Twenty space questions, from the planets and the Moon to black holes and the people who flew there, each with three answers and the fact behind the right one. Play them as a quiz, or read the list with the answers marked.
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The same questions as the quiz, right answer highlighted and the fact under it. Print the page for a quiz night: the print layout keeps the questions and answers only. The Space topic in Lock&Learn holds 127 facts in all.
On which planets does it rain diamonds?
It rains diamonds on Neptune and Uranus. Deep inside the ice giants, crushing pressure squeezes carbon out of methane and compresses it into diamonds that sink toward the core.
Source: NASA
Where does a day outlast the entire year?
A day on Venus lasts longer than its year. Venus takes 243 Earth days to spin once on its axis, but only 225 to orbit the Sun, so its day is longer than its year.
Source: NASA
How much of the Solar System is just the Sun?
The Sun is 99.8% of the Solar System's mass. Everything else (all planets, moons, asteroids and comets combined) adds up to about 0.2% of the Solar System's total mass.
Source: NASA
What would a teaspoon of a dead star weigh?
A teaspoon of neutron star weighs billions of tons. Neutron stars pack more mass than the Sun into a sphere the size of a city, making their matter almost unimaginably dense.
Source: NASA
More stars in the sky, or sand grains on Earth?
There are more stars than grains of sand on all Earth's beaches. Astronomers estimate the observable universe holds roughly a septillion stars, far outnumbering every grain of sand on every beach on Earth.
Source: NASA
Where is the tallest volcano we know of?
Mars has a volcano two and a half times the height of Everest. Olympus Mons rises about 22 km above the Martian plains. It's the largest volcano in the Solar System, roughly the size of France at its base.
Source: NASA
What does space smell like?
Astronauts say space smells like seared steak and hot metal. The scent clings to suits and tools after spacewalks. Astronauts describe it as burnt metal, gunpowder, or seared steak.
Source: NASA astronaut reports
How many Earths fit inside the Sun?
About 1.3 million Earths could fit inside the Sun. The Sun's volume is so vast that if it were hollow, you could pour in over a million copies of our planet.
Source: NASA
How long will the Apollo footprints survive?
Footprints on the Moon could last millions of years. With no wind, water or weather to erase them, the Apollo astronauts' bootprints may outlive most things humans have ever built.
Source: NASA
How many sunrises can you watch in one day?
Astronauts on the ISS see 16 sunrises every day. The International Space Station orbits Earth at about 28,000 km/h, circling the planet once every 90 minutes.
Source: NASA
How big can a storm get?
Jupiter's Great Red Spot is a storm bigger than Earth. The giant storm is about 1.3 times the width of Earth, wide enough to swallow our planet, though it has been slowly shrinking for over a century.
Source: NASA
Which planet could float on water?
Saturn would float in a big enough bathtub. Saturn is mostly gas: its average density is lower than water's, the only planet in the Solar System that light.
Source: NASA
How old is the sunlight hitting you right now?
Sunlight takes 8 minutes and 20 seconds to reach you. Light crosses the 150 million km from the Sun to Earth in just over eight minutes. You always see the Sun as it was, not as it is.
Source: NASA
Where would you age four times faster?
A year on Mercury is just 88 days long. Mercury races around the Sun so fast that four of its years fit into one of ours.
Source: NASA
What might one day collide with the Milky Way?
The Milky Way and Andromeda may collide one day. Andromeda is approaching at about 400,000 km/h. Long thought certain in around 4.5 billion years, a 2025 study now puts the odds of a merger closer to 50-50.
Source: Nature Astronomy (2025)
How can two parts of the same planet be different ages?
Earth's core is about 2.5 years younger than its surface. Gravity slows time, so the intense pull at Earth's centre has let the core age a touch slower than the crust across 4.5 billion years.
Source: Wikipedia
What bizarre shape might the newborn Earth have taken?
Earth may once have been a doughnut-shaped cloud of vapour. After a giant collision, Earth may have briefly become a synestia: a spinning, doughnut-shaped cloud of vaporised rock, before settling into a sphere.
Source: Wikipedia
What could you do on Titan that's impossible on Earth?
You could fly on Titan by flapping artificial wings. Saturn's moon has air thicker than ours and gravity a seventh of Earth's, so with wings strapped on, a human could genuinely flap up into the sky.
Source: NASA
What did astronomers try to scrub away before realising it was the Big Bang's echo?
Pigeon droppings were once blamed for the Big Bang's echo. In 1964 two astronomers chasing a strange hiss scrubbed pigeon mess off their antenna before realising the noise was radiation left over from the Big Bang.
Source: Wikipedia
Where did the gold on Earth actually come from?
Much of the universe's gold comes from colliding stars. Gold and platinum are forged when two neutron stars smash together and fling out neutron-rich matter, not in the everyday fusion of ordinary stars.
Source: Wikipedia
This page has 20, each with three answers and the fact that settles it. They are the first 20 of the 127 facts in the Space topic of Lock&Learn, which holds the rest.
Yes. Read them out, print the page (the right answers are marked) or play the quiz on a shared screen. Each question has one right answer and two plausible wrong ones, and the fact under it gives you something to say after the reveal. Please do not republish the questions elsewhere.
Every fact names its source under the answer, from space agencies and museums to encyclopedias and published research. Lock&Learn writes each one as a teaser question with three answers, and the fact that settles it.
Install Lock&Learn, then touch and hold your Lock Screen, tap Customize, tap the widget area and choose Lock&Learn. A question waits on every screen-wake; you guess, tap, and reveal the verified fact behind the answer. Pick the topics you like and the widget rotates through them.
Yes. Lock&Learn is free on iOS: every topic opens with a free preview and another question unlocks daily. Lock&Learn+ is an optional upgrade that opens every topic in full.