Astronomy Picture of the Day - The Images not Posted during the Government Shutdown - Ida and Dactyl: Asteroid and Moon

NASA ^ | 17 Oct, 2025 | Image Credit: NASA, JPL, Galileo Mission

[MtnClimber]

Explanation: This asteroid has a moon. The robot spacecraft Galileo enroute to explore the Jovian system in 1993, encountered and photographed two asteroids during its long interplanetary voyage. The second minor planet it photographed, 243 Ida, was discovered to have a moon. The tiny moon, named Dactyl, is only about 1.6 kilometers across and seen as a small dot to the right in the image. In contrast, Ida is much larger, measuring about 60 kilometers long and 25 km wide. In fact, Dactyl is the first moon of an asteroid ever discovered. But now many asteroids are known to have moons. Minor planet names Ida and Dactyl were taken from Greek mythology.

---

TOPICS: Astronomy; Astronomy Picture of the Day; Science
KEYWORDS: 243ida; apod; asteroid; asteroids; astronomy; dactyl; nasa; science; thatsnomoon

[MtnClimber]

To be added or removed from the Astronomy Picture of the Day ping list please send me a request via "Private Reply" (Mail).

For more detail go to the link and click on the image for a high definition image. You can then move the magnifying glass cursor then click to zoom in and click again to zoom out. When zoomed in you can scan by moving the side bars on the bottom and right side of the image.

[MtnClimber]

[MtnClimber]

Pinging the APOD list

🪐 🌟 🌌 🍔

[DannyTN]

Idadactyl...Ptero’s sister.

[Diogenesis]

[AFB-XYZ]

Biden in space! Heh. :-)

[Verginius Rufus]

“Dactyl” is from the Greek word for “finger.” Someone should compose some dactylic hexameters in honor of Dactyl.

[NavyShoe]

Dactylicious!

[telescope115]

Due to Ida’s irregular shape, I can’t help but wonder what kind of orbit its moon Dactyl has.

Wikipedia has a page on Dactyl, and explains why Dactyl’s orbit isn’t fully known..

https://en.wikipedia.org/wiki/Dactyl_(moon)