The Encyclopedia
of the Unknown.
Explore life beyond Earth, unexplained encounters and ancient worlds. Discover what we know, what we claim, and what the evidence actually tells us.
Start exploring
Browse the encyclopedia
Europa: NASA/JPL/University of Arizona · Galileo composite, enhanced color. Labels describe specific claims.
Recently updated entries
Versioned editorial historyEnceladus
An ocean beneath the ice. Cassini revealed a world with liquid water, organic chemistry and energy sources — compelling conditions for research into habitability.
Europa
Jupiter’s icy moon is a major target in the search for environments that could support life. Evidence for an ocean does not establish that it is inhabited.
Cassini mission
The spacecraft investigation of Saturn that transformed research on Enceladus and other icy worlds.
The habitable zone
A useful astronomical starting point: orbital distances at which surface liquid water might be possible under suitable conditions.
Biosignatures
Potential indicators of biological processes require environmental context and careful testing of nonbiological explanations.
Ancient worlds, closer scrutiny
Explore ancient civilizations
Extraordinary monuments.
Human histories.
Place the pyramids in their archaeological context. Follow the records behind the wonder.
Simon Matzinger / Wikimedia Commons · CC BY 4.0 · Cropped for display.
Knowledge is connected.
Open the knowledge graphFurther reporting, in context.
AliensPortalCurrent reporting complements the durable encyclopedia. These are source-linked reports, with their original editorial provenance.
Behind every entry, a source.
Visit the document archiveNASA’s 2023 UAP independent study
A methodological report recommending how data, calibrated observations and scientific practice can improve the study of UAP.
ODNI’s 2021 preliminary UAP assessment
An official preliminary assessment organized around reports, data limitations and possible explanatory categories.