1. Formation of Our Solar System
By the Lunar and Planetary Institute For Use in Teacher Workshops
Image: Lunar and Planetary Laboratory:

2. Some data to explain: 1. Planets isolated
2. Orbits ~circular / in ~same plane
3. Planets (and moons) travel along orbits in same direction…. same direction as Sun rotates (counter- clockwise viewed from above)
Data we must explain:
1. Planets are isolated from each other.
2. Planetary orbits are nearly circular.
3. All orbits lie in almost the same plane.
4. All planets travel along their orbits in the same direction…. same direction of Sun rotation - CCW
5. Most planets rotate in this same direction - CCW
a.Venus - slowly CW
b.Uranus - on its side
c.Pluto - on its side - captured asteroid?
d.Moons go CCW around planets (few exceptions)
6. The revolution of most of the moons is in this same direction.
7.The Solar System is highly differentiated: rocky (slow rotators, few or no moons) vs. gaseous planets (fast rotators, many moons).
8.Asteroids: old, different from rocky or gaseous planets.
9.Comets: old, icy, do not move on the same plane as the planets. Exist in a swarm called the Oort cloud, very far from the Sun.
The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun's north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.
Lunar and Planetary Institute image at

3. Some more data to explain:
4. Most planets rotate in this same direction
Mercury 0° Venus 177° Earth 23° Mars 25°
Jupiter 3° Saturn 27° Uranus 98° Neptune 30°
NASA images edited by LPI

4. And some more data to explain:
5. Solar System highly differentiated:
Terrestrial Planets (rocky, dense with density ~4-5 g/cm3)
Jovian Planets (light, gassy, H, He, density 0.7-2)
Terrestrial Planets
This image shows the terrestrial planets Mercury, Venus, Earth and Mars approximately to scale. The terrestria lplanets are compact, rocky, Earth-like planets. (Copyright Calvin J. Hamilton)
Jovian Planets
This image shows the Jovian planets Jupiter, Saturn, Uranus and Neptune approximately to scale. The Jovian planets are named because of their gigantic Jupiter-like appearance. (Copyright Calvin J. Hamilton)
Planets
Terrestrial Small Dense ( g/cm3) Rocky + Metals
Jovian Large Low density ( g/cm3) Gaseous
Images: Lunar and Planetary Laboratory:

5. How Did We Get a Solar System?
Image: LPI
10,000 gas molecules / cc – vanishingly small compared to Earth degrees K.
ABOUT THIS IMAGE:
This active region of star formation in the Large Magellanic Cloud (LMC), as photographed by NASA's Hubble Space Telescope, unveils wispy clouds of hydrogen and oxygen that swirl and mix with dust on a canvas of astronomical size. The LMC is a satellite galaxy of the Milky Way.
This particular region within the LMC, referred to as N 180B, contains some of the brightest known star clusters. The hottest blue stars can be brighter than a million of our Suns. Their intense energy output generates not only harsh ultraviolet radiation but also incredibly strong stellar "winds" of high-speed, charged particles that blow into space. The ultraviolet radiation ionizes the interstellar gas and makes it glow, while the winds can disperse the interstellar gas across tens or hundreds of light-years. Both actions are evident in N 180B.
Also visible etched against the glowing hydrogen and oxygen gases are 100 light-year-long dust streamers that run the length of the nebula, intersecting the core of the cluster near the center of the image. Perpendicular to the direction of the dark streamers, bright orange rims of compact dust clouds appear near the bottom right of and top left corners of the image. These dark concentrations are on the order of a few light-years in size. Also visible among the dust clouds are so-called "elephant trunk" stalks of dust. If the pressure from the nearby stellar winds is great enough to compress this material and cause it to gravitationally contract, star formation might be triggered in these small dust clouds. These dust clouds are evidence that this is still a young star-formation region.
This image was taken with Hubble's Wide Field Planetary Camera 2 in 1998 using filters that isolate light emitted by hydrogen and oxygen gas. To create a color composite, the data from the hydrogen filter were colorized red, the oxygen filter were colorized blue, and a combination of the two filters averaged together was colorized green. The amalgamation yields pink and orange hydrogen clouds set amid a field of soft blue oxygen gas. Dense dust clouds block starlight and glowing gas from our view point.
Huge cloud of cold, thinly dispersed interstellar gas and dust – threaded with magnetic fields that resist collapse
Hubble image at

6. How Did We Get a Solar System?
Image: LPI
ABOUT THIS IMAGE:
Strangely glowing dark clouds float serenely in this remarkable and beautiful image taken with NASA's Hubble Space Telescope. These dense, opaque dust clouds - known as "globules" - are silhouetted against nearby bright stars in the busy star-forming region, IC These globules were first found in IC 2944 by astronomer A.D. Thackeray in 1950.
Although globules like these have been known since Dutch-American astronomer Bart Bok first drew attention to such objects in 1947, little is still known about their origin and nature, except that they are generally associated with areas of star formation, called "HII regions" due to the presence of hydrogen gas.
The largest of the globules in this image is actually two separate clouds that gently overlap along our line of sight. Each cloud is nearly 1.4 light-years (50 arcseconds) along its longest dimension, and collectively, they contain enough material to equal over 15 solar masses. IC 2944, the surrounding HII region, is filled with gas and dust that is illuminated and heated by a loose cluster of O-type stars. These stars are much hotter and much more massive than our Sun. IC 2944 is relatively close by, located only 5900 light-years (1800 parsecs) away in the constellation Centaurus.
Thanks to the remarkable resolution offered by the Hubble Space Telescope, astronomers can for the first time study the intricate structure of these globules. The globules appear to be heavily fractured, as if major forces were tearing them apart. When radio astronomers observed the faint hiss of molecules within the globules, they realized that the globules are actually in constant, churning motion, moving supersonically among each other. This may be caused by the powerful ultraviolet radiation from the luminous, massive stars, which also heat up the gas in the HII region, causing it to expand and stream against the globules, leading to their destruction. Despite their serene appearance, the globules may actually be likened to clumps of butter put onto a red-hot pan.
It is likely that the globules are dense clumps of gas and dust that existed before the massive O-stars were born. But once these luminous stars began to irradiate and destroy their surroundings, the clumps became visible when their less dense surroundings were eroded away, thus exposing them to the full brunt of the ultraviolet radiation and the expanding HII region. The new images catch a glimpse of the process of destruction. Had the appearance of the luminous O-stars been a bit delayed, it is likely that the clumps would actually have collapsed to form several more low-mass stars like the Sun. Instead they are now being toasted and torn apart.
The hydrogen-emission image that clearly shows the outline of the dark globules was taken in February 1999 with Hubble's Wide Field Planetary Camera 2 (WFPC2) by Bo Reipurth (University of Hawaii) and collaborators. Additional broadband images that helped to establish the true color of the stars in the field were taken by the Hubble Heritage Team in February The composite result is a four-color image of the red, green, blue and H-alpha filters.
Object Names: Thackeray's Globules, IC 2944
Concentrations of dust and gas in the cloud; material starts to collect (gravity > magnetic forces)
Hubble image at

7. How Did We Get a Solar System?
Gravity concentrates most stuff near center
Heat and pressure increase
Collapses – central proto-sun rotates faster (probably got initial rotation from the cloud)
1.Interstellar gas and dust cloud: diameter 1 ly. Gravitational collapse.
2.Solar nebula: 100 AU diameter, rotating disk. Dust particles in inner nebula are broken down because of warmer temperatures. Dust particles from 10 AU on out remain. Inner nebula starts to cool.
Image: LPI

8. How Did We Get a Solar System?
Rotating, flattening, contracting disk - solar nebula!
Equatorial Plane
Orbit Direction
Gravitational collapse eventually leads to the disk
NASA artwork at

9. How Did We Get a Solar System?
4.Gravitational accretion: planetesimals have sufficient gravity to attract material gravitationally. Larges bodies dominate and grow rapidly. The largest bodies form protoplanets. Protomoons form around them. Smaller bodies suffer numerous collisions and fragment. Some planetesimals, through gravitational interactions with the large protoplanets, are ejected into the outer solar system forming the Oort cloud of comets.
Fusion ignition of the Sun followed by 1 my period of violent solar activity. Solar winds sweep lighter materials (H, He, H2O, Ammonia, etc) outward from the Sun, leaving the inner solar system enriched in refractory materials such as silica and iron.
After ~10 million years, material in center of nebula hot enough to fuse H
“...here comes the sun…”
NASA/JPL-Caltech Image at

10. How Did We Get a Solar System?
Metallic elements (Mg, Si, Fe) condense into solids at high temps. Combined with O to make tiny grains
Lower temp (H, He, CH4, H2O, N2, ice) - outer edges
Planetary Compositions
3.Condensation and accretion: dust particles form condensation nuclei. Through collisions, particles grow rapidly in size. At about 0.5 AU only metallic grains condense. At about 1 AU rocky silicate grains condense. At about 3 AU water ice particles condense. Planetesimals, up to a few km across, are formed.
ABOUT THIS IMAGE:
The top view, taken by NASA's Hubble Space Telescope, is the first visible-light image of a dust ring around the nearby, bright young star Fomalhaut (HD ). The image offers the strongest evidence yet that an unruly planet may be tugging on the dusty belt. The left part of the ring is outside the telescope's view. The ring is tilted obliquely to our line of sight.
The center of the ring is about 1.4 billion miles (15 astronomical units) away from the star. The dot near the ring's center marks the star's location. Astronomers believe that an unseen planet moving in an elliptical orbit is reshaping the ring.
The view at bottom points out important features in the image, such as the ring's inner and outer edges. Astronomers used the Advanced Camera for Surveys' (ACS) coronagraph aboard Hubble to block out the light from the bright star so they could see the faint ring. Despite the coronagraph, some light from the star is still visible in this image, as can be seen in the wagon wheel-like spokes that form an inner ring around Fomalhaut.
The suspected planet may be orbiting far away from Fomalhaut, near the dust ring's inner edge, between 4.7 billion and 6.5 billion miles (50 to 70 astronomical units) from the star. Only Hubble has the exquisite optical resolution to resolve that the ring's inner edge is sharper than its outer edge, a telltale sign that an object is gravitationally sweeping out material like a plow clearing away snow.
The ring is in the Fomalhaut system's frigid outer region, about 12 billion miles (133 astronomical units) from the star. This distance is much farther than our outermost planet Pluto is from the Sun. The ring's relatively narrow width, about 2.3 billion miles (25 astronomical units), indicates that an unseen planet is keeping the ring from spreading out.
Fomalhaut, a 200-million-year-old star, resides 25 light-years from the Sun in the constellation Piscis Austrinus (the Southern Fish).
The ring is tinted red for image analysis. The Hubble observations were taken over a five-month period in 2004: May 17, Aug. 2, and Oct. 27.
Object Names: Fomalhaut, HD
Image Type: Astronomical/Illustration
CREDIT: NASA, ESA, P. Kalas and J. Graham (University of California, Berkeley), and M. Clampin (NASA's Goddard Space Flight Center)
Hubble photo at

