Universe Update, July 2014
By Ryan Wyatt
The third Thursday of every month, 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. This month, we’ll start at the Sun…
Our star goes through an eleven-ish-year cycle of activity that includes a “maximum” and a “minimum,” but also varies considerably from one cycle to the next. The current cycle, which began in January 2008, ranks as one of the dullest in the last century, with a particularly quiescent period in the last month, prompting the folks at SpaceWeather.com to ask, Where Did All the Sunspots Go? (And to quip, “Solar Max is not finished, it's just miniature.”)
Indeed, even at its most minature, the Sun cranks out magnetic fields, charged particles, and other radiation at a prodigious rate. Indeed, the Sun generated a significant solar storm back in 2012 that could have caused significant damage to modern technologies here at home if it had been directed toward Earth. Or as the New York Post described it in typically hysterical terms, “Solar flare nearly destroyed Earth 2 years ago: NASA.” Yikes!
Here at Earth’s distance from the Sun, we detect mostly the Sun’s magnetic field and the charged particles carried along with it… But if you reside as close to the Sun as, say, the MESSENGER spacecraft currently in orbit around Mercury, you can actually detect uncharged particles speeding away from the Sun—specifically, solar neutrons generated in the same energetic environments where the Sun’s powerful magnetic storms are born. Neutrons only last about 15 minutes outside the nucleus of an atom (after which time they decay into a proton, an electron, and an antineutrino), so they don’t have time to reach Earth before they effectively fizzle out. And yet, because the neutrons aren’t whipped around by magnetic fields (unlike the charged electrons and protons), they offer clues about the origin of the Sun’s energetic phenomena.
Moving on from the Sun, I’ll keep talking about objects in our solar system, but I’ll actually be avoiding the planets in favor of asteroids, comets, and moons…
For example, the second-largest asteroid, Vesta! This bad puppy ain’t big enough to qualify as a dwarf planet, but it nonetheless has a lot in common with the much larger Earth, and weirdly enough, about 5% of all meteorites discovered on Earth originated on this relatively tiny object, a mere 500 kilometers across. Vesta piqued astronomers’ interest enough to motivate sending the spacecraft Dawn there for an extended visit.
Those many earthbound meteorites, for example, mostly seem to have originated from a single, huge impact nearly a billion years ago. How huge? Enough to splatter 1% of Vesta’s mass all over the inner Solar System!
However ginormous that seems, the impact didn’t manage to tear its way all the way through the asteroid’s crust. (Y’see, part of what makes Vesta relatively similar to our home planet is that it appears to have a core, mantle, and crust, just like Earth.) A recent announcement describes how the chemistry of debris on the asteroid’s surface doesn’t match what we’d expect to find in its interior—in other words, the huge impact that created the debris only penetrated to the asteroid’s crust, no deeper. That means the crust goes down more than 80 kilometers, far deeper than expected. Because our current models of planet formation suggest that Earth and other planets formed from objects like Vesta (well, lots and lots of them sticking together), that means we need to rethink the details of our cosmic origins.
This is a great example of how geologists (planetary or otherwise) study the composition of materials to tell us about the history of Earth and other objects in the Solar System. As a press release from the Planck Institute for Solar System Research poetically describes it, “Rocks are silent storytellers: because each mineral is created only under certain conditions, they provide insight into the evolution of the body on which they are found.” Thus, the press release goes on to announce that other tell-tale signs on Vesta’s surface prove that much of its surface chemistry originated from impacts of smaller objects on its surface—more clues about the history of the asteroid and of our solar system in general.
For such a tiny place, Vesta has a lot to tell us about our past!
On the comet front, the Rosetta mission made breaking news throughout the month with its increasingly high-resolution images of Comet 67P/Churyumov-Gerasimenko (“67P” to its friends). Some folks even decided the nucleus of the comet looked a little like a rubber ducky. As of the end of July, the spacecraft is getting a remarkably sharp view of the comet (see above image), which still lies nearly 2,000 kilometers away. Rosetta will arrive at 67P next month, then land a probe on the comet’s surface in November!
We are also measuring how much water is sublimating from the comet’s surface: “ESA’s Rosetta spacecraft has found that comet 67P/Churyumov–Gerasimenko is releasing the equivalent of two small glasses of water into space every second, even at a cold 583 million kilometers from the Sun.”
Now, heading toward Saturn, we’ll forego a visit to the ringed planet, but we’ll take a close look at its giant moon Titan.
