Starship Asterisk*

Ida and Dactyl: Asteroid and Moon

Explanation: This asteroid has a moon. The robot spacecraft Galileo on route to Jupiter in 1993 encountered and photographed two asteroids during its long interplanetary voyage. The second minor planet it photographed, 243 Ida, was unexpectedly discovered to have a moon. The tiny moon, Dactyl, is only about 1.6 kilometers across and seen as a small dot on the right of the sharpened featured image. In contrast, the potato-shaped Ida is much larger, measuring about 60 kilometers long and 25 km wide. Dactyl is the first moon of an asteroid ever discovered -- now many asteroids are known to have moons. The names Ida and Dactyl are from Greek mythology.

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Ida's shape appears to be a long way from spherical, while Dactyl is very round!
How stable will the latter's orbit be, when the gravity field around Ida must vary around it?
John

JohnD wrote: ↑Sun May 28, 2023 10:12 am Ida's shape appears to be a long way from spherical, while Dactyl is very round!
How stable will the latter's orbit be, when the gravity field around Ida must vary around it?
John

Two body systems are stable. That assumes they are point masses, of course, so this isn't a perfect two-body system. Still, the bodies are far enough apart in comparison to their sizes that they're likely to remain as they are until they encounter another asteroid.

I estimate that when Dactil was captured it would have had random orbits until the sum of "pulls" of the different orbits settled into a neutral one.

I know the metric system has advantages, but this case I think "mile" in diameter is better.
Of course, dactyl is also a foot or a finger and the Greeks counted three or ten of them.
And it has two craters, named after the Dactyls Acmon and Celmis.
Great photo. too.

Jim Armstrong wrote: ↑Sun May 28, 2023 5:02 pm I know the metric system has advantages, but this case I think "mile" in diameter is better.
Of course, dactyl is also a foot or a finger and the Greeks counted three or ten of them.
And it has two craters, named after the Dactyls Acmon and Celmis.
Great photo. too.

The first time this one was posted in APOD, which is one of the very first ones, the diameter was mentioned in miles.
https://apod.nasa.gov/apod/ap950630.html

Dactyl is so close to Ida that despite it's size, it actually looks almost as bright and big as the moon looks in our skies!
And with the things I've read about it, it appears that solar eclipses possibly happen often on Ida's surface, as Dactyl cast it's shadow on the stoney asteroid. And think about it, you could actually run and stay on the eclipsed region until it ends

Rauf wrote: ↑Sun May 28, 2023 5:38 pm Dactyl is so close to Ida that despite it's size, it actually looks almost as bright and big as the moon looks in our skies!
And with the things I've read about it, it appears that solar eclipses possibly happen often on Ida's surface, as Dactyl cast it's shadow on the stoney asteroid. And think about it, you could actually run and stay on the eclipsed region until it ends

A list of space tour attractions

1) run across Ida staying in eclipse spot and not jumping at escape velocity
2) dive with large swipfins through 100 meters of snowflakes and snowballs of a Saturn's ring tip from night side to the light of day
3) fly by flapping on-arm wings in a thick atmosphere and low gravity of a distant planet's moon to a high peak

VictorBorun wrote: ↑Sun May 28, 2023 6:12 pm

Rauf wrote: ↑Sun May 28, 2023 5:38 pm Dactyl is so close to Ida that despite it's size, it actually looks almost as bright and big as the moon looks in our skies!
And with the things I've read about it, it appears that solar eclipses possibly happen often on Ida's surface, as Dactyl cast it's shadow on the stoney asteroid. And think about it, you could actually run and stay on the eclipsed region until it ends

A list of space tour attractions

1) run across Ida staying in eclipse spot and not jumping at escape velocity
2) dive with large swipfins through 100 meters of snowflakes and snowballs of a Saturn's ring tip from night side to the light of day
3) fly by flapping on-arm wings in a thick atmosphere and low gravity of a distant planet's moon to a high peak

There's a nice challenge in Ida you could try. Try this: Jump and reach Dactyl without help from any kind of jetpack. You must aim very carefully or... well you know the consequences.

Rauf wrote: ↑Sun May 28, 2023 6:31 pm

VictorBorun wrote: ↑Sun May 28, 2023 6:12 pm

Rauf wrote: ↑Sun May 28, 2023 5:38 pm Dactyl is so close to Ida that despite it's size, it actually looks almost as bright and big as the moon looks in our skies!
And with the things I've read about it, it appears that solar eclipses possibly happen often on Ida's surface, as Dactyl cast it's shadow on the stoney asteroid. And think about it, you could actually run and stay on the eclipsed region until it ends

A list of space tour attractions

1) run across Ida staying in eclipse spot and not jumping at escape velocity
2) dive with large swipfins through 100 meters of snowflakes and snowballs of a Saturn's ring tip from night side to the light of day
3) fly by flapping on-arm wings in a thick atmosphere and low gravity of a distant planet's moon to a high peak

There's a nice challenge in Ida you could try. Try this: Jump and reach Dactyl without help from any kind of jetpack. You must aim very carefully or... well you know the consequences.

too bad that neither Ida nor Dactyl are tough enough to welcome tours. We will have to build replicas, visually and gravitationally the same but less inspiring

Sa Ji Tario wrote: ↑Sun May 28, 2023 3:57 pm I estimate that when Dactil was captured it would have had random orbits until the sum of "pulls" of the different orbits settled into a neutral one.

It's pretty hard to come up with a realistic scenario for Ida to capture Dactyl. Most likely the pair were ejected together when the parent body was destroyed, or Dactyl was gently knocked off of Ida's surface by a subsequent collision with another small body.

Ida got mooned one day by Dactyl and the two became partners! Unexpectedly!