Universe Update, October 2012
By Ryan Wyatt
The third Thursday of every month, give or take, Morrison Planetarium hosts “Universe Update” at the 6:30 planetarium shows 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. Y’see, the planetarium sports a tricked-out three-dimensional atlas of the Universe, so I can take you places virtually while talking about the latest astronomy news. This month, I presented last week, on the fourth Thursday, which serves as a warning to check out the special NightLife planetarium page before planning your trip!
At any rate, 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.
We’ll begin very close to home! In fact, enveloping our home planet… The European Space Agency (ESA) announced that “Earth’s magnetosphere behaves like a sieve,” describing results from ESA’s quartet of satellites called Cluster, which monitor the magnetic environment around Earth—what they call “our planet’s first line of defence against the bombardment of the solar wind.” The magnetosphere, it turns out, allows a considerable fraction of solar wind particles to permeate the region around Earth, so we should perhaps rethink our common analogy of a “shield” (I think “sieve” sounds a little wimpy, but I’m hard pressed to come up with something between a sieve and a shield…). NASA takes credit for the discovery, too, BTW. One more example of collaboration… By the scientists if not the press offices!
Speaking of the solar wind, particles streaming from the Sun are now identified as the “likely source of water locked inside lunar soils,” in announcements from the University of Michigan and the University of Tennessee. We detected water on the Moon’s surface some time ago, but its origin has remained unclear. According to the new theory, the solar wind deposits protons on the Moon’s surface, wich then combine with lunar oxygen to create water. Yang Liu from the University of Tennessee: “When those protons hit the lunar surface with enough force, they break apart oxygen bonds in soil materials to join together and form water. This does not happen on Earth because our atmosphere and magnetic field protect us from being bombarded by these protons, but the moon lacks this protection.” Cf. the previous story about Earth’s magnetosphere… Turns out a sieve (or whatever analogy you prefer) is better than nothing!
Moving farther afield, you may have heard about the Mini Cooper-sized rover currently exploring Mars. It recently set out on its long trek up the side of Mount Sharp (a.k.a. Aeolis Mons) and stopped along the way to sample and test its first rock, “Jake Matijevic” (pronounced “matt-EE-oh-vick” and named for an engineer who worked on several Mars missions). According to NASA, this first rock surprised geologists: “On Earth, rocks with composition like the Jake rock typically come from processes in the planet’s mantle beneath the crust, from crystallization of relatively water-rich magma at elevated pressure.” Or, in the words of Ralf Gellert of the University of Guelph in Ontario, Canada: “Jake is kind of an odd Martian rock.”
Curiosity doesn’t just zap rocks, though! Another instrument on board, the Dynamic Albedo of Neutrons instrument (but you can calll it “DAN”) measures water abundance on the martian surface. And a preliminary report suggests that Gale Crater, where the rover landed, is drier than expected—at least compared to measurements from the orbiting Mars Odyssey spacecraft. “The prediction based on previous measurements using the Mars Odyssey orbiter was that the soil in Gale Crater would be around 6% water. But the preliminary results from Curiosity show only a fraction of this,” said Maxim Mokrousov of the Russian Space Research Institute, the lead designer of the instrument. The orbiting spacecraft measures large swaths of the martian surface, whereas DAN looks right underneath the rover, so perhaps water abundance varies widely over the region.
Moving farther from home to visit the largest planet in the Solar System, we have a great story that highlights collaboration between amateur and professional astronomers. A news release describes work done by Glenn Orton, a senior research scientist at NASA’s Jet Propulsion Laboratory in Pasadena. Orton is studying global changes in Jupiter—and for the giant planet, that means global changes in its weather systems. We only see Jupiter’s cloud tops, although some layers lie deeper than others, and using infrared light, astronomers can uncover what’s happening beneath the uppermost layers of its atmosphere. Orton and his team took numerous infrared images of Jupiter, then compared them with amateur astronomers’ increasingly high-quality images taken in visible light. Combining multiple sets of data allows astronomers to tease out changes occurring over the last several years. They have also spotted many small objects colliding with the largest planet! “It does appear that Jupiter is taking an unusual beating over the last few years, but we expect that this apparent increase has more to do with an increasing cadre of skilled amateur astronomers training their telescopes on Jupiter and helping scientists keep a closer eye on our biggest planet,” Orton said. “It is precisely this coordination between the amateur-astronomy community that we want to foster.”
I already mentioned the giant impact scenario that describes the origin of Earth’s moon, but according to a press release from the University of California, Santa Cruz (UCSC), a similar process might be responsible for the distribution of Saturn’s moons. Jupiter has four huge moons, the Galilean satellites, which account for 99.998% of the total mass of staff orbiting Jupiter, along with scads of puny ones; Saturn, on the other hand, has a half-dozen mid-sized moons dwarfed by the massive moon Titan. The new proposal suggests that the middleweight moons were spawned when several larger bodies merged to form Titan. “We think that the giant planets got their satellites kind of like the Sun got its planets, growing like miniature solar systems and ending with a stage of final collisions,” said Erik Asphaug, professor of Earth and planetary sciences at UCSC. “In our model for the Saturn system, we propose that Titan grew in a couple of giant impacts, each one combining the masses of the colliding bodies, while shedding a small family of middle-sized moons.”
