Welp, this is the 750^th issue of this Bad Astronomy Newsletter.

That feels like it should be a thing, doesn’t it? I mean, we like anniversaries that end in 0, and also ones that end in five though maybe a bit less — unless they make simple fractions of 100 like 25 and 75 do. I’d expect we could extend that out to bigger factors of 10, like 1,000, making 250 and 750 special, but somehow it doesn’t seem as big a deal to me. Maybe 750 seems more special than 800 or 900, but only a shadow of what 1,000 will be like.

Ever since I increased the publishing rate to three issues per week I think these special number have diminished a little, too, since they come more often. 156 issues per year means I pass a big mod(100)=0 kilometerstone^* at least once per year, and every other year it gets passed twice. That leaves 750 in a sort of mathematical limbo.

Or — and I admit this is remote but possible — I might be overthinking this. Either way, happy 750^th to the BAN, and let’s get to some spacey stuff, eh?

^* As I’ve said before, I love the metric system but it really screws up metaphors.

Some not-great news from the European Space Agency: the Gaia spacecraft suffered a double whammy recently. It was hit by a micrometeoroid, then a solar storm disrupted some critical electronics on board. The spacecraft seems to be doing better now, though, which is good news.

Gaia has been in operation for more than 10 years now. Its mission is to map the sky, getting incredibly precise measurements of the positions, colors, and brightnesses of stars. Over time, Earth’s motion around the Sun causes the stars to move due to parallax, which can be used to get the distances to the stars with pretty high accuracy. Also, stars move as they orbit each other in multiple systems as well as around the galactic center, and this can be measured as well. A huge, huge amount can be learned from these motions (like structures in the Milky Way, what’s going on with satellite galaxies of the Milky Way, finding invisible black holes, and a bajillion other things), making Gaia a truly spectacular resource for astronomers.

Which is why this news is a little concerning.

Micrometeoroids are tiny bits of rock or metal zipping around the solar system, shrapnel blasted off when asteroids collide. There are a vast number of these wee bits of flotsam orbiting the Sun. Spacecraft get hit often enough, though usually the damage is quite minor (JWST, for example, was hit by one in May of 2022, and engineers were able to compensate for the damage done).

The one that hit Gaia, though, damaged the observatory’s sunshield that protects the detectors from the Sun’s glare. That means a bit more sunlight is hitting than before. The good news here is that there is software onboard that automatically rejects measurements made where there’s a lot of background light. That is a little bit troublesome, because some observations of some stars have to be rejected, but Gaia takes so many observations that ditching a handful doesn’t severely impact the measurements.

Not long after this incident, though, some electronics onboard Gaia were damaged, most likely by the solar storms in May that caused aurorae all over the planet (and other planets, too). Gaia is hardened against radiation to prevent such problems, but the storm was a doozy, and Gaia has been up there a while now. Its nominal mission was only six years, so it’s well beyond that now. Issues like this aren’t unexpected. You hope they don’t happen, of course, but sometimes they do. 

The damaged hardware controlled one of the detectors on the spacecraft. Gaia has a lot of these sensors, but this one specifically was used to confirm the detection of stars. With it out of commission, Gaia was suddenly generating vast numbers of false detections of stars.

This sounds bad, but actually the fix is relatively easy. All those false detections are seen by the computers onboard Gaia, so all engineers had to do for a workaround was raise threshold for how faint an object Gaia detects to count as a star, eliminating a lot of the fainter false positives due to the lack of the sensor. There are some that still get sent to the ground, but not many, and those are easy to cull.

This was implemented, and things are better now. The spacecraft is back to routine operations. That’s good news! The thing about Gaia is, it looks at the same stars over and over again, scanning the whole sky repeatedly. Stars move slowly, or by very small amounts, but that builds up over time (if a star moves a teeny amount in one year, it moves 20 times amount that in 20 years), so the longer Gaia’s in operation the better its data get.

In fact there’s been more cool Gaia science news released recently, and I’ll be writing about that later. It’s truly amazing how much you can learn by simply looking really really carefully at stars for a long time. Hopefully Gaia will be with us for a long time to come.

My thanks to the ESA media team and Gaia Mission Scientist Timo Prusti for explaining some details of what happened to the spacecraft.

Since this is the 750^th issue, how about a lovely pic to mark the occasion? Because my oh my, our planet is absolutely gorgeous.

That is an image of ice floating in the frigid waters off the southeastern coast of Greenland, taken by NASA’s Terra Earth-observing satellite on June 4, 2024. It originated inside the Arctic Circle and is following currents south. The image is about 500 kilometers across.

I could write tons about this, but instead I’ll just send you to the fantastic Earth Observatory Image of the Day site, where I found it. I love that site, and check it every day over lunch to see what wonders await. I know, I’m an astronomer, but sometimes looking down from space is just as lovely as looking up from the ground. Earth is spectacular, and by venturing off it to look back, we see it in a different way and learn far more about it.

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!