Solar System Practice Tests

solar system science for the 2027 Division B season, with the event focus on habitability within and beyond the Solar System.

Event focus 2027 (habitability)

• Division B event; 2027 topic = habitability within and beyond the Solar System
• Know what makes worlds habitable, where livable environments exist in our solar system, and how we find and evaluate exoplanets

Formation and structure

• Nebular hypothesis: solar system formed ~4.6 billion years ago from a collapsing molecular cloud; sun ignited via fusion; planets accreted from the disk
• Frost line: boundary beyond which ices could condense; inside = rocky terrestrial planets; outside = gas/ice giants
• Order: Mercury, Venus, Earth, Mars (terrestrial) | Jupiter, Saturn (gas giants), Uranus, Neptune (ice giants)
• Asteroid belt between Mars and Jupiter; Kuiper Belt beyond Neptune (Pluto, other dwarf planets); Oort Cloud = distant comet reservoir
• Age dating: crater counts (more craters = older surface), radiometric dating of meteorites

Key planet facts

• Mercury: smallest, no atmosphere, extreme temperature swings, fastest orbit
• Venus: runaway greenhouse, hottest surface (~465 °C), sulfuric acid clouds, rotates backward slowly
• Earth: liquid surface water, plate tectonics, strong magnetic field, life
• Mars: evidence of ancient water (valleys, minerals), thin CO₂ atmosphere, Olympus Mons (largest volcano), Valles Marineris
• Jupiter: largest; Great Red Spot; Galilean moons; strong radiation
• Saturn: ring system; density less than water (would float)
• Uranus: rotates on its side (98° axial tilt); Neptune: fastest winds

Moons and ocean worlds (habitability focus)

• Io: most volcanically active body (tidal heating)
• Europa: subsurface saltwater ocean under ice = prime habitability candidate
• Ganymede: largest moon in the solar system, own magnetic field
• Callisto: heavily cratered, possible subsurface ocean
• Titan (Saturn): thick N₂ atmosphere, methane/ethane lakes and rain (cryovolcanism)
• Enceladus (Saturn): south-polar geysers vent ocean material into space (Cassini flew through them)
• Triton (Neptune): retrograde orbit (captured Kuiper Belt object), nitrogen geysers
• Our Moon: formed by giant impact; phases, tides, libration

Habitability criteria

• Habitable zone (Goldilocks zone): range of distances where liquid water is stable on the surface; depends on star luminosity
• Requirements for life as we know it: liquid water, energy source, CHNOPS elements, stable environment
• Life can exist WITHOUT sunlight (chemosynthesis at hydrothermal vents) - widens habitability beyond the zone
• Extremophiles on Earth (acid, radiation, heat, salt) set the bounds for what counts as extreme
• Planetary protections: magnetic field deflects solar wind (Mars lost its atmosphere), atmosphere regulates temperature, large moon stabilizes axial tilt
• Greenhouse effect: keeps Earth ~33 °C warmer than it would otherwise be; too much = Venus

Exoplanets (beyond the solar system)

• Detection methods: transit (dip in starlight - Kepler/TESS), radial velocity (Doppler wobble), direct imaging, microlensing
• Over 5,000 confirmed; small rocky worlds in habitable zones are known (e.g., TRAPPIST-1 system, Proxima b)
• Biosignatures being sought: oxygen + methane together, water vapor, seasonal changes
• SETI: radio/optical searches; Drake Equation organizes factors estimating communicating civilizations

Missions to know

• Cassini-Huygens (Saturn/Titan), Galileo and Europa Clipper (Jupiter system), Juno (Jupiter), Voyager 1/2 (interstellar space), Perseverance + Ingenuity (Mars sample caching), New Horizons (Pluto/Kuiper Belt), OSIRIS-REx (asteroid sample return), DART (asteroid deflection test), JWST (atmospheres of exoplanets)

Small bodies

• Asteroids: rocky/metallic; types (C, S, M); belt + near-Earth objects
• Comets: dirty snowballs (ice + dust); coma and tails form near the sun; ion tail points AWAY from the sun (solar wind) regardless of direction of motion; dust tail curves along orbit
• Meteoroid (in space) → meteor (streak in atmosphere) → meteorite (lands)
• Meteor showers: Earth crossing comet debris trails (Perseids, Geminids)

Common mistakes

• Pointing comet tails toward (or trailing behind) the comet - ion tails point away from the SUN
• Calling Venus habitable because it is "Earth's twin" (greenhouse makes it lethal)
• Forgetting moons count as habitability candidates (Europa, Enceladus, Titan) even outside the habitable zone
• Mixing up meteor/meteorite/meteoroid terminology
• Assuming the habitable zone guarantees life (Mars is in ours; Venus was too)