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The Cassini space probe’s fatal plummet into Saturn has revealed that the gas giant’s innermost ring sheds icy showers of rain and organic molecules into the planet’s upper atmosphere at an incredible rate.
Cassini finished a 13-year stint exploring Saturn and its moons just more than a year ago, but many scientific findings related to the dramatic exit are still being revealed. The probe swung through the gap between the giant planet and its famous rings 22 times, collecting as much data as possible before plunging into the planet’s atmosphere and burning up.
For years, researchers have known about Saturn’s “ring rain,” or the fact that the ring system around the planet delivers water to the upper atmosphere. But during its final swings around Saturn, Cassini’s gadgets measured the constant shