1.3 Building the Solar System Flashcards
1
Q
How much of the solar system is comprised of the sun? Which is the next largest object?
A
- Over 98%
- The next most massive object, Jupiter, is less than 1% of the sun’s mass
2
Q
How do other objects in the solar system rotate?
A
The plane of the ecliptic, an imaginary two-dimensional surface that extends throughout the solar system, passing through the center of the Sun that aligns with Earth’s orbit.
3
Q
What remains between Jupiter and Mars?
A
an area of irregularly shaped solid materials called the Asteroid Belt
4
Q
What extends beyond Neptune’s orbit, and even further?
A
- Kuiper belt
- Further: Oort cloud
5
Q
The closer a planet is to the sun…
Pace of orbit
A
the less time it takes to make one complete orbit
6
Q
Which planets rotate opposite of the sun? (retrograde)
A
Most planets rotate in the same direction as their orbit around the Sun, with notable exceptions being Venus and Uranus, which exhibit retrograde rotation
7
Q
What do current theories suggest about solar system formations?
A
- All solar systems form from interstellar dust and gas clouds.
- These clouds consist of: gases left over from the formation of the universe during the Big Bang, as well as material from the deaths of stars.
- Stars can shed material gradually as they approach old age or eject it explosively, as is the case for high-mass stars, through violent supernova events
8
Q
What composes “interstellar dust and gas clouds”?
What can be made of them?
A
- Hydrogen and helium
- Followed by significant quantities of carbon, oxygen, neon, magnesium, and silicon.
- From these elements, several planet-forming solids can emerge, including ices of various compositions, oxides, and metals.
9
Q
What are inner planets mainly composed of?
A
We can infer that the inner planets (with densities ranging from 3.9 to 5.5 g/cm³) are primarily composed of metal oxides
10
Q
What are outer planets mainly composed of?
A
Outer planets (with densities between 0.7 and 1.6 g/cm³) must also contain significant quantities of ices to account for their lower densities.
11
Q
The Solar Nebular Disc Model
A
proposes that the solar system formed from a collapsing cloud of interstellar gas and dust around 4.5-4.6 billion years ago
12
Q
Large Molecular Cloud
What started the collapse?
Solar Nebular Disc Model - TIMELINE
A
- Begin with molecular cloud: several light-years, mainly hydrogen and helium, along with organic molecules, silicates, and volatiles such as methane and water.
13
Q
Large Molecular Cloud - What started the collapse?
How did this form stars?
Solar Nebular Disc Model - TIMELINE
A
- A “gravitational kick,” possibly from a nearby supernova
- This collapse would concentrate material in specific areas, eventually leading to the formation of new stars.
Such a “star-generating” region of a galaxy is called a stellar nursery - Our sun likely formed in such a nursery, in close proximity to its stellar siblings, but drifted apart and now independently orbit the Milky Way Galaxy.
14
Q
Pre-Solar Nebula and the Protoplanetary Disc
Solar Nebular Disc Model - TIMELINE
A
- The region of the large molecular cloud that would eventually form our solar system is called the Pre-Solar Nebula
- Nebula, collapsing 4.5-4.6 billion years ago, started to spin - creating a vortex in which most of the mass became concentrated toward the center of rotation.
- Due to the conservation of angular momentum, the rotation speed increased as more mass was drawn into the central region (eventually becoming the sun)
- After about 100,000 years, this rotational collapse caused the outer regions of the nebula to flatten into a disc of material, approximately 200 astronomical units (AU) across
15
Q
The Young Sun
Solar Nebular Disc Model - TIMELINE
A
- As mass was added to the central area of the contracting cloud, it heated up due to gravitational collapse, converting kinetic energy (movement) into heat. At this stage, the Sun was in its “T-Tauri phase” of development.
16
Q
The Young Sun - Nuclear Fusion
Solar Nebular Disc Model - TIMELINE
A
- Within 50 million yrs, the Sun had accumulated sufficient mass for nuclear fusion to begin.
- In this process, high temperatures and pressures allowed positively charged hydrogen nuclei to overcome their repulsion and fuse, forming helium in a series of steps, with energy released at each step
- With this, the Sun entered its “main sequence” stage as a yellow dwarf star.
- Solar winds—continuous flows of charged particles from the Sun—cleared the remaining material from the protoplanetary disc.
17
Q
Planetesimals
+ snowline
Solar Nebular Disc Model - TIMELINE
A
- Before the Sun entered its main sequence phase, the matter drawn towards the center of the protoplanetary disc would have been hot
- At 1 AU, it is estimated that temperatures would have been around 1000K - too hot for any volatiles to condense, but it is sufficiently cool for refractory materials (those resistant to heat), such as silicates and metals, to accumulate
- Only at a point between the current orbits of Jupiter and Mars (around 2.7 AU) were temperatures cool enough to allow volatile materials to condense and form ice. This region is referred to as the snowline
18
Q
Planetesimals - What formed exclusively witihin the snowline? Beyond?
Solar Nebular Disc Model - TIMELINE
A
- Only rocky, silica, and metal-rich planetesimals would form
- Outside the snowline (the region beyond the snowline and away from the Sun), refractory materials would still accrete to form the rocky cores of the planets, but with the addition of icy materials not present closer to the young Sun
19
Q
Chondrites - how can we look into early stages of solar system development?
Solar Nebular Disc Model - TIMELINE
A
- Chondritic meteorites: composed of millimeter-sized spheres called chondrules = once molten rock droplets in space that formed either like “raindrops” as the hot nebular gas cooled or when fragments of nebular dust were heated beyond their melting point during periods of high radiation activity from the T-Tauri Sun
- Chondrites have a composition similar to the building blocks of the planets and are considered “primitive” in nature.
- They are believed to be remnants from the early stages of the solar system before planet formation occurred.
20
Q
What are chondrites composed of?
Solar Nebular Disc Model - TIMELINE
A
- Dominated by silica, iron, magnesium, and oxygen in various compounds.
- Also present, but forming less than 9% of their composition, are aluminum, calcium, nickel, and sodium, along with six other rarer elements.
21
Q
Protoplanets & Differentiation
Solar Nebular Disc Model - TIMELINE
A
- As the planetesimals continued to accrete and became larger, gravity would start to pull them into roughly spherical bodies called protoplanets
- Higher concentrations of radioactive elements, gravitational pressure, and kinetic energy from impacts would have caused areas of the protoplanet to melt
- Under gravity, heavy components would sink towards the center, while lighter elements would rise towards the surface, a process known as differentiation
22
Q
Protoplanets & Differentiation - Achondrites
Solar Nebular Disc Model - TIMELINE
A
- Evidence of differentiation = achondrites - have compositions similar to basaltic lava rocks, rich in silicates.
- Others, known as iron metal achondrites, are composed of metallic iron-nickel crystallized in a distinctive interleaving pattern called Widmanstätten texture
- This texture forms only when molten metals cool slowly over millions of years.
- Iron metal achondrites were once the cooled cores of protoplanets, while silicate-rich achondrites are remnants of the more silicate-rich mantles and “crust” that surrounded them.
23
Q
Protoplanets to Planets
Solar Nebular Disc Model - TIMELINE
A
- about 100,000 years after the formation of the Sun, protoplanets stopped accumulating material
- it was collisions between these differentiated bodies that allowed the terrestrial planets to grow larger (evident in axis tilts, Mercury’s large core vs overall volume - indicating mantle was knocked off, moon as well)
24
Q
Evidence for SNDM
A
- Sun contains 98% of the mass in the solar system, reflecting the collapsing nebula in the collapsing cloud.
- The densities and sizes of planets consistent with the temperature gradient in the protoplanetary disc: rocky planets inside the snowline and icy-gassy bodies outside the snowline.
- The protoplanetary disc accounts for the planets orbiting in the plane of the ecliptic.
- Rotation of the protoplanetary disc: why all planets orbit the Sun in the same direction.
- Chondrites
- Achondrites
- Large collisions between protoplanets
- Other planetary systems in the early stages of development surrounded by protoplanetary discs.
25
We know that planetary bodies differentiate, but how did that occur? **There are two possibilities:**
## Footnote
Formation of Earth
1. Heterogeneous accretion
2. Homogeneous accretion
26
Heterogeneous accretion
## Footnote
Formation of Earth
* Suggests that the first materials to accrete from the nebula were metals, followed later by silicates
* This implies a period when the only solid materials available were metals, which would accrete to form the core
27
Heterogeneous accretion - evidence against
## Footnote
Formation of Earth
* Evidence from **chondrites** indicates that calcium-aluminum silicates were likely the first materials to solidify out of the protoplanetary disc.
* Additionally, the **dating of iron-metal achondrites** indicates they formed after the oldest silicate minerals in chondrites. As such, it would not be possible for metals to be present without silicates.
* Further evidence against the Heterogeneous Accretion hypothesis comes from **observations of nebulae surrounding young stars**, which are known to contain both silicates and metals.
28
Homogeneous Accretion
## Footnote
Formation of Earth
* suggests that the materials in the early Earth were initially cool and homogeneously mixed.
29
Homogeneous Accretion - Two important properties of iron and silicates support:
## Footnote
Formation of Earth
1. The densities of iron and silicates are quite different: iron being denser, while silicates are much lighter
2. Silicates and iron are **immiscible**, *meaning they do not mix but form discrete layers*. As the Earth melted, these two materials would have separated, allowing the iron to migrate relatively quickly toward the Earth’s center under gravity
30
Homogeneous Accretion - immiscible: where would the heat come for materials to migrate?
1. Kinetic energy released as heat during impact events
2. Heat from gravitational compression
3. Heat from radioactive materials with short half-lives that have now completely decayed. A half-life is the time it takes for half of a radioactive material to decay into a stable (non-radioactive) substance.
4. Heat from radioactive materials with long half-lives that are still decaying today
5. Heat generated as the liquid metal migrated toward the core
The core likely developed rapidly and is thought to have formed within the first 1% of the solar system’s history. In Topic 2.1, we will study more about the Earth's internal structure.
31
The Giant Impact Hypothesis
## Footnote
Formation of the Moon
* According to this theory, a protoplanet approximately the size of Mars, informally referred to as Theia, **had a close encounter with Earth in a grazing impact**
* As a result, **the cores of the two planets merged**, **while a significant portion of their silicate mantles was ejected to form a disk of material that eventually coalesced to form the Moon.**
32
The Giant Impact Hypothesis - how does it explain traits of the moon?
1. Since the impact was light, most of the material that eventually formed the Moon consisted of *lighter mantle materials* with a lower iron content than the core. **This explains why the Moon’s rocks are deficient in iron**, and its iron core is relatively small, making up just 20% of its diameter compared to 50% for Earth.
2. The impact generated substantial heat; causing the loss of various volatile substances and some moderately refractory elements, such as potassium, in the plume of material that eventually formed the Moon. **This explains why these substances are relatively less abundant on the Moon compared to Earth.**
3. Explains the very circular orbital characteristics of the Moon.
4. Provides insight into the age difference between the Moon and Earth. Since the impact occurred after much of Earth had formed, it **explains why the Moon is approximately 50 million years younger than the planet it orbits.**
