EPS 365 Final

Venus Atmosphere

-Atmosphere of CO2

-Clouds of sulfuric acid

-Dry-negligible H2O

-Pressure ~90 atm

-Low velocity surface winds

-High altitude winds 360 mi/hr from east to west.

-High surface temps from “greenhouse effect”

-Slow surface erosion rate

-Low to no chance of life

Greenhouse Effect

Even though cloud tops of Venus are highly reflective, sunlight ultimately reaches & warms the surface. The surface then readiates heat back in the infrared.

Sunlight that penetrates to the lower atmosphere & the surface re-radiates back in the infrared wavelength. Result is a much higher surface temp than would be present without the blanketing effect of the atmosphere.

Clouds of Venus are high at about 50km with a clear CO2 atmosphere below.

Venus has a much warmer atmosphere near the planet’s surface than the Earth’s, but it’s actually colder at high altitudes

Venus Surface

Two main sources of data about surface of Venus:

Observations from Venusian orbit (Pioneer Venus, Magellan)
Vega and Venera Surface Measurements

Absent:
Venusian meteorites

Need: New generation of surface measurements by landed spacecraft. Venus sample return

Venera/Vega geochemical analyses of the surface - basaltic

Minerology hasn’t been determined

Opaque atmosphere severely limits remote sensing

Radar backscatter and thermal emission are main sources of data on minerology - no ground truth calibration

Crater density and pristine appearance suggest young surface

No radiometric ages exist - large uncertainty in Venusian geologic time scale - many untested assumptions in models of Venusian surface evolution.

Venus Surface Features

Planitia: Low plains

Terra: Extensive land masses

Planum: Plateus

Corona: Ovoid-shaped volcanic features

Volcanic Craters: ~1000 randomly distributed, few are less than ~2km

No plate tectonics

No true continents or ocean basins

Visible vs Radar

Orange hues in radar images are not “real” — based on color images recorded by Soviet Venera 13 and 14 missions

Radar Images from Magellan

Bright regions: high radar reflectivity - “rough“

Dark regions: Low reflectivity - “smooth“

Addams Impact Crater

Radar bright outflow associated with the 90km crater stretches over 600 km to the east.

Sif Mons Shield Volcano

Sif Mons is 2km high and 300km in diameter. Large shield volcanoes on Venus have similar shapes to Hawaiian-type basaltic shield volcanoes.

Lava Channel

About 2km wide and shows branches and islands along the length. Low viscosity, high temperature lava such as komatite

Small Shield Volcanoes

Magellan radar image of Boann Corona, Venus. Note the large number of shield volcanoes within the flooded corona. The corona is about 225 km across the shortest side.

Corona Chain

Volcanic Pancake domes

These domes appear to have been formed by the extrusion of high viscosity lava, which accounts for their flattened tops and steep edges. The largest dome is 62 km in diameter.

“Tick”

These volcanic features are characterized by a caldera within a smooth depression surrounded by a raised rim with radial spurs. The rim in this case has a diameter of about 30 km.

Nova

Magellan image of a nova, a radial network of grabens, in Themis Regio, Venus. There have been about 50 novae identified on Venus, which consist of closely spaced graben radiating from a central area. This nova is about 250 km in diameter, concentrated to the south.

Maxwell Montes

The Maxwell Montes are the highest mountains on Venus, rising up to 11 km above the mean planetary surface. The 105 km diameter Cleopatra crater can be seen in the center of the image.

Venus Tectonics

Tectonic zones of deformed crust are common in the “Terra” and “Regios”.

Tesserae are terrains that have been intensely modified by compression and folding. They consist of interlacing ridges and valleys.

Venus Interior

Internal composition can only be guessed at – for the time being we assume chondritic or similar to Earth.

No on-surface geophysical data exists.

Internal structure is inferred from geomorphology.

No plate tectonics.

Mantle flow is probably unlike Earth’s.

No magnetic field – 100% liquid iron core?

Core has less mass than Earth’s (only 23% of total planet).

Core with less iron & more light elements or just a smaller size ?

 Moment of inertia unknown.

Vital Moon Statitistics

•Averages 236,000 miles from the earth.

•Closest distance (perigee) is about 220,000 miles,

•Greatest distance (apogee) is about 255,000 miles.

•Diameter about 2160 miles, roughly 1/4 that of the earth

•Mass 1/81 that of earth. Surface gravity 1/6 that of earth

•Takes 29-1/2 days to circle earth.

Moon Evolution

Moon almost uniquely preserves evidence of early planetary evolution:

Large enough to differentiate & produce a variety of rocks over time

Small enough to have cooled and preserved this early history

Early Earth (Venus, Mars?) history lost; Asteroids cooled early

Three Major Early Evolution Questions: 

Nature of early magma ocean and initial lunar differentiation.

Evolution of internal reservoirs that produced highland and basaltic rocks (age and geochemistry).

Nature (time & flux) of early bombardment and effects on rocks.

Four Hypothesies for Formation of Moon

Fission: Moon derived from spinning Earth bulge.

Co-accretion: Earth-Moon formed in place as mini-solar system. (not likely)

Capture: Passing Moon captured by Earth’s gravity. (also hypothesis for Mar’s moons)

Giant Impact: Collision of proto-Earth with Mars-sized object.

The name of the hypothesized protoplanet

is derived from the mythical Greek titan Theia, who gave birth to the Moon goddess Selene

Why is Giant Impact a viable hypothesis?

The Earth has a large iron core, but the moon does not. This is because Earth's iron had already drained into the core by the time the giant impact happened. Therefore, the debris blown out of both Earth and the impactor came from their iron-depleted, rocky mantles. The iron core of the impactor melted on impact and merged with the iron core of Earth, according to computer models.

