Links
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- 243 Ida on Wikipedia
243 Ida
Details
243 Ida is the elongated main-belt asteroid that NASA's Galileo spacecraft flew past in 1993, discovering that it has a tiny moon of its own – Dactyl. Ida became the first asteroid known to have a natural satellite, proving that even small bodies can hold companions.
243 Ida matters because it overturned a long-held assumption: that asteroids were lonely, single rocks. When NASA's Galileo spacecraft flew past in 1993, its images revealed a tiny companion just over a kilometer across orbiting the asteroid — later named Dactyl. Ida became the first asteroid confirmed to have a moon of its own.
That discovery was more than a curiosity. A satellite lets scientists weigh the asteroid directly from the moon's orbit, yielding Ida's density and hinting at its porous, fractured interior. The existence of such pairs also showed that collisions in the asteroid belt can fling off fragments that settle into orbit rather than escaping, making small two-body systems a natural outcome of a violent history.
That is why Ida belongs on this scale. It is a heavily cratered, elongated body about 60 kilometers long, yet its real importance is the speck beside it. Ida proved that even modest asteroids can be miniature systems, and it opened the study of the many asteroid moons we know today.
26.1km
Key facts
- Category
- Asteroids
- Object class
- S-type main-belt asteroid
- Mass
- ~42 trillion tonnes
- Scale fact
- 59.8 kmmaximum extent
- Estimated age
- ~4.5 billion years
- Composition
- Silicate rock with metal
Scale context
Where 243 Ida sits on the full axis
By size on the journey, 243 Ida sits between Helene and 253 Mathilde. The band below compares 243 Ida with nearby S-type main-belt asteroid objects so the size jump stays easy to read.
Shared physical scale
45.7km
Together, these objects make the size change around 243 Ida easy to compare at a glance.
Sources
References for 243 Ida
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.