Asteroid with its own moon

[Klapaucius]

Just saw this in the Washington Post

 

https://www.washingtonpost.com/science/2020/02/14/astronomers-spy-near-earth-asteroid-that-has-its-own-moon/?utm_campaign=wp_post_most&utm_medium=email&utm_source=newsletter&wpisrc=nl_most

[kerbiloid]

On topic

https://en.wikipedia.org/wiki/Minor-planet_moon

[ThatGuyWithALongUsername]

Yeah, this isn't really all that new. We've even visited one before (although it was by surprise): https://en.wikipedia.org/wiki/243_Ida

Edited February 14, 2020 by ThatGuyWithALongUsername

[Klapaucius]

4 hours ago, ThatGuyWithALongUsername said:

Yeah, this isn't really all that new. We've even visited one before (although it was by surprise): https://en.wikipedia.org/wiki/243_Ida

That does not make it any less cool.

[ThatGuyWithALongUsername]

Just now, Klapaucius said:

That does not make it any less cool.

I did not say it did. It makes it cooler!

[magnemoe]

It looks like its pretty common, however having an moon who is rounder than you as above would be a bit embarrassing 

[Shpaget]

"My moon is rounder than yours!"

- 243 Ida, Asteroid playground, circa 3 Ga

[RealKerbal3x]

Gilly?

[magnemoe]

Now an moon with its own sub moon would be cool. Guess we find it out in the kuiper belt as the tidal forces from the sun will be very weak while large moons seems to be common. 

[kerbiloid]

Spoiler

  

8 hours ago, magnemoe said:

Now an moon with its own sub moon would be cool.

https://elderscrolls.fandom.com/wiki/Secunda

Quote

The astronomic definitions of both Masser and Secunda are prone to much discussion. At first glance, both seem to be moons of Nirn; however, on observation of the two moons in both Oblivion and Skyrim, Secunda actually revolves around Masser, showing that Secunda is in fact Masser's moon. Despite this, both moons can still be considered satellites of Nirn, as the center of mass of the Masser-Secunda system is what orbits the planet.

 

 

[Zeiss Ikon]

On 2/15/2020 at 6:26 AM, magnemoe said:

Now an moon with its own sub moon would be cool. Guess we find it out in the kuiper belt as the tidal forces from the sun will be very weak while large moons seems to be common. 

Even without outside perturbation, most three-body systems are long term unstable.  Lagrange libration points are a partial exception; they're only metastable (L4 and L5 more so than the other three), and depend on large mass ratios (i.e. you couldn't depend on a Lagrange point to make Earth/Luna stable with a second moon as heavy as Luna).  With setups that could remain stable for geologic time, the view would be unspectacular -- it'd generally be a tiny moon orbiting a rather large one, and likely well out of the plane of the large moon's orbit (i.e. an accidental or artificial capture, not something that formed in place).  For our Moon, only near-polar orbits can last even a few decades due to a combination of Earth's influence and masscons in the Lunar crust.  Everything left in Lunar orbit by Apollo (Apollo 10 LEM descent and ascent stages, Apollo 11 LEM ascent stage, as I recall, before they started crashing the ascent stage for the seismic experiments) has long since fallen.

Principia mod with RSS has enough data about the Moon's mass distribution to model this accurately, if you want to play with it.  You can use just those two plus Hyperedit for this kind of play -- no need to go through a full RO install.

[magnemoe]

1 hour ago, Zeiss Ikon said:

Even without outside perturbation, most three-body systems are long term unstable.  Lagrange libration points are a partial exception; they're only metastable (L4 and L5 more so than the other three), and depend on large mass ratios (i.e. you couldn't depend on a Lagrange point to make Earth/Luna stable with a second moon as heavy as Luna).  With setups that could remain stable for geologic time, the view would be unspectacular -- it'd generally be a tiny moon orbiting a rather large one, and likely well out of the plane of the large moon's orbit (i.e. an accidental or artificial capture, not something that formed in place).  For our Moon, only near-polar orbits can last even a few decades due to a combination of Earth's influence and masscons in the Lunar crust.  Everything left in Lunar orbit by Apollo (Apollo 10 LEM descent and ascent stages, Apollo 11 LEM ascent stage, as I recall, before they started crashing the ascent stage for the seismic experiments) has long since fallen.

Principia mod with RSS has enough data about the Moon's mass distribution to model this accurately, if you want to play with it.  You can use just those two plus Hyperedit for this kind of play -- no need to go through a full RO install.

I know about the Moon gravity abnormality, caused by asteroid impacts created areas with lots of metal close to the surface who disturb orbits. 
Not so much of an problem for high orbits. but then you get more disturbance because the earth and the sun. 

And yes its sound cooler than it would be, more like an tiny asteroid in orbit around Triton. Outer system is best here as space is much flatter. 

[Space Nerd]

13 hours ago, magnemoe said:

Apollo 10 LEM descent and ascent stages

I thought the ascent stage is in a solar orbit?

[magnemoe]

1 hour ago, Space Nerd said:

I thought the ascent stage is in a solar orbit?

Snoopy or Apollo 10 accent stage ended up in solar orbit so did the first Saturn 5 3rd stages. Late Saturn 5 3rd stages was dropped so they hit the moon for seismic experiments.

One of the 3rd stages came close, got captured by the moon and did a couple of orbits before Moon kicked it out again. If you play KSP a lot you know Mun has an chance to capture asteroids. 

[Zeiss Ikon]

19 hours ago, magnemoe said:

Snoopy or Apollo 10 accent stage ended up in solar orbit

That's "gone" in terms of the Lunar near-equatorial orbit it was left in.  The other stages I mentioned (Apollo 10 LEM descent stage and Apollo 11 LEM ascent stage), left in Lunar orbit, have (AFAIK) gone too low and impacted the surface over the past fifty years.

Which happens depends strongly on how high/what inclination/orientation/eccentricity the initial stage orbit was.  As I noted, near-polar Moon orbits can actually be stable enough to stay a good while.

I didn't count the Saturn transfer stages because they were never inserted into Lunar orbit.

[RealKerbal3x]

19 hours ago, Zeiss Ikon said:

I didn't count the Saturn transfer stages because they were never inserted into Lunar orbit.

Yeah, some of the S-IVBs went into heliocentric orbit, and some were deliberately crashed into the Moon to calibrate the seismometers that the astronauts put on the surface.