National Geographic Tales of the Weird

by David Braun

  The heart of Arp 220 is highly obscured by dust that can’t be penetrated by visible wavelengths. But radio waves can travel through such a dense environment to reach telescopes on Earth.

  TRUTH:

  INTERFEROMETRY USES THE COMBINED POWER OF MANY TELESCOPES, AS OPPOSED TO A SINGLE, HUGE TELESCOPE, TO CREATE HIGH-RESOLUTION IMAGES THAT CAN PROBE DEEP INTO THE UNIVERSE.

  “Something Amazing”

  Ultimately the data revealed about 40 radio sources near the center of Arp 220. By watching how these sources changed over time in two different radio wavelengths, astronomers could tell that seven of the objects were stars that had exploded around the same time.

  Astronomers estimate that our Milky Way galaxy sees only a single supernova every hundred years, on average, Batejat said. But the highly active Arp 220, with its dynamic cycles of star birth and death, behaves more like how young galaxies probably did more than ten billion years ago.

  “We hope this might lead to interesting discoveries on how stars formed [and died] in the early universe,” Batejat said. What’s more, such relatively fresh supernovae “are rare, and they have short lives of a few decades maximum” before they settle into supernova remnants, he said. “So discovering seven such supernovae at once is something amazing.”

  OUTER SPACE GOLD MINE

  Meteors Delivered Gold to Baby Earth

  “There’s gold in them thar meteors!” says a new study that supports the theory that meteors delivered gold and other metals to Earth billions of years ago.

  Not all that glitters is gold. But Earth would have a lot less of the glittery stuff if not for a massive rain of meteors about 3.9 billion years ago, according to a new study.

  Based on analysis of some of the world’s oldest rocks, scientists have the first direct evidence that a cataclysmic meteor shower changed early Earth’s chemical composition. The find offers support for the theory that meteors delivered gold and other precious metals to infant Earth.

  Gold Sank in “Magma Ball” Earth

  The presence of precious metals in Earth’s mantle and crust poses a puzzle because these elements are attracted to iron. When Earth first formed roughly 4.5 billion years ago, the planet was basically a ball of magma. As the planet cooled, denser material sank toward the center, eventually producing a core made mostly of iron.

  But that means any iron-loving—or siderophile—elements present in the primordial magma should have also retreated toward the core. In fact, based on the composition of meteorites thought to be akin to early Earth, our planet should have enough gold in its present-day core to cover the entire globe with a 12-foot-thick (4-meter-thick) layer of the precious metal.

  “All that stuff disappeared into the core, but we still find some gold around [the surface],” said study co-author Matthias Willbold of the University of Bristol. One possible answer for where the precious metals came from is that a “firestorm” of meteors called the terminal bombardment added a veneer of material to Earth’s surface some 650 million years after the planet’s formation.

  “Our work shows that most of the precious metals on which our economies and many key industrial processes are based have been added to our planet by lucky coincidence when the Earth was hit by about 20 billion billion tonnes of asteroidal material.”

  Matthias Willbold

  study co-author, University of Bristol

  Chemical Clues

  To find proof for this theory, Will-bold and colleagues studied rock samples from the Isua Greenstone Belt in Greenland. Although the Greenstone rocks date to about 3.8 billion years ago—close to the time of the terminal bombardment—“the mantle source from which these rocks are coming is from 4.5 billion years ago,” Willbold said. That means the rocks should retain chemical signatures that predate the massive meteor shower.

  By comparing those ancient rocks with modern ones, the researchers found that the two samples have different tungsten isotope ratios. Tungsten-182 was produced only in the first 50 million years of the solar system. But the Greenland rocks have more tungsten-182 than tungsten-184, the version of the element more commonly found in modern rocks.

  “These rocks that we found on Greenland are the only ones that show an anomalous tungsten condition,” Willbold said—a sign that meteor impacts did in fact change Earth’s surface composition.

