2 solar system energy

THE EARTH IN SPACE

Overview

  • Key themes covered in this section include:

    • Solar System

    • Various celestial bodies

    • Earth and the Moon

    • The Sun

    • Energy cycles.

Learning Objectives

By the end of this section, students should be able to:

  • Describe the origin of the Solar System.

  • List and describe the main groups of objects in the Solar System.

  • Apply scientific laws to the motion of these celestial objects.

  • Explain the flow of energy from the Sun to the Earth's surface, along with the energy cycle within the Earth system.

1. Solar System

  • Comprised of a single star, the Sun.

  • Contains numerous objects that orbit the Sun, including:

    • Planets

    • Dwarf planets and minor planets

    • Asteroids and meteoroids

    • Comets

    • Satellites (moons) orbiting various planets.

2. Origin of the Solar System

  • Estimated to have formed approximately 4.567 billion years ago (4.567 x 10^9 years), identifiable by the age of the oldest solid meteorite particles.

  • This age is represented in two different notations:

    • Mega-annum (Ma)

    • Giga-annum (Ga)

  • Formation process:

    • The entire Solar System condensed from a vast gaseous nebula under gravitational attraction.

    • The central dense body within this nebula formed the Sun.

    • Remaining dust and gas created a disk, which went on to condense into planets and other bodies.

3. Current Formation of Star Systems

  • Formation of other star systems is ongoing, with some nebulae resolvable, thought to contain developing planets. Examples:

    • HL Tauri protoplanetary disc shows potential planet formation locations.

    • AB Aurigae disc exhibits a distinctive twist indicating planet formation, akin to Neptune's distance from the Sun.

4. Gravity in the Solar System

  • All celestial objects in the Solar System maintain their orbits due to gravitational forces.

  • Orbits arise from a balance between gravitational pull and the momentum of the objects:

    • Without external force, objects would continue moving in a straight line.

  • The gravitational force varies with distance, described mathematically by:

    • F∝1d2F \propto \frac{1}{d^2}, where $d$ is the distance.

  • Orbits are typically elliptical, as per Kepler's laws.

5. Shape of Orbits

  • Kepler’s First Law states that orbits are elliptical, with the Sun positioned at one focus of the ellipse.

  • The eccentricity of Earth's orbit is about 0.0167, indicating that the distance from Earth to the Sun varies by approximately 1.67%.

  • Orbital speed varies; planets move faster when closer to the Sun due to gravitational forces. Kepler’s Second Law states that equal areas are swept out in equal times.

6. Orbital Period

  • Orbital period ($p$) is related to average distance from the Sun ($d$) through:

    • p2∝d3p^2 \propto d^3 (Kepler's Third Law).

  • This indicates that planets further from the Sun take significantly longer to complete their orbits.

7. Temperature Variation in the Solar Nebula

  • The variation in temperature during planet formation influenced the distribution of elements among planets and other objects:

    • Volatile elements, such as hydrogen, are more prevalent in the outer planets.

8. Components of the Solar System

  • Small bodies include:

    • Comets: Small bodies on highly elliptical orbits, composition similar to jovian planets; they may represent samples of the early solar system.

    • Dwarf Planets, Asteroids, and Meteoroids:

    • Small bodies with diverse compositions (e.g., rock and metallic iron).

    • Located primarily between Mars and Jupiter, as well as elsewhere in the Solar System.

    • Asteroids and meteoroids, when entering Earth's atmosphere, become meteors (shooting stars). If they reach the ground, they are termed meteorites.

9. Types of Planets

  • Jovian Planets (Outer Planets): Include Jupiter, Saturn, Uranus, and Neptune. Common attributes include:

    • Thick hydrogen-rich atmospheres.

    • Possible liquid hydrogen interiors and denser rocky cores.

  • Terrestrial Planets (Inner Planets): Include Mercury, Venus, Earth, and Mars. Common attributes include:

    • Predominantly metallic cores composed mostly of iron.

    • Rocky mantles rich in silicon, oxygen, magnesium, and iron.

