planets most similar to our own.
•We Will compare several features of these planets:
• Interiors
• Surfaces
• Atmospheres
• Magnetospheres
• Moons
Comparative Planetology
The Early HistoryThe terrestrial planets formed 4.6 billion years ago from the inner solar nebula.
Four main stages of evolution:
Most traces of bombardment (impact craters) now destroyed on Earth by later geological activity
Two sources of heat in planet’s interior:
• Potential energy of infalling material
• Decay of radioactive material
Earth’s InteriorDirect exploration of Earth’s interior (e.g. drilling) is impossible.
Earth’s interior can be explored through seismology:
earthquakes produce seismic waves.
Two types of seismic waves:Pressure waves:
Particles vibrate back and forth
Shear waves:
Particles vibrate up and down
Seismology
Seismic waves do not travel through Earth in straight lines or at constant speed.
They are bent by or bounce off transitions between different materials or different densities or temperatures.
Such information can be analyzed to infer the structure of Earth’s interior.
Venus and Mars
Two most similar planets to Earth:
• Similar in size and mass • Atmosphere
• Similar interior structure• Same part of the solar system
Yet, no life possible on either one of them.
Interior
Basic structure:
Solid crust
Solid mantle
Liquid core
Solid inner core
interior gets hotter towards the center.
Earth’s core is as hot as the sun’s surface; metals are liquid.
Melting point = temperature at which an element melts
(transition from solid to liquid)
Melting point increases with increasing
pressure towards the center
=> Inner core becomes solid
The Rotation of Venus
• Almost all planets rotate counterclockwise, i.e. in the same sense as orbital motion.
• Exceptions: Venus, Uranus and Pluto
• Venus rotates clockwise, with period slightly longer than orbital period.
Possible reasons:
• Off-center collision with massive protoplanet
• Tidal forces of the sun on molten core
Mars• Diameter ≈ 1/2 Earth’s diameter
• Very thin atmosphere, mostly CO2
• Rotation period
= 24 h, 40 min.• Axis tilted against orbital plane by 25o, similar to Earth’s inclination (23.5o)
• Seasons similar to Earth Growth and shrinking of polar ice cap
• Crust not broken into tectonic plates
• Volcanic activity (including highest volcano in the solar system)
The Active Earth
About 2/3 of Earth’s surface is covered by water.
Mountains are relatively rapidly eroded away by the forces of water.
Earth’s surface geology is much more dynamic than Venus and Mars.
Tectonic PlatesEarth’s crust is composed of several distinct tectonic plates, which are in constant motion with respect to each other Plate tectonics
Evidence for plate tectonics can be found on the ocean floor
… and in geologically active regions all around the Pacific
Plate TectonicsTectonic plates move with respect to each other.
Where plates move toward each other, plates can be pushed upward and downward formation of mountain ranges, some with volcanic activity, earthquakes
Where plates move away from each other, molten
lava can rise up from below volcanic activity
Earth’s Tectonic History
History of Geological Activity
Surface formations visible today have emerged only very recently compared to the age of Earth.
The Surface of VenusEarly radar images already revealed mountains, plains, craters.
Venera 13 photograph of surface of Venus:
Colors modified by clouds in
Venus’s atmosphere
More details from orbiting and landing spacecraft:
After correction for atmospheric
color effect:
Radar Map of Venus’s Surface
Surface features shown in artificial colors
• Scattered impact craters
• Volcanic regions
• Smooth lava flows
Lava Flows
Young, uneven lava flows (shown: Lava flow near Flagstaff, AZ) show up as bright regions on radar maps.
Surface Features on Venus
Smooth lowlands
Highland regions:
Maxwell Montes are ~ 50 % higher than Mt. Everest!
Craters on VenusNearly 1000 impact craters on Venus’s surface:
Surface not very old.
No water on the surface; thick, dense atmosphere
No erosion
Craters appear sharp and fresh
Volcanism on Earth
Volcanism on Earth is commonly found along subduction zones
(e.g., Rocky Mountains).
This type of volcanism is not found on Venus or Mars.