 

The moon has exactly the same oxygen isotope composition as the Earth, whereas Mars rocks and meteorites from other parts of the solar system have different oxygen isotope compositions. This shows that the moon formed form material formed in Earth's neighborhood.

If a theory about lunar origin calls for an evolutionary process, it has a hard time explaining why other planets do not have similar moons. (Only Pluto has a moon that is an appreciable fraction of its own size.)

Lunar Magma Ocean

Cooling causes magma ocean to crystalize. Fedlspar crystals, which are calcium rich and bouyant in magma. Olivine crystals sink in the magma ocean. Pyroxene crystals also sink in the magma ocean.

Lunar Surface

There are two primary types of terrain on the Moon: the heavily cratered and very old highlands and the relatively smooth and younger maria. The maria (which comprise about 17% of the Moon's surface) are huge impact craters that were later flooded by molten lava. Most of the surface is covered with regolith, a mixture of fine dust and rocky debris produced by meteor impacts. For some unknown reason, the maria are concentrated on the near side.

Lunar Minerology

Only four minerals - plagioclase feldspar, pyroxene, olivine, and ilmenite - account for about 98% of the crystalline material of the lunar crust.

Some of the most common minerals at the surface of the Earth are rare or have never been found in lunar samples. These include quartz, calcite, magnetite, hematite, micas, amphiboles, and certain sulfide minerals.

Lunar Rocks

Most of the lunar crust, often called the highlands, consists of rocks that are rich in a particular variety of plagioclase feldspar known as anorthite. As a consequence, rocks of the lunar crust are said to be anorthositic because they are plagioclase-rich rock with names like anorthosite, noritic anorthosite, or anorthositic troctolite.

Lunar Anorthosite

When the moon first formed it probably had a surface composed mostly of feldspar-rich igneous rocks. This rock type still exists today and makes up the lunar highlands, which is the lighter-colored part of the moon visible from Earth. This 4.4-billion-year-old rock sample is an anorthosite collected from the lunar highlands of the moon by Apollo 16 astronauts.

Lunar Breccias

The crust of the Moon began to form about 4.5 billion years ago. While it was forming and for some time afterwards, it experienced intense bombardment from meteors, many of which were huge. The rocks of the crust have been repeatedly broken apart by some impacts and glued back together by others. As a consequence, most rocks from the lunar highlands are breccias, a word meaning a rock composed of fragments of older rocks.

Mare Basalts

Mare basalts cover about 17% of the surface of the Moon, but it is estimated that they account for only about 1% of the volume of the crust.

Starting about the time of the period of intense bombardment, the lunar mantle partially melted. The resulting magmas rose through the crust to the surface, ponding in low spots. These low spots were mainly the huge craters and basins. When filled with lava-filled they are usually called mare (singular) and maria (plural).

Lunar Samples

·Lunar Sample Laboratory at NASA JSC in Houston is chief repository for samples from Apollo 11,12,14,15,16,&17

·382 kg

·2196 original samples

·Now subdivided into 86,000 samples

·Samples distributed to scientists and educators worldwide

· 80% by weight remains pristine

White Sands Test Facility

15% of Apollo Moon Rocks

Top Ten Discoveries from Lunar Samples

The Moon is not a primordial object -- it is a differentiated terrestrial planet made of igneous rock. 

 

2.  The Moon has an ancient crust that preserves its early history – impact crater record has been calibrated using absolute ages of rock samples.

  

3.  The youngest Moon rocks are virtually as old as the oldest Earth rocks. The earliest processes and events that probably affected both planetary bodies can now only be found on the Moon.  

 

4.  The Moon and Earth may be genetically related and formed from different proportions of a common reservoir of astromaterials -- the Moon is highly depleted in iron and in volatile elements that are needed to form atmospheric gases and water.

 

5.  The Moon is lifeless; it contains no living organisms, fossils, or native organic compounds.

6.  All Moon rocks originated through high-temperature processes with little or no involvement with water. They are roughly divisible into three types: basalts, anorthosites, and breccias. 

 

7.  Early in its history, the Moon was melted to great depths to form a “magma ocean”. The lunar highlands contain the remnants of early, low density rocks that floated to the surface of the magma ocean.  

 

8.  The lunar magma ocean was followed by a series of huge asteroid impacts that created basins which were later filled by lava flows.  

 

9. The surface of the Moon is covered by a rubble pile of rock fragments and dust, called the lunar regolith, produced by innumerable meteorite impacts through geologic time.

 

10. The regolith contains a unique radiation history of the Sun to a degree of completeness that we are unlikely to find elsewhere.

Moon’s Early History

Formation likely from an impact of Mars-size proto-planet with the Earth

Similar material in Moon to crust material of the Earth

Small core implies different total composition the Earth (lacking Earth's core material abundance ratio)

 

Surface solidifies quickly

Captures early composition and character of Moon & solar system

 

Bombardment from planetesmals at beginning of formation is easily seen in impact craters

•

Internal heating increases because of radiation and crust formation

Forces the interior liquid rock to flow into large craters

Forms the Mare (volcanic seas)

Lunar Surface Chronology

4.6 By

•Layer of plagioclase-rich crust floats on more dense liquid magma during early lunar formation

•Heavier olivine, pyroxene, and ilmenite (FeTiO₃) sank to form source areas for mare basalts

4.4 By

•KREEP rocks form as upper liquid mantle crystallizes

•Partial melting events are probably responsible for the Mg-rich highland rock. This is indicated by some similarities in composition of Mg-rich, plagioclase and KREEP compositions. Partial melting could have also been at deeper depths.

•Intense meteoric bombardment reduces much of highlands to rubble - as seen in Apollo samples

•FeO-rich material remaining after magma solidifies moves into lower crust, making KREEP-like basalt regions in later basalt flows

3.9 By

•Remelting or partial melting produces maria volcanism (effusive, not eruptive). These flows fill large basins produced by earlier, intense bombardment. Remelting/partial melting due to radioactive processes in the interior.

