96. Just poking around the universe

This afternoon the Artemis II successfully completed its mission with a splashdown in the Pacific Ocean. Wonderful! Big applause for the science, for the dreaming, for the engineering, for getting some new glimpses of our fragile planet from space and for totally new views of the moon's backside! 

Meanwhile, I've been wondering how the ship slowed down from its 24,000 mph hurtle through deep space to a mere 17 mph as it approached the Earth's surface. I haven't found answers that satisfy me—those that I have found include aerobraking and eleven parachutes. (The best source of information I found was a thread on Reddit, but still—I'd really love a nifty video direct from NASA. NASA—do you hear me?) 

Anyway, as I wandered through the internet, I got to wondering about our atmosphere—which was ostensibly helping to put the brakes on the Artemis II. And once again, as so often, I realized (with some delight: there's so much to learn!) how ignorant I am. Check out this rather simplistic illustration:

So, what really slays me here is the Thermosphere, with temperatures from 930°F to 3600°F. This right after the Mesosphere, with a high temp of 5°F. What? And then, beyond the Thermosphere: absolute zero. How is that even possible? 

As a certain scientific type in this household explained, it doesn't mean the Thermosphere is hot. There are very, very few molecules out there. But what molecules there are (mainly atomic and molecular oxygen, molecular nitrogen, and atomic helium), they have a high temperature. I'm still trying to wrap my head around that. Why are they so high-temp? (The short answer is that they directly absorb intense, high-energy UV and X-ray radiation from the sun.) 

And now I'm resisting doing further research into the auroras—are they super high-temp too? But not hot? What is hot? What is cold? What exactly is an aurora? I'm so confused...

And then finally, I'm not even sure where this came from—it could be Mr. Science mentioned it—I learned that Elon Musk has launched over 10,000 LEO (low earth-orbit) Starlink satellites in the last seven years (since 2019). His plan is to have 1 million satellites as orbital data centers, "addressing the immense energy needs of AI on Earth." The 10,000 are already making earth-based astronomy harder to do. But 1 million? And for AfuckingI?I am beyond horrified.

Until last year, said satellites orbited at 550 km (340 miles), but they've now lowered the orbit to 480 km (298 miles) "to increase safety by reducing space debris and enabling faster re-entry of inactive satellites." Now I need to find out what "re-entry of inactive satellites" actually means.  

There's so much I don't know. But I have to say, it was a relief to venture imaginatively into space today, and avoid the earth-bound news, which never fails to be infuriating anymore.