  In general, based on the rate of impacts during the terminal bombardment, meteors slamming into Earth may have added about half a percent of the material now in the planet’s mantle, Willbold said. That may not seem like much, but it works out to about 20 billion billion tons, he added.

  PITCH BLACK

  Darkest Planet Found

  Coal-black, reflecting almost no light, this newfound world is off-the-charts dark—and the cause is a mystery, experts say.

  It may be hard to imagine a planet blacker than coal, but that’s what astronomers say they’ve discovered in our home galaxy with NASA’s Kepler space telescope.

  Exotic Exoplanet

  Orbiting only about three million miles out from its star, the Jupiter-size gas giant planet, dubbed TrES-2b, is heated to 1,800 degrees Fahrenheit (980 degrees Celsius). Yet the apparently inky world appears to reflect almost none of the starlight that shines on it, according to a new study.

  “Being less reflective than coal or even the blackest acrylic paint—this makes it by far the darkest planet ever discovered,” lead study author David Kipping said. “If we could see it up close it would look like a near-black ball of gas, with a slight glowing red tinge to it—a true exotic amongst exoplanets,” added Kipping, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

  “Being less reflective than coal or even the blackest acrylic paint—this makes it by far the darkest planet ever discovered.”

  David Kipping

  astronomer, Harvard-Smithsonian Center for Astrophysics

  NASA’s Planet Detector

  The Earth-orbiting Kepler spacecraft was specifically designed to find planets outside our solar system. But at such distances—TrES-2b, for instance, is 750 light-years from us—it’s not as simple as snapping pictures of alien worlds.

  Instead, Kepler—using light sensors called photometers that continuously monitor tens of thousands of stars—looks for the regular dimming of stars. Such dips in stellar brightness may indicate that a planet is transiting (passing in front of a star, relative to Earth), blocking some of the star’s light; in the case of the coal-black planet, blocking surprisingly little of that light.

  Black Planet Spurs Dimmest of Dimming

  When a planet passes in front of its star, the world’s shaded side faces Kepler. But as the planet begins orbiting to the side of and “behind” its star, its star-facing side comes to face the viewer. The amount of starlight grows until the planet, becoming invisible to Kepler, passes fully behind its star.

  Watching TrES-2b and its star, Kepler detected only the slightest such dimming and brightening, though enough to ascertain that a Jupiter-size gas giant was the cause. The light reflected by the newfound extrasolar planet, or exoplanet, changed by only about 6.5 parts per million, relative to the brightness of the host star.

  Experts believe the newfound gas-giant is black with a slight red glow. (Photo Credit 7.10)

  “This represents the smallest photometric signal we have ever detected from an exoplanet,” Kipping said. What’s more, as the coal-black planet passed in front of its star, the starlight’s dimming was “so small that it’s like the dip in brightness we would see with a fruit fly going in front of a car headlight.”

  The Dark Mystery of TrES-2b

  Current computer models predict that hot-Jupiter planets—gas giants that orbit very close to their stars—could be only as dark as Mercury, which reflects about 10 percent of the sunlight that hits it. But TrES-2b is so dark that it reflects only 1 percent of the starlight that strikes it, suggesting that the current models may need tweaking, Kipping said.

  Assu
ming the new study’s measurements are sound, what exactly is making the new planet’s atmosphere so dark? “Some have proposed that this darkness may be caused by a huge abundance of gaseous sodium and titanium oxide,” Kipping said. “But more likely there is something exotic there that we have not thought of before. It’s this mystery that I find so exciting about this discovery.”

  TrES-2b may even represent a whole new class of exoplanet—a possibility Kipping and company hope to put to the test with Kepler, which has so far detected hundreds of planets outside our solar system.

  Go Kepler, Go!