11. How Did We Get a Solar System?
3.Condensation and accretion: dust particles form condensation nuclei. Through collisions, particles grow rapidly in size. At about 0.5 AU only metallic grains condense. At about 1 AU rocky silicate grains condense. At about 3 AU water ice particles condense. Planetesimals, up to a few km across, are formed.
Inner Planets:
Hot – Silicate minerals, metals, no light elements, ice
Begin to stick together with dust  clumps
Image: LPI

12. How Did We Get a Solar System?
3.Condensation and accretion: dust particles form condensation nuclei. Through collisions, particles grow rapidly in size. At about 0.5 AU only metallic grains condense. At about 1 AU rocky silicate grains condense. At about 3 AU water ice particles condense. Planetesimals, up to a few km across, are formed.
Accretion - particles collide and stick together … or break apart … gravity not involved if small pieces
Form planetesimals, up to a few km across
Image: LPI

13. How Did We Get a Solar System?
4.Gravitational accretion: planetesimals have sufficient gravity to attract material gravitationally. Larges bodies dominate and grow rapidly. The largest bodies form protoplanets. Protomoons form around them. Smaller bodies suffer numerous collisions and fragment. Some planetesimals, through gravitational interactions with the large protoplanets, are ejected into the outer solar system forming the Oort cloud of comets.
Fusion ignition of the Sun followed by 1 my period of violent solar activity. Solar winds sweep lighter materials (H, He, H2O, Ammonia, etc) outward from the Sun, leaving the inner solar system enriched in refractory materials such as silica and iron.
Gravitational accretion: planetesimals attract stuff
Large protoplanets dominate, grow rapidly, clean up area ( takes ~10 to 25 My)
Image: LPI

14. How Did We Get a Solar System?
1. The smaller protoplanets ( inner solar nebula) are unable to accrete gas because of their higher temperature.
5.Gravitational accretion of gas: the largest protoplanets in the coolest parts of the solar nebula accrete gas. The smaller protoplanets in the inner solar nebula are unable to accrete gas because of their higher temperature.
Jupiter and Saturn form first? Sweep up H and He – leave C, O, and N for the others?
6.Sweep of debris: over about 1 billion years, the material left over from the solar system formation is cleared. The Sun enters its T-Tauri phase and blows the remaining gas out of the solar system. The Jovian planets strongly influence the orbits of the remaining planetesimals (comets), either throwing them out into the Oort cloud or inward, where they collide with the terrestrial planets. Terrestrial planets obtain their atmospheres, and particularly water, from the constant impact of cometary material. In a process that remains uncertain, Jupiter influences the region of the asteroid belt so that some material remains in stable solar orbits but is unable to coalesce into a larger body.
WHEN?
Refractory elements (heavier elements stable at higher temperatures) condensed in the inner nebula. Terrestrial Planets.
Volatile elements (lighter elements stable at lower temperatures) condensed in the outer nebula. Jovian Planets.
Outer Solar System
Cold – ices, gases – 10x more particles than inner
May have formed icy center, then captured lighter gases (Jupiter and Saturn first? Took H and He?)
Image: LPI