Shield Volcanoes
Found above hot spots:
Fluid magma chamber, from which lava erupts repeatedly through surface layers above.
All volcanoes on Venus and Mars are shield volcanoes
Shield Volcanoes
Tectonic plates moving over hot spots producing shield volcanoes Chains of volcanoes
Example: The Hawaiian Islands
Volcanism on Venus
Sapas Mons (radar image)
2 lava-filled calderas~ 400 km (250 miles)
Lava flows
Volcanic Features on Venus
Baltis Vallis: 6800 km long lava flow channel (longest
in the solar system!) Coronae: Circular bulges formed by volcanic activity
Aine Corona
Pancake Domes:
Associated with volcanic
activity forming coronae
Some lava flows collapsed after molten lava drained away
Lakshmi Planum and Maxwell Mountains
Radar image
Wrinkled mountain formations indicate compression and wrinkling, though there is no evidence of plate tectonics on Venus.
Tales of Canals and Life on Mars
Early observers (Schiaparelli, Lowell) believed to see canals on Mars
This, together with growth/shrinking of polar cap, sparked imagination and sci-fi tales of life on Mars.
We know today: “canals” were optical illusion; do not exist!
No evidence of life on Mars.
The Geology of Mars
Giant volcanoes
Valleys
Impact craters
Vallis Marineris
Reddish deserts of broken rock, probably smashed by
meteorite impacts.
The Geology of MarsNorthern Lowlands: Free of craters; probably re-surfaced a few billion years ago.
Southern Highlands: Heavily cratered; probably 2 – 3 billion years old.
Possibly once filled with water.
Volcanism on Mars
Volcanoes on Mars are shield
volcanoes.
Olympus Mons:
Highest and largest volcano
in the solar system.
Volcanism on Mars
Tharsis rise (volcanic bulge):
Nearly as large as the U.S.
Rises ~ 10 km above mean radius of Mars.
Rising magma has repeatedly broken through crust to form volcanoes.
Hidden Water on MarsNo liquid water on the surface:
Would evaporate due to low pressure.
But evidence for liquid water in the past:
Outflow channels from sudden, massive floods
Collapsed structures after withdrawal of sub-surface water
Splash craters and valleys resembling meandering river beds
Gullies, possibly from debris flows
Central channel in a valley suggests long-term flowing water
Hidden Water on Mars
Gusev Crater and Ma’adim Vallis:
Giant lakes might have drained repeatedly through the Ma’adim Vallis into the crater.
Ice in the Polar Cap
Polar cap contains mostly CO2 ice, but also water.
Multiple ice regions separated by valleys
free of ice.
Boundaries of polar caps
reveal multiple layers of dust, left behind by
repeated growth and melting of
polar-cap regions.
Evidence for Water on Mars
Large impacts may have ejected rocks into space.
Galle,
the “happy face crater” Meteorite ALH84001:
Identified as ancient rock from Mars.Some minerals in this meteorite were deposited in water Martian crust must have been richer in water than it is today.
Atmospheres
Atmospheric composition severely altered (
secondary atmosphere) through a combination of two processes:
1) Outgassing: Release of gasses bound in compounds in the interior through volcanic activity
Terrestrial planets had primeval atmospheres from remaining gasses captured during formation
2) Later bombardment with icy meteoroids and comets
The Structure of Earth’s Atmosphere
The ozone layer is
essential for life on Earth since it protects the atmosphere
from UV radiation
Composition of Earth’s atmosphere is further influenced by:
• Chemical reactions in the oceans,
• Energetic radiation from space (in particular, UV)
• Presence of life on Earth
The temperature of the atmosphere depends critically on its albedo = percentage of sun light that it reflects back into space
Depends on many factors, e.g., abundance of water vapor in the atmosphere
Human Effects on Earth’s Atmosphere1) The Greenhouse Effect
Earth’s surface is heated by the sun’s radiation.
Heat energy is re-radiated from Earth’s surface as infrared radiation.
CO2, but also other gases in the atmosphere, absorb infrared light
Heat is trapped in the atmosphere.