3 By

•End of most igneous activity (including mare formation)

•Continuing but reduced meteoric bombardment

•Mass range of bombarding material from 10-15 to 1020 g

3 By to present
Surface processes include meteoric activity (fracturing of surface rock and formation of regolith) and radiation (solar wind and cosmic rays), some magmatism.

South Pole – Aitken Basin

(Giant South Polar Basin)

Very Large (d~2500 km) and Very Old (>4 Ga)

Deep-seated Mantle as clasts within breccias and impact melt.

Old basalts derived from different mantle composition.

Old highland rock not modified by younger impact basin.

Away from influence of areas of moon rich in U, Th, K, REE.

Farside of the Moon: albedo (left) and topography (right) derived from Clementine data.The outer ring of South Pole-Aitken (SPA) Basin is shown with a dotted line (after Wilhelms, 1987). The enormous SPA Basin is not located at the South Pole, but derives its name from the fact that it extends from the South Pole to the crater Aitken near the equator

Mare Nectaris

The Nectaris Basin, in the southeastern quadrant of the lunar nearside, is about 860 kilometers across. It is more degraded than the other basins, indicating that it is older than Imbrium and Orientale. Samples returned by the Apollo 16 mission suggest an age of 3.92 billion years for this basin.

Mare Orientale

The Orientale Basin occurs near the western limb of the lunar nearside and is only partially visible from telescopes on Earth. This classic multi-ring basin is 930 kilometers in diameter. Material from this basin was not sampled by the Apollo program, so the basin's precise age is not known. However, it is the freshest impact basin on the Moon and is believed to be slightly younger than the Imbrium Basin, which formed about 3.85 billion years ago.

Copernicus

The crater Copernicus, 93 kilometers in diameter, is one of the most prominent features on the Moon's nearside. It is a relatively fresh crater, believed to have formed less than 1 billion years ago. Its system of bright rays is quite prominent at full Moon.

Tycho

The crater Tycho, 85 kilometers in diameter, is the youngest large impact crater on the Moon's nearside. Ejecta from this crater was spread across much of the nearside of the Moon and is visible in the form of bright rays at full Moon. One such ray crosses the Apollo 17 landing site, 2000 kilometers from Tycho. Laboratory analysis of samples from this landslide suggest that Tycho's age is about 100 million years.

Lunar Interior

  The Moon's crust averages 68 km thick and varies from essentially 0 under Mare Crisium to 107 km north of the crater Korolev on the lunar far side.

Below the crust is a mantle and probably a small core (roughly 340 km radius and 2% of the Moon's mass). Unlike the Earth, however, the Moon's interior is no longer active.

The Moon's center of mass is offset from its geometric center by about 2 km in the direction toward the Earth. Also, the crust is thinner on the near side.

Significant Lunar Features

Rays around more recent craters

Highlands and Maria

Crust of Moon is largely anorthosite and gabbro (or norite)

Maria are mostly basalt

Maria almost exclusively on earth-facing side

Tidally locked to earth

Same side always faces earth

Moon slightly elongated

Small moonquakes occur when moon nearest earth

Moon causes tides on Earth

Most marked in oceans but a small tide occurs in the solid earth, too.

Tides are slowing Earth's rotation - Earth rotated about 400 times/year 500,000,000 years ago.

As Earth slows, it transfers its rotation (angular momentum) to the Moon, causing it to get farther from Earth.

Moonquakes occur about 800 mi. deep in Moon, just outside core

Small molten core, probably magnesium-iron silicate or iron sulfide but may be nickel-iron like Earth's.

Core boundary not sharp.

Diameter of core about 500 miles.

No magnetic field now but seems to have had one early in its history.

 

Moon differs chemically from Earth

Very poor in water

Depleted in volatile elements

Richer in some metals, such as titanium

No surface water, life or atmosphere

Meteorites Historical

Meteorites were originally thought by many cultures to have supernatural powers or that they were gifts from the gods or heaven.

Meteorite Classification

Chondrites: relatively unaltered, formed as aggregates of primitive solar system material, unmelted asteroids, chondrules usually present, 86% of falls.

Achondrites: processed by melting, formed from magma, crust or mantle of asteroid, no chondrules, 8% of falls.

Iron meteorites: processed by melting, asteroidal core, 7% of falls.

Stony-iron meteorites: processed by melting, core-mantle boundary of asteroid, 1% of falls.

Chondrites

Chondrites are more or less undifferentiated, primordial matter that has remained nearly unchanged for the last 4.5 billion years. These stony meteorites formed nearly simultaneously with the Sun.

It is thought that small droplets of olivine and pyroxene condensed and crystallized from the hot primordial solar nebula in form of small spheres that we nowadays call chondrules.

Chondrules accreted with other material that condensed from the solar nebula forming a matrix that constitutes chondrites and chondritic parent bodies (asteroids).

In their chemical composition, chondrites resemble the Sun, depleted of the most volatile elements like hydrogen and helium.

 However, the distribution of elements has not been uniform in the original solar nebula - elemental composition varied as did the conditions under which the chondritic parent bodies formed.

 Different asteroids formed in various regions of the primordial solar nebula under different conditions.

Those parent bodies were further subjected to different thermal and chemical processes as well as to impacts with other asteroids resulting in a variety of chondrites, which have been categorized into several clans, groups, and subgroups.

Carbonaceous Chondrites

Carbonaceous chondrites or C chondrites represent some of the most pristine matter known, and their chemical compositions match the chemistry of the Sun more closely than any other class of chondrites.

Carbonaceous chondrites are primitive and undifferentiated meteorites that formed in oxygen-rich regions of the early solar system so that most of the metal is not found in its free form but as silicates, oxides, or sulfides.

