Eps Sci 3 Lecture 2. Universe, Scale, and Forces

Planets in order

1. Sun

2. Mercury

3. Venus

4. Earth

5. Mars

6. Jupiter

7. Saturn

8. Uranus

9. Neptune

How do a planet's size and mass affect its characteristics?

A planet’s size and mass influence its:

• gravity

• composition

• atmospheric retention

3 domains in the solar system

1. terrestrial planet: mercury, venus, earth, and mars (aka rocky planets close to the sun)

2. giant planet domain: jupiter, saturn, uranus, and neptune (aka large planets containing substantial gas or ice-rich material)

3. comet domain: kuiper belt and distant oort cloud objects (aka icy and rocky bodies in outer solar system)

3 domains in the solar system: terrestrial planet domain

mercury, venus, earth, and mars (aka rocky planets close to the sun)

3 domains in the solar system: giant planet domain

jupiter, saturn, uranus, and neptune (aka large planets containing substantial gas or ice-rich material)

3 domains in the solar system: comet domain

kuiper belt and distant oort cloud objects (aka icy and rocky bodies in outer solar system)

Why might life exist on icy moons rather than only on Earth-like planets?

some icy moons, such as Europa and Enceladus, may contain liquid water oceans beneath their icy surfaces, showing that life could potentially exist in environments unlike Earth

(life does not necessarily require an Earth-like planet or surface oceans)

Solar System patterns

1. planetary orbits are nearly coplanar (most planets orbit approx in same plane)

2. planes orbit sun in same direction

3. orbits are nearly circular = low eccentricity

4. most planets orbit in same general direction of their orbital motion (except venus and uranus)

5. rocky planets are closer to sun, while giant planets are further away

Why so solar system patterns exist and what does this say about the solar system?

plants formed from sharing rotating disk of gas and dust surrounding young Sun → material gradually accumulated into larger objects → planets

planets’ orbital directions and planes are similar → evidence that solar system formed through common physical processes rather than as random collection of planets

Our cosmic address

Earth, solar system, orion arm, milky way galaxy, local group of galaxies, larger cosmic structures, and the observable universe

(Earth is one extremely small part of the larger universe)

Big Bang (aka beginning of the universe’s expansion)

• universe is approx 13.6-13.8 billion years old

• as space expanded, the distances between distant galaxies generally increased

• mainly produced hydrogen and helium

Cosmic Microwave Background (CMB)

ancient radiation left over from early universe

• initially, universe was so hot and dense that light could not travel freely over long distances

• once universe cooled enough for neutral atoms to form, light could travel much more freely

→ evidence that the early universe was hot and dense

Timeline

1. universe expands

2. temp decreases

3. particles and atoms form

4. gravity organizes matter into stars and galaxies

Elements that came from the Big Bang

hydrogen and helium

Elements that came from the stars

carbon, oxygen, iron, etc

inside stars, nuclear fusion produces heavier elements from lighter nuclei

Main takeaway of how elements were created:

Big Bang nucleosynthesis primarily created light elements; later generations of stars produced many of the heavier elements needed for planets and life

How is matter distributed through the universe?

matter is distributed unevenly, forming enormous filaments, galaxy clusters, and relatively empty regions called voids

Why is matter distributed unevenly throughout the universe?

gravity attracts matter, causing regions with slightly higher density to attract additional matter and gradually form larger structures

Higher density → stronger gravitational attraction → more matter accumlates → larger cosmic structures form

How many stars are there?

10^11 stars in Milky Way, 10^11 stars in the galaxies of the observable universe = 10^11 × 10^11 = 10^22 stars

Star formation

galaxy collision → gas compression → gravitational collapse → star formation → potential planet formation from disks of surrounding material

Astronomical distances: astronomical unit (AU)

distances with planetary systems (150 million km) → avg distnce between Earth and the Sun

Astronomical distances: light year (ly)

distance light travels in one year (9.46 trillion km)

Astronomical distances: parsec (pc)

distances between stars (3.26 light years)

Astronomical distances: megaparsec (Mpc)

distances between galaxies (1 million parsec)

How do astronomers know the universe is expanding?

