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Dactyl
Details
Dactyl is the tiny moon of the main-belt asteroid 243 Ida and the first asteroid moon ever discovered. Galileo photographed it during the 1993 Ida flyby, settling a long-running question about whether asteroids could keep natural satellites.
Dactyl changed the picture of what an asteroid could be. When Galileo flew past 243 Ida in 1993, the spacecraft captured a tiny companion in the same system. Scientists found it while examining the returned images months later, making Dactyl the first natural satellite ever discovered around an asteroid.
That discovery mattered beyond one small moon. Before Dactyl, asteroid satellites were plausible but unconfirmed. Its presence showed that even a body as modest as Ida could hold a companion, and it opened a new way to investigate small-body systems through the motion of one object around another.
Dactyl remains a barely resolved world: an irregular body only about 1.6 kilometers across at its longest dimension. Yet its scientific role is much larger than its size. It turned asteroid moons from a prediction into an observed class of object.
699m
Key facts
- Category
- Moons
- Object class
- Asteroid moon
- Scale fact
- 1.6 kmmaximum extent
- Host
- 243 Ida
Scale context
Where Dactyl sits on the full axis
By size on the journey, Dactyl sits between 162173 Ryugu and 103P/Hartley 2. The band below uses nearby Moons objects for context.
Shared physical scale
25.4km
Together, these objects make the size change around Dactyl easy to compare at a glance.
Sources
References for Dactyl
Measurements and descriptive context are compiled by the Scale of Space team from the references below. If you find an error, please let us know.
Between the smallest and the largest, perspective is everything.
About
Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.