  The primary goal of NASA’s Kepler space telescope mission is to find rocky, Earthlike planets orbiting in stars’ habitable zones—the regions in which planets receive enough heat from their stars for liquid water to exist. While the finds haven’t quite yet met those criteria, they do show that Kepler is working as expected, offering a “tantalizing hint at what we can expect in a few years’ time,” says Greg Laughlin, an astronomer at the University of California, Santa Cruz.

  “As Kepler discovers more and more planets by the day, we can hopefully scan through those and work out if this is unique or if all hot Jupiters are very dark,” Kipping said. Meanwhile, the very darkness of the new exoplanet suggests perhaps a catchier moniker for TrES-2b, Kipping said. “Maybe an appropriate nickname would be Erebus”—ancient Greece’s god of darkness.

  POOR LITTLE PLUTO

  Should Pluto Be a Planet?

  Astronomers are still quarreling over Pluto’s status. The debate rages on as new finds continue to fuel the arguments over whether little Pluto should regain its planetary status—or not.

  Officially, Pluto is still not a planet.

  But years after the ruling that demoted the icy object to dwarf planet, people continue struggling with the definition, and the debate over what exactly should be called a planet remains as contentious as any political divide. “Maybe it’s just an argument over semantics, but we ought to be worried about semantics. We learned that lesson when the definition was changed,” said Marc Kuchner, a planetary scientist at NASA’s Goddard Space Flight Center in Maryland.

  TRUTH:

  IF YOU WEIGH 150 POUNDS ON EARTH, YOU WOULD WEIGH ABOUT 10 POUNDS ON PLUTO.

  Passionate about Pluto

  “After the ruling, astronomers everywhere were besieged by complaints from everyone big and small. A planet is a very personal thing—we think of the Earth, the moon, and the other planets as part of our home, and maybe that’s why we got so upset about Pluto.”

  Since the 2006 ruling, astronomers have also made a number of scientific advances that further cloud the issue, from discoveries of planets that don’t orbit stars to new models of how our own solar system may have rearranged itself since birth.

  Pluto’s Little Oddities

  The issue of whether Pluto should be a planet first arose in the 1970s, when scientists were able to refine their estimates for the mass and size of the distant body. With each new measurement, Pluto got lighter and tinier, until astronomers realized that the object is in fact smaller than Earth’s moon and has a very low density.

  Then in 1978, scientists announced they’d found a moon of Pluto—but one that’s almost half its size, making it the largest moon in relation to its parent body. During the ensuing decades, scientists continued to find similarly large objects in Pluto’s neighborhood, a region of the solar system beyond the orbit of Neptune called the Kuiper belt.

  “You don’t know how you’re supposed to feel about it at first. I’d like us all to think about the dwarf planets out there as new siblings that we have to get to know and learn to love.”

  Marc Kuchner

  planetary scientist, NASA’s Goddard Space Flight Center

  Definition Decision

  The biggest challenge for Pluto came in 2005, when Caltech astronomer Mike Brown announced that he’d found a Kuiper belt object more massive than Pluto—a potential tenth planet provisionally called 2003 UB313. The discovery prompted the IAU to convene a committee to decide on an official definition of a planet.

  “It was a bureaucratic problem, as it had to do with naming rights for these kinds of things,” said Owen Gingerich, the Harvard-Smithsonian astronomer who chaired the committee. After all, if 2003 UB313 really was a new planet, it would need a proper name on which everyone could agree.

  The committee initially proposed that there be two categories of planets: the classical planets and the group of planetlike bodies beyond Neptune, to be called plutons, “as a way of tipping our hat to Pluto,” Gingerich said. The planetlike object Ceres would have to be in a separate class because it resides in the main asteroid belt, between the orbits of Mars and Jupiter. So the committee suggested it be called a dwarf planet.

  An artist’s depiction of Pluto and its largest moon, Charon, are seen from one of the dwarf planet’s smaller moons. (Photo Credit 7.11)

  The draft definition was put to a vote in 2006 at the IAU general assembly in Prague, the Czech Republic. What emerged from the session is that, to be a planet, an object must

  1. be in orbit around the sun,

  2. have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and

  3. have cleared the neighborhood around its orbit.