Light

• doppler effect: how observed wavelengths change due to relative motion

  • source moving towards us = blueshift

  • source moving away from us = redshift (also occurs because space expands while light travels through it)

Edwin Hubble’s relationship

the farther away a galaxy is, the faster it generally recedes from us

Hubble’s law

v = H0d

• v = recession velocity

• H0 = Hubble constant

• d = distance to galaxy

Why does the age of the universe matter for astrobiology?

Age of the universe: 13.6 billion years

age of the earth: 4.5 billion years

→ the universe existed for a longer time years before Earth was created = if life arose on the other planets, had much more time to evolve

4 fundamental forces

• gravity

• electromagnetism

• strong nuclear force

• weak nuclear force

Force

• F = ma

• Newtons (N) = 1 kg*m/s²

Gravity

attractive force between object’s with mass

• weakest force

• Gravitational force: F = G(M1M2/d²)

• greater mass produces greater gravitational attraction

• greater distance produces weaker gravitational attraction

• organizes planets, stars, galaxies

Electromagnetism

the electromagnetic force acts between electrically-charged particles

• chemical bonds allow atoms to form molecules: H2O, proteins, and DNA

• without electromagnetism, the chemistry necessary for life would not exist

• charged particles, atoms, chemical bonds

Strong nuclear force

• positively charged protons

• binds quarks and atomic nuclei

• but extremely short for nuclear binding

Weak nuclear forces

• particle transformation, radioactive decay

• extremely short range

Bigger connection of forces to astrobiology

1. gravity gathers into stars

2. electromagnetism influences how charged particles interact

3. strong nuclear forces enable nuclear binding

4. weak nuclear forces allow transformations involved in certain nuclear reactions

→ explain how stars form and produce energy

Energy

capacity to do do work and energy is conserved

• cannot be created nor destroyed — can only be transformed/transferred

• unit Joules (J) = 1 N*m

• E = mc²

Potential energy

stored energy associated with the configuration/condition of a system

• gravitational potential energy, chemical energy, nuclear energy

• U = -(GMm/r)

Kinetic energy

energy associated with motion

• KE = 1/2mv²

Possible factors that can power the Sun

1. chemical burning

2. gravitational energy

Possible factors that can power the Sun: chemical burning

NOT POSSIBLE: chemical reactions cannot produce enough energy to power the sun over its enormous lifetime (roughly 200 years)

Possible factors that can power the Sun: gravitational energy

gravitational energy can release energy (about 10^7 = 10 million years, but sun’s total lifetime is approx 10 billion years)

How the Sun produces energy

1. gravity compresses the sun’s core → high temp and pressure

2. electromagnetic repulsion resists fusion because positively charged protons repel each other

3. nuclei can approach closely enough through their KE and quantum tunneling

4. nuclear interactions allow fusion, with the weak interaction playing an essential role in the sun’s proton-proton chain

5. energy is released because the resulting products have less total mass than the initial particles

Sun’s long-lasting energy reason:

nuclear fusion

nuclear fusion

in sun’s core, hydrogen produces helium

• issue: hydrogen nuclei are protons, which repel each other

• to fuse, nuclei must approach close enough for strong nuclear force to bind them

  • high temp: nuclei move rapidly and can approach one another more closely during collisions

  • high pressure and density: sun’s gravity compresses material toward center → high density and pressure

The difference in mass is converted into energy: ∆E = ∆mc² significance

• energy that eventually reaches space as sunlight

• energy that warms the earth and photosynthesis

Fusion vs fission

fusion: small nuclei combinto form larger nuclei

fission: heavy nucleus splits into smaller ojbects

Dark matter

• 27%

• gravitational effects can be measured

• thought to play important role in formation and organization of cosmic structures

Dark energy

• 68%

• the unknown component associated with the accelerated expansion of the universe

Ratio of ordinary and dark matter and dark energy

• ordinary matter: 5%

• dark matter (gravitational effects): 27%

• dark energy (accelerating expansion of the universe): 68%