Thoughts from a Planetarian: Universe Update for May 2020

The third Thursday of every month, Morrison Planetarium hosts “Universe Update” as its 6:30 planetarium show during NightLife—but with the California Academy of Sciences currently closed, that didn’t happen last night, so I had the chance to share a similar program at yesterday morning’s Academy Breakfast Club—and again at last night’s NightSchool! (You can watch the recorded presentations on YouTube here and here.) I covered slightly different stories on each segment, so as an added bonus, I decided to provide these notes on some of my favorite astronomy stories from the past month.

Normally, I take NightLife audiences on a guided tour of the Universe while I’m sharing these astronomical highlights. You can enjoy a flatscreen (sigh, less impressive) version of this journey in the videos linked above. But in brief, the planetarium sports a three-dimensional atlas of the Universe, which allows us to take audiences places virtually while talking about the latest astronomy news. It provides context to the remarkable discoveries astronomers are making on a daily basis. Because I always start at Earth and work my way out to cosmological distances, I’ll list the news stories in the same order—from closest to farthest from home.

The first story starts at Jupiter… A few hundred million kilometers from home, but close by, relative to where we’re headed!

In a great example of how observatories collaborate across great distances—and across large swathes of the electromagnetic spectrum—NASA’s Juno mission, NASA’s Hubble Space Telescope, and NSF’s Gemini Observatory all joined forces to explore Jupiter’s atmosphere. The largest planet in the Solar System cooks up some pretty violent storms, most famously the Great Red Spot, which has persisted for centuries, although it appears to be shrinking. But the giant planet’s atmosphere works very differently from Earth’s, so planetary scientists are interested in making detailed studies of Jupiter’s storms.

The Juno spacecraft orbits Jupiter once every 53.5 days or so. It spends just a little of that time near the planet (and subject to the powerful and damaging effects of Jupiter’s intense radiation environment, but more on that in a moment), zipping by quickly with each orbit. On each pass over the planet’s cloud tops, Juno detected radio emission that corresponded to lightning flashes deeper in the atmosphere. By coordinating their observations with Juno’s flybys, Hubble and Gemini were able to make detailed maps of Jupiter that corresponded with the orbiter’s detections of lightning. As Wong explained: “Scientists track lightning because it is a marker of convection, the turbulent mixing process that transports Jupiter’s internal heat up to the visible cloud tops.”

While Hubble imagery mostly reveals the upper layers of the atmosphere, Gemini observes longer-wavelength, lower-energy infrared light that originates deeper down. The spectacular infrared image of Jupiter showcased on this page shows the giant planet in a whole new light—infrared light, to be specific! And the bright portions of that image help planetary scientists tease out the cloud structure to understand storms better. Using data from Juno, Hubble, and Gemini, researchers discovered that lightning strikes and storm systems take shape over deep clouds of liquid and frozen water.

(A big Bay Area shout out, by the way! The team of researchers is led by Michael Wong and Imke de Pater, both at UC Berkeley.)

Meanwhile, in orbit around Jupiter, we find one of the places in the Solar System that seems most amenable to life. The moon Europa shows evidence of a subsurface ocean under a thick crust of ice—where you’ll find more water than all Earth’s oceans combined! Even though radiation from Jupiter’s magnetosphere punishes Europa’s surface and makes it quite inhospitable to life, the icy crust may be more than ten kilometers (six miles) thick, thus protecting what lies beneath. NASA and the European Space Agency (ESA) both have missionsplanned to get a closer look at Europa.

In the meantime, planetary scientists have to make do with 20-year-old data from NASA’s Galileo mission (even the artwork on the official website looks dated). An event that took place in 2000 has really captured people’s attention—during a flyby of Europa, Galileo’s magnetometer detected deviations in Jupiter’s magnetic field that could have been caused by a plume of water escaping from the moon. Tantalizing but far from definitive evidence.