15. How Did We Get a Solar System?
1. The smaller protoplanets ( inner solar nebula) are unable to accrete gas because of their higher temperature.
5.Gravitational accretion of gas: the largest protoplanets in the coolest parts of the solar nebula accrete gas. The smaller protoplanets in the inner solar nebula are unable to accrete gas because of their higher temperature.
6.Sweep of debris: over about 1 billion years, the material left over from the solar system formation is cleared. The Sun enters its T-Tauri phase and blows the remaining gas out of the solar system. The Jovian planets strongly influence the orbits of the remaining planetesimals (comets), either throwing them out into the Oort cloud or inward, where they collide with the terrestrial planets. Terrestrial planets obtain their atmospheres, and particularly water, from the constant impact of cometary material. In a process that remains uncertain, Jupiter influences the region of the asteroid belt so that some material remains in stable solar orbits but is unable to coalesce into a larger body.
WHEN?
Refractory elements (heavier elements stable at higher temperatures) condensed in the inner nebula. Terrestrial Planets.
Volatile elements (lighter elements stable at lower temperatures) condensed in the outer nebula. Jovian Planets.
Early burst of solar wind - sweeps debris out of system
Gravitational accretion of gas for protoplanets in the coolest nebular parts
Image: LPI

16. How Did We Get a Solar System?
The Asteroid Belt
? Should have been a planet instead of a debris belt? Jupiter kept it from forming
All of Eros Date: This picture of Eros, the first of an asteroid taken from an orbiting spacecraft, is a mosaic of four images obtained by NEAR on February 14, 2000, immediately after the spacecraft's insertion into orbit. We are looking down over the north pole of Eros at one of the largest craters on the surface, which measures 4 miles (6 kilometers) across. Inside the crater walls are subtle variations in brightness that hint at some layering of the rock in which the crater formed. Narrow grooves that run parallel to the long axis of Eros cut through the southeastern part of the crater rim. A house-sized boulder is present near the floor of the crater; it appears to have rolled down the bowl-shaped crater wall. A large number of boulders is also present on other parts of the asteroid's surface. The surface of the asteroid is heavily cratered, indicating that Eros is relatively old. Image Credit: NASA
Eros image at

17. How Did We Get a Solar System?
Beyond the Gas Giants - Pluto, Charon and the Kuiper Belt objects
Chunks of ice and rock material
Little time / debris available to make a planet – slower!!
This view of Pluto was taken by the Hubble Space Telescope. It shows a rare image of tiny Pluto with its moon Charon, which is slightly smaller than the planet. Because Pluto has not yet been visited by any spacecraft, it remains a mysterious planet. Due to its great distance from the sun, Pluto's surface is believed to reach temperatures as low as -240°C (-400°F). From Pluto's surface, the Sun appears as only a very bright star.
Image can be found at

18. Play Doh Activity

19. Early in the Life of Planets
Planetesimals swept up debris
Accretion + Impacts = HEAT
Eventually begin to melt materials
Iron, silica melt at different temperatures
Iron sank – density layering
Terrestrial Planet Interiors Mercury Mercury has an average density of 5430 kilograms per cubic meter, which is second only to Earth among all the planets. It is estimated that the planet Mercury, like Earth, has a ferrous core with a size equivalent to two-thirds to three-fourths that of the planet's overall radius. The core is believed to be composed of an iron-nickel alloy covered by a mantle and surface crust. Venus It is believed that the composition of the planet Venus is similar to that of Earth. The planet crust extends to around kilometers below the surface, under which the mantle reaches to a depth of some 3000 kilometers. The planet core comprises a liquid iron-nickel alloy. Average planet density is 5240 kilograms per cubic meter. Earth The Earth comprises three separate layers: a crust, a mantle, and a core (in descending order from the surface). The crust thickness averages 30 kilometers for land masses and 5 kilometers for seabeds. The mantle extends from just below the crust to some 2900 kilometers deep. The core below the mantle begins at a depth of around 5100 kilometers, and comprises an outer core (liquid iron-nickel alloy) and inner core (solid iron-nickel alloy). The crust is composed mainly of granite in the case of land masses and basalt in the case of seabeds. The mantle is composed primarily of peridotite and high-pressure minerals. Average planet density is 5520 kilograms per cubic meter. Mars Mars is roughly one-half the diameter of Earth. Due to its small size, it is believed that the martian center has cooled. Geological structure is mainly rock and metal. The mantle below the crust comprises iron-oxide-rich silicate. The core is made up of an iron-nickel alloy and iron sulfide. Average planet density is 3930 kilograms per cubic meter. Pluto The structure of Pluto is not very well understood at present. Nevertheless, spectroscopic observation from Earth in the 1970s has revealed that the planet surface is covered with methane ice. Surface temperature is -230?C (-382?F), and the frozen methane exhibits a bright coloration. However, with the exception of the polar caps, the frozen methane surface is seen to change to a dark red when eclipsed by its moon Charon. Average planet density is 2060 kilograms per cubic meter. The low average density requires that the planet must be a mix of ice and rock. Image Credit: Lunar and Planetary Institute
Image from LPI:

