[ad_1]
The Moon is the celestial body closest to the Earth in the entire universe. We have been studying it for centuries, millennia, so you think we would have understood.
But this is not the case. It turns out that it's not just big rock that hangs in space! It's complicated, with varied terrain, a mix of constituents and a rich history that has changed a lot since its inception.
Yet, surprisingly, there are features, important features, that we are trying to understand. Get this: There is this type of surface structure that is so big that they are visible in a small telescope, and I was surprised that a) I only heard about it recently and that 2) scientists are only beginning to understand what is forming them.
They are called lunar whirlpools and they are just adorable.
It's a lunar whirlwind, called Reiner Gamma *. Is not it beautiful?
It's also terribly strange. On the one hand, this is not an elevation function! In other words, the angle of illumination, like a crater rim or a mound is not lit by the sun on one side and shaded on the other. A whirlwind is therefore not topographical; it's as if it had been painted on the pre-existing surface. This is what we call an albedo function, a change in brightness due to reflectivity.
Unlike other surface features, it is not clean and well defined. It has a softer appearance, again like an aerosol paint. It's also long and winding. In this way, it's like a groove, a sinuous channel at the surface cut by lava that flows billions of years ago (in fact, you can see a very narrow groove at the top of the image; are much larger). But this is obviously not a channel. The people at Lunar Reconnaissance Orbiter have a great zoomable image that will help you feel this particularity.
It's big too. The big blob of Reiner Gamma is more than 25 kilometers in diameter and the rest continues for more than 100 kilometers. Several other whirlpools are known, including a couple on the other side. They tend to be found in the maria, huge ancient sites filled with lava – these are the darker spots on the moon that you can see in the eye. This makes the surface rather smooth and tends to be dark. In fact, "maria" is the Latin word for "seas" because they are blue when they are seen in the day.
So what are they?
A great clue appeared at the very beginning of the 1970s. Apollo 15 and 16 mapped the magnetic field of the Moon and discovered that these whirlpools were in areas where the magnetism was more intense. Is not it interesting! But what does that mean?
The moon does not have a global magnetic field like Earth. This certainly took place a long time ago, probably between 1 and 2.5 billion years ago. But the melted nucleus of the Moon is finally solidified, and it takes one to generate the magnetic field (in what is called a dynamo).
What remains today are local magnetism spots, in most cases an imprint of the original field left in the rocks. When the surface solidified, the iron atoms in the minerals aligned with the field, and even when the field died, this alignment remained. Even in some places, the local field is stronger than you would expect from the old dynamo.
So what does magnetism have to do with whirlpools? You may already know that the Earth's magnetic field acts as a shield against the solar wind, a stream of subatomic particles blowing from the Sun. The charged particles can be deflected by a magnetic field or follow the field lines and be routed to different locations (such as geomagnetic poles), depending on their interaction with the field.
The same is true for the moon. In this case, the global field of the Moon does not exist, so in general, the solar wind is free to hit the surface. This changes the chemistry of the minerals there, darkening them over time. In fact, it is a way to get the age of some features; the brightest characteristics tend to be younger because they have not been exposed to the wind for so long.
For whirlpools, the idea is that the magnetic field embedded in the rocks, however weak, could still be strong enough to affect the incoming wind. If the field is aligned correctly, the wind is deflected from one place to the other. The protected area remains bright while the affected area darkens.
So cool, that explains the changing albedo. But what's the problem with the swirls that are long and winding?
A new study may have the answer to that. Planetary scientists have looked at what the magnetic field of the small areas of the Moon would look like, given the various underground features, adapting them to the changing nuances of the eddies. They discovered that they could reproduce a looped magnetic field (similar to that around a bar magnet) where it emerges from the surface at dark spots and reaches its apex above the surface over- above bright spots. When they did, they saw that everything that caused this could not exceed 3 km underground (so very shallow), and should be quite long (as one could expect) .
So what can we do?
Do you remember rilles? The lava flowing along the surface hollowed out these long channels, and sometimes the top of the lava cooled enough to form a "roof" above. When this happens, the lava can be so well insulated that it can stay hot for hundreds of miles. Not only that, but lava can hold more iron than surface rocks, so it can form a stronger magnetic field. We also see such features near the eddies: as I have already noted, for example, there is not far from Reiner Gamma in this picture. Mare Ingenii is a small impact element on the far side of the Moon, with swirls, and a collapse pit where the roof of a lava tube has collapsed.
The researchers also found that dikes could also be the cause of the disease. These are magma intrusions, where molten rocks can be pressed between layers of other rocks. On Earth – for example, in the Colorado Black Canyon that I've seen and honestly, you should go there if you get the chance – the rocks around the dike can erode, leaving Huge vertical walls of harder materials exit the canyon walls. Something like this under the Moon's surface could also generate the right kind of magnetic fields to explain the whirlpools.
Unbelievable! A so strange and beautiful feature, and a mechanism so cool to create one. In some ways, they remind me of iron filings on a piece of paper with a magnet under them … but with a piece of paper a hundred klicks long, a magnet bar so weak that you could barely detect it, and a stream of radiation for a billion years or so to make it all visible.
And speaking of that … Reiner Gamma is located at Oceanus Procellarum, the huge dark region of the western part of the near side of the Moon. It gets sunny shortly before the full moon and is big enough to be relatively easy to spot in my telescope. It will be visible in the lunar phase cycle underway from September 22nd.
I have already marked my calendar. It's not often that I write about something that I can go out and see! It will be fun to try to get there.
*Surface features on the Moon are sometimes named. A large crater a few tens of kilometers across could have a proper name, then smaller craters around the same name followed by a letter. Other features that are not craters may be designated by Greek letters. Reiner crater, to the right of Reiner Gamma in the picture, about 30 km in diameter, with about a dozen craters around Reiner A and so on.
Source link