Under a thick layer of atmosphere, Titan’s surface has long tantalized astronomers. We know it has lakes and other bodies of, well, liquid muck, but now we’re also seeing evidence for seasonal changes, as the moon warms and cools with changing warmth from the Sun. “Bright spots in a large lake on Titan suggest that Saturn’s largest moon supports processes similar to Earth’s water cycle,” says Stanford’s Howard Zebker. But the frozen stuff is denser than its liquid form, so instead of floating, it sinks! “On Earth, ice floats and we get icebergs,” Zebker said. “On Titan, icebergs would sink.” Either way, we can observe the bright spots on Titan’s lakes appearing and disappearing with the seasons.
Waaay underneath Titan’s surface, astronomers have discovered evidence for an underground ocean. And now, according to a NASA press release, the “ocean on Saturn moon could be as salty as the Dead Sea.” Studying the shape of the moon as well as its gravitational influence on the Cassini spacecraft reveals that the ocean lying under Titan’s surface is quite dense, which “indicates the ocean is probably an extremely salty brine of water mixed with dissolved salts likely composed of sulfur, sodium and potassium. The density indicated for this brine would give the ocean a salt content roughly equal to the saltiest bodies of water on Earth.”
Leaving our solar system behind, we cross many light years in a matter of seconds, and we begin to encounter some of the many planetary systems that exist relatively close to home (albeit not close enough to relocate if and when we screw up our own pale blue dot). In the past month, we learned that some well-known “exoplanets” might actually be artifacts of the observations, which underscores the difficulty of interpreting the data.
Nonetheless, we feel confident that thousands of these exoplanets do indeed exist, and critically, most of them need better names… With monikers such as Gliese 581c and HD189733b and (one of the better ones) 51 Pegasi b, these planets need our help! At long last, the International Astronomical Union (IAU) has come to the aid of these poorly-christened worlds, introducing NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. “The proposed names will be submitted by astronomy clubs and non-profit organisations interested in astronomy, and votes will be cast by the public from across the world through the web platform NameExoWorlds. This platform is under development by the IAU in association with Zooniverse. The intention is that millions of people worldwide will be able to take part in the vote. Once the votes are counted, the winning names will be officially sanctioned by the IAU, allowing them to be used freely in parallel with the existing scientific nomenclature, with due credit to the clubs or organizations that proposed them.” The poor planets should be forever grateful…
To form planets (or even planet building blocks such as Vesta), we know that dust is an important cosmic ingredient. And astronomers know that dust is kind of a cosmic by-product, found all over the place, but its exact origins remain mysterious. We know that supernovae have something to do with the story, and although the details elude us, observations announced this month indicate that “these cosmic dust factories make their grains in a two-stage process, starting soon after the explosion, but continuing long afterwards.”
Leaving our stars and planets behind, we can head to the outskirts of our own Milky Way Galaxy, where astronomers have recently discovered the most distant stars in our galaxy (you can also check out the press release here). These two stars—ULAS J0744+25 and ULAS J0015+01—could use better names as much (or more) than those poor exoplanets I just mentioned, but the punchline is that they lie extremely far away—775,000 and 900,000 light years, respectively. (For comparison, the Sun lies a mere 30,000 light years from the center of the Milky Way.) Interestingly, astronomers discovered these far-away giants while searching for smaller, fainter stars much closer to home.
(Now that we’ve departed our galaxy, I’ll make a brief aside at this galactic scale… My vote for goofiest astronomy headline of the month: “Hi-ho! Astronomers discover seven dwarf galaxies” from Yale University, of all places.)
Our last story takes us to a truly cosmic scale…
Once upon a time, shortly after the Big Bang, the Universe was a hot mess. As it expanded and cooled, the electrons and protons (charged particles, remember) whizzing around all by their lonesome ended up combining into atoms (electrically neutral) in a process called “recombination” for some inexplicable reason. Then things got dull. For, like, hundreds of millions of years, during a period that astronomers call (in all seriousness) the Dark Ages. No stars, no galaxies, bo-ring.
Flash forward to a billion years after the Bing Bang, and the Universe seems to have re-ionized itself. To accomplish this feat would require a lot of ultraviolet (UV) light… But where did it come from? According to a new press release from Georgia Tech, computer simulations now reveal that the faintest galaxies illuminated the early universe!
This comes as a bit of a surprise, because most attention has focussed on large galaxies—with many, many stars emitting scads of UV light—as the primary culprit. But using sophisticated computer code led astronomers to a different conclusion. From the press release: “The researchers used computer simulations to demonstrate the faintest and smallest galaxies in the early universe were essential. These tiny galaxies—despite being 1000 times smaller in mass and 30 times smaller in size than our own Milky Way galaxy—contributed nearly 30 percent of the UV light during this process.”
The lesson? Don’t underestimate the little guys!
That’s all for now. Check back for next month’s update! Or join me at NightLife on Thursday, August 21st, 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: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA