BAN #104: Greasy dust, Chinese rover on the move

Pic o’ the Letter

A cool or lovely or mind-bending astronomical image/video with a short description so you can grok it

Say now this is terribly cool: The Lunar Reconnaissance Orbiter has taken images of the Chinese lunar lander Change’e-4 several times over the past few months, enough to see the rover Yutu-2 actually, well, roving!

[Credit: NASA/GSFC/Arizona State University]

On the upper left is the before shot, taken a few weeks before the January 3, 2019 landing date. The upper right shows the lander a month after touchdown, and you can see the rover as a black dot to the upper left of it (that’s the highest res image taken so far). The lower left shows them again a few hours later, when the orbiter was off to the side and had to slew over to see them, and the lower right on February 28 when Yutu-2 had roved some more.

There’s an animation that flips between these images on the LRO page, too.

These images were taken when the Sun was low, but over the next few months LRO’s orbit over the landing site will align with the Sun being higher, so it’ll be easier to see things like the rover’s tracks; high Sun means no shadows, but changes in the surface regolith (the powdery dust made of crushed rock that covers the Moon) are easier to see as brightness changes. That’ll be neat, to see where the rover has gone and how it’s done that. Those will also show how much of the surface was disturbed by the rocket exhaust as the lander touched down.

As always, I urge you to check in on the LRO blog for images like these and also just spectacular shots of the Moon in general. It’s one of my favorite sites.

Space news

Space is big. That’s why we call it “space”

This is weird. Space is greasy.

Contrary to popular belief, space isn’t empty. There’s this stuff floating between stars, what astronomers generically call the interstellar medium (or ISM if you want to feel like an astronomy insider). It’s composed of two main components: gas (mostly hydrogen), and dust. The dust is itself made up of two components: tiny grains of silicaceous material (aka rock), and long carbon-based molecules.

[Huge clouds of opaque dust block the starlight behind it, so we see it in silhouette in the galaxy. Credit: ESO/VVV Survey/D. Minniti & Acknowledgement: Ignacio Toledo]

In the case of the carbony stuff, it’s mostly generated in either supernova explosions, or in the winds of red giant stars. There’s a particular kind of red giant called a carbon star, for example, that has a lot of carbon in it (and even regular red giants and massive red supergiants have some too), and it blows this stuff into space.

The carbon forms molecules when it cools, and these come in two forms too: aromatic (literally, they smell, like naphthalene, the stinky ingredient in mothballs, and tend to form in rings), and aliphatic. That latter one is what makes long complex molecules, and the name comes from the Greek meaning oil. Yup: Aliphatic compounds are greasy.

[Diagram of an aliphatic carbon molecule. Credit: D. Young (2011), The Galactic Center]

To find out which one predominates in the ISM, some scientists mimicked the conditions in a red giant blowing a wind into space: They created a plasma (a very hot ionized gas) laden with carbon and let it expand and cool into a vacuum. They then used spectroscopy to check the identity of the black goo that deposited itself in the chamber, and found out it’s mainly aliphatic.

So, according to their experiment, as much as a quarter to one half of the carbon dust in the ISM is greasy.

At least it’s not smelly.

Speaking of which, their next experiment will be to see how much of the material is aromatic. Presumably it makes up the rest, but who knows? If they knew the answer in advance it wouldn’t be an experiment.

Et alia

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