What’s so exciting about a plume of water? Well, you might call it “Enceladus envy.” That moon of Saturn has persistent plumes of material erupting from near its south pole, and NASA’s Cassini spacecraft detected organic compounds in the stuff spouting into space. Basically, if life exists under the icy crust of either Europa or Enceladus, then it should change the chemistry of the water—and it saves a lot of drilling if the water is making its way into space all on its own. (A couple things to note, though: Enceladus is a lot smaller than Europa, with weaker gravity and a thinner crust to boot, so plumes probably form more easily.) So, yeah, plumes would be nice.

Back to the 20-year-old data. A group from the Max Planck Institute for Solar System Research announced “new evidence of watery plumes” in a press release from last week. That headline is a little deceptive, but the results are quite spiffy. The scientists took a look at different Galileo data—from the Energetic Particles Detector (EPD) instead of the magnetometer. The good ol’ EPD sifted through the energetic particles trapped in Jupiter’s magnetic field, and during that same flyby in 2000, it detected significantly fewer charged particles near the moon. That could be the moon shadowing the detector and blocking the particles, but wait…

Enter the computer simulations! Using the laws of physics and a lot of number crunching, scientists can examine many scenarios for why things look the way they do. When they tried to re-create the 2000 event in their virtual laboratory, the researchers discovered that their simulations only succeeded when they included a plume erupting from Europa. High-energy charged particles then absorbed electrons from the plume, and thus neutralized, they could escape Jupiter’s magnetic field. Wheee!

So is it “new evidence”? Not really in my book, but these simulations provide another clue that Europa may be releasing some of its subsurface into space—perhaps not as consistently or continuously as Enceladus, but hey, not every moon needs to be an overachiever like Enceldaus.

Moving a little farther out in the Solar System, it’s always fun to talk about things that aren’t planets or moons—after all, a lot of stuff orbits the Sun! Asteroids and comets, for example. And while most of them were born with the rest of the Solar System 4.6 billion years ago, not all of them were. Some, it turns out, are intruders from other planetary systems…

The story begins in 2014 with the discovery of the asteroid Ka‘epaoka‘awela, which orbits the Sun basically going the wrong way round—opposite the direction of all the planets and pretty much everything else. The object was subsequently determined to have originated from outside the Solar System (je m’excuse, mais cette article est en français). Not surprising, since the formation of planetary systems involves a cloud of gas and dust that collapses to form a rotating disk of planets, asteroids, comets, and everything else—with everything pretty much swirling in the same direction as the original gas cloud. Something going the wrong way certainly looks like it doesn’t belong.

Cue more computer simulations! Researchers looked at a bunch of asteroids with weird orbits (maybe not as weird as Ka‘epaoka‘awela’s, but weird enough). Using computational processes to “turn back the clock” a few billion years, the scientists found that 19 asteroids were not part of the protoplanetary disk from which the Sun, planets, and other awesome stuff in our solar system formed. Instead, these objects resided far outside the plane of the disk and must have originated somewhere else… They are likely interstellar interlopers who have taken up residence in our neck of the woods.

(I ran across this video that does a pretty decent job of describing the result. The host Anton starts with the words, “Hello, wonderful person…” Which is pretty endearing, too.)

Now let’s step outside our solar system to explore a bit farther…

When we look up at a clear night sky, we see a multitude of stars twinkling back at us. (For those of us living in San Francisco, maybe fewer than those who live in less light-polluted parts of the world…) Some are close by, some far away, but for every single star we see in a dark, dark sky on Earth, there are tens of millions more we don’t see, all part of our Milky Way Galaxy. And the term “star” is a bit squishy—some objects clearly shine like “stars” while others glow dimly, not sustaining fusion in their cores but still visible in infrared light—and possibly looking quite a bit like that Gemini image of Jupiter that I mentioned earlier.

These “little stars that couldn’t” are known as brown dwarfs, and even that term encompasses a lot of different kinds of objects that blur the lines between lightweight stars and massive planets.

The closest known brown dwarf, Luhman 16 (actually a pair of brown dwarfs, Luhman 16A and Luhman 16B), lies at a distance of 6.5 light years—the third closest system to ours after Alpha Centauri and Barnard’s Star. This month, astronomers announced that they had observed “Jupiter-like cloud bands” on Luhman 16A. Our colleagues at Caltech created this artist’s rendition of the system (and this video, too), to give you a sense of what this object might look like.

