Photo: NASA / JPL / CalTech
Large moons of Saturn
Researchers using the Subaru telescope in Hawaii have discovered 20 more moons orbiting Saturn.
This brings the total orbit around the planet to 82, surpassing Jupiter, with a total of 79 discovered so far.
These new satellites are about five kilometers in diameter, and their discovery is an indicator of the quality of modern telescopes.
Our Earth has a pretty big moon. Mercury and Venus have none, and Mars has two.
However, the giant planets Jupiter, Saturn, Uranus and Neptune have large collections of moons, and as our instruments improve and our planes pass, we find more.
Is this due to the planets acquiring new moons, or is this simply due to improvements in our instruments?
Thanks to the few telescopes we see, almost every year we notice an asteroid passing near us, sometimes closer to us than the moon.
Even when that happens, and the Earth's gravitational pull on that asteroid is stronger than Earth's drag on the moon, the asteroid doesn't catch on; passes and continues on its orbit around the sun.
The reason is simple. As the asteroid approaches Earth, it accelerates as the Earth draws. As it spins around the Earth, it will travel fast enough to escape into space at the speed it had before it met us, although it would probably move in a different direction.
To be caught, it takes something to slow it down a bit. The empty space vacuum has nothing to do with it, which is why our Earth is surrounded only by the moon, the satellites we have activated, and the growing accumulation of space junk.
There may be a small extra moon we haven't found yet. The same is true of the giant planets Jupiter, Saturn, Uranus and Neptune.
Everything that orbits the sun that flies past them will return to space. However, this was not always the case.
The solar system formed by the collapse of a large cloud of gas and dust. It collapsed into a rotating disk, and the center became sunshine. In the remaining disk material, smaller disks formed, which disintegrated to form planets and their moons. These moons orbit in the same direction as the rotation of the planets.
For example, our Earth rotates to the east and that is the direction of the moon's orbital motion. While the disk material remains, an object orbiting the sun and approaching it may be entertaining enough for that material to be captured, becoming a new moon.
This is probably the case for giant planets, since they were formed from large disks, which provide particularly large "hunter roles".
These outer additions can end up in any orbit, and may even move in the opposite direction to other moons. Saturn's seventeen moons have these reverse or "retrograde" orbits, suggesting that they are external augments.
In the outer solar system, around the giant planets there are possibilities for passing objects that appear to be trapped but are not actually. If the encounter is at the right speed and at the right distance from the planet, an object can make an almost complete orbit before it descends back into space.
This apparent orbit can take many years, so it will take time and some careful measurements to find out if an object is a distant moon or a visitor.
Data on these new satellite moons was collected between 2004 and 2007, which provided enough information for some new computer algorithms to extract orbits for new discoveries.
Over the next few years, as our telescopes and computations improve, we expect to find even smaller moons, perhaps as little as one kilometer, and the count to climb.
- Mercury and Venus may be visible very little south-west after sunset if the sky is clear.
- Jupiter and Saturn lie in the southwest after dark.
- The Moon Will Reach The Last Quarter Of The 21st.