Correct: C. Saturn

Saturn is the planet most famous for its spectacular and complex ring system. While the other three gas giant planets (Jupiter, Uranus, and Neptune) also have rings, Saturn's are by far the largest, brightest, and most visible from Earth. These rings are made mostly of billions of pieces of water ice, along with some rocky debris and dust, ranging in size from tiny grains to pieces as large as mountains.

Correct: A. Venus

Venus is the hottest planet in our solar system, with surface temperatures reaching a scorching 465C (900F)-hot enough to melt lead. Even though Mercury is closer to the Sun, Venus is hotter because it has a thick, dense atmosphere made mostly of carbon dioxide. This atmosphere acts like a heavy blanket, trapping the Sun's heat in a "runaway greenhouse effect." Venus is also completely covered by thick clouds of sulfuric acid.

Correct: B. Jupiter

Jupiter has the maximum gravity of all the planets in our solar system because it is by far the most massive. The surface gravity on Jupiter is about 24.79 m/s, which is more than 2.4 times stronger than Earth's gravity 9.8 m/s. If you could stand on the "surface" of Jupiter (which is actually a gas giant), you would feel so heavy that you would find it nearly impossible to lift your own feet.

Correct: A. Plasma

Plasma is the primary state of matter found in stars, including our Sun. It is a highly energized gas in which the atoms have been stripped of their electrons, resulting in a soup of positively charged ions and free electrons. Because it contains charged particles, plasma is highly conductive and responds strongly to magnetic fields.

Correct: A. Venus

Venus is the hottest planet in the Solar System, with surface temperatures reaching about 465C 900F. This is due to its incredibly thick atmosphere of carbon dioxide, which creates a runaway greenhouse effect.

Correct: A. Jupiter

Jupiter is famous for its Great Red Spot, a massive, persistent high-pressure storm that has been raging for at least 150 years (and possibly much longer). The storm is large enough to contain the entire Earth.

Correct: B. A measure of distance

A Light Year is the distance that light travels in a vacuum in one Julian year-approximately 5.88 trillion miles (9.46 trillion km). It is a unit of distance used to measure the vast gaps between stars and galaxies.

Correct: C. Titan

Titan is the largest moon of Saturn and the second-largest moon in the Solar System. It is the only moon known to have a dense atmosphere and the only place besides Earth where clear evidence of stable bodies of surface liquid has been found (though it's liquid methane and ethane, not water).

Correct: C. Ganymede

Ganymede, a moon of Jupiter, is the largest moon in the Solar System. It is even larger than the planet Mercury, though it has less mass. It is the only moon known to have its own magnetic field.

Correct: D. Andromeda

The Andromeda Galaxy is the closest major galaxy to our Milky Way. It is a spiral galaxy located about 2.5 million light-years from Earth.

Correct: A. A star explosion

A supernova is a powerful and luminous stellar explosion that occurs during the last evolutionary stages of a massive star's life. It can briefly outshine an entire galaxy and radiates as much energy as the Sun is expected to emit over its entire lifespan.

Correct: B. Hydrogen

The Sun is composed mostly of the chemical elements Hydrogen (about 73% of its mass) and Helium (about 25%. The rest is made up of heavier elements like oxygen, carbon, and iron.

Correct: A. Neptune

Neptune is often called the "Blue Giant" (or an "Ice Giant") because of its deep blue color and its massive size (it is the 4th largest planet). Its blue color comes from methane in its atmosphere, which absorbs red light and reflects blue.

Correct: A. Neptune

The Great Dark Spot was a massive storm system on the planet Neptune, similar to Jupiter's Great Red Spot. It was first observed by the Voyager 2 spacecraft in 1989.

Correct: B. Olympus Mons

Olympus Mons on Mars is the largest volcano in the Solar System. It is a shield volcano that stands about 13.6 miles (22 km) high, making it nearly three times the height of Mount Everest.

Correct: C. Exoplanet

An exoplanet (or extrasolar planet) is a planet that orbits a star outside our Solar System. Since the first discovery in 1992, thousands of exoplanets have been confirmed using telescopes like Kepler and TESS.

Correct: B. Copernicus

Nicolaus Copernicus, a Renaissance-era polymath, proposed the heliocentric model, which placed the Sun at the center of the universe rather than the Earth. This was a revolutionary idea that challenged the long-held "geocentric" view.

Correct: D. A cloud of gas/dust

A nebula is a giant cloud of dust and gas in space. Some nebulae are "stellar nurseries" where new stars are being born, while others are the remains of dying stars.

