ORIONORIONConstellation

OrionOrion

Orion the HunterOrion the Hunter Orion was thought to be a great hunter, always

traveling with his faithful hunting dogs (Canis Major, Canis Minor).

Killed by the Scorpion (Scorpio) and thus lives on the opposite side of the celestial sphere.

May also be chasing the Pleiades (the Seven Sisters) closer to him in the sky.

Orion’s Major StarsOrion’s Major StarsAlpha – Betelgeuse (mag. 0.45)

◦Red Giant (dying star) which appears slightly redish-yellow

Beta – Rigel (mag. 0.18)◦Blue giant (early to midlife) which

appears slightly blueish-white

OrionOrion

Orion’s ObjectsOrion’s ObjectsM42 – The Orion Nebula

(Telescope)

Orion’s ObjectsOrion’s ObjectsHoreshead & Flame Nebula

(Hubble)

Orion’s ObjectsOrion’s ObjectsBarnard’s Loop

Extra Credit (+3)Extra Credit (+3)

1. Clearly photograph entire constellation

2. Identify Rigel, Betelgeuse, M42

COMPARATIVE COMPARATIVE PLANETOLOGY: PLANETOLOGY: VENUS AND MARSVENUS AND MARS

Chapter 22

Venus & MarsVenus & MarsTwo most similar planets to Earth

◦Location◦Size and Shape◦Atmosphere◦Interior Structure

Life is impossible on both

VenusVenus

MarsMars

The Rotation of VenusThe Rotation of Venus

Almost all planets rotate in the same sense as orbital motion.

Exceptions◦ Venus, Uranus

The Rotation of VenusThe Rotation of VenusVenus 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

UV image

The Atmosphere of VenusThe Atmosphere of Venus

Extremely inhospitable:◦ 96 % - CO2

◦ 3.5 % - N2

◦ 0.5% - H2O, HCl, HF

UV image

The Atmosphere of VenusThe Atmosphere of Venus 4 thick cloud

layers◦ surface invisible from

Earth

Very stable circulation patterns with high-speed winds (up to 240 km/h)

Very efficient greenhouse

Extremely high surface temperature up to 745 K (880 F)

The Surface of VenusThe Surface of VenusEarly radar images already

revealed mountains, plains, craters.◦More details from orbiting and

landing spacecraft:

Lava FlowsLava Flows

Young, uneven lava flows (shown: Lava flow near Flagstaff, AZ) show up as bright regions on radar maps.

Radar Map of Venus’s Radar Map of Venus’s SurfaceSurface

Scattered impact craters

Surface features shown in artificial colors

Volcanic regions

Smooth lava flows

Surface Features on VenusSurface Features on Venus

Smooth lowlands Highland regions:

Maxwell Montes are

~ 50 % higher than Mt. Everest!

Craters on VenusCraters on Venus

Craters on VenusCraters 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 EarthVolcanism on Earth

Volcanism on EarthVolcanism on EarthVolcanism on

Earth is commonly found along subduction zones (e.g., Rocky Mountains).

This type of volcanism is not found on Venus or Mars.

Shield VolcanoesShield VolcanoesFound 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 VolcanoesShield Volcanoes

Tectonic plates moving over hot spots producing shield volcanoes Chains of

volcanoes

Shield VolcanoesShield Volcanoes

The Hawaiian Islands

Sapas MonsSapas Mons

250 miles

Lakshmi Planum and Lakshmi Planum and Maxwell MountainsMaxwell Mountains Radar image

Wrinkled mountain formations indicate compression, though there is no evidence of

plate tectonics on Venus.

A History of VenusA History of VenusComplicated history; still poorly

understood.

Very similar to Earth in mass, size, composition, density,◦ no magnetic field Core solid?

A History of VenusA History of Venus Solar wind

interacts directly with the atmosphere, forming a bow shock and a long ion tail.

CO2 produced during outgassing remained in atmosphere

Any water present on the surface rapidly evaporated

A History of VenusA History of Venus

Pancake Domes: Associated with

volcanic activity forming coronae

Heat transport from core mainly through magma flows close to the surface ( coronae, pancake domes, etc.)

Volcanic Features on Volcanic Features on VenusVenus

Baltis Vallis: 6800 km long lava flow channel (longest

in the solar system!)

Coronae: Circular bulges formed by volcanic

activity

MarsMarsRoughly half the

size of Earth

Axis tilted against orbital plane by 25-degrees

Very thin atmosphere, mostly CO2

Rotation period 24 h, 40 min.

MarsMarsSeasons 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)

Canals and Life on MarsCanals and Life on MarsEarly observers

believed to see canals on Mars

This, together with growth/shrinking of polar cap, sparked imagination and sci-fi tales of life on Mars.

Life on MarsLife on MarsNo evidence of life on Mars

Face on MarsFace on Mars

Happy Happy Face Face CraterCrater

Galle Crater,

the “happy face crater”

The Atmosphere of MarsThe Atmosphere of MarsEven thin Martian

atmosphere evident through haze and clouds covering the planet

Occasionally, strong dust storms can enshroud the entire planet.

The Atmosphere of MarsThe Atmosphere of MarsVery thin: Only 1% of pressure on

Earth’s surface

95 % - CO2

Reddish color of the surface◦Most of the Oxygen bound in oxides

in rocks

History of Mars’s History of Mars’s AtmosphereAtmosphereAtmosphere 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).

The Geology of MarsThe Geology of Mars

The Geology of MarsThe Geology of Mars

Reddish deserts of broken rock, probably smashed by meteorite

impacts.

The Geology of MarsThe Geology of Mars

The surface features on Mars have most recently been explored close-up by the Mars rovers Spirit and

Opportunity.

The Geology of Mars (2)The Geology of Mars (2)Northern 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.

Olympus MonsOlympus Mons

Highest and largest volcano in the solar system.

Tharsis RiseTharsis RiseNearly 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 MarsHidden Water on MarsNo liquid water on

the surface:◦ Would evaporate

due to low pressure.

Evidence for liquid water in the past:◦ Outflow channels

from sudden, massive floods

Hidden Water on MarsHidden Water on Mars

Collapsed structures after withdrawal of sub-surface water

Valleys resembling meandering river beds

Hidden Water on MarsHidden Water on Mars

Central channel in a valley

Gullies from debris flows

Hidden Water on MarsHidden Water on MarsHematite

concretions in Martian Rocks, photographed by the Mars Rover Opportunity

Sedimentary rock layers, formed by rapidly flowing water.

Ice in the Polar CapIce in the Polar CapPolar cap

contains mostly CO2 ice, but also water.

Multiple ice regions separated by valleys free of ice.

Evidence for Water on Evidence for Water on MarsMars

Large impacts may have ejected rocks into space.

Meteorite ALH84001◦ Identified as

ancient rock from Mars.

◦ Some minerals in this meteorite were deposited in water

The Moons of MarsThe Moons of Mars

Phobos Deimos

The Moons of MarsThe Moons of MarsTwo small moons: Phobos and Deimos.

Too small to pull themselves into spherical shape.

Dark grey, low density.

Very close to Mars◦ orbits around Mars faster than Mars’ rotation.

Probably captured from outer asteroid belt.