Transcript Venus and Mars (Professor Powerpoint)

Venus
•Rotation Period (very slow) 243 days
(retrograde- rotates backward) (upside down)
•Radius 6051 Km
•Avg Distance from Sun 0.723 A.U.
•Solar Revolution Period 224 Earth days
•Eccentricity 0.007
•Albedo (avg) 0.65
•In terms of mass, radius, and density, Venus is a
near-twin of the Earth
Venus
Appearance
Easy to observe
(greatest elongation ~47º).
Very bright in the sky ( “Morning star or Evening star”)
Goes through phases like the Moon.
Completely covered with clouds, can’t see the surface
Geology
Spacecraft investigation of surface of Venus
Continents- 2 , 2-3 km high
Craters Volcanoes(some active), plains, and valleys.
Surface
75% covered with lowland lava plains
similar in origin to lunar maria
–
•
Possible evidence of plate tectonics
Volcanoes
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•
•
Many different volcanic features on surface
Largest volcano – Sirf Mons- 500 km
(300 miles across and 3 km (2 mi) high
Thousands of smaller volcanoes
On Venus’ surface
Atmospheric pressure = 90x Earth
Igneous rocks, primarily basalts
Surface temperature: 700K (850F)
Atmosphere of Venus
Composition : CO2 is 96%, N2 is 3%
Sulfur dioxide (SO2) in middle atmosphere
Troposphere - Thick layer of sulfuric acid
These gases were vented from inside Venus through
volcanoes. Clouds are mostly sulfuric acid
CO2 and H2O are vented from volcanoes
CO2 builds up causes a Runaway Greenhouse Effect
Venus’ Atmosphere
Composition : CO2 is
96%, N2 is 3%
Incoming
sunlight is
mostly
reflected
by the
clouds
Sulfur dioxide (SO2) in
middle atmosphere
Clouds are mostly
sulfuric acid
Some
incoming
sunlight gets
through
Surface composed of
Igneous rocks, primarily basalts
Surface temperature:
700K (850F)
CO2 buildup causes
runaway green house
Most heat
radiation is
absorbed by
carbon
dioxide
Basic Geology of Venus
• Heat flows from the interior to surface via
conduction, not through edges of plates as
on the Earth, and possible Plate Tectonics
• High temperature leads to soft, thin crust
• Has little or no magnetic field; surprising
since iron core must be molten. Slow
rotation – 243 earth days!
• Topography: Mostly flat, rolling plains
similar to earth’s ocean floors
• Impact crater density shows surface is
about 800 million years old
Impact Craters
Very few smaller craters due to the thickness of
the planet’s atmosphere.
Crater counts show that much of the surface is ~500
million years old. Something dramatic happened about
~500 million years ago. catastrophic resurfacing ?
The best data we have comes from the Magellan
spacecraft 1990-1993
Lava Channels
Somewhat like Hadley Rille, but much bigger;
100’s of miles long, and 1.2 miles wide
High Venus temperatures may allow very long flows
The Soviet Venera series of landers were eventually successful in
landing on Venus but cameras didn’t last very long. (ve ner ah)
Lava channel
Lava domes
Pancake
Typical corona
Made by
eruptions of
very thick lava
flowing out
evenly.
The “Tick”
High Velocity Winds
There are winds in the upper part of the Venusian
atmosphere with velocities as large as 300 km/hour.
Absence of Water Vapor
The clouds contain little water vapor.
Most of the water made its way to the upper
atmosphere, where it was lost to interplanetary
space.
The clouds reflect 65% of incident solar radiation,
much more than the Earth’s 30% or the Moon’s 11%.
Why some atmospheres are lost
Big planets hold atmospheres better.
–Earth would retain an atmosphere better than Mercury or Moon
Cold planets have lower Vgas so hold atmospheres better
–Heavier gases have lower Vgas so are retained better than
light ones
–CO2 or O2 retained better than He, H2, or H
–Even with “heavy” gases like H2O you can have loss of H
if solar UV breaks H2O apart. That is what happens on Venus.
•Mars
Mars
Orbital period
Semi-major axis
Mass
Radius
Surface Gravity
Escape speed
Rotational Period
Inclination
Surface Magnetic Field
Surface Temperature
Number of Moons
Day 11 Mars
•1.88 years (687 days)
1.52 AU
0.11 x Earth
0.53 x Earth
0.38X Earth
5.0 Km/s
1.026 days
23.98°
1/800 x Earth
about 150-310 K
2
Mars' Atmosphere
•Mars has a very thin atmosphere (1/150 of Earth's
atmosphere)
•95.3% CO2 (by volume)
•2.7 % Nitrogen , 1.6% Argon
•0.13% Oxygen , 0.07% CO
•0.03% Water (variable)
Temperatures like Antarctica, with some extremes.
Fog, clouds exist, water only as a gas or solid on the
surface
Observations & spacecraft conclude that Mars :
•Has a reddish hue caused by red dust and rocks
on the surface.
•Has polar ice caps waxing and waning with the
seasons known to be composed both of dry ice
and water ice.
•Has no "canals" but rather features that are
the edges of mountain ranges.
•Has areas of changing color that we now believe
to be due to blowing sand, not vegetation.
Volcanoes on Mars
Tharis region: field of large volcanoes
– Uplifted continent about the size of North America
– Volcanically active at one time
The physics of finding water on Mars
LIQUID water exists over a very NARROW range in
TEMPERATURE
- if T is too high  gas
- if T is too low  solid (ice)
The TEMPERATURE of water will depend on the
ATMOSPHERIC PRESSURE
- if Pressure is too low – water will vaporize (evaporate)
- if Pressure is too high – water will stay liquid!
Mars’ atmospheric pressure is ~1% of Earth’s
- LOW pressure
- LOW temperature  FROZEN WATER (ice!)
Where is the water today?
•Much of the water may have escaped to space, and
some is locked up in N Polar Cap.
•Much could be stored in subsurface ice
(permafrost).
Water features present - evidence for large scale
floods.
More Earth-like in the past (1.8 - 3.5 billion years
ago?)
Current water erosion possible
Due to low pressure any ice would sublimate directly to a gas.
Surface
water ice and frost on the ground
Soil: clay and iron oxides
Rocks - many volcanic in origin, not as
basaltic as expected . (mixing of crust +
mantle material)
Low winds most of the time
Occasional global dust storms
Other rocks appear to be sedimentary water produced
•Even though atmosphere is thin, high winds can
create dust storms
Mars’ Two Moons
Deimos “Panic”
•Deimos: 16 km long & 10 km wide
•Deimos orbits in 30 hours 18 minutes
Captured asteroids? Most likely
Phobos “Fear”
•Phobos: 28 km long & 20 km wide
•Phobos orbits in 7 hours 59 minutes
Captured asteroids? Most likely
Mariners to Mars
Mariner 4 - July 14, 1964. “Everything Changed” Returning a whopping 22 (!!) pictures (many so poor
as to be useless) during flyby.
Lots of craters - looked much like our lifeless
Moon. Elation & depression amongst planetary
scientists
Mariners 6 & 7 - 1969
More of the same, but higher quality images
The impression created by Mariner 4 was not changed,
only enforced. Mars seemed as dead as the Moon. There
seemed little chance of finding anything resembling living
organisms here. But not so fast ……
• Mariner 9 was the first spacecraft to orbit another planet
- arrived at Mars 14 November 1971
- orbited Mars for more than a year
Major dust storm on Mars when Mariner 9 arrived!
-surface was not visible for an entire month
-however, the cones of major volcanoes (new discovery) were
visible. Even though dust covered, there were several ‘crater-like’
features visible rising above the dust.. volcanoes.
Viking 1 & 2 - 1976
Each consisted of an Orbiter and a Lander
•landing site chosen from Orbiter images – two different regions in
Northern Lowlands
• revealed that the surface of Mars was littered with jagged rocks
and fine dust everywhere. Rocks were probably result of craterforming impact (“ejecta”), they resembled lava rocks on Earth.
Face on Mars?
Sharper mage sent back in 1998 by Mars Global Surveyor
Spirit and Opportunity
– Arriving in January 2004
– Two landers/rovers
– Mission : characterize a wide range of rocks and
soils that hold clues to past water activity on Mars
The blueberries
These little nodules are
were found near
Meridiani Planum,
called “blueberries”.
the landing site of
They’re made of minerals
NASA’s Mars
that usually only
Exploration Rover
Opportunity.
form under water.