Podcaster: Morgan Rehnberg
Link : http://cosmicchatter.org
Black holes: http://cmns.umd.edu/news-events/features/2407
Description: In this episode of the Monthly News Roundup, we check in with spacecraft all over the solar system. New observations could shed light on a fascinating astronomical mystery.
Bio: Morgan Rehnberg is a graduate student in astrophysics and planetary science at the University of Colorado – Boulder. When not studying the rings of Saturn, he develops software to help search for asteroids that might hit the Earth. He blogs and podcasts about astronomy and space science at http://cosmicchatter.org.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2014, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at firstname.lastname@example.org.
You’re listening to the 365 Days of Astronomy podcast for August 31st, 2014. I’m Morgan Rehnberg and this is the Monthly News Roundup. This episode was produced by Cosmic Chatter August 26th from Boulder, Colorado.
Let’s begin this month with the long anticipated arrival of Rosetta. Launched more than ten years ago by the European Space Agency, the Rosetta spacecraft has spent the last decade journeying to Comet 67P/Churyumov–Gerasimenko. Since that’s quite the mouthful, let’s just call it 67P, shall we? After winding through the solar system, Rosetta has finally caught up with this wanderer and has matched its speed to fly in formation about 100 kilometers away.
You might recall that it’s going to take only about nine years for New Horizons to journey all the way out to distant Pluto, so what took Rosetta so long? It all has to do with its mission. Unlike New Horizons, which will fly by Pluto before heading out of the solar system, Rosetta plans an extended study of Comet 67P. This means it needs to exactly match the comet’s speed, but, unlike planets, 67P doesn’t have nearly enough mass to slow Rosetta down. Like one plane intercepting another, the spacecraft needs to approach the comet at just the right angle, which required a long and twisted trip through the solar system. Along the way, it passed Mars once and Earth three times, as well as flying by a couple of asteroids for close inspections.
Now that Rosetta is flying in formation with 67P, it will slowly begin to approach closer and closer. When it’s just a stone’s throw away later this year, it will release a tiny lander named Philae. Using a harpoon-like winch, this small craft will lower itself to the surface to make our first in situ observations of a comet.
Why do comets interest us? There’s actually a number of reasons. For one, most comets originate from the so-called “Oort Cloud,” a huge collection of icy bodies at the very edge of the Sun’s influence, far beyond the orbit of Pluto. They are too faint to see and too far away to visit, so we must wait until they come to us. Far away from the gravitational influence of planets like Jupiter, the comets of the Oort Cloud have likely remained undisturbed for nearly the entire age of the solar system. This means that they represent a unique window into our ancient past. Finally, many scientists believe that comets may have been instrumental in the early history of planet Earth itself, delivering much of the water and organic material that supports life as we know it.
If comets are your thing, then 2014 is the year for you. In additional to Rosetta’s groundbreaking work at 67P, another comet will be getting right in our face. In just a couple of months, Comet C/2013 A1 Siding Spring will pass just one hundred thousand kilometers from the planet Mars. That’s closer than the Moon is to Earth. Newly-arrived MAVEN will have an unprecedentedly close view of this object and, if it looks up, the rover Curiosity will see the comet stretching across the sky. Now, that will be a sight to see…
Next up, a trip to another galaxy to shed some light on a longstanding mystery in astronomy. In the century since Einstein’s theory of General Relativity first enabled their prediction, we’ve found black holes all over the universe. One thing, however, has long puzzled astronomers: black holes seem to either be pretty small or really, really big. So-called stellar mass black holes are the leftover cores of giant stars; they can weigh up to tens of times more than our Sun. Supermassive black holes, on the other hand, are millions or even billions of times heavier and are found at the centers are nearly all galaxies. But, why aren’t there any in the middleweights out there?
Since the 1970s, astronomers have speculated that a number of observed black holes might fill this gap, but measuring the mass of a black hole is very tricky business. A paper published this month in the journal Nature, however, seems to have broken through this barrier.