Not too far away from Luhman 16 (or the Sun, for that matter), the “star” TRAPPIST-1 hosts seven Earth-ish-sized planets, and the system was actually the topic of the first “Cosmic Conversation” we held on the Morrison Planetarium Facebook page last Friday. I put quotes around the word star because the planets are in orbit around an extremely faint, “ultra-cool” red dwarf, not terribly dissimilar from the brown dwarfs I was just describing.

Last week, researchers announced a stunningly detailed observation of the TRAPPIST-1 system, measuring the rotation of three of the planets compared to the parent star. It turns out that the planets are rotating in nearly perfect alignment with the star—consistent with the way planets form from disks, as I described above. This alignment is reassuring, since the TRAPPIST-1 system should be fairly pristine, not subject to outside disruptions, which reinforces the aforementioned theory of planet formation.

That’s great news—the scientific equivalent of dotting the i’s and crossing the t’s on a very important idea. But I have to say that what’s really cool is that we’re actually starting to see planets forming around other stars!

Case in point: the amazing images of a disk around AB Aurigae showing remarkable spiral structures and swirls of materials where planets are taking shape. The press release refers to “signs of planet birth,” and it’s hard to disagree with what might be the first direct evidence of a planet forming. We’ve seen whole galleries of similar systems, but this image is pretty special! And a great way to cap off our stories about planets and exoplanets this month.

Now we head about 1,000 light years from home—to the closest black hole to Earth! (Part of HR 6819, a star system that is actually visible to extraordinarily eagle-eyed observers in the Southern Hemisphere, without the aid of a telescope or even binoculars!) The two stars visible in HR 6819 exhibit motion influenced by an unseen companion, which implies the existence of a black hole. Check out this awesome animation of what the system might look like.

As their name suggests, black holes don’t make their presence known by shining brightly (or even dimly, like a brown dwarf). Instead, we have to look for their gravitational influence on other objects—such as the two visible stars in the HR 8619 system.

And don’t worry! Even though this is the closest black hole we’ve yet discovered, it’s not headed toward Earth, gobbling stuff up en route. Black holes get a bad rap (I blame Disney), but they don’t just wander through space looking for hapless spacecraft or civilizations to devour. Besidese, 1,000 light years is still a long, long ways from us—and there are probably black holes even closer to home! We just haven’t found them yet…

For my last story, I’ll just note that in addition to the other tools I’ve mentioned (e.g., spacecraft, Earth-bound observatories, and computational models), our understanding of the Universe depends on laboratory experiments, too! Case in point: this week’s announcement about solving the longstanding mystery of matter and antimatter. Much like the press release about “new evidence” of plumes on Europa, the headline is a bit overwrought, but the results are interesting.

Turns out there is indeed a longstanding problem about the prevalence of matter in the Universe. Matter and antimatter are two sides of the seemingly symmetrical coin in physics, but most of what we see around us is “ordinary” matter, not antimatter (and yeah, okay, 96% of the Universe is actually “dark,” but I’m talking about the 4% that isn’t). As far as we understand, at the beginning of the Universe, matter and antimatter should have been created in equal quantities, but no… So what gives? Why did matter win out?

The short answer is that we don’t know, but one possibility is that neutrons possess an electric dipole moment in excess of what’s predicted by the Standard Model of particle physics. In addition to other effects, this could change the shape of some atomic nuclei, causing them to become pear-shaped instead of (roughly) spherical. Researchers in the U.K. have found that the element thorium-228 possesses just such an asymmetrical nucleus, making these nuclei (and similar ones) interesting subjects for further study.

So… Is is right to say that the “longstanding mystery of matter and antimatter may be solved,” as it says in the press release? Maybe not. But it’s pretty intriguing nonetheless…

Thanks for tuning in this month for “Universe Update”! More to come next month, via YouTube, Facebook, and this good ol’ webpage.