ASTR230

Most common elements By weight

Hydrogen (H) Helium (He) Oxygen (O) Carbon (C) Neon (Ne) Iron (Fe)

By number (atoms)

Hydrogen (H) Helium (He) Carbon (C) Oxygen (O) Nitrogen (N) Neon (Ne)

Why these are most common

H & He formed right after the Big Bang. C, O, N, Fe, etc. form later via stellar fusion and supernovae. Heavier elements spread by stellar explosions — recycled into new stars and planets.

Right side (nonmetals)

Gain electrons → oxidizers (O, F, Cl).

Left side (metals)

Lose electrons → reducers (Li, Na, Ca)

Covalent

Electrons shared

Ionic

Electrons transferred

Elements That Mimic Carbon

Group 14 - C, SI, GE, SN, PB - All can form 4 bonds, but only carbon forms strong multiple bonds

Mars water issue

Mars’ pressure < triple point of water → liquid phase unstable,  Even if warm, water boils or sublimates instantly.

Inner system

Only rocks/metals survive

Outer system

Ices and gases condense

SiO₂ (silica) is solid at room temp (quartz), not gas like CO₂

Silicon bonds are rigid → no flexible molecules → poor for biochemistry

Three Main Atmospheric Attributes

Composition - Pressure - Temperature

Ozone Layer

Found in stratosphere, O₃ absorbs UV-B and UV-C radiation., Exists there because UV intensity is high enough to both create and destroy O₃.

O₃ as a Biosignature

O₃ → comes from O₂, which is unstable unless continuously produced by life. So detecting lots of O₃ = likely biological activity.

Layers of Earth’s Atmosphere

Troposphere, Stratosphere, Mesosphere, Termosphere, exosphere

Troposphere

weather, temp ↓ with height

Stratosphere

ozone layer, temp ↑

Mesosphere

meteors burn, temp ↓

Thermosphere

auroras, temp ↑

Exosphere

merges with space

Earth atmosphere

Strongly oxidizing (O₂ + O₃).

Venus Atmosphere

Weakly oxidizing (CO₂, sulfur).

Mars Atmosphere

Surface oxidizing, not atmosphere

Oxidation

Loss of e⁻ / gain of O = oxygen rich

Reduction

Gain of e⁻ / loss of O = hydrogen rich

Too small, too hot terrestrial atmosphere

H,He escapes

Sources of Terrestrial Water

Volcanic outgassing , Comet and asteroid impacts

Why Earth Has a Stratosphere

O₃ absorbs UV → temperature inversion forms

Venus’ H₂O

Split by UV → H escaped, O bound to rocks.

Mars’ N₂:

Lost to space + trapped in rocks.

Earth’s CO₂

Stored in carbonate rocks and oceans

The Great Oxygenation Event

O₂ reacted with dissolved Fe → banded iron formations, Once iron sinks saturated, O₂ built up in air, Led to mass extinction of anaerobes + formation of ozone layer.

Jupiter’s (and Saturn’s) Magnetic Field

Caused by liquid metallic hydrogen (a fluid phase). 

Uranus & Neptune Magnetic Fields

Generated by ionic “slush” of water, ammonia, methane ices under high P/T.

Jupiter Color

ammonium hydrosulfide & sulfur compounds

Saturn Color

less sulfur, more hazeSaturn’s Smooth Bands

Saturn’s Smooth Bands

Lower mass → weaker convection → less turbulence

Conditions for Prebiotic Life

Liquid solvent, Energy source, Organic chemistry, Stable environment

Europa

Subsurface liquid water, tidal heating, energy from magnetic interactions → promising

Titan

Methane/ethane lakes, thick atmosphere, rich organic chemistry, cryovolcanism → complex prebiotic potential