This is the Greenhouse Effect.
The Greenhouse Effect occurs naturally and is essential to maintain a comfortable temperature on Earth,but human activity, in particular CO2 emissions from cars and industrial plants, is drastically increasing the concentration of greenhouse gases.
Global Warming
• Human activity (CO2 emissions + deforestation) is drastically increasing the concentration of greenhouse gases.
• As a consequence, beyond any reasonable doubt, the average temperature on Earth is increasing.
• This is called Global Warming
• Leads to melting of glaciers and polar ice caps
( rising sea water levels) and global climate changes, which could ultimately make Earth unfit for human life!
Human Effects on the Atmosphere2) Destruction of the
Ozone LayerOzone (= O3) absorbs UV radiation, (which has damaging effects on human and animal tissue).
Chlorofluorocarbons (CFCs) (used, e.g., in industrial processes, refrigeration and air conditioning) destroy Ozone.
Destruction of the ozone layer as a consequence of human activity is proven (e.g., growing ozone hole above the Antarctic);
UV image
Extremely inhospitable:
96 % carbon dioxide (CO2)3.5 % nitrogen (N2)Rest: water (H2O), hydrochloric acid (HCl), hydrofluoric acid (HF)
4 thick cloud layers ( surface invisible to us from Earth).
Very stable circulation patterns with high-speed winds (up to 240 km/h)
Extremely high surface temperature up to 745 K (= 880 oF)
Very efficient “greenhouse”!
UV image
The Atmosphere of Venus
The Atmosphere of MarsVery thin: Only 1% of pressure on Earth’s surface
95 % CO2
Even thin Martian atmosphere evident through haze and clouds covering the planet
Occasionally: Strong dust storms that can enshroud the entire planet.
The Atmosphere of Mars
Most of the Oxygen bound in oxides in rocks
Reddish color of the surface
History of Mars’s AtmosphereAtmosphere probably initially produced through outgassing.
Loss of gasses from a planet’s atmosphere:
Compare typical velocity of gas molecules to escape velocity
Gas molecule velocity greater than escape velocity
gasses escape into space.
Mars has lost all lighter gasses; retained only heavier gasses (CO2).
Earth’s Magnetic Field
• Convective motions and rotation of the core generate a dipole magnetic field
• Earth’s core consists mostly of iron + nickel: high electrical conductivity
The Role of Earth’s Magnetic FieldEarth’s magnetic field protects Earth from high-energy
particles coming from the sun (solar wind).
Surface of first interaction of solar wind with Earth’s magnetic field = Bow shock
Region where Earth’s magnetic field dominates = magnetosphere
Some high-energy particles leak through the magnetic field and produce a belt of high-energy particles around Earth: Van Allen belts
The Aurora (Polar Light)
As high-energy particles leak into the lower magnetosphere, they excite molecules near the Earth’s magnetic poles, causing the aurora
A History of VenusComplicated history; still poorly understood.
Very similar to Earth in mass, size, composition, density, but no magnetic field Core solid?
Heat transport from core mainly through magma flows close to the surface ( coronae, pancake domes, etc.)
Solar Wind InteractionSolar wind interacts directly with the atmosphere, forming a Solar wind interacts directly with the atmosphere, forming a bow shock and a long ion tail. bow shock and a long ion tail.
COCO22 produced produced
during outgassing during outgassing remained in remained in atmosphere (on atmosphere (on Earth: dissolved in Earth: dissolved in water).water).
Any water present Any water present on the surface on the surface rapidly evaporated rapidly evaporated → feedback → feedback through through enhancement of enhancement of greenhouse effectgreenhouse effect
The Moons of Mars
Phobos
Deimos
Two small moons: Phobos and
Deimos.
Too small to pull themselves into spherical shape.
Very close to Mars; orbits around Mars faster than Mars’ rotation.
Typical of small, rocky bodies: Dark grey, low density.
Probably captured from outer asteroid belt.
Earth’s Moon
Earth has an unusually large moon… details next time.
We will discuss the Moon and Mercury
Read Units 37 and 38
For Next Time