The team, led by astronomers at the University of Maryland, studied a black hole known as M82 X-1, located in the nearby galaxy M82. First discovered by NASA’s Chandra X-ray Observatory in 1999, M82 X-1 was subsequently studied for six years by another NASA satellite, the Rossi X-ray Timing Explorer. Over that time, it performed about 800 observations of the X-rays emanating from the disk of material falling into the black hole.
The X-ray light collected seemed to pulse and, upon closer examination, astronomers identified two distinct periods. One series of pulses occurred at a rate of 5.1 per second. A different series flashed 3.3 times per second. Divide these numbers and you find a ratio of almost three to two. More than that, it turns out that this beat is characteristic of a black hole’s size, a fact already used to measure the masses of smaller black holes. When the same techniques were applied to M82 X-1, a mass of about 425, plus or minus 100 times larger than the Sun was found. This makes M82 X-1 the first confirmed intermediate-class black hole.
Why is it important to find these medium-sized objects? Understanding their history could help unravel mysteries about their supermassive siblings. Although we have a good idea how small black holes form, the ones found at the centers of galaxies are more enigmatic. Did they form with their galaxies or before? How could they grow so large? Only by understanding the lifecycle, if you will, of a black hole can we hope to answer these questions.
Space might seem empty and, for the most part, it is. But, there is no such thing as a 100% vacuum and space is no exception. Gas and dust float through our solar system all the time. Most numerous are molecules of interplanetary hydrogen and interplanetary dust, tiny chips of material knocked off the surfaces of asteroids and planets during impacts. But a little bit comes from even farther away – so-called interstellar dust. This is dust that has floated away from other solar systems and into our own. And, this month, we found out we might have a little right here on Earth.
When I say we might have a little, I mean a little in the most concrete sense. Scientists with the Stardust mission announced this month that they have identified seven particles of interstellar dust. That’s right – seven.
Stardust was launched by NASA in 1999 with an ambitious goal: to collect particles from the tail of a comet and return them to the Earth. Five years later it flew by Comet Wild-2 (“Vilt-2”), extended a tennis-racket sized collection tray and swept up a bunch of particles. Two years later, it dropped the tray back into Earth’s atmosphere for scientists to retrieve and analyze.
So, if the samples were returned eight years ago, why are we just discovering these particles now? To answer this question, we need to understand a bit about how Stardust worked. Objects in space tend to be moving at speeds almost unimaginable here on Earth. As Stardust passed Wild-2, it was travelling with a relative velocity of 6.1 kilometers per second, or more than 13,000 miles per hour. If the spacecraft’s collection tray were simply a bucket, the particles striking it would just vaporize. Somehow, the particles needed to be slowed down gently, yet still quickly. The solution was to use a silica substance known as aerogel. A thousand times less dense than glass, aerogel is 99.8 percent empty space. When a dust particle strikes the surface, the aerogel gives way, but still slows its motion. It’s kind of like sticking your hand into a spider web.
As these particles swoop in, they carve tiny streaks in the aerogel, hundreds of times longer than their own size. The only way to find the microscopic particles is to look for the streaks, and the only way to find the streaks is to painstakingly examine photographs. A lot of photographs: more than a million, in fact. To speed up the search, astronomers crowdsourced the examination to citizen scientists, who identified the streaks for scientists to follow up on. Most streaks correspond to the intended target: Wild-2’s cometary tail. But, seven were on the side facing away from the comet – a prime target for a fast-moving interstellar dust particle.
These aren’t actually the first interstellar dust particles we’ve found, but they are different in an important way. All previous particles were found hidden deep within ancient meteorites. By dating the rock encasing them, we know these particles are billions of years old. The ones found by Stardust, on the other hand, are probably no more than 50 to 100 million years old – relative newcomers to our solar system!