Most of them contain water or minerals that have been altered in the presence of water, and some of them contain larger amounts of carbon as well as organic compounds. The most primitive carbonaceous chondrites have never been heated above 50°C.

Ordinary Chondrites

Chondrites of this clan are designated as "ordinary" just because they are the most common class of stony meteorites, representing more than 85% of all witnessed chondrite falls.

The mineralogies of ordinary chondrites are primarily composed of olivine, orthopyroxene, and a certain percentage of more or less oxidized nickel-iron. Based on the differing content of metal and differing mineralogical compositions the ordinary chondrites have been subdivided into three distinct groups that are designated as H, L, and LL chondrites.

Achondrites

The term "achondrite" was orginally used to describe a stony meteorites without chondrules, and this lack of chondrules was the primary characteristic used to distinguish the two major stony groups, achondrites and chondrites.

However some chondrites (very primitive or highly equilibrated) lack chondrules.

Achondrites can be thought of as stony meteorites that have been melted.

Achondrites are samples of differentiated planetary bodies, and therefore represent a very heterogeneous class of meteorites. Most of them are primitive; that is, nearly chondritic in composition with an age similar to the primordial chondrites.

These so-called primitive achondrites are the residues from partial melting that took place on small parent bodies having chondritic compositions.

More evolved achondrites, have experienced a more extensive igneous processing including magmatic processes similar to geological activities encountered on Earth.

Some of these achondrites are basalts, plagioclase and pyroxene-rich volcanic rocks that represent the upper crust of their parent bodies. Others are olivine-rich plutonic rocks that formed in deeper regions of the crust and experienced prolonged thermal processing

Several groups of evolved achondrites can be assigned to specific parent bodies. The meteorites of the HED group are believed to be samples of 4 Vesta, one of the largest asteroids in our solar system.

Other basaltic achondrites, such as aubrites and angrites, are also considered to have an asteroidal origin, although their parent body is unknown.

A few rare achondrites can be assigned to larger parent bodies - the true planets and their moons.

 

The rare meteorites of the LUN group are genuine pieces of our own Moon - a fact that has been proven by comparisons to samples of Moon rocks that were returned to Earth by the Apollo missions during the late 60's and early 70's.

The equally rare achondrites of the SNC group are believed to have their origin on the planet Mars.

Iron Meteorites

Iron meteorites are characterized by the presence of two nickel-iron alloy metals: kamacite and taenite.

These, combined with minor amounts of non-metallic phases and sulfide minerals, form the three basic subdivisions of irons. Depending upon the percentage of nickel to iron, these subdivisions are classified as:

hexahedrites (4-6% Ni)

octahedrites (6-12% Ni)

ataxites (12+% Ni)

 

Octahedrites, which are the most common type of iron meteorite, exhibit a unique structural feature called the Widmanstätten pattern when etched with a weak acid. This unique crystal pattern is the result of the combination of the two nickel-iron minerals kamacite and taenite being present in approximately equal amounts.

Stony-Iron Meteorites

Stony-irons consist of almost equal amounts of nickel-iron alloy and silicate minerals. Although all stony-irons may not be genetically related or have similar composition, they are combined into one group and divided into two subgroups for convenient classification.

The Pallasite group is characterized by olivine crystals surrounded by a nickel-iron structure which forms a continuous enclosing network around the silicate portion.

Mesosiderites, on the other hand, consist mainly of plagioclase and pyroxene silicates in the form of heterogeneous aggregates intermixed with the metal alloy. No distinct separation between the metal and silicate phases is readily apparent as it is with the Pallasites.

Dar al Gani 749

Carbonaceous Chondrite (95kg)

Largest Meteorite ever found in Libya

Tagish Lake Carbonaceous Chondrite

On January 18, 2000 A brilliant fireball followed by loud detonations was widely observed over the Yukon Territory and northern British Columbia. The fireball was also detected by satellites in Earth orbit. Dust clouds from terminal fragmentation events were widely observed.

Pieces of a 56-metric-ton meteorite rained down over a wide area of Canada. Many pieces landed on the frozen Tagish Lake, allowing scientists to recover numerous samples, and giving the meteorite its name.

Mr. Jim Brook recovered several dozen meteorites totaling ~1 kg on the ice of Taku Arm, Tagish Lake, on January 25 and 26 .

Between April 20 and May 8, ~500 additional specimens were located on the ice of Taku Arm and a small, unnamed lake 1.5 km to the east.  Only ~200 were retrieved however, as many had melted down into the ice making their collection time consuming; recovery was prioritized based on meteorite mass and degree of disaggregation.  The total mass collected was between 5 and 10 kg. The strewn field is at least 16 km by 3 km, oriented ~S30°E.

Asteroids

Asteroids are rocky and metallic objects that orbit the Sun but are too small to be considered planets. They are known as minor planets.

Asteroids range in size from Ceres, which has a diameter of about 1000 km, down to the size of pebbles. Sixteen asteroids have a diameter of 240 km or greater.

They have been found inside Earth's orbit to beyond Saturn's orbit. Most, however, are contained within a main belt that exists between the orbits of Mars and Jupiter. Some have orbits that cross Earth's path and some have even hit the Earth in times past.

Asteroids are material left over from the formation of the solar system.

One early hypothesis suggested that they were the remains of a planet that was destroyed in a massive collision long ago. Given the variety of asteroids, a single parent body is highly unlikely.

More likely, asteroids are material that never coalesced into a planet. In fact, if the estimated total mass of all asteroids was gathered into a single object, the object would be less than 1,500 kilometers (932 miles) across -- less than half the diameter of our Moon.

Asteroid Classification

 Asteroids are classified into a number of types according to their spectra (and hence their chemical composition) and albedo:

                      

C-type (and rarer B-, F-, and G-types)

 more than 75% of known asteroids

 extremely dark (albedo 0.03)

 similar to carbonaceous chondrite meteorites?