    • Thin rocky crusts that vary significantly due to the geological processes affecting each planet.

10. Satellites

  • Satellites, generally smaller than their parent planets, orbit around them:

    • The Moon, Earth’s satellite, is comparatively large and similar in structure to terrestrial planets.

    • The Moon's gravitational influence generates tides on Earth.

11. Earth's Axis and Seasons

  • The tilt of the Earth's axis relative to its orbit produces seasonal changes. Important points include:

    • Energy flux to the Earth's surface varies based on the tilt and season.

    • Tilt is currently approximately 23.5°, varying between 21.5° and 24.5° over a 41,000-year cycle.

12. Precession and Eccentricity of Orbits

  • Precession involves the tilt direction of the Earth's axis and rotates relative to its elliptical orbit over a period of 23,000 years.

  • Eccentricity changes over a period of 100,000 years, varying from ~⅓% to ~6%, with Earth's orbit currently at approximately 1.67%.

13. Tides

  • The gravitational pull of the Moon, along with the Sun, generates tides on Earth, influenced by their orbital mechanics.

14. The Sun

  • The Sun is characterized as a standard star with:

    • Radius of approximately 700,000 km, about 109 times the diameter of Earth.

    • Mass of around 10^30 kg, 300,000 times that of Earth.

    • Total energy output of 3.8 x 10^26 W (Watts).

15. Electromagnetic Radiation

  • Electromagnetic radiation is depicted as waves, where the relationship between wavelength ($\lambda$) and frequency ($f$) is governed by:

    • c=f×λc = f \times \lambda or λ=cf\lambda = \frac{c}{f}, where $c$ is the speed of light (approximately 3×108m/s3 \times 10^8 m/s).

16. Solar Spectrum

  • The solar spectrum contains a range of wavelengths:

    • Most solar energy is output within wavelengths of 10^-5 to 10^-7 m, encompassing various forms of electromagnetic radiation:

    • Including but not limited to radio waves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

17. Variation of Solar Behavior

  • Solar behavior exhibits cyclical variations such as sunspots, which are dark patches signaling turbulence within the Sun and influencing magnetic storms on Earth. The sunspot cycle is approximately a 11-year period.

18. Sun's Energy Reach to Earth

  • Of the Sun's total energy output of 3.8 x 10^26 W, 1.74 x 10^17 W (or 174,000 TW) reaches Earth, where the sunlight at the top of the atmosphere averages about 1366 W/m^2.

19. Energy Flux on Earth

  • The energy flux on Earth is maximized when the Sun is directly overhead, and it diminishes elsewhere due to the energy being spread over a larger surface area.

  • The flow of solar energy creates variations in energy availability corresponding to seasonal changes.

20. Earth's Energy Cycle

  • Defined in terms of energy units:

    • Energy is measured in Joules (J), with common power units:

    • 1 KiloWatt (kW): 1000 W

    • 1 MegaWatt (MW): 1 million W

    • 1 GigaWatt (GW): 1 billion W

    • 1 TeraWatt (TW): 1 trillion W

  • Solar energy input is roughly 174,000 TW, with other energy contributions if categorized as:

    • Tides 3 TW

    • Geothermal energy 47 TW

    • Volcanoes 0.3 TW

    • Heat flow 36 TW.

  • Reflectivity of the Earth leads to approximately 52,000 TW being reflected back into space, signifying the Earth's albedo is around 30%.

21. Energy Transformation and Storage

  • Solar energy is transformed and stored within different systems:

    • Converted to heat: Approximately 81,000 TW heats the atmosphere.

    • Evaporation and melting contribute about 40,000 TW.

22. Human Impact on Energy Cycle

  • Human activities contribute to the energy cycle, particularly through extraction of fossil fuels, currently estimated at 16 TW.

Conclusion

  • The intertwined and complex dynamics within the Solar System and Earth's energy cycle underscore the essential principles of physics, geology, and environmental science that govern planetary behavior, climate patterns, and forces at play within our cosmos.