September 11, 2023

Neptune Has No Chance of Meatballs

Gosh, has it been a month already? Welcome to issue 2 of my re-launched newsletter. This month, let's take a look at the furthest planet from the sun¹ and the mystery of its missing clouds.

Neptune's Clouds Vanish; Sun Implicated

35 years ago, Voyager 2 gave us an unprecedented look at Neptune during its flyby of the farthest plane from the sun. Voyager 2 revealed four intact rings, six new moons, and a highly tilted magnetic field. It sent back stunning pictures of long clouds streaming to the west, pushed by winds blowing at more than 1,200 miles per hour. An anticyclone the size of the Earth squatted just below the equator. We, of course, named it the Great Dark Spot.

Because Neptune is far away and our atmosphere makes astronomy harder, we didn't get another close look at it for five years. When we did, the Hubble Space Telescope revealed a changed planet. The Great Dark Spot was gone. A year later, though, another dark spot appeared, this one in the northern hemisphere. We learned that Neptune's cloudy atmosphere changed dramatically over the course of weeks.

Since then, we've monitored Neptune using Hubble Space Telescope and, thanks to the adaptive optics that remove atmospheric distortions, the Keck Observatory. Neptune's cloud cover has varied. Some years it's thicker. Some years it's thinner.

Then, as of October 2019, the clouds all but vanished. Only one small patch remained, hugging the south pole. By 2020, even that was gone.

This caught the eye of researchers at UC Berkeley. Overseen by Imke de Pater, undergraduate Erandi Chavez led a team that went through nearly thirty years of images from Hubble, the Keck Observatory, and the Lick Observatory. They found a link between the amount of clouds and the sun's cycle.

Approximately every eleven years, the sun's magnetic field decreases to zero and then flips, north becoming south and vice versa. It's not on a precise schedule. The flip happens in as few as eight or as many as fourteen years. Neptune's cloud density lines up with those cycles. UV light from the sun may trigger cloud formation through a photochemical reaction. That light is tied to solar flares, which wax and wane in time to the solar cycle. Two years after the sun's UV light peaks, Neptune's clouds do, too.

This is wild. Neptune's 30 times further away from the sun than we are. It's so far that light takes four hours to reach it, and it's only 1% as strong as what we experience on Earth. And yet it's enough to drive Neptune's clouds.

While this isn't the first time the link between sunlight and Neptune's clouds have been suggested, it is the strongest evidence to date. Even with the thirty years of data, though, questions remain. What's the process that links UV light and clouds? We see more bright clouds, but it's not obvious why the UV light doesn't make Neptune darker by darkening haze and aerosols.

All of this serves to remind me how big space is, and what long time scales planets operate on. The UC Berkeley team's 30 years of data only covered two and a half solar cycles. It isn't even 20% of Neptune's "year" around the Sun. I spent my graduate years trying to observe dynamics that took place in less than a second. Stories like this are a stark reminder of how long the universe can take to reveal its secrets.

(Here's the original paper, as well as the freely available pre-print for those of us without university access to the journal Icarus.)

What's Up With Stephen?

I'm a guest at Multiverse Convention on October 20-22 in Atlanta. Multiverse is a cross-media weekend con that I've been eyeing for the past few years, and I'm excited to get to participate. Will I be moderating a panel on AI in writing and other creative fields? Signs point to yes! Tickets are $65 for the weekend. If you're in Atlanta, I'd love to see you there.

Beyond that, Small Wonders, the SFF flash fiction and poetry magazine I co-edit, is rocking along. We're in the middle of issue 3 and have gotten our feet under us and a rhythm down. I encourage you to stop by and read what we're publishing. If you're so inclined, you can even pick up a subscription or individual issue as an ebook. A subscription gets you the ebook at the first of the month plus every story and poem in your inbox for your lunchtime reading.

What I'm Vibing With

• Man who tried to cross the ocean in a human hamster wheel banned from the sea.
• We went from folks joking about a crab magazine to writer Rachel Handley making it a reality. You can submit your crab-themed stories to Crab Tales Magazine and donate to help them raise their pay rate.
• I was not prepared for a mutiny of Carmelite nuns in Texas. "It involves allegations and accusations of illicit sexual relationships, drug use, theft, abuse, spying, planted evidence, and plots to steal a multimillion-dollar property."
• The last big Reddit community protesting the API changes has given in.
• Towards a theory of the millennial ambition psycho.
• This is a great and eminently readable deep dive on the Navy spending billions on the Littoral Combat Ships.
• A.R. Moxon reframed how I think about calls for "friendship" across political divides, providing both deep insight and the amazing description, "professional mourner of crumbling civility and amateur shoe filler David Brooks".

Finally, I have to let you know that we got a new puppy this weekend named Feferi and she's giving way more than the LD50 of cute.