20. Planetary Interiors Differentiation
Image from LPI:
Differentiation
Separation of homogenous interior into layers of different compositions
Early – hottest time – dense iron-rich material  core
Releases additional heat
Leaves mantle with molten ocean enriched in silica
Crust eventually forms from lightest material
Planets hot enough for heavy materials (Fe, Ni) sink  core
Lighter material go to surface  crust / mantle
Some planets still have liquid core  magnetic field
Terrestrial Planet Interiors Mercury Mercury has an average density of 5430 kilograms per cubic meter, which is second only to Earth among all the planets. It is estimated that the planet Mercury, like Earth, has a ferrous core with a size equivalent to two-thirds to three-fourths that of the planet's overall radius. The core is believed to be composed of an iron-nickel alloy covered by a mantle and surface crust. Venus It is believed that the composition of the planet Venus is similar to that of Earth. The planet crust extends to around kilometers below the surface, under which the mantle reaches to a depth of some 3000 kilometers. The planet core comprises a liquid iron-nickel alloy. Average planet density is 5240 kilograms per cubic meter. Earth The Earth comprises three separate layers: a crust, a mantle, and a core (in descending order from the surface). The crust thickness averages 30 kilometers for land masses and 5 kilometers for seabeds. The mantle extends from just below the crust to some 2900 kilometers deep. The core below the mantle begins at a depth of around 5100 kilometers, and comprises an outer core (liquid iron-nickel alloy) and inner core (solid iron-nickel alloy). The crust is composed mainly of granite in the case of land masses and basalt in the case of seabeds. The mantle is composed primarily of peridotite and high-pressure minerals. Average planet density is 5520 kilograms per cubic meter. Mars Mars is roughly one-half the diameter of Earth. Due to its small size, it is believed that the martian center has cooled. Geological structure is mainly rock and metal. The mantle below the crust comprises iron-oxide-rich silicate. The core is made up of an iron-nickel alloy and iron sulfide. Average planet density is 3930 kilograms per cubic meter. Pluto The structure of Pluto is not very well understood at present. Nevertheless, spectroscopic observation from Earth in the 1970s has revealed that the planet surface is covered with methane ice. Surface temperature is -230?C (-382?F), and the frozen methane exhibits a bright coloration. However, with the exception of the polar caps, the frozen methane surface is seen to change to a dark red when eclipsed by its moon Charon. Average planet density is 2060 kilograms per cubic meter. The low average density requires that the planet must be a mix of ice and rock. Image Credit: Lunar and Planetary Institute

21. Planetary Interiors Differentiation Continues!
Image from LPI:
Differentiation
Continues!
Radioactive decay = primary heat source
Partial melting of mantle material  rising magma  volcanoes / lava flows
Planets hot enough for heavy materials (Fe, Ni) sink  core
Lighter material go to surface  crust / mantle
Some planets still have liquid core  magnetic field
Terrestrial Planet Interiors Mercury Mercury has an average density of 5430 kilograms per cubic meter, which is second only to Earth among all the planets. It is estimated that the planet Mercury, like Earth, has a ferrous core with a size equivalent to two-thirds to three-fourths that of the planet's overall radius. The core is believed to be composed of an iron-nickel alloy covered by a mantle and surface crust. Venus It is believed that the composition of the planet Venus is similar to that of Earth. The planet crust extends to around kilometers below the surface, under which the mantle reaches to a depth of some 3000 kilometers. The planet core comprises a liquid iron-nickel alloy. Average planet density is 5240 kilograms per cubic meter. Earth The Earth comprises three separate layers: a crust, a mantle, and a core (in descending order from the surface). The crust thickness averages 30 kilometers for land masses and 5 kilometers for seabeds. The mantle extends from just below the crust to some 2900 kilometers deep. The core below the mantle begins at a depth of around 5100 kilometers, and comprises an outer core (liquid iron-nickel alloy) and inner core (solid iron-nickel alloy). The crust is composed mainly of granite in the case of land masses and basalt in the case of seabeds. The mantle is composed primarily of peridotite and high-pressure minerals. Average planet density is 5520 kilograms per cubic meter. Mars Mars is roughly one-half the diameter of Earth. Due to its small size, it is believed that the martian center has cooled. Geological structure is mainly rock and metal. The mantle below the crust comprises iron-oxide-rich silicate. The core is made up of an iron-nickel alloy and iron sulfide. Average planet density is 3930 kilograms per cubic meter. Pluto The structure of Pluto is not very well understood at present. Nevertheless, spectroscopic observation from Earth in the 1970s has revealed that the planet surface is covered with methane ice. Surface temperature is -230?C (-382?F), and the frozen methane exhibits a bright coloration. However, with the exception of the polar caps, the frozen methane surface is seen to change to a dark red when eclipsed by its moon Charon. Average planet density is 2060 kilograms per cubic meter. The low average density requires that the planet must be a mix of ice and rock. Image Credit: Lunar and Planetary Institute