By studying these particles, astronomers can gain firsthand knowledge of the composition of other parts of our galaxy. And, by comparing these samples to those locked in meteorites, we may be able to understand how that composition has changed. While seven particles isn’t enough, there may yet be more hiding within the aerogel of Stardust’s collectors. So, if you’d like a chance to spot a truly otherworldly object, join the Stardust@Home project and help advance science, one dust particle at a time.
It’s tough to believe, but it was two years ago this month that we sat gripped in seven minutes of terror as a hovering sky crane lowered NASA’s latest Mars rover to the surface of the Red Planet’s Gale Crater. Let’s take a look back at what the Mars Science Laboratory, better known as Curiosity, has discovered so far.
The mission was designed with four primary objectives in mind: First and foremost, scientists wanted to evaluate the habitability of ancient Mars. Following up on the work of the Mars Exploration Rovers Spirit and Opportunity, Curiosity was also to study the climate and geology of Mars. Finally, the rover is designed to measure and study the radiation environment on the Martian surface – a vital precursor to human exploration.
Right off the bat, Curiosity had no trouble identifying aspects of the Martian surface conducive to ancient life. Landing in a region of Gale Crater known as Yellowknife Bay allowed the rover easy access to clay-based sedimentary rocks, an ideal energy source for microbial life. Billions of years ago, streambeds like the one that formed Yellowknife Bay could have provided all the conditions necessary for sustaining life on Mars.
Year two has been a bit less eventful, as Curiosity drives towards Mount Sharp, a towering peak about ten kilometers from the rover’s landing site. Once it reaches the base of the mountain, exposed layers of rock will provide scientists with an excellent cross section of the geologic history of Mars. The way has not been easy, however, and sharp rocks have caused damage to the rover’s six wheels. Despite this, mission controllers are confident that Curiosity is well equipped to continue its journey.
The near future holds more driving for the rover, but also a new chance for collaboration. Next month, NASA’s latest mission to Mars, the MAVEN orbiter, arrives to study the middle and upper atmosphere of the planet. When combined with ground-based observations from Curiosity, scientists hope to finally piece together a complete picture of the Martian atmosphere.
Finally this month, the twenty-fifth anniversary of a major milestone in the history of exploration. It was in August of 1989 that Voyager 2 made the first and, to date, only flyby of the planet Neptune. The images it returned revealed a stunningly-blue world, with an atmosphere dotted by white clouds of methane ice. A faint ring system encircled the planet and fourteen moons, from the tiny to the enormous, hung in orbit.
In fact, it was one of these moons that stole the show. Neptune’s moon Triton is the solar system’s sixth largest and images from Voyager 2 revealed a world unlike any other ever glimpsed. Twisted, tortured terrain wove through regions of incredible smoothness. Clouds of nitrogen seemed to drift across a surface so cold that even distant Pluto couldn’t compare. And all this was discovered from observations of just forty percent of the moon’s surface.
So, in twenty-five years, why haven’t we gone back to explore this tantalizing world? Cynics would tell you that it’s because NASA has lost its ambition, settling for yet another mission to Mars in place of a truly challenging and groundbreaking mission like Voyager. But, fairer, I think, is the realization that the solar system is chock full of incredible places to visit and, enticed by rapid gratification, we’re starting with the ones nearby.
And what of the Voyagers? Well, just two years ago, Voyager 1 became the first manmade object to venture into interstellar space. We still receive signals from both vessels, relaying scientific observations about ever-more-distant parts of the Universe. We’ll continue to hear from them for about another ten years or so, at which point their nuclear-fueled power systems will run dry and they will continue off to silently travel the stars.
Thanks for listening to this episode of the Monthly News Roundup. For more astronomy news and commentary, visit http://cosmicchatter.org or follow @cosmic_chatter on Twitter. As always, you can contact us with your comments and corrections at email@example.com. See you in September!
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365 Days of Astronomy
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