S-type

 15-20% of known asteroids

 relatively bright (albedo .10-.22)

 metallic nickel-iron mixed with iron- and magnesium-silicates

 similar to stony-iron meteorites and ordinary chondrites?

 

M-type

 most of the rest

 bright (albedo .10-.18)

 nickel-iron

 similar to iron meteorites?

D- and P-type

Outer edge of main belt, Trojans, and Jupiter’s small moons

Very dark

Ultra-primitive organic compounds

Notable Asteroids

1 Ceres - The largest and first discovered asteroid, by G. Piazzi on January 1, 1801. Ceres comprises over one-third the 2.3 x 10²¹ kg estimated total mass of all the asteroids.

 
2 Pallas - The 2nd largest asteroid and second asteroid discovered, by H. Olbers in 1802.

 
3 Juno - The 3rd asteroid discovered, by K. Harding in 1804.

 
4 Vesta - The 3rd largest asteroid, Vesta appears to have a basaltic crust overlying an olivine mantle, indicating differentiation has occurred. Imaged by the Hubble Space Telescope in 1995.

What is a comet?

Comets consist largely of compounds of carbon, hydrogen, oxygen, and nitrogen, i.e. so-called “CHON” compounds. These compounds include ices of water, ammonia, methane, carbon monoxide, and smaller amounts of other, more complex compounds.

Comets are also made of dust containing silicate minerals found in the crusts of the terrestrial planets, and a mix of silicate and “CHON” similar to that found in carbonaceous chondrites.

When far from the sun the comet is a cold, dark "ice ball" only a few km across. As it nears the sun it begins to "melt" and forms nucleus.

Eventually a coma extending as much as 100 000 km from the nucleus forms.

 

The comet becomes surrounded by a sheath of hydrogen gas that is easily excited to glow. The pale white light that we see is the result of fluorescence . Cometary tails can reach tens of millions of km in length!

The Orbits of Comets

Comets are classified as either short-period or long- period objects:

 

Short Period: (such as Halley's) with periods from years to decades, low orbital inclination and prograde motion.

 

Long Period: centuries to thousands of years (Hyakutake: Period 18 400 a), any inclination and just as likely retrograde as prograde

A comet in a long, elliptical orbit becomes visible when the sun's heat vaporizes its ices and pushes the gas and dust away in a tail.

Orbit of Tempel-Tuttle

The orbit of the Leonids' parent body, comet Tempel-Tuttle, projected onto the ecliptic plane (i.e., the plane in which the Earth orbits the Sun). The indicated positions of the planets and the comet are those of February 28, 1998, the date of the comet's closest approach to the Sun.

Kuiper Belt

Disk-shaped region beyond the orbit of Neptune that contains countless icy objects; the source of short-period comets such as Halley.

Oort Cloud

A roughly spherical volume, extending more than 100,000 AU from the Sun, in which up to a trillion small icy bodies are thought to reside; the source region for “new” and long-period comets.

Galilean Moon

In order from Jupiter they are:

• Io: briglty-colored volcanic body

• Europa: an ice-covered world

• Ganymede: a rock and ice body with some old cratered areas and some young terrains

• Calisto: old, cratered body resembling Earth’s moon.

All except Callisto have metallic (iron/nickel) cores, shown in grey, surrounded by rock in brown. The rock shells in Europa and Ganymede are surrounded by liquid water (blue) and ice (white). Callisto is shown as partially differentiated mixture of ice and rock.

Relative masses of the Jovian moons. Io and Callisto together are about 50%, as are Europa and Ganymede. The Galileans so dominate the system that all the other Jovian moons put together are not visible at this scale

Galileo Galilei

As a result of improvements Galileo Galilei made to the telescope, with a magnifying capability of 20X, he was able to see celestial bodies more distinctly than was ever possible before. This allowed Galilei to discover in either December 1609 or January 1610 what came to be known as the Galilean moons.

The discovery of celestial bodies orbiting something other than Earth dealt a blow to the then-accepted Ptolemaic world system, which held that Earth was at the center of the universe and all other celestial bodies revolved around it.

Io

Jupiter’s third largest; it is the innermost of the Galilean moons.

Orbit: 422,000 km from Jupiter

Io is slightly larger than Earth's Moon.

Diameter: 3630 km

Io may be somewhat similar in bulk composition to the terrestrial planets, primarily composed of molten silicate rock.

Recent data from Galileo indicates that Io has a core of iron (perhaps mixed with iron sulfide) with a radius of at least 900 km.

Io is probably the most volcanically active bodies in the solar system.

Heat source for volcanism is tidal energy created by gravitational interactions with Jupiter.

Heat Flow

Io    >2.5 Watts/m²

Earth    0.06 Watts/m²

Geothermal  1.7 Watts/m²

Moon   0.02 Watts/m²

Io Volcanism

Io’s volcanism is characterized by calderas, lava lakes, lava flows, and plumes.

Over 120 large calderas (volcanic with shalow sloping …) have been identified. The more we look, the more we find.

Europa

Its surface is among the brightest in the solar system, a consequence of sunlight reflecting off a relatively young icy crust.

Its surface is also among the smoothest, lacking the heavily cratered appearance characteristic of Callisto and Ganymede.

Lines and cracks dominate Europa’ exterior

Europa may be internally active, and its crust may have, or had in the past, liquid water which can harbor life.

About forty years ago, astronomer Gerard Kuiper and others showed that Europa’s crust was composed of water and ice

Europa’s Interior

Europa's radius is 1565 km, a bit smaller than our Moon's radius (1738 km).

Europa has a metallic (iron, nickel?) core.

The core is surrounded by a rock shell (shown in brown).

The rock layer of Europa is in turn surrounded by a shell of water in ice or liquid form.

Ganymede

Ganymede has had a complex geological history. It has mountains, valleys, craters and lava flows.

