Book site, JWST takes a peek at Uranus

My book

This is about Under Alien Skies, isn’t it? Yes. Yes it is.

My book, Under Alien Skies: A Sightseer’s Guide to the Universe, comes out NEXT WEEK woooohoooooo!

If somehow you’ve missed the gazillion times I’ve mentioned it here, you can read all about it in the issue where I announced it.

And now it has its own website! I bought the URL underalienskies.com a couple of years ago in anticipation, and finally got it put together (well, I wrote the copy, but website guy Vinny Green did the backend stuff).

It has some info about the book, the blurbs we got (Bill Nye! John Green! Laura Helmuth! Zach Weinersmith!), and a bunch of ways to order it online:

UNDERALIENSKIES.COM

As reminder, pre-orders are the lifeblood of authors. It tells the publisher how well the book is doing and, critically, helps it rank in various lists. If you want a copy, please get one! I also narrated the audiobook, if that’s your thing.

Thanks!

Pic o’ the Letter

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

URANUS!*

Holy ringed ice giants! That image was taken by JWST on February 6, 2023. It shows the planet itself, its set of complex rings, and some interesting features in the planet’s atmosphere.

So, Uranus (which, honestly, is usually pronounced YOO-rin-us or yoo-RAN-us) is similar to Jupiter and Saturn in that is a giant planet — about four times the diameter of Earth, and roughly 14 times the mass of our own home world — but it also has a lot of things like water, ammonia, and methane in it. For historical reasons planetary scientist call those “ices” (even though deep down in the planet they can be liquid or gas) so technically Uranus is an ice giant.

Unlike the other big planets, Uranus is tipped over 98° with respect to its orbit; compare that to Earth’s 23° tilt. Because of that, for half its orbit the north pole points toward the Sun, and for the other half it’s in darkness. Right now it’s springtime in the northern hemisphere of Uranus, with the north pole just starting it’s long, 42-Earth-year day period. In the image, the north pole is to the right.

In visible light, the kind we see, the planet is rather dull, a nearly featureless blue-green color that’s obvious even in small telescopes. The upper atmosphere is mostly methane, which absorbs red light pretty strongly, letting the blue and green part through to reflect back to us.

But in infrared light, with longer wavelengths than our eyes can detect but where JWST is designed to see, the planet has many atmospheric features that pop up. For example, there’s that huge white “polar cap” covering its north pole. Unlike our polar caps, or the ones on Mars, this one is likely made of ice clouds. It appears when the cap starts its long day, so clearly it’s made up of something that forms when sunlight strikes the atmosphere (or maybe as the air warms up and stuff from deeper down gets dredged up). However, it’s not known what it is! Uranus is a long way off and difficult to observe; the hope is that JWST observations may help clear that up.

The rings are amazing in this shot. Like Saturn’s they’re mostly water ice, but unlike Saturn’s they’re very dark. Likely ultraviolet light from the Sun has zapped simple organic molecules there and turned them dark. These molecules, called tholins, can be red, brown, or black, and we see them a lot on icy moons and bodies like Pluto.

11 of the 13 known rings can be seen in this image. They’re narrow, and that’s not well understood either. Sometimes small moons can orbit just inside and outside individual ringlets and corral them via gravity; for this reason they’re called shepherd moons (Saturn has several, as does Enya).

In the wide view a lot of Uranus’s moons can be seen. A thing I love: they’re named after characters in Shakespeare’s “A Midsummer Night’s Dream” and others in his plays. So there is Oberon and Titania, Ariel and Umbriel, and even Puck. Incredibly, besides the planet and its moons, pretty much every other object in this image is a distant galaxy, picked up because they tend to be brighter in these wavelengths, and because JWST is a huge ‘scope, with its 6.5-meter mirror system. It can easily see very faint objects.

These images are among the best ever taken of Uranus; only Voyager 2 (which flew by the planet in 1986) and the giant Keck telescope in Hawai’i got this sort of sensitivity and resolution (ability to see tiny details). Unlike a lot of other objects on the sky, planets change on short timescales; years, months, and even days. Planetary astronomers like to check in as often as possible to see what’s what out there, and take a peek at goings-on in the atmosphere, the moons, and the rings.

Uranus is wildly different from Earth, but that’s the important aspect of it: it obeys the same set of physical laws Earth does, but the conditions aren’t the same. It’s bigger, more gaseous, colder, and there’s more elbow room out there than in the inner solar system. We can study how it behaves and compare them with what we see here and come to know our own planet that much better.

I do love space, and astronomy. But I’m fond of our own world, too, and whatever we can do to understand it better is a good thing.

* Sigh, first, yes, haha, but I have literally heard every single joke about the planet, and the only two that are funny are the one from Futurama (which, frankly, is genius) and, to be utterly immodest, one I myself came up with.

OK? OK.

Et alia

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!