Correct: B. Ursa Major

Ursa Major (the "Great Bear") is the constellation that contains the famous group of seven stars known as the Big Dipper. The Big Dipper is an "asterism," not a constellation itself.

Correct: A. Titan

Titan is the largest moon of Saturn and the second-largest moon in the entire solar system. It is unique because it is the only moon known to have a dense atmosphere and the only place other than Earth where stable bodies of liquid surface have been found. However, its lakes and rivers are made of liquid methane and ethane rather than water.

Correct: C. Hydrogen

Hydrogen is the main gas in the Sun, making up about 73% of its total mass. The Sun produces energy through nuclear fusion, where hydrogen atoms are crushed together to form helium. This process releases a massive amount of light and heat that sustains life on Earth.

Correct: C. Saturn

Saturn is the second-largest planet in our solar system, after Jupiter. It is a gas giant made mostly of hydrogen and helium and is most famous for its spectacular and complex ring system. Saturn is so less dense than water that it would actually float if you could find an ocean big enough to hold it.

Correct: D. A massive storm

The Great Red Spot on Jupiter is a massive storm that has been raging for at least 400 years. It is an anticyclonic storm, meaning it rotates counterclockwise, and is located in Jupiter's southern hemisphere. The storm is so large that it could swallow Earth several times over-its width has varied but is typically about 16,000 kilometers (10,000 miles).

Correct: D. Ganymede

Ganymede is the largest moon in the entire solar system, orbiting Jupiter. It has a diameter of 5,268 kilometers (3,273 miles), making it larger than the planet Mercury and about three-quarters the size of Mars. Ganymede is the only moon known to have its own magnetic field and likely has a subsurface ocean beneath its icy crust.

Correct: D. A star

A supernova is the explosion of a star at the end of its life cycle. It is one of the most energetic events in the universe, briefly outshining an entire galaxy. Supernovae occur either when a massive star runs out of nuclear fuel and its core collapses under gravity, or when a white dwarf accretes enough material from a companion star to trigger runaway nuclear fusion.

Correct: B. Spiral

The Milky Way is a spiral galaxy, specifically a barred spiral galaxy with a central bar-shaped structure composed of stars. Spiral galaxies are characterized by their flat, rotating disks with spiral arms that wind outward from the center. The Milky Way has four major spiral arms and is about 100,000 light-years in diameter.

Correct: A. Copernicus

Nicolaus Copernicus proposed that the Earth revolves around the Sun in his work "De revolutionibus orbium coelestium" (On the Revolutions of the Celestial Spheres), published in 1543. This heliocentric model challenged the long-held geocentric view that placed Earth at the center of the universe. Copernicus's theory laid the foundation for modern astronomy.

Correct: B. Hydrogen

The Sun is mostly made of hydrogen, which accounts for about 73% of its mass, followed by helium at about 25%. All other elements-including oxygen, carbon, neon, and iron-make up less than 2% of the Sun's mass. In its core, nuclear fusion converts hydrogen into helium at temperatures of about 15 million degrees Celsius, releasing enormous amounts of energy.

Correct: D. A region of infinite gravity

A black hole is a region of spacetime where gravity is so strong that nothing-not even light-can escape. It forms when a massive star collapses under its own gravity at the end of its life. The boundary of a black hole is called the event horizon, and at its center lies a singularity, a point of infinite density where our understanding of physics breaks down.

Correct: D. Mars

Mars has the largest volcano in the solar system: Olympus Mons. It stands about 22 kilometers (13.6 miles) high, nearly three times taller than Mount Everest, and spans about 600 kilometers (370 miles) in diameter-roughly the size of Arizona. Olympus Mons is a shield volcano, built up by countless lava flows over billions of years.

Correct: C. Meteorite

A meteorite is a meteor that survives its passage through Earth's atmosphere and hits the surface. Before entering the atmosphere, it is called a meteoroid. While passing through the atmosphere, it becomes a meteor (or "shooting star") as friction with air molecules heats it to incandescence. If any part survives to reach the ground, it becomes a meteorite.

Correct: A. Neptune

Neptune takes the longest to orbit the Sun of any planet in the solar system, with an orbital period of about 165 Earth years. This means that since its discovery in 1846, Neptune has completed only one orbit (in 2011). Its average distance from the Sun is about 4.5 billion kilometers (2.8 billion miles).

Correct: C. Yuri Gagarin

Yuri Gagarin was the first human in space, launched on April 12, 1961, aboard the Vostok 1 spacecraft. He completed one orbit of Earth in 108 minutes, reaching an altitude of 327 kilometers (203 miles). Gagarin became an international hero and was awarded the title Hero of the Soviet Union.