Ganymede is mottled by both light and dark regions. It is heavily cratered especially in the dark regions implying ancient origin.

The bright regions show a different kind of terrain - one which is grooved with ridges and troughs. These features form complex patterns and have a vertical relief of a few hundred meters and run for thousands of kilometers.

 

The grooved features were apparently formed more recently than the dark cratered area perhaps by tension from global tectonic processes.

Boundary between dark and light Ganymede

A sharp boundary divides the ancient dark terrain of Nicholson Regio from the younger, finely striated bright terrain of Harpagia Sulcus

(213 by 97 kilometers or 132 by 60 miles.)

The craters Gula (38 km) and Achelous (32 km) (bottom), in the grooved terrain of Ganymede, with ejecta "pedestals" and ramparts

Callisto

Callisto is the second largest moon of Jupiter, the third largest in the solar system, and is about the same size as Mercury. It orbits just beyond Jupiter's main radiation belt.

Callisto is the most heavily cratered satellite in the solar system. Its crust is very ancient and dates back 4 billion years, just shortly after the solar system was formed.

Callisto has the lowest density (1.86 gm/cm³) of the Galilean satellites. From recent observations made by the Galileo spacecraft, Callisto appears to be composed of a crust about 200 kilometers (124 miles) thick.

Beneath the crust is a possible salty ocean more than 10 kilometers (6 miles) thick. Beneath the ocean, is possibly a mixture of rock and ice, with rock increasing downward.

Callisto lacks large mountains. This is probably due to the icy nature of its surface. Impact craters and associated concentric rings are about the only features to be found on Callisto.

The largest craters have been erased by the flow of the icy crust over geologic time. Two enormous concentric ring, impact basins are found on Callisto.

The largest impact basin is Valhalla (lower left). It has a bright central region that is 600 kilometers in diameter, and its rings extend to 3000 kilometers in diameter. The second impact basin is Asgard. It measures about 1600 kilometers in diameter.

Titan

Saturn’s largest moon

It has a planet-like atmosphere which is more dense than those of Mercury, Earth, Mars and Pluto. The atmospheric pressure near the surface is about 1.6 bars, 60 percent greater than Earth's.

Titan's atmosphere is predominantly made up of nitrogen with other hydrocarbon elements which give Titan its orange hue.

These hydrocarbon rich elements are the building blocks for amino acids necessary for the formation of life.

It is believed that Titan's environment may be similar to that of the Earth's before life began putting oxygen into the atmosphere.

Titan - Earth comparison

Titan is the largest moon of Saturn and the second largest moon in the solar system after Jupiter's moon Ganymede, and it is larger by diameter than the smallest planet, Mercury (although only half as massive).

Titan's diameter is roughly 50% larger than Earth's moon and it is 80% more massive.

Titan was the first known moon of Saturn, discovered in 1655 by the Dutch astronomer Christiaan Huygens

Cassini/Huygens

is a ESA/NASA mission to the Saturnian System. The spacecraft consists of the NASA Saturn Orbiter and the detachable ESA Huygens Probe designed to explore the atmosphere of Titan, Saturn largest moon.

After landing, Huygens photographed a dark plain covered in small rocks and pebbles, which are composed of water ice. The two rocks just below the middle of the image on the left are smaller than they may appear: the left-hand one is 15 centimeters (6 inches) across, and the one in the center is 4 centimeters (about 1.5 inches) across, at a distance of about 85 centimeters (about 33 inches) from Huygens.

Titan Sea

This feature on Titan is at least 100,000 square kilometers (39,000 square miles), which is greater in extent than Lake Superior (82,000 square kilometers or 32,000 square miles), which is Earth's largest surface area lake.

This side-by-side image shows a Cassini radar image (on the left) of what is the largest body of liquid ever found on Titan's north pole, compared to Lake Superior (on the right). This close-up is part of a larger image (see PIA09182) and offers strong evidence for seas on Titan. These seas are most likely liquid methane and ethane.

Origin and Evolution of Titan’s Atmosphere

Saturn, being considerably smaller than Jupiter, probably was not as hot during its formation and evolution. Thus Titan retained a significant amount of its volatile inventory and this explains this moon’s dense atmosphere.

Early measurements from Earth-based instruments suggested that Titan’s atmosphere was dominated by methane (CH4), however Voyager 1 determined that the dominant gas is molecular nitrogen N2 (82-99%) just as on Earth.

Titan has 10 times more N2 than Earth’s atmosphere.

Methane is only a few percent of the Titan atmosphere

Titan Orbit

The orbit of Titan, highlighted in red among the other large inner moons of Saturn. The outer moons are Iapetus and Hyperion; the inner moons are Rhea, Dione, Tethys, Enceladus and Mimas.

Titan is tidally locked in synchronous orbit around Saturn

Triton

Neptune’s largest moon
Triton is the largest moon of Neptune, with a diameter of 2,700 kilometers (1,680 miles).

Triton is colder than any other measured object in the Solar System with a surface temperature of -235° C (-391° F).

It has an extremely thin atmosphere. Nitrogen ice particles might form thin clouds a few kilometers above the surface. The atmospheric pressure at Triton's surface is about 15 microbars, 0.000015 times the sea-level surface pressure on Earth.

Near-IR spectroscopy shows that Triton's high-albedo surface is covered largely with N2 ice, with <1% CH4 and a small amount of CO dissolved in the N2. Solid CO2 and H2O are also seen in the spectrum.

Triton is the only large satellite in the solar system to circle a planet in a retrograde direction -- in a direction opposite to the rotation of the planet.

It has a density of about 2.066 grams per cubic centimeter. This means Triton contains more rock in its interior than the icy satellites of Saturn and Uranus do.

The relatively high density and the retrograde orbit has led some scientists to suggest that Triton may have been captured by Neptune as it traveled through space several billion years ago.