Meanwhile, on Titan’s surface, odd surface features have come to light (or rather, shown up on radar), observed by NASA’s orbiting Cassini spacecraft. Most interestingly, radar images have revealed the shorelines of ancient seas, yielding clues as to the recent history of Titan’s surface. Earth and Titan are the only places in the Solar System with stable liquid on their surfaces (although Titan’s seas consist of hydrocarbons rather than water), but Titan’s liquids show up only around the moon’s northern hemisphere. According to the press release, “a new analysis of Cassini images collected from 2008 to 2011 suggests there were once vast, shallow seas at Titan’s south pole as well. Ontario Lacus, the largest current lake in the south, sits inside of the dry shorelines, like a shrunken version of a once-mighty sea.” In a process similar to Milankovitch cycles on Earth, Titan’s climate may vary over tens of thousands of years, leading liquid hydrocarbons to transition from pole to pole… 50,000 years ago, the southern hemisphere might have been the wet side of the moon!
Looking at Titan in the long term, Athena Coustenis from the Paris-Meudon Observatory in France has analyzed data from more than thirty years of spacecraft missions—including Voyager 1’s visit in 1980, Infrared Space Observatory data from 1997, and Cassini observations from 2004 to present—along with ground-based observations. Because it takes nearly thirty years for Saturn to orbit the Sun, we now have a full “Saturn year” of data. The result? “Titan shows surprising seasonal changes!” The atmosphere appears to exhibit long-term variation in distribution of liquids on its surface and patterns of weather in its atmosphere—evidently driven by the light and heat from the distant Sun. Coustenis says, “It’s amazing to think that the Sun still dominates over other energy sources even as far out as Titan, over 1.5 billion kilometers from us.”
Even farther from the Sun than Saturn and its moon Titan lies Uranus… Another world that shows remarkable weather activity! New observations with the ground-based Keck Observatory have greatly improved the detail with which we can observe weather on the planet—the sharpest images of the planet to date. On Uranus, wind speeds can climb up to 560 miles per hour, in spite of the Sun’s weak radiation at that distance. The new technologies will allow scientists to monitor weather features whose movements can help trace out the planet’s high-speed winds.
Outside of the Solar System, but still quite close to home, the big news of the month is the discovery of an Earth-mass exoplanet in orbit around Alpha Centauri B—right next door to us, in the stellar system closest to our own. In case you’re thinking of packing your bags and moving, you should note that our fastest spacecraft would take about 10,000 years to reach the Alpha Centauri system, and once you arrived at the newly-discovered world, you would encounter a fairly inhospitable place. Orbiting a mere six million kilometers from its parent star, the admittedly Earth-sized planet is certainly almost scorched and dry. That said, during your 10,000-year journey, we might luck out and find another planet in the system (a bit of a gamble, though). Your travel plans aside, the current work is crazy impressive: like most exoplanet discoveries, the observation of minute back-and-forth motion in the parent star allows astronomers to determine the parameters of the system (the approximate mass of the planet, how long it takes to orbit its parent star, etc.), and these represent the highest-precision measurements of this kind ever made. The star moves back and forth at around a mile and hour—about the speed of a crawling baby! We covered this story already on Science Today, BTW, and I also wanted to point out that Luiz Calçada produced a lovely and accurate image for the press release that shows Alpha Centauri A, Alpha Centauri B, and our own Sun as seen from the newly-discovered planet.
These days, exoplanet discoveries come at us fast and furious, and the variety of worlds—as well as the tools and techniques used to ferret them out—fairly boggles the mind. In the past month, we had citizen scientists discovering a four-star system with an exoplanet in the mix, an “ultra-compact planetary system” that could offer clues as to how planets migrate into varying orbits over time, and even a likely diamond planet with “fundamentally different chemistry from Earth.” Science fiction planets seem, well, mundane by comparison.
The spiffiest visualization of the month comes from the European Southern Observatory’s announcement about the unexpected spiral structure observed inside a cloud of gas shed by an ancient star. Spectacular, detailed observations have revealed waves of material soughed off by the star, probably shaped by the gravitational influence of an orbiting companion. Astronomers have had to tease apart wavelengths of light to reconstruct what’s happening around the red giant, allowing them to create the video above, revealing the star in cross-section—a bit like an MRI of different “slices” through the star. Amazing stuff.
