Two New Satellites for Jupiter
skyandtelescope.com
skyandtelescope.com
While a relevant size comparison, this is potentially misleading characterization of our ability to detect these types of satellites. 1 km at 588 million km works out to an angular size of ~6e-6 radians, or 3e-4 arcseconds. The resolution of the telescopes that took the discovery data are typically* 0.3-1 arcseconds (depending on the atmospheric conditions at the site). So the telescope is not even close to being able to directly measure the physical scale of the moon in question. Best case, it's off by ~3 orders of magnitude. (Note of course there are variations in the apparent angular size due to the orbits of Earth and the Moon, but even at the closest the moon is too small to be directly resolved by current ground-based telescopes).
The reason we are able to detect these moons is a combination the albedo of the moon (its reflectiveness) and the still somewhat bright sunlight at the distance of Jupiter. So the main requirement here is that the telescope can see faint objects.
* - Note that near-infrared telescopes on the ground can achieve higher resolution with corrective "adaptive optics", but that is limited to follow-up observations of objects, not initial survey work.
Sketchy! I don't suppose we have a prediction for the next anticipated lunar collision? Surely this system isn't stable.
If two moons in opposite orbits collide, then there would presumably be an even more spectacular event when the majority of the combined mass of those moonlets fall straight down into Jupiter. Imagine a ~1km ball of magma zipping past the Roche limit and punching a hole right through the Jovian atmosphere.
Having a quick look at the data shows the inner moons travel in prograde, while the outer ones travel in retrograde.
So although there may still be collisions in the future, unfortunately it looks like most of the collisions happened long long ago.
Collisions in the main asteroid belt have been observed, but only after impact. The signature is a puff of dust from the impact that fades after hours or days as the dust spreads. The statistics are imprecise, but collisions between kilometer-scale asteroids might have decades or hundreds of years between them.
Impacts are rare though. There's a reason they call it space. If you were standing on an asteroid in the main belt, the nearest asteroid to you would be so far away that you could not see it.
Saturn’s mid-sized moons are like the monsters in late-night horror movies. Smash them into tiny pieces, and they glue themselves back together as new versions of the old moons. This new finding contradicts a theory that Saturn’s rings were caused by moons colliding.
[1]: https://www.newscientist.com/article/2132906-saturns-moons-c...