Universe Update, August 2014
By Ryan Wyatt
The third Thursday of every month, the Morrison Planetarium hosts “Universe Update” at the 6:30 planetarium show during NightLife. I select my favorite astronomy stories from the past month, and I give a brief run-down of current discoveries while taking audiences on a guided tour of the Universe. As you may or may not know, the planetarium sports a three-dimensional atlas of the Universe, so we can take you places virtually while talking about the latest astronomy news.
I always start at Earth and work my way out to cosmological distances, so I’ll list the news stories in the same order—from closest to farthest from home. Typically, this approach leaves little room for a connecting storyline between the different news items. But a couple themes emerge from the stories I’ve selected this month, most notably related to the origin and evolution of planets and planetary systems… And the stuff between the planets and the stars.
We’ll start at the Moon (can’t get much closer, cosmologically speaking, than that). A recent press release announced quite simply that it’s still hot inside the Moon, which doesn’t sound much like news, but… We tend to think of Earth’s only natural satellite as a geologically dead object, slowly cooling off ever since the giant impact that formed it billions of years ago. But observations from the Japanese Kaguya (SELENE, Selenological and Engineering Explorer) mission revealed “an extremely soft layer deep inside the Moon,” warmed and softened by Earth’s gravitational influence. Basically, the same forces that cause oceans to experience tides cause the Moon’s interior to warm. And (spoiler alert) this process happens elsewhere in the Solar System as well… More on that in a moment.
As we leave the Moon behind, we find the orbits of the inner planets—Mercury, Venus, Earth (of course), and Mars—and just beyond, the majority of the asteroids. That said, many asteroids venture outside the “asteroid belt” we learned about in elementary school, and some follow orbits that take them even closer to the Sun than Earth. These rocky little worlds get a lot of attention because they can strike our home planet (ask the dinosaurs how well that worked out for them) or be mined for valuables (ask James Cameron about investing opportunities).
One such asteroid, with the memorable name (29075) 1950 DA, gets some press for its relatively high (but still miniscule) probability of impacting Earth in nearly 800 years, but this month, it got a different kind of attention. A press release from the University of Tennessee describes a new explanation for what actually holds the asteroid together—its high-speed rotation should cause it to fly apart—and researchers are suggesting that relatively exotic Van der Waals forces may play a significant role in keeping the “rubble pile” asteroid from disintegrating. Given that these forces normally hold together tiny things like molecules, this is no small feat! Nature magazine published the research paper as well as a great article with an accompanying audio interview.
Most comets reside even farther out than your average asteroid, but some venture close to the Sun. These visitors to the Inner Solar System typically don’t last very long, since light and heat from the Sun eventually causes them to evaporate (or more accurately, sublimate), forming the long tails that we earthbound observers have long associated with these occasional, unpredictable celestial guests. You may have heard of Comet ISON’s fateful journey last year, which ended with the comet disintegrating during its close approach to the Sun.
The comet du jour is certainly 67P/Churyumov–Gerasimenko (or “67P” for Russian-challenged astronomy buffs), what with its impending visit from the European Space Agency’s Rosetta spacecraft, which will soon send a probe down to the comet’s surface. Initial images made the comet’s nucleus look a little like a rubber ducky, with two oblong masses connected by a narrow neck. And now high-resolution images from the spacecraft are helping narrow the choices for a landing site for the aforementioned probe.
We can’t send a probe to every single comet, however, so we need to study observe of them from here on Earth…
The totally amazing, new Atacama Large Millimeter/submillimeter Array (ALMA) studied the atmospheres around two comets—ISON and Lemmon—to uncover the complex chemistry spewing from their heated nuclei. The press release describes what motivates the work: “Comets contain some of the oldest and most pristine materials in our Solar System. Understanding their unique chemistry could reveal much about the birth of our planet and the origin of organic compounds that are the building blocks of life. ALMA's high-resolution observations provided a tantalizing 3D perspective of the distribution of the molecules within these two cometary atmospheres, or comas.” When we observe a chemical in a comet’s coma, however, are we seeing chemistry that’s remained in cold storage since the early days of the Solar System—or perhaps the chemicals form as a byproduct of reactions occurring as the comet heats up close to the Sun? The ALMA observations confirmed the latter, that some of the chemical compounds, at the very least, are “produced during the breakdown of large molecules or organic dust in the coma.”