If that is the case, tidal heating could have melted Triton in its originally eccentric orbit, and the satellite might even have been liquid for as long as one billion years after its capture by Neptune.

Dark streaks across Triton's south polar cap surface, thought to be dust deposits left by eruptions of nitrogen geysers.

Pluto

Pluto was discovered in 1930

and is usually farther from the Sun than any of the nine planets; however, due to the eccentricity of its orbit, it is closer than Neptune for 20 years out of its 249 year orbit.

Pluto crossed Neptune's orbit January 21, 1979, made its closest approach September 5, 1989, and remained within the orbit of Neptune until February 11, 1999. This will not occur again until September 2226.

Surface of the Pluto is resolved in these NASA Hubble Space Telescope pictures, taken with the European Space Agency's (ESA) Faint Object Camera (FOC) aboard Hubble.

Clyde Tombaugh

(February 4, 1906 – January 17, 1997) was an American astronomer. He is best known for discovering the dwarf planet Pluto in 1930,

Clyde Tombaugh (left) discussing search for near-Earth satellites with Dr. Lincoln LaPaz (right), March 3, 1954. Photo from The Albuquerque Journal

Tombaugh at his family's farm with his homemade telescope

Pluto-Kuiper Belt Mission

Launched Jan. 19, 2006 arrival at Pluto July 2015

There is a thin atmosphere that freezes and falls to the surface as the planet moves away from the Sun. The Pluto-Kuiper Belt Mission will allow scientists to study the planet before its atmosphere freezes.

New Horizons: Mission Objectives

Map surface composition of Pluto and Charon

Characterize geology and morphology ("the look") of Pluto and Charon

Characterize the neutral atmosphere of Pluto and its escape rate

Search for an atmosphere around Charon

Map surface temperatures on Pluto and Charon

Search for rings and additional satellites around Pluto

PLUS... conduct similar investigations of one or more Kuiper Belt Objects

Clearly visible are both Pluto and the Texas-sized Charon. The image was made from a distance of about 71 million miles (115 million kilometers)-roughly the distance from the Sun to Venus.

This high-resolution image captured by NASA’s New Horizons spacecraft combines blue, red and infrared images taken by the Ralph/Multispectral Visual Imaging Camera (MVIC). Pluto’s surface shows a remarkable range of subtle colors, enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds. The bright expanse is the western lobe of the “heart,” informally known as Tombaugh Regio. The lobe, informally called Sputnik Planum, has been found to be rich in nitrogen, carbon monoxide, and methane ices.

Charon in Enhanced Color NASA's New Horizons captured this high-resolution enhanced color view of Charon just before closest approach on July 14, 2015.

486958 Arrokoth

New Horizons color composite image of Arrokoth showing its red color, suggesting organic compounds. So far, it is the only KBO besides Pluto and its satellites to be visited by a spacecraft.

It is a contact binary 36 km (22 mi) long, composed of two planetesimals 21 km (13 mi) and 15 km (9 mi) across

With an orbital period of about 298 years and a low orbital inclination and eccentricity, Arrokoth is classified as a cold classical Kuiper belt object.

Oort Cloud

Is a postulated spherical cloud of comets situated about 50,000 AU from the Sun. This is approximately 1000 times the distance from the Sun to Pluto or nearly a light year. The outer extent of the Oort cloud places the boundary of our Solar System at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun.

In 1950 the Oort Cloud hypothesis was put forward by Dutch astronomer Jan Hendrik Oort to explain an apparent contradiction: comets are destroyed by several passes through the inner solar system, yet if the comets we observe had really existed for billions of years (since the origin of the solar system), all would have been destroyed by now.

According to the hypothesis, the Oort cloud contains trillions of comet nuclei, which are stable because the sun's radiation is very weak at their distance. The cloud provides a continual supply of new comets, replacing those that are destroyed. In order for it to supply the necessary volume of comets, the total mass of comets in the Oort cloud must be many times that of Earth.

Mars Facts

Mass (kg)	6.421e+23
Mass (Earth = 1)	1.0745e-01
Equatorial radius (km)	3,397.2
Equatorial radius (Earth = 1)	5.3264e-01
Mean density (gm/cm^3)	3.94
Mean distance from the Sun (km)	227,940,000
Mean distance from the Sun (Earth = 1)	1.5237

Rotational period (hours)	24.6229
Rotational period (days)	1.025957
Orbital period (days)	686.98
Mean orbital velocity (km/sec)	24.13
Orbital eccentricity	0.0934
Tilt of axis (degrees)	25.19
Orbital inclination (degrees)	1.850
Equatorial surface gravity (m/sec^2)	3.72
Equatorial escape velocity (km/sec)	5.02
Visual geometric albedo	0.15

Mars Atmosphere

•Carbon Dioxide: 95.3%

•Nitrogen: 2.7%

•Argon: 1.6%

•Oxygen: 0.13%

•Water: 0.03%

•Neon: 0.00025 %

Air pressure: 6-11 millibars

varies with South Pole CO2 ice

Average temperature -63° C (-81° F) Max. temperature of 20° C (68° F) Minimum of -140° C (-220° F).

17th Century

1659
The Dutch astronomer Christiaan Huygens (1629 - 1695) draws Mars using an advanced telescope of his own design. He records a large, dark spot on Mars, probably Syrtis Major. He notices that the spot returns to the same position at the same time the next day, and calculates that Mars has a 24 hour period.

1666
Giovanni Cassini (1625 - 1712) observes Mars and determines that the rotational period, or length of one Mars day is 24h, 40m.

1672
Huygens is the first to notice a white spot at the south pole, probably the southern polar cap.

1698
Huygens publishes Cosmotheoros, which discusses what is required of a planet to support life, and speculates about intelligent extraterrestrials. This is one of the first published expositions of extraterrestrial life.

