Solar System — Set 2

Correct Answer: A. Habitable zone around a star

• **Goldilocks Zone** = the habitable zone around a star where conditions are 'just right' for liquid water to exist on a planet's surface. • **1 AU from Sun** — Earth is located within the Sun's Goldilocks Zone, enabling life to thrive. • 💡 Wrong-option analysis: Zone with high gold deposits: completely unrelated to astronomy; Coldest region in space: the opposite of habitable; Zone of asteroid belts: asteroid belt is between Mars and Jupiter, not a habitable zone.

Correct Answer: A. Pluto

• **Pluto** = reclassified as a 'Dwarf Planet' by the International Astronomical Union (IAU) in 2006 because it failed to clear its orbital neighborhood. • **2006 IAU decision** — Pluto is now classified as a Kuiper Belt object; it was the 9th planet before reclassification. • 💡 Wrong-option analysis: Haumea: already classified as dwarf planet, not the one reclassified in news; Eris: discovered in 2005, prompted the debate but Pluto was reclassified; Ceres: reclassified as dwarf planet in the same 2006 decision but was already known as a minor planet.

Correct Answer: B. Nuclear Fusion

• **Nuclear Fusion** = the process in the Sun where hydrogen nuclei combine under extreme heat and pressure to form helium, releasing vast energy. • **15 million °C** — the temperature at the Sun's core where fusion occurs, converting 600 million tonnes of hydrogen per second. • 💡 Wrong-option analysis: Nuclear Fission: splitting of heavy atoms (used in nuclear reactors), not in the Sun; Chemical Combustion: a chemical reaction requiring oxygen; Radioactive Decay: natural disintegration of unstable nuclei, not the Sun's primary energy source.

Correct Answer: D. Mercury

• **Mercury** = the smallest planet in the solar system, also the closest to the Sun with no moons. • **4,879 km diameter** — Mercury's diameter is just 4,879 km, about 38% of Earth's diameter. • 💡 Wrong-option analysis: Mars: second smallest planet; Venus: similar in size to Earth; Earth: 5th largest planet.

Correct Answer: A. Corona

• **Corona** = the outermost layer of the Sun's atmosphere, visible as a pearly white halo during a total solar eclipse. • **1–3 million °C** — the Corona is paradoxically hotter than the Sun's surface (5,500°C), extending millions of km into space. • 💡 Wrong-option analysis: Core: innermost layer where fusion occurs; Chromosphere: the layer just above the photosphere, red in color; Photosphere: the visible surface of the Sun, not the outermost layer.

Correct Answer: D. Earth

• **Earth** = known as the 'Blue Planet' because about 71% of its surface is covered with water, giving it a blue appearance from space. • **71% water coverage** — Earth's oceans cover approximately 361 million square kilometers of its surface. • 💡 Wrong-option analysis: Saturn: known for its rings, appears yellow-brown; Neptune: appears blue due to methane gas, not called 'Blue Planet'; Uranus: appears blue-green, not designated Blue Planet.

Correct Answer: D. Jupiter

• **Ganymede** = the largest moon of Jupiter and the largest moon in the entire solar system, even bigger than Mercury. • **5,268 km diameter** — Ganymede's diameter exceeds that of Mercury (4,879 km) and it is the only moon with its own magnetic field. • 💡 Wrong-option analysis: Saturn: its largest moon is Titan; Neptune: its largest moon is Triton; Uranus: its largest moon is Titania.

Correct Answer: A. Perihelion

• **Perihelion** = the point in a planet's orbit where it is closest to the Sun; Earth reaches perihelion around January 3. • **147 million km** — Earth's distance from the Sun at perihelion, compared to 152 million km at aphelion. • 💡 Wrong-option analysis: Aphelion: the farthest point from the Sun (opposite of perihelion); Perigee: closest point to Earth in Moon's orbit; Apogee: farthest point from Earth in Moon's orbit.

Correct Answer: B. Carbon Dioxide

• **Carbon Dioxide** = makes up about 96% of Venus's atmosphere, creating an extreme greenhouse effect. • **465°C surface temperature** — Venus is the hottest planet due to its CO₂-driven greenhouse effect, despite being farther from the Sun than Mercury. • 💡 Wrong-option analysis: Oxygen: comprises only ~0.003% of Venus's atmosphere; Nitrogen: comprises ~3.5% but is not the majority; Methane: found on gas giants, negligible on Venus.

Correct Answer: A. Uranus

• **Uranus** = spins on its side with an axial tilt of about 98 degrees, making it appear to roll along its orbital path. • **98° axial tilt** — Uranus's extreme tilt is believed to have been caused by a massive collision with an Earth-sized object in its past. • 💡 Wrong-option analysis: Neptune: has a tilt of 28°, similar to Earth; Jupiter: tilt of only 3°; Saturn: tilt of about 27°.