22. Pause to recall the Play Doh accretion activity
But wait, there’s more ….
We can differentiate!

23. When did Our Solar System Form … How do We Know?
Image: Lunar and Planetary Laboratory:

24. When Did the Solar System Form?
4.56 billion years ago
How do we know? (evidence for formation)
Lunar samples to 4.6 Ga
Meteorites Ga
Earth – 3.9 (or 4.4 Ga)
The meteorite "offers us a snapshot of the original composition of the entire solar system before the planets formed," said Michael Zolensky, a scientist at NASA's Johnson Space Center (JSC). "It tells us what the initial materials were like that went into making up the Earth, the Moon and the Sun.“
Photo: Sikhote-Alin meteorite This is one fragment of the Sikhote-Alin meteorite. It is about 15 cm across. The photograph shows the original meteorite surface, melted into thumb-print shapes during its flight through our atmosphere. (Photo by Carl Allen, NASA JSC photo S )
Lunar Meteorite: The fusion crust on the 663-gram meteorite is evident in this view. The small cube in the corner is 1 cm on each side. (from NASA photo S )
Lunar meteorite at
Meteorite photo by Carl Allen at

25. How Do We Know How Our Solar System Formed?
Analysis of the 4.5-billion-year-old meteorite, which exploded in the Earth's upper atmosphere January 18 and rained fragments over part of Canada's Yukon Territory, are expected to show what conditions were like when the solar system began to form.
Initial formation of Jupiter near "snow line" at 4 AU. Jupiter’s large mass and high gravity attracted much of the material available from its region of the solar nebula. This left the asteroid belt too depleted in mass to form a planet and resulted in a relatively small mass for the planet Mars. Jupiter’s high mass also makes it a magnet for comets and asteroids, sweeping them up or slinging them out of the solar system. It has been estimated that without Jupiter the frequency of impact between asteroids and comets and the Earth would have been 1000 times greater.
The meteorite "offers us a snapshot of the original composition of the entire solar system before the planets formed," said Michael Zolensky, a scientist at NASA's Johnson Space Center (JSC). "It tells us what the initial materials were like that went into making up the Earth, the Moon and the Sun."
The meteorite is a carbonaceous chondrite, a rare type that accounts for only 2 percent of all meteorites. While carbonaceous chondrite asteroids are relatively common, meteorites from them are rare because they break up as they enter the Earth's atmosphere or from weathering processes after landing.
Carbonaceous chondrites are particularly interesting because they are rich in organic materials, including amino acids that are the building blocks for life Because such meteorites show no signs of "processing" since their formation 4.5 billion years ago, they are thought to be the best sample of the dust cloud from which the solar system formed.

26. Solar System Samples Meteorites
Bottom line – meteorites tell us about the composition and processes that took place to form our Solar System
Some are unaltered – give us dates and composition (and process)
Some are altered – process information (metamorphism, differentiation) (and composition)
Some come from different places within a planet – again, composition and process
Meteorites and their message
- Meteorites are bits of solar system that enter earth's atmosphere. Most burn up from friction (never hit). ~500/year baseball-sized.
- Rare bigger ones hit, including a big one about 65 Ma (10 km diameter in Mexico).
- Big ones cause local melting of any rocks that they hit. Explosive craters.
5 types: Stones, irons and stony-irons: DESCRIPTION
1) Chondrites - 79% - most common
- tiny balls (chondrules) of mafic minerals formed by rapid cooling.
- Age = 4.6 Ga. Oldest rocks of solar system.
2) Carbonaceous Chondrites - 5% - chondrites, plus minor organic compounds such as amino acids.
- Composition same as Sun (for non-volatile elements like C, Si, Al, Fe, Mg).
3) Achondrites - 8% similar to terrestrial mafic igneous rocks, some with brecciated texture.
4) Iron Meteorites - 6% - intergrowths of iron-nickel alloys.
- Large crystals indicating slow crystallization.
5) Stony-irons - 2% - mixture of iron-nickel and silicate minerals.
5 types: INTERPRETATION
1) Carbonaceous Chondrites - chondrites + carbon.
- Represent protoplanetary material formed at condensing of the solar nebula and never remelted.
2) Iron Meteorites - iron-nickel alloys.
- Core of differentiated protoplanets.
3) Achondrites - mafic igneous rocks, some brecciated.
- Represent somewhat younger pieces of igneous rocks produced on larger asteroids.
4) Stony-irons - mix: iron-nickel and silicate minerals.
- Interpreted to represent the transition zone between an iron-nickel core and a silicate mantle.
5) Chondrites - mafic silicates formed by rapid cooling.
- May represent crystallization as drops from melted silicates as a result of asteroid collisions in the accretionary phase.
Will Eros hit Earth?
Not anytime soon. Using telescope-mounted digital cameras, NASA researchers have found more than 350 near-Earth asteroids larger than 1 kilometer (about 0.6 miles) in diameter. From this information they estimate anywhere from 500 to 1,000 similar-sized NEAs could be spinning around our solar system. Good news is the scientists say none of the asteroids they’re tracking will hit Earth in the near future. In addition, what the NEAR mission learns about Eros will help scientists if they ever do spot an asteroid headed our way.
Dawn's goal is to characterize the conditions and processes of the solar system's earliest epoch by investigating in detail two of the largest protoplanets remaining intact since their formations. Ceres and Vesta. The top level question that the mission addresses is the role of size and water in determining the evolution of the planets. Ceres and Vesta are the right two bodies with which to address this question, as they are the most massive of the protoplanets, baby planets whose growth was interrupted by the formation of Jupiter. Ceres is very primitive and wet while Vesta is evolved and dry. The three principal scientific drivers for the mission are first that it captures the earliest moments in the origin of the solar system enabling us to understand the conditions under which these objects formed. Second, Dawn determines the nature of the building blocks from which the terrestrial planets formed, improving our understanding of this formation. Finally, it contrasts the formation and evolution of two small planets that followed very different evolutionary paths so that we understand what controls that evolution.
Image:
And

