Runaway Greenhouse Effect

• Because Venus’s atmosphere is much deeper and denser than Earth’s, a much smaller fraction of the infrared radiation leaving the planet’s surface escapes into space.

• The result is a much stronger greenhouse effect than on Earth and a correspondingly hotter planet.

• The outgoing infrared radiation is not absorbed at a single point in the atmosphere; instead, absorption occurs at all atmospheric levels.

  • The arrows indicate only that absorption occurs, not that it occurs at one specific level; the arrow thickness is proportional to the amount of radiation moving in and out.

Landing on Venus

(a) The first direct view of the surface of Venus, radioed back to Earth from the Soviet Venera 9 spacecraft, which made a soft landing on the planet in 1975. The amount of sunlight penetrating Venus’s cloud cover is about the same as that reaching Earth’s surface on a heavily overcast day.

(b) Another view of Venus, in true color, from Venera 14. Flat rocks like those visible in part (a) are seen among many smaller rocks and even fine soil on the surface. This landing site is not far from the Venera 9 site shown in (a). The peculiar filtering effects of whatever light does penetrate the clouds make Venus’s air and ground appear peach colored—in reality, they are most likely gray, like rocks on Earth. 

Differentiation

• Earth is not homogeneous; it has a layered structure.

• Density and compositions are different for different layers:

  • CRUST - Low Density

  • MANTLE - Medium Density

  • CORE - High Density

Why?

• Earth was molten at some time.

• Higher-density parts sank to the core

• Lower-density parts displaced toward the surface

• Therefore Earth's central temperature become hot like the surface of the Sun.

What heated the Earth's center?

• Earth grew by capturing material from its surroundings

• This increased its gravitational field and therefore speed of material striking to surface increased

• Therefore generated heat made the Earth molten

  • Earth began to differentiate.

  • As heavy material sank to the center;

  • More gravitational energy released,

➤ which caused interior temperature to increase further.

• Bombardment continued:

➤ a thin layer of surface continue to be molten

Radioactivity

• Heavy elements like Uranium, Thorium and Plutonium release energy as they decay (break up) into lighter elements.

• This energy also heated the Earth

• Released energy from the decay is very small. However:

  • Large amount of these elements stored in Earth.

  • Earth had enough time to accumulate this energy

  • Created energy at interior parts couldn't leak into space because rocky surface was opaque to the heat (rock is a poor conductor)

Earth's Magnetosphere

• It is discovered by artificial satellites in late 1950s

• It is created by the planet's magnetic field.

• Our magnetosphere extends far beyond the atmosphere.

• It will look like a bar magnet when observed close to the Earth.

• The magnetic field lines runs from South to North and they intersect the Earth's surface vertically.

• The poles are roughly aligned with Earth's spin axis.

• The poles are not fixed and they drift with 10 km/year

  • North Pole is at 80 degree North (northern Canada)

  • South Pole is at 60 degree South (off the coast of Antarctica)

Van Allen Belts

• The magnetosphere contains two doughnut-shape zones of high energetic charged particles above the surface

  1. Located about 3 000 km - catching heavier protons

  2. Located about 20 000 km - catching mostly electrons

• They are named as belts because

• • their efficiency are the highest at the equator

  • they completely surround the planet

• The particles in the belts originated from the Sun and they are carried by the solar wind.

• • Neutral particles and EM radiation are unaffected by the Earth's magnetism

  • But charged particles (electrons and protons) are strongly influenced

  • They spiral around the magnetic field lines and they are trapped in the Earth's magnetic field creating the zones (aka. belts).

• Therefore, the belts creates an invisible shield to protect the planet surface from energetic charged particles.

Aurora

The particles that can escape from Van Allen belts penetrates into lower layers of the atmosphere.

• Particles collide with air molecules

• They fall back to their ground states

• Their energy re-emit in visible spectrum; named as Aurora

• This event are observed mostly in higher latitude regions.

• The event can be observed on other planets too.

Shape of Magnetosphere

• It is not symmetric

• It looks like a tear-drop

• Sunlit side is compressed by the solar wind;

• It extends to 10 Earth radii from the Earth; named as magnetopause

The tides

• Ocean level fluctuates in daily base.

• This is due to gravitational influence of the Moon and the Sun on Earth

• This deforms the Earth's surface depending on the distance separating any two objects

  • The Moon's gravitational attraction is greater on the side of Earth that faces the Moon than on the opposite side.

  • Earth becomes slightly elongated with the long axis of the distortion pointing towards the Moon.

  • Earth's oceans undergo the greatest deformation because liquid can most easily move around on Earth.

• • The ocean becomes:

    • a little deeper in some places (along the equator)

    • shallower in others (closer to the poles)

  • Adding the Sun's effect:

    • Sun is farther away but its mass is so much greater.

    • Its tidal influence is about half of Moon's tidal influence

Tidal Force

• Average gravitational interaction determines the object's orbit

• Adding tidal force to the gravitational influence deforms both bodies

• This deformation can be estimated as 1 / r3 

Earth's Rotation

• Earth's spin is slowing due to tidal bulge offset

  • The rate of slow down is 1.5 msec / year

• Therefore the Moon is spiraling slowly away from the Earth by 4 cm / year

• This slow down will stop when the offset becomes zero

  • then Earth's rotation period will become 47 days

  • and the distance to the Moon will become 550 000 km.

Martian Polar Caps

The southern (a) and northern (b) polar caps of Mars are shown to scale in these mosaics of Mariner 9 images. These are the residual caps, seen here during their respective summers half a Martian year apart.

The southern cap is some 350 km across and is made up mostly of frozen carbon dioxide.

The northern cap is about 1000 km across and is composed mostly of water ice. The inset shows greater detail in the southern cap.