Mondo Knows

Mondo Knows Facts

1,090 Interesting Facts, Each One Checked and Sourced

A searchable library of short, surprising facts about space, animals, the human body, geography, history, science, technology, food and the world around you. Each fact is written in a paragraph rather than a headline, cites where it came from, and sends you somewhere useful next: a quiz on the same subject, a game, a puzzle, or the tool that works the idea out.

Fact of the day ยท Animals

Sea cucumbers expel internal organs through their anus to deter predators

A threatened sea cucumber ejects sticky toxic gut filaments.

When attacked by crabs or fish, sea cucumbers violently contract body wall muscles to expel Cuverian tubules and internal organs out through their anus. The sticky white filaments tangle predators, and the sea cucumber regrows its digestive tract within a few weeks.

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1090 facts

SpaceA day on Venus is longer than its yearVenus turns so slowly that its day outlasts its trip around the SunNASA ScienceSpaceVenus is the hottest planet in the solar systemThick greenhouse gases trap heat to make Venus hotter than MercuryNASA ScienceSpaceThe Moon is slowly drifting away from EarthLuni-solar tidal friction pushes the Moon outward by roughly four centimetres each yearNASA ScienceSpaceJupiter has the shortest day of any solar system planetThe gas giant completes a full rotation in under ten hoursNASA ScienceSpaceThe Sun holds nearly all the mass in the solar systemOver 99 percent of all matter in the solar system resides inside the SunNASA ScienceSpaceMars hosts the largest volcano in the solar systemOlympus Mons on Mars stands about two and a half times taller than Mount EverestESASpaceSaturn rings consist almost entirely of water iceBillions of icy fragments range from microscopic specks to house-sized bouldersNASA ScienceSpaceA single teaspoon of a neutron star weighs billions of tonnesSuper-dense collapsed stellar cores pack enormous mass into tiny spheresESASpaceThe Milky Way will collide with the Andromeda GalaxyIn four billion years our home galaxy will merge with its nearest large neighbourEncyclopaedia BritannicaSpaceVoyager 1 is the farthest human object from EarthLaunched in 1977 the robotic probe is now travelling through interstellar spaceNASA ScienceSpaceMercury experiences extreme surface temperature swingsWithout a thick atmosphere Mercury swings from scorching days to freezing nightsNASA ScienceSpaceUranus rotates almost entirely on its sideAn axial tilt of 98 degrees causes extreme seasons lasting over 20 yearsESASpaceNeptune features the fastest winds in the solar systemSupersonic storms on Neptune reach speeds over two thousand kilometres per hourNASA ScienceSpacePluto features a giant heart-shaped nitrogen glacierSputnik Planitia is a vast plain of frozen nitrogen ice on the dwarf planetNASA ScienceSpaceSaturn moon Titan has lakes and seas of liquid methaneTitan is the only world besides Earth known to host stable liquid on its surfaceESASpaceEnceladus erupts giant geysers of water ice into spaceA global subsurface ocean vents through cracks near the south pole of Saturn moonNASA ScienceSpaceEuropa may hold twice as much water as all Earth oceans combinedA deep saltwater ocean sits concealed beneath the icy crust of Jupiter moonNASA ScienceSpaceGanymede is the largest moon in the solar systemJupiter giant satellite is larger than both Mercury and PlutoESASpaceIo is the most volcanically active body in the solar systemTidal forces from Jupiter squeeze Io to drive hundreds of lava eruptionsNASA ScienceSpaceSunlight takes roughly eight minutes to reach EarthLight travels 150 million kilometres across space at 300,000 kilometres per secondNASA ScienceSpaceSpace is completely silent because sound needs a medium to travelWithout air or gas particles sound waves cannot propagate through the cosmic vacuumNASA ScienceSpaceA full NASA spacesuit costs millions of dollars to produceCustom life support systems turn every spacesuit into a tiny personal spacecraftNASA ScienceSpaceFootprints left on the Moon will last for millions of yearsWithout wind or water erosion Apollo astronaut tracks remain undisturbedSmithsonian InstitutionSpaceSaturn is the only solar system planet less dense than waterThe massive gas giant would float if placed in a vast oceanic basinNASA Science

Facts that can change over time are reviewed and updated. Sources are named on every fact so you can check the working yourself. If something here looks wrong, Mondo would rather know than be confidently incorrect.

Questions people ask

Where do the 1,090 facts come from?
Every fact names its source, usually NASA, the ESA, a museum, a university or a peer-reviewed paper, and links to it. They are grouped into 13 categories including space, animals, the human body, history and science.
How do I use the fact library?
Search by word, filter by category, or use the surprise button for a random fact. Each fact also links onward to a quiz, game or calculator on the same subject, so one fact can become a five-minute detour.
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The wording is ours, so quote it with a credit and a link. Photographs are licensed separately: each carries its own credit and licence, and only public-domain or Creative Commons images are used.