These cometary tales (pun intended) may seem esoteric, but each observation helps us piece together the chemical history of our planetary system—and helps illuminate the larger story of life’s origins.
Moving away from the inner solar system, we come to the realm of the giants—Jupiter, Saturn, Uranus, and Neptune—but we won’t visit the gassy planets. Instead, I want to highlight a couple stories about two fascinating moons, one of Jupiter’s and one of Saturn’s.
Back in 1979, imagery from Voyager 1 confirmed the existence of volcanoes on Jupiter’s moon Io. Astronomers have been studying the tiny moon ever since. Much as the Moon’s interior is heated by the tidal action of Earth’s gravity (see above), poor little Io gets stretched and pulled to an even greater degree by its giant parent planet. All this energy gets released in nearly constant volcanic outbursts, but about a year ago, astronomers observed “a hellacious two weeks” of activity, including one of the brightest volcanoes ever seen in the Solar System! Pretty crazy stuff, especially observed from hundreds of millions of miles away.
Meanwhile, around Saturn, we find similar activity on the tiny, icy moon Enceladus. Instead of Io’s pyrotechnics, however, the Cassini spacecraft reports observing 101 geysers spewing from the moon’s south pole. Furthermore, scientists matched up geysers to tiny hot spots, observed in infrared light. “Once we had these results in hand we knew right away that heat was not causing the geysers but vice versa,” said Carolyn Porco, leader of the Cassini imaging team from Space Science Institute in Boulder, Colorado and lead author on the first paper. “It also told us the geysers are not a near-surface phenomenon but have much deeper roots.”
Beyond the Solar System, we have plenty of stories to tell about new exoplanet discoveries—we’ve cataloged more than 1,800 planets outside the Solar System, and we continue to refine our observations to tease out amazing details about individual worlds, light years upon light years away from us. For example, this month, the Hubble Space Telescope announced the characterization of three “surprisingly dry” exoplanets, which surprised scientists by having “only one-tenth to one one-thousandth the amount of water predicted by standard planet-formation theories.” More work for those who want to understand how these systems form and evolve.
(If you happen swing by the Academy between September 2, 2014, and January 15, 2015, you can learn more about these discoveries when you see Life: A Cosmic Story at Morrison Planetarium. Our enthusiastic presenter team will highlight the latest exoplanet results in every show!)
But the most spectacular exoplanetary announcement this month comes from the ALMA telescope I mentioned earlier…
Planets form from disks of material that swirl around their parent stars, and we observe many of these nascent planetary systems around nearby stars. But take a look at the image above—that’s an actual image from ALMA (with a few added details from the Hubble Space Telescope) showing a pair of stars with their accompanying dust disks. Notice that the disks don’t line up! The two stars are like spinning tops that don’t line up with one another, in spite of the fact that they formed together and have “grown up” together. ALMA also measured the rotation of the disks and confirmed the weirdness of the system. As the press release notes, “These new ALMA observations provide the clearest picture ever of protoplanetary discs in a double star. The new result also helps to explain why so many exoplanets—unlike the planets in the Solar System—came to have strange, eccentric or inclined orbits.” The Universe continues to surprise us.
Taking an excursion outside our home galaxy, the Milky Way, it’s worth noting that we’ve traveled (virtually in the planetarium, mentally in this blog post) millions of times farther than we have physically explored. Our fastest, most distant spacecraft have traveled only a dozen or so light hours from Earth, and yet we have a pretty decent idea of what our galaxy (100,000-some-odd light years in diameter) looks like and what it’s made of.
Determining its mass is a bit of a challenge, though, and the Royal Astronomy Society recently announced that there’s “less to the Milky Way than previously thought.” They base their estimate on observations of the Milky Way’s large, similar neighbor, the Andromeda Galaxy, which lies some 2.5 million light years away. Turns out we weigh in at about half the mass of our neighbor… But that still makes us the two most massive members by far of our Local Group, which mostly includes so-called dwarf and irregular galaxies.
That’s all for now. Check back for next month’s update! Or join me at NightLife on Thursday, September 18th, and check out “Universe Update” live in the Morrison Planetarium.
Ryan Wyatt is the Director of Morrison Planetarium and Science Visualization at the California Academy of Sciences.
Image: B. Saxton (NRAO/AUI/NSF); K. Stapelfeldt et al. (NASA/ESA Hubble)