27. Passed through Comet Wild 2 Coma 1/2004
Earliest history of Solar System - chemical and physical info about formation and building blocks of planets (rest of stuff was pulled into the Sun or other planets….)
Sample Return
1/15/2006
Stardust
Passed through Comet Wild 2 Coma 1/2004
As the ices of the comet nucleus evaporate, they expand rapidly into a large cloud around the central part of the comet. This cloud, called the coma, is the atmosphere of the comet and can extend for millions of miles. The cloud is very thin, however, with only a 100 particles in a cubic centimeter
Stardust image at
Info and images at

28. We Can Also Look Around ….
A Hubble Space Telescope view of a small portion of the Orion Nebula (1600 LY away) reveals five young stars (probably a few million years old). Four of the stars are surrounded by gas and dust trapped as the stars formed, but were left in orbit about the star. These are possibly protoplanetary disks, or "proplyds," that might evolve on to agglomerate planets. The proplyds which are closest to the hottest stars of the parent star cluster are seen as bright objects, while the object farthest from the hottest stars is seen as a dark object. The field of view is only 0.14 light-years across.
The Orion Nebula star-birth region is 1,500 light-years away, in the direction of the constellation Orion the Hunter.
The image was taken on 29 December 1993 with the HST's Wide Field and Planetary Camera 2.
Close-up of "Proplyds" in Orion
Thanks Hubble!
Hubble images at
and

29. Comets
Dirty snowballs - small objects of ice, gas, dust, tiny traces of organic material
Every comet has a nucleus , a stable, porous central mass of ice, gas, and dust that if often between 1 and 10 kilometers (0.6 to 6 miles) in size. The ice is made of varying amounts of water, carbon dioxide, ammonia, and methane. The dust may contain hydrogen, oxygen, carbon, nitrogen, silica, and some metals. The nucleus may have traces of hydrocarbons.
How big are comets? A comet's nucleus is typically 1 to 10 kilometers (0.6 to 6 miles) across. The tail, however, can stretch for tens of millions of kilometers.
What are comets are made of? Most of our information comes from studying the spectra of different comets. Scientists study the light reflected by different parts of a comet. Gases contain different elements. Each element (such as hydrogen), molecule (such as water), or ion (an electrically charged element or molecule) has a distinct pattern of emission or absorption that can be determined in the laboratory; this pattern is known as its spectrum. By matching patterns between laboratory measurements and comet observations, scientists can determine the composition of the comet.
Every comet is made of the same basic ingredients — ice and dust. However, comets probably vary in how much of the ice is water ice and how much is ice made of other substances, such as methane, ammonia, and carbon dioxide. Comets also vary in the different types of trace elements and hydrocarbons are present.
Several space missions, such as the European Space Agency's Giotto mission, have explored comets and provided detailed imagery of comet surfaces. A few missions are intended to sample comets. After a successful rendezvous with Comet Wild 2, NASA's Stardust mission will return comet dust and gas samples to Earth in January NASA's Deep Impact mission will encounter Comet Tempel 1 in July 2005, and will release a projectile into the comet surface to excavate a hole and expose a fresh surface on the nucleus. The spacecraft will collect data on comet emissions and will relay the data to scientists on Earth. While the data from these missions will be from only a few comets and might not be representative, the data will greatly improve our understanding of comet compositions.
Image from:

30. Comet Parts Nucleus, Coma
As comets approach our Sun [within about 450 million kilometers (280 million miles)], they heat up and the ice begins to sublimate (change from a solid directly to a gas). The gas (water vapor, carbon monoxide, carbon dioxide, and traces of other substances) and dust forms an “atmosphere” around the nucleus called a “coma.” Material from the coma gets swept into the tail.
As comets move close to the Sun, they develop tails of dust and ionized gas. Comets have two main tails, a dust tail and a plasma tail. The dust tail appears whitish-yellow because it is made up of tiny particles — about the size of particles of smoke — that reflect sunlight. Dust tails are typically between 1 and 10 million kilometers (about 600,000 to 6 million miles) long. The plasma tail is often blue because it contains carbon monoxide ions. Solar ultraviolet light breaks down the gas molecules, causing them to glow. Plasma tails can stretch tens of millions of kilometers into space. Rarely, they are as long as 150 million kilometers (almost 100 million miles). A third tail of sodium has been observed on Comet Hale-Bopp.
Comets are enveloped in a broad, thin (sparse) hydrogen cloud that can extend for millions of kilometers. This envelope cannot be seen from Earth because its light is absorbed by our atmosphere, but it has been detected by spacecraft.
Image from
Image credit: K. Jobse, P. Jenniskens and NASA Ames Research Center
Nucleus, Coma
Dust tail – white, “smoke,” reflects sun. 600,000 to 6 million miles long
Ion tail – Solar UV breaks down CO gas, making them glow blue. 10’s of millions of miles

