Happy BAN 5th!, SciAm Sun article, The mysterious origin of Deimos

Subscribers are, to me, the jewel-like stars born in huge nebulae

About this newsletter

Ooo, meta

I am easily distracted, and so with the book getting published and getting ready to travel to Nebraska at the time and a ridiculous amount of stuff going on at home I totally forgot that April 16th was the fifth anniversary of the BAN!

The first issue of this newsletter was sent out to people on April 16, 2018. Looking at my subscriber stats, I think there were about 400 subbies back then. My, this place has grown a bit since then! The total subscriber list is edging toward 18,000 right now, with over 1,500 paid subscribers, too. That’s amazing to me. It’s really terrific knowing so many folks are willing to let me clog their inbox with whatever is on my mind, and I cannot tell you how much I appreciate it.

I can show you, kinda, by reducing the subscription price: As I wrote last Monday, I dropped prices 20% to celebrate the book coming out (when really I should’ve done it for the anniversary, but either way, hey, savings). Until tomorrow — Tuesday, May 2, 2023 — the rate is $4/month or $40/year. You can get the special price by going to this page and signing up.

Anyway, here we are, 557 issues and some half a million words later. If you’ve been around since Day 1, thanks! In fact, you know what? I’ve opened comments up to everyone, paid and free, so if you’ve been around that long please let me know! If not, leave a comment anyway. I like reading about what folks are thinking.

And to everyone, thanks again. I do love sharing my joy of the Universe with you ­­— and whatever else has caught my attention, earthly or otherwise — and without you this newsletter would just be me shouting into the vacuum.

SciAm What SciAm

Stuff I’ve written for Scientific American

Speaking of writing…

My latest published article in Scientific American is one I was really tickled to write about: Was the Sun born in a rural or metropolitan setting? Or, less colloquially, was it born in a huge nebula that formed thousands of stars, or in a teeny one all by itself?

This is a question I’ve wondered about for a long time, so I was amused to see astrophysicist and scicommer Cheyenne Polius tweet about it. She was excited to announce she was an author on a paper, and when I saw the title I thought it would be interesting to read. I was literally a third of the way through the abstract when I realized this work could tell the difference between different kinds of stellar nurseries, and I laughed out loud when I read the last sentence in the abstract, saying just that.

You can read my article to get the lowdown. It was interesting and fun to write.

As it happens, after my article published I got an email from another colleague, Guillermo Abramson, who had written on the same topic, but covering a different paper by astronomers who used a similar technique as Cheyenne’s team! Funny how that works sometimes.

And to add the cherry on top, I wrote about exactly this topic in my book Under Alien Skies, discussing huge nebulae like the Orion Molecular Cloud and tiny ones like Barnard 68 (the latter is one of my favorite objects because it’s just objectively so cool). If you want to read about them, well, you know where to go.

Pic o’ the Letter

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

And now for some actual astronomy…

In 2020, the United Arab Emirates launched (via a Japanese rocket) Misbar Al-Amal — the Hope Probe — to Mars. The uncrewed mission arrived at the Red Planet in 2021, and has been taking images and spectra designed to investigate the Martian atmosphere.

On March 10, 2023, its orbit brought it very close to Mars’s wee moon Deimos, a smooth, lumpy space potato about 15 x 12 km in size. It took quite a few images, but one in particular is just simply staggering:

Holy dread and terror*!

I have not been able to determine if this image is actually color made from frames taken in different filters, or colorized from a single filter image, but I suspect it’s the former; the camera, called EMI, has multiple filters allowing color images to be constructed. Either way, it’s gorgeous. During the sequence of images, Mars moved into the background of the shots, providing the amazing framing of this portrait.

The origin of Deimos is a mystery. The leading idea, though not at all settled, is that it’s an asteroid captured by Mars. However, it’s incredibly difficult physically to do that, and this hypothesis has many problems. For one, Deimos would have to shed a lot of energy of motion for it to go into orbit around Mars — typically, asteroids are moving way too quickly to simple settle into an orbit around the planet, and something has to pump the brakes. That can happen with large planets that have thick atmospheres; if the rock plunges through the air it can slow considerably, and if the angle is just so it can come back up and go into orbit. But that’s a tricky dance, and Mars doesn’t have much atmosphere. Also, the moon has a circular orbit over the equator of Mars, which is very unlikely without its orbit being modified (usually via tides) over time. Mars doesn’t have strong tides, so it’s not at all clear if there’s been enough time for it to circularize.

Hope’s observations deepen this mystery.

Deimos has not been studied up close very much, and only one side of it has been mapped using spectra to determine its composition. It’s been thought to have a similar composition as what are called C- and/or D-type asteroids, which are rich in carbon, consistent with it being a captured asteroid.

But these new observations by Hope show that its composition is more similar to Mars itself than an asteroid. Taken at face value this lends credence to the more traditional idea that the moon was formed from material flung into orbit after a large asteroid or comet hit Mars. But that has problems too; why is the orbit of Phobos so much lower than that of Deimos if they both formed from the same event? And having separate two moon-forming events seems unlikely, too.

So, we still have a mystery! But at least now there’s more data to play with. I’ll keep my eyes open for any papers published about this weird little moon. I’d love to know how it came to be.

* The Martian moons Phobos and Deimos are named after the sons of the Greek god of war Ares, and their names mean Fear (which is where we get the word phobia) and Dread/Terror.

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!