18th Century

1777-1783
Sir William Herschel (1738 - 1822), the British Astronomer Royal, studied Mars with telescopes he built himself. Herschel believed that all the planets were inhabited and that there were even intelligent beings living in a cool area under the surface of the sun.

Herschel also mistakenly assumed that the dark areas on Mars were oceans, and the lighter regions land. When two faint stars passed very close to Mars with no effect to their brightness, Herschel correctly assumed that Mars had a tenuous atmosphere. He speculated that Martian inhabitants "probably enjoy a situation similar to our own."

Giovanni Schiaparelli

What emerged from long hours at the eyepiece in September 1877 was the most (optimistically) detailed map of Mars ever published. With the additional features he filled in over the next decade, it became a standard reference in planetary cartography, still in use until the dawn of the space probe era, and the scheme he devised for naming major Martian features survives to this day. He used Latin and Mediterranean place names taken from ancient history, mythology, and the Bible.

In an influential 1893 article, Schiaparelli maintained that Mars is a planet of seasonal change, with a temporary sea forming around the northern polar cap as it melted each spring. In support of his belief in a Martian atmosphere rich in water vapor he pointed to the spectroscopic observations of Hermann Vogel. The canals, he asserted, comprised "a true hydrographic system" and perhaps "the principal mechanism ... by which water (and with it organic life) may be diffused over the arid surface of the planet."

Percival Lowell

Percival Lowell made this globe of Mars summarizing his observations of the planet for the year 1901.

The straight lines represent features that were first "seen" by the Italian astronomer Giovanni Schiaparelli in 1877. He called them canali, an Italian word meaning channels.

 The canali were also observed by Lowell who concluded they were canals built by intelligent beings. The canals supposedly supplied water from the melting polar caps to a desert world.

In his book "Mars as the Abode of Life", published in 1908, Percival Lowell presented his theory that Mars' canals were built by intelligent beings.

Space Age Mars

Collier’s Space Series (1952-1954) influenced thousands of people, some who became wonder struck supporters and some who became active participants in American space history.

Das Marsprojekt is a visionary technical overview of what would be needed for a successful human mission to Mars. It was written in 1948 by von Braun and published in the early 1950’s in German and then English, and appeared later in the Collier’s Space Series.

Mars Topology

The highest point on Mars is at the top of the volcano Olympus Mons and lies at an altitude of 27 km above the datum surface. The lowest point is at the bottom of the Hellas impact basin in the southern hemisphere and lies 4 km below the datum surface. That's a difference of nearly 31 km.

In comparison, the differential between the highest and lowest points on Earth (Mt. Everest and the bottom of the Mariana Trench in the Pacific) is only 20 km.

Since Mars has no oceans and hence no 'sea level', a zero-elevation surface or mean gravity surface must be selected. Zero altitude (datum) is defined by the 610.5 Pa (6.105 mbar) atmospheric pressure surface (approximately 0.6% of Earth's) at a temperature of 273.16 K. This pressure and temperature correspond to the triple point of water.

Martian Surface

Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km (20,000 ft) high.  - Tharsis: a huge bulge on the Martian surface that is about 4000 km across and 10 km high.  - Valles Marineris: a system of canyons 4000 km long and from 2 to 7 km deep. - Hellas Planitia: an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter.

Much of the Martian surface is very old and cratered, but there are also much younger rift valleys, ridges, hills and plains.

Valles Marineris

Largest canyon in the Solar System (4000 km)

Low Elevation

Relatively dense atmosphere

The floor of Valles Marineris may be lake beds sediments, retaining climatological and paleobiological records.

Tharsis Bulge

Ascraeus Mons (top right), Pavonis Mons (middle) and Arsia Mons (lower left).

Olympus Mons

24 kilometers high, 500 kilometers diameter

Martian Core

If the Martian core is dense (composed of iron), then the minimum core radius would be about 1300 kilometers. If the core is made out of less-dense material such as a mixture of sulfur and iron, the maximum radius would probably be less than 2000 kilometers.

Martian Moons

Phobos and Deimos may be composed of carbon-rich rock like C-type asteroids. But their densities are so low that they cannot be pure rock. They are more likely composed of a mixture of rock and ice. Both are heavily cratered. New images from Mars Global Surveyor indicate that Phobos is covered with a layer of fine dust about a meter thick, similar to the regolith on the Earth's Moon.

Phobos and Deimos are believed to be captured asteroids.

Phobos

Phobos is the larger and innermost of Mars' two moons. Phobos is closer to its primary than any other moon in the solar system, less than 6000 km above the surface of Mars.

It is also one of the smallest moons in the solar system.

Diameter: 22.2 km (27 x 21.6 x 18.8)

Phobos is doomed: because its orbit is below synchronous altitude and tidal forces are lowering its orbit (current rate: about 1.8 meters per century). In about 50 million years it will either crash onto the surface of Mars or (more likely) break up into a ring. (This is the opposite effect to that operating to raise the orbit of the Moon.)

Deimos

However, there are other ideas about the origin of Mars's moons. One, favored by Duxbury, is that they are lightly accumulated ejecta from asteroid impacts on the Martian surface, with Phobos composed of ejecta orbiting Mars faster than the planet rotates; and Deimos, whose orbit is further out and orbital motion slower, composed of ejecta orbiting more slowly than the planet rotates.

Mars North Polar Cap

This image is an oblique view of the north polar cap of Mars. Unlike the south polar cap, the north polar cap consists of mostly water-ice.

Giant Impact Origin for Northern Lowland?

Borealis Basin is 5,300 miles across, would require an impactor the size of Pluto (1,200 mi diameter)

South Polar Cap

This image shows the south polar cap of Mars as it appears near its minimum size of about 400 kilometers (249 miles). It consists of frozen carbon dioxide and water ice. The amount of carbon dioxide in the south polar cap may be less than previously thought and is an area of active research.