31. Naming Comets
How are comets named? Comets are named after the person who first reports their discovery. For example, Comet Halley is named for Edmund Halley, who determined that comets observed in 1531, 1607, and 1682 had essentially the same orbits and thus were a single comet. Based on his calculations, he correctly predicted the comet's return in 1758, but unfortunately, he did not live to see Comet Halley. Sometimes more than one person reports a new comet at the same time. In that case, the names are combined — as in the cases of Comet Hale-Bopp or Comet Shoemaker-Levy.
NASA/ JPL image of Comet Halley at

32. Where do Comets Originate?
What do the orbital paths of comets look like? Based on observations of how comets move through the sky, scientists have determined that comets travel around our Sun in highly elliptical (oval-shaped) orbits. The time it takes to make a complete orbit is called a comet's period. Comet periods typically range from a few years to millions of years.
Where do comets come from? Comets are divided into short-period comets and long-period comets. Short period comets — such as Comet Halley — revolve around our Sun in orbits that take less than 200 years. Their orbital paths are close to the same plane of orbit as Earth and the other planets, and they orbit our Sun in the same direction as the planets. Based on these orbital characteristics, short-period comets are believed to originate in the Kuiper belt, a disk-shaped region extending beyond Neptune. The Kuiper belt contains small, icy planetary bodies, only a few of which have been imaged. These are the “leftovers” from early solar system formation. Occasionally the orbit of a Kuiper belt object will be disturbed by the interactions of the giant planets in such a way that it will have a close encounter with Neptune and either be flung out of the solar system or pushed into an orbit within our solar system.
Long period comets — such as Comet Hale-Bopp or Comet Hyakutake — take more than 200 years to orbit our Sun. Their orbital path is random in terms of direction and plane of orbit. Based on calculations from their observed paths, long-period comets are believed to originate in the Oort cloud. The Oort cloud is a spherical envelope that may extend 30 trillion kilometers (approximately 20 trillion miles) beyond our Sun. Oort cloud objects have never been imaged.

33. What’s in a Tail?
What happens when a comet approaches our Sun? In the cold far reaches of our solar system, in the Kuiper belt and Oort cloud, comets are essentially just small chunks of ice and dust. Comets are nearly invisible except when they get close to our Sun. As a comet approaches our Sun, it begins to heat up and the ice begins to sublimate — to change from a solid to a gas with no liquid stage. Some of the dust is left behind as the ice sublimates. It forms a dark, protective crust on the surface of the nucleus and slows the melting. In some places the protective layer is thinner, and jets of gas break through. The gas and dust form the cloud of the coma.
Our Sun emits a solar wind, a constant flow of gas and particles (mostly protons and electrons) that streams outward at 350 kilometers (about 220 miles) per second. Sunlight and solar wind sweep the dust and gas of the coma into trailing tails. Because sunlight and solar wind always flow outward from our Sun's surface, the tails always point away from our Sun no matter what direction the comet is moving in its orbit. This means that the tails can be in front of the comet as the comet moves away from our Sun on its return to the outer part of its orbit.
Two distinct tails develop — the plasma tail and the dust tail. The different shapes and angles of the tails are caused by the way different particles are affected by our Sun. The thinner, longer plasma tail forms a straight line extending from the comet. The particles in this ion tail are electrically charged and are pushed away from our Sun by the solar wind. The shorter dust tail is curved slightly. The larger particles in the dust tail do not have an electric charge and are not affected by the solar wind. Instead, the dust particles shed from the comet are repelled by the force of the sunlight and “lag behind” the comet in its movement around our Sun.
Comet tails get longer and more impressive as the comet gets closer to our Sun. As the comet approaches our Sun, it gets hotter and material is released more rapidly, producing a larger tail. Scientists estimate that a comet loses between 0.1 and 1 percent of its mass each time it orbits our Sun.
Image credit: K. Jobse, P. Jenniskens and NASA Ames Research Center

34. Comet – Planet Interactions
What happens when Earth passes through the path of a comet? Meteor showers occur when Earth passes through the trail of dust and gas left by a comet along its elliptical orbit. The particles enter Earth's atmosphere and most burn up in a lively light show — a meteor shower. Some meteor showers, such as the Perseids in August and the Leonids in November, occur annually when Earth's orbit takes it through the debris path left along the comet's orbit. Comet Halley's trails are responsible for the Orionids meteor shower. For upcoming meteor showers and viewing suggestions, explore Sky and Telescope's Meteor Showers page.
Image from