The Solar System: Properties, Origin Hypotheses, and Recent Discoveries

32 question-and-answer flashcards covering Solar System structure, elemental composition, origin hypotheses, the protoplanet model, and recent space-mission discoveries.

What celestial objects make up the Solar System?

The Sun, eight planets, dwarf planets (e.g., Pluto), natural satellites, asteroids, comets, Kuiper-belt objects, and interplanetary dust.

In which galaxy and galactic structure is the Solar System located?

The Milky Way Galaxy, specifically the Orion arm of its spiral structure.

Approximately how wide is the Milky Way Galaxy?

About 100,000 light-years across.

About how long does the Solar System take to orbit the Milky Way’s center?

Roughly 240 million years.

Where is most of the Solar System’s mass concentrated, and where is most of its angular momentum found?

Mass is concentrated in the Sun, while angular momentum is mainly held by the outer planets.

What is the general shape and plane of planetary orbits in the Solar System?

Planetary orbits are nearly elliptical and lie in almost the same plane.

How does a planet’s orbital period relate to its distance from the Sun?

Orbital period increases with increasing distance; inner planets move faster, outer planets slower.

What orderly spacing property is observed among the planets?

Planets are located at regular intervals from the Sun.

In which rotational direction do most planets spin?

Most planets rotate prograde (same direction as their revolution).

List four key characteristics of the inner terrestrial planets.

Made of high-melting-point materials (silicates, Fe, Ni); rotate more slowly; have thin or no atmospheres; high densities and low volatile content.

List four key characteristics of the outer gas-giant planets.

Larger size, rapid rotation, thick H-He-rich atmospheres, low densities with fluid interiors containing ices (H₂O, NH₃, CH₄).

Which planet’s orbital precession cannot be fully explained by Newtonian mechanics and led to relativity tests?

Mercury.

Why does Earth retain little hydrogen and helium compared with the Sun?

Earth’s gravity is too weak to retain these light gases, unlike the Sun and large planets.

What does the presence of heavy elements like uranium on Earth imply about the Solar System’s origin?

The material likely came from a supernova; the Sun is a second-generation star formed from recycled matter.

What is the basic idea of the Nebular Hypothesis?

A rotating interstellar nebula contracts, the center forms the Sun, and the surrounding disc forms the planets.

What major problem does the Nebular Hypothesis face?

It fails to explain the present distribution of angular momentum between Sun and planets.

What did Buffon’s 1749 encounter hypothesis propose?

A Sun-comet collision ejected matter that condensed into planets.

Name two strengths of encounter hypotheses regarding planetary properties.

They explain (1) common direction of planetary rotation and (2) higher density of inner planets.

What was James Jeans’ 1917 suggestion about Solar System formation?

A near collision between the Sun and another star pulled off solar material that condensed into planets.

What is the Chamberlain–Moulton planetesimal hypothesis?

A massive star’s near pass drew filaments from the Sun; these cooled into planetesimals that accreted into protoplanets.

Summarize Otto Schmidt’s accretion theory.

The Sun moved through a dense interstellar cloud, capturing a dusty envelope that later formed planets, but planet-formation timescales exceed Solar System age.

What distinguishes Woolfson’s capture theory from earlier encounter ideas?

The Sun strips a filament from a proto-star; collisions close to the Sun create terrestrial planets, condensations farther out create gas giants—yielding different ages for Sun and planets.

Outline the key steps of the Protoplanet Hypothesis.

4.6 Ga gas-dust cloud contracts; central mass forms proto-Sun; disc material forms planetesimals and proto-planets via accretion; collisions shape planets and moons; solar wind blows volatiles outward, producing present Solar System.

According to the Protoplanet Hypothesis, how did Earth’s Moon form?

A giant impact ejected mantle material that coalesced into the Moon, matching lunar–mantle compositions.

What role did early solar wind play in planetary composition?

It swept hydrogen, helium, and other volatiles from the inner Solar System toward the outer regions, aiding gas-giant formation.

Why are meteorites crucial to understanding Solar System origins?

Their constituents have changed little since formation, preserving early Solar System chemistry and supporting current theories.

Which mission achieved the first successful Mars surface operations, and when?

NASA’s Viking landers, 1975.

What recent evidence suggests liquid water activity on Mars?

High-resolution images showing seasonal dark streaks interpreted as briny water flows.

What was the primary goal of ESA’s Rosetta mission, and what did it find about comet water?

To study comet 67P/Churyumov–Gerasimenko; it found cometary water’s isotopic composition differs from Earth’s water.

When did NASA’s New Horizons fly by Pluto, and what surprising surface feature was observed?

14 July 2015; crater-free plains indicating geologic activity within the last ~100 million years.

What three learning competencies are targeted in this Earth & Life Science module?

(1) Identify large- and small-scale Solar System properties, (2) discuss origin hypotheses, and (3) become familiar with recent Solar System discoveries.

What internal layering resulted from Earth differentiation?

Crust, mantle, and core, each with distinct compositions.