Hey Washington DCers! I will be giving my “Under Alien Skies” talk on October 8 (tomorrow!) at 6:30 p.m. at the Greenewalt Lecture Hall. This is a tour of Saturn, its moons, and its rings, as if you are a tourist on board a spaceship visiting the most gorgeous planet in the solar system. It’s based on my book of the same title, and is a lot of fun! You can get more info about the talk at the Eventbrite page. And it’s free! Come see me and learn about this ridiculously cool planetary bauble. This event is sponsored by Carnegie Science’s Earth and Planets Laboratory as part of their Neighborhood Lecture Series.

On September 17, 2024, the asteroid 2024 ON (literally the letters O and N) passed Earth at a distance just about 1 million kilometers, or less than three times the distance to the Moon. In astronomical terms that’s pretty close, though on human terms it’s a long hike.

Astronomers took advantage of the close pass to ping 2024 ON with radar, which can be used to create images of the rock. What they got was a surprise, though not a big one: it’s peanut-shaped.

This isn’t a huge surprise because a lot of small objects show two lobes like this. Remember 67P/Churyumov-Gerasimenko? And Dinkinesh’s moon? In that last link I talk a bit about how these might form, and while we have lots of ideas it’s not entirely clear what specific mechanisms are at play.

Each little image shows the 2024 ON at a different time, and you can see it rotating as it passed us. The bright spots are probably boulder sitting on the surface, which are good at reflecting radar.

This is all nifty, but when I first read about this rock, it actually caused me some concern. It was discovered less than two months before it passed Earth. That’s not a lot of lead time. It could have just as easily been on an impact trajectory as opposed to one that whizzed past us.

This is concerning because 2024 ON is about 350 meters long, end-to-end. That’s a big rock, enough that if it hit it would be a global catastrophe. Not enough to wipe us out as a species, but certainly enough to bring civilization to its knees no matter where it hit.

That’s why I write things like this; to raise awareness that these asteroids are out there, and while we’re doing a fantastic job in spotting them, that job’s not done. So it’s good news that big survey telescopes are coming online soon that will sweep the skies and find even more of these things. The more we look, and the better we look, the more lead time we have and the less likely one of these rocks can sneak up on us. And, should we need to, perhaps we can do something about it.

Sometimes, you just need a spectacular pic of a gorgeous galaxy from Hubble (especially after that last story). Let me help you with that:

That is NGC 3430, a spiral galaxy roughly 80 – 100 million light-years away (I see a big spread in distances listed, for some reason). That’s not exactly in our back yard, but close enough that it can be seen in moderate-sized telescopes. By my eye it looks to be tipped to our line of sight by about 60° or so (where 0 is face-on and 90 is edge-on).

It’s a beauty! It has a small, bright core and those wide-flung arms, and tons of dark dust clouds. That indicates to me that it’s actively making stars; the most massive ones are luminous and blue, so in general that makes the arms look blue. You have to be careful, though, because blue isn’t always blue.

What I mean by that is that the colors in an image can’t always be trusted. It depends on the filters used to make the image, and how those sub-images were processed together to make the result. To get a true natural-color image you need to use three filters — red, green, and blue, or something near those three in the spectrum. In this case, though, only two filters were used, one that lets yellow-green light (a wavelength of 555 nanometers) through and the other that sees near-infrared light (814 nm). These were then assembled in a way to mimic three colors, but it’s not a true natural color image.

If it were I’d expect to see zillions of reddish-pink gas clouds dotted throughout the spiral arms, where hydrogen gas is aglow from newborn stars. But the filters used don’t see that kind of light, so they’re not in the image.

This observation was taken to look at an exploding star, the core collapse supernova SN2004ez. The light from that event reached Earth in 2004, and this image is part of a much larger observation project on Hubble to look at such supernovae, to investigate the environment around them. The massive progenitor stars tend to blow out a lot of material before they explode, and that affects both the explosion itself as well as space around them for many light-years. The observing program looks at these stars, sometimes many years after the supernova, to see if the light from the explosion lights up the surrounding previously ejected gas; from that a lot can be learned about the star before it exploded.

Happily for us, SN2004ez blew in a very pretty galaxy! I never get tired of looking at spirals. They’re my favorite. 

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