Universe Update, October 2013
By Dan Brady
The third Thursday of every month, Morrison Planetarium hosts “Universe Update” at the 6:30 planetarium shows during NightLife. We select our favorite astronomy stories from the past month, and give a brief run-down of current discoveries while taking audiences on a guided tour of the Universe.
We start all of our Universe Updates right above Earth. Today we’ll start at the International Space Station. This month the orbital home to six astronauts has some big screen time with Sandra Bullock and George Clooney floating around inside. Apparently Gravity cost $100 million to produce. Well, the ISS cost considerably more—closer to $150 billion. But you can get into space for a lot less. Virgin Galactic is getting closer and closer to sending space tourists into sub-orbit (although questions about the input of black carbon into our atmosphere cause some concerns) for the low, low cost of two hundred and fifty thousand dollars. Come on, you’ve got that in your wallet or piggy bank, right?
The big news lately comes from around the neighborhood, our solar system. Juno is a spacecraft on its way to Jupiter—it was launched in 2011—and it’s designed to get a close-up view of Jupiter’s surface. But getting there is tough, since Jupiter gets as far as a billion kilometers away from Earth. So we had to use our home planet as a slingshot, taking advantage of our gravity to send Juno on a direct course to its target. Juno is still only halfway there: the spacecraft isn’t planning on arriving at Jupiter until mid-2016.
Speaking of our large, gaseous neighbors, some new data are telling us about what lies deep under their swirling cloud tops. We know there’s carbon in the atmospheres of Jupiter and Saturn, but when you then add immense heat and pressure from their enormous mass you get—diamonds! It’s possible that they’re just floating around in the atmosphere, planets full of diamonds (among other things). All the more reason to keep exploring out here: perhaps Juno will help fill in some of the details and confirm what we suspect.
Some of the most exciting stuff for star watchers isn’t these big planets but tiny balls of ice and dust, headed directly for the Sun. Several comets are hanging out in our neighborhood, so let’s figure out what they really are and where they come from.
Comets are mostly ice and dust—compared to asteroids, which are mainly rock and metal. We usually see them in slanted, elliptical orbits, because they come from the Oort Cloud—a frigid region of our solar system filled with potential comets, where ice is so cold it’s harder than rocks here on Earth. Some get close enough to the Sun that they start to get sucked in, like ISON. As the comet approaches the inner Solar System, the solar wind—energetic particles from the Sun—intensifies, blowing off dust and melting the ice, giving the comet a tail. This also means that comet tails always point directly away from the Sun, no matter where they are: sometimes these tails are behind the comet, but sometimes they’re out to the side, or even in front.
The comet ISON has been in the Solar System for some time, but only in the last month have astronomers been able to see it through telescopes as it swings farther from the Sun as seen from Earth (the comet continues to get closer to the Sun in space, but our perspective on the comet changes as it revolves around the Sun). Soon, we expect to get a great view in the night sky, and we won’t even need special equipment to get a glimpse. Astronomers were worried that it was going to get so close to the Sun that it might melt completely, but recent images from the Hubble space telescope show ISON holding it together.
These objects are small, and very dark until they get close enough to make a tail, so it’s often amateur astronomers who discover the new ones. Australian Terry Lovejoy just discovered his fourth comet (so it’s named after him), and it’ll be visible in November as well.
There’s been a lot of news in the Solar System lately, but this is a Universe Update, so let’s fly out and investigate some exciting developments a bit farther away from home…
Exoplanets, planets orbiting other stars, have been hot news lately. Astronomers have discovered thousands of candidates and more than 900 confirmed exoplanets, but for the vast majority, we only know the basic facts—orbital period (the length of their year), distance from their star, their size, and in some cases, what they’re made of. The next step is to figure out what’s on their surfaces: organic compounds, metals, or even liquid water. That last item is an essential ingredient to every bit of life on Earth, so it’s exciting to find in any form orbiting another star.
And that’s exactly what we see around the white dwarf GD 61, 150 light years from Earth. Watery asteroids are orbiting this tiny star that’s three times heavier than our own sun. While the orbiting asteroids are small (only about 500 meters across), it’s estimated that 26% of them may be frozen water. With so little gravity and such a hot parent star, this may not be a system that holds aliens of any form. But this observation tells us that water is out there, and these same techniques can be used to search for H2O in places more likely to have some extraterrestrials.
Each day we discover something new, and often unexpected, about these exoplanets. This past week, we learned that some don’t even orbit a star. A cleverer person than I might make a Star Wars-Death Star joke, something about that not being a moon, but I’ll spare you the misery. This is PSO J318.5-22, a rogue brown dwarf, the first we have directly imaged. What’s a brown dwarf, you ask? Great question. Years ago, we all learned the difference between stars and planets. Stars fuse hydrogen and helium, make heat and light, and planets orbit these stars—even the biggest, like Jupiter, aren’t big enough to start nuclear fusion. Well, you can forget all of that now. Brown dwarfs seem to occupy the muddy in-between: bigger than Jupiter, smaller than a star, and some, but not a lot, of nuclear fusion. Enough to warm the object and make it visible, but not enough to become bright like our sun. Sometimes they orbit other stars, sometimes they orbit each other, and sometimes—nothing at all. Pluto’s demotion notwithstanding, we can draw a spectrum between the rocky planets such Earth, all the way through giant planets and into stars. The line isn’t so clear after all.
Our galaxy is nice and all, but shouldn’t we check in on our neighbors? As we leave the Milky Way, local groups of galaxies zoom by. At this scale, each point of light is a whole galaxy, containing billions or even trillions of stars. And although we appear to be right at the center of the Universe (or just feel that way), that’s just the point from where we’re taking all the pictures. Someone in one of these neighboring galaxies would see themselves as the center as well. Confusing, I know, but when we’re dealing with a universe that’s accelerating outward, it starts to fit in.
Now, we’re zooming past early galaxies, and their precursors, quasars. As we look farther out into the Universe, we find we’re also looking back in time. Light takes time to move from place to place—it doesn’t move instantaneously—so we can measure distances using the time it takes light to travel, as well. We can look back at early galaxies, billions of years old, and learn how our galaxy may have formed. That is, until we reach the edge of what we can see, about 300,000 years after the Big Bang. This is the cosmic microwave background radiation, a baby picture of our universe. It was discovered by accident, and it permeates every inch of the Universe, giving it a constant temperature a few degrees above absolute zero, but it’s a barrier to our ability to look at our origins. Before this moment in our history, the Universe was so hot and so dense that not even light could travel through, which means we can’t look any deeper into space—any farther into the past.
Don’t tell that to the scientists in Switzerland, though. With the Large Hadron Collider, they’ve reached energies approaching the conditions of the Big Bang. While we can’t look at the event itself, at least we can build a model. And with that model they found the above image. Clear as day, right? It’s evidence of the particle that gives everything in the Universe mass. Such a simple concept was pretty hard to prove, which is why the scientists involved got a Nobel prize for it last week. This particle has all sorts of crazy properties, most incredibly, that it decays in less than one sextillionth of a second, making this image and the discovery all the more impressive. While these particles are everywhere, all the time, detecting them and photographing the result took enormous time and patience. Maybe not quite as much as it took to trigger the Big Bang in the first place, but still impressive.
Until next month…
Dan Brady is a planetarium presenter at the California Academy of Sciences. He earned his BS in Physics from UCLA and has taught science since 2008.