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

Geology

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

Spacecraft investigation of surface of Venus

Continents- 2 , 2-3 km high

Craters Volcanoes(some active), plains, and valleys.

(greatest elongation ~47º).

AppearanceEasy to observe

–         75% covered with lowland lava plains       similar in origin to lunar maria

•      Possible evidence of plate tectonics

•          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

Volcanoes

Surface

On Venus’ surfaceAtmospheric pressure = 90x EarthIgneous rocks, primarily basalts

Surface temperature: 700K (850F)

Atmosphere of Venus

Composition : CO2 is 96%, N2 is 3% Sulfur dioxide (SO2) in middle atmosphere

These gases were vented from inside Venus through volcanoes.

Troposphere - Thick layer of sulfuric acid

Clouds are mostly sulfuric acid CO2 and H2O are vented from

volcanoesCO2 builds up causes a Runaway Greenhouse Effect

Composition : CO2 is

96%, N2 is 3% Sulfur dioxide (SO2) in middle atmosphere

Clouds are mostly sulfuric acid

Surface temperature: 700K (850F)

Venus’ Atmosphere

Surface composed ofIgneous rocks, primarily basalts

CO2 buildup causes runaway green house

Incoming sunlight is mostly reflected by the clouds

Some incoming sunlight gets through

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

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 1990-1993Lava Channels

Somewhat like Hadley Rille, but much bigger; 100’s of miles long, and 1.2 miles wide

Very few smaller craters due to the thickness of the planet’s atmosphere.

High Venus temperatures may allow very long flowsThe Soviet Venera series of landers were eventually successful in landing on Venus but cameras didn’t last very long. (ve ner ah)

Lava channel

The “Tick”

Lava domes Typical corona

Made by eruptions of very thick lava flowing out evenly.

Pancake

High Velocity WindsThere are winds in the upper part of the Venusian atmosphere with velocities as large as 300 km/hour.

Absence of Water VaporThe 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

–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.

Cold planets have lower Vgas so hold atmospheres better

•MarsOrbital period Semi-major axis Mass Radius Surface Gravity Escape speed Rotational PeriodInclinationSurface Magnetic FieldSurface Temperature Number of Moons

•1.88 years (687 days) 1.52 AU0.11 x Earth0.53 x Earth0.38X Earth 5.0 Km/s 1.026 days 23.98°1/800 x Earthabout 150-310 K2

Mars Day 11 Mars

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 MarsTharis region: field of large volcanoes–   Uplifted continent about the size of North America –   Volcanically active at one time

The physics of finding water on MarsLIQUID 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!)

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

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).

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

  Low winds most of the time  Occasional global dust storms

Other rocks appear to be sedimentary - water produced

Rocks - many volcanic in origin, not as basaltic as expected . (mixing of crust + mantle material)

•Even though atmosphere is thin, high winds can create dust storms

Deimos “Panic”•Deimos: 16 km long & 10 km wide

•Deimos orbits in 30 hours 18 minutes

Captured asteroids? Most likely

Mars’ Two Moons

Phobos “Fear”

Captured asteroids? Most likely

•Phobos: 28 km long & 20 km wide

•Phobos orbits in 7 hours 59 minutes

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 crater-forming 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 blueberrieswere found nearMeridiani Planum,the landing site ofNASA’s MarsExploration RoverOpportunity.

These little nodules are called “blueberries”.They’re made of minerals that usually only

form under water.