  Instead of plutons, the IAU members present voted that Pluto, Ceres, and 2003 UB313—now known as Eris—would all be called dwarf planets, and that this term is not for a subclass of planets but is for a unique category of solar system objects.

  Exoplanet Exceptions

  At the time of the ruling, the IAU noted that the new definition does not apply to anything outside the solar system, leaving it unclear how the organization defines the planetary objects found orbiting other stars.

  Since 2006, there’s been an explosion in the number of these extrasolar planets, or exoplanets, known to exist, with the current count at more than 700 and rising. Many are bigger than the gas giant Jupiter, but astronomers have found an increasing number of worlds close to Earth’s mass, some of which may be habitable. And in the past few years astronomers have even found rocky planets akin to Earth’s mass that don’t orbit stars at all.

  By the current IAU definition, none of these objects are official planets because they violate the first rule about orbiting the sun. “I was disappointed when I learned that exoplanets were not included in the definition,” said NASA’s Kuchner.

  The second part of the definition, that planets must be massive enough to be nearly round, helped draw a line between bodies such as Pluto and large asteroids such as 433 Eros, a 21-mile-long (34-kilometer-long) space rock shaped somewhat like a peanut; the third rule, whether an object has cleared its orbital neighborhood, has proved the most controversial.

  Search for Planet X

  A self-taught astronomer from Kansas, Clyde Tombaugh built powerful homemade telescopes in the 1920s to scan the night skies. Hoping to get some feedback, he sent his findings to astronomers at the Lowell Observatory. Instead of a critique, he got a job offer and joined the staff at Lowell as part of their team searching for “Planet X,” the elusive planet beyond Neptune. After ten months of observations and photographing 65 percent of the sky, Tombaugh’s persistence paid off when he discovered the body we now know as Pluto.

  Judgment Calls

  Kuchner, who was a graduate student under Caltech’s Brown, thinks this part of the definition is the most subjective. In baseball, he said, “If you have a foul ball, it’s because the ball landed on one side of the line—that’s pretty clear. But it’s harder to say if something’s a strike … That relies on someone calling it.” In the case of defining a planet, IAU made the call, and “now we have to use this definition and try to play the game.”

  Overall, he added, the ruling was crucial for limiting the number of things in the solar system that deserve to be called planets. “We really didn’t have a choice,” he said. “It was either going to be ei
ght planets or a whole lotta planets. Nature sort of forced our hand.”

  But other astronomers aren’t in favor of placing those kinds of limits. “There are more than 200 bones in the human body. Does that mean we should redefine bones to make life easier for medical students?” argued Timothy Spahr, head of the IAU’s Minor Planet Center based in Cambridge, Massachusetts.

  Instead the IAU definition makes life more complicated for astronomers, he said, because the notion of whether an orbital neighborhood has been cleared remains hazy. As an example, Spahr points to the increased number of known Earth-crossing asteroids, including roughly 8,000 that are considered near-Earth objects. While these space rocks don’t exactly share our planet’s orbit, they do cross it, in the sense that when they are closest to the sun, they are inside Earth’s orbital path.

  “There’s certainly no big donut where Earth is, just a big mass of objects” that could be said to share our neighborhood, he said. This mass of objects will probably always exist, as asteroids in the main belt collide, break apart, and send new material on orbits closer to Earth’s. “In 50 million years our orbital neighborhood will look pretty much the same.” By some counts, that means Earth will not ever clear its orbit of debris.

  What Kind of Planet Are You?

  For his part, Spahr favors a simpler definition than the current version. “Orbiting a star and round is a good way to start,” he said. Planetary scientist Alan Stern at the Southwest Research Institute calls it the Star Trek criteria. He added: “If you can look out the viewfinder of the Enterprise and see it’s round, it’s a planet.”