Unless you’ve been been asleep for the last decade or so, you’ve probably heard about dark matter, the mysterious stuff that interacts with ordinary matter (like us) only through the force of gravity. We know that our home galaxy, the Milky Way, is embedded in a dark matter halo, but how big, how massive? A research team from the National Astronomical Observatory of Japan has announced a refined measurement of the Sun’s speed around the galactic center, which in turn reveals the amount of matter (dark or otherwise) in the Milky Way. Once they account for the stars and other material in our galaxy, they come up with a value for the mass of dark matter that’s about 20% greater than previous estimates. A little like changing out your bathroom scale and finding you’ve gained a few pounds!
UCLA astronomer Andrea Ghez has tracked thousands of stars near the galactic center for many, many years–in part because you have to track them for quite a while to determine their trajectories and figure out how they’re affected by the gravitational pull of the black hole. This month, she and her team have announced the discovery of a particularly interesting star (dubbed, uninterestingly, S0-102) that orbits the black hole in about 11.5 years—the shortest orbit of any star yet discovered. Most stars have orbital periods in excess of sixty years, so S0-102 comes as a welcome addition to the catalog—the previous record-holder, S0-2, takes 16 years to orbit, and as we noted in an earlier Science Today post, these zippy stars can help define the exotic gravitational environment around the black hole. “It is the tango of S0-102 and S0-2 that will reveal the true geometry of space and time near a black hole for the first time,” Ghez said. “This measurement cannot be done with one star alone.”
Keeping an eye on action going on even closer to the supermassive black hole, NASA’s NuSTAR satellite has, for the first time, detected an energetic X-ray burst that probably resulted from material being dragged into the black hole, heated to about 180 million degrees Fahrenheit in the process.
NuSTAR may have a lot more to observe in less than a year or so… Scientists at Lawrence Livermore National Laboratory (LLNL) have used computer models to simulate the black hole’s gravitational effects on a could of gas and dust known as G2 (yes, an even less inspired name than S0-102, if you can believe it). Beginning next September, the intense gravitational field of the black hole will rip the cloud apart, and in a process that will last for at least several months, it will shed energy and become greatly distorted. The result? More fireworks visible in X-rays and radio wavelengths to telescopes here on Earth and out in space.
Two articles describe discoveries that make use of a technique known as gravitational lensing, which allows astronomers to measure the amount of mass in a given volume of space. An increasingly powerful tool for understanding the universe at large, albeit tricky to wrap one’s head around.
The first announcement comes from the University of Utah, where astronomers have found evidence that “big galaxies are crashing into other big galaxies to make even bigger galaxies,” according to astronomer Adam Bolton. “Most recent studies have indicated that these massive galaxies primarily grow by eating lots of smaller galaxies. We’re suggesting that major collisions between massive galaxies are just as important as those many small snacks.” Nice to know those galaxies aren’t ruining their appetites!
But the second announcement strikes me as possibly the most important story of the month. I mentioned the Milky Way’s dark matter halo, but dark matter also plays a critical role in the evolution of structure in the Universe, driving the increase in density that allows fro the formation of galaxies, stars, planets—and life! So we’d love to know more about it, or it least how it’s distributed in space. All our computer models suggest that, over time, dark matter gets stretched into long filaments, forming the so-called “cosmic web” that characterizes the large-scale structure of the Universe. So… (Take a deep breath! You’ve soldiered on through a significant build-up.) Astronomers using the Hubble Space Telescope have studied one of these filaments in three dimensions—for the very first time. The filament extends 60 million light years from one of the most massive galaxy clusters known, and if it’s at all typical of other filaments in the cosmic web, then more than half of all the mass in the Universe may reside in these structures! Far more than most theorists had predicted.
Scientists at the University of Cambridge claim to have found “giant black holes lurking in survey data” (there they go, lurking again), which had previously gone undetected because they sit enshrouded in thick dust. The poster child supermassive black hole, cleverly named ULASJ1234+0907, clocks in at 10 billion times the mass of the Sun—a full 10,000 times the mass of the Milky Way’s relatively wimpy supermassive black hole—making it one of the most massive black holes ever seen. 400 more such giants might hiding out, as yet undetected, in the observable universe.
And an announcement in much the same vein describes a quasar embedded in an especially dusty galaxy. Quasars shine quite brightly in the distant universe—appearing as points of light from here on Earth, but actually enormous bright beacons billions of light years away. Normally, the Hubble Space Telescope can disentangle the faint light of the beacon’s host galaxy, but in this particular case, artificially removing the light from the quasar left no trace of surrounding starlight. According to Rogier Windhorst of Arizona State University: “The underlying galaxy is everywhere much fainter than expected, and therefore must be in a very dusty environment throughout. It’s one of the most rip-roaring forest fires in the universe. It’s creating so much smoke that you’re not seeing any starlight, anywhere. The forest fire is complete, not a tree is spared.” Hmmm. Windhorst might have exhausted that metaphor, but we can at least take his point: this is a very unusual phenomenon, one of the dustiest galaxies yet observed.
Ryan Wyatt is the director of Morrison Planetarium and Science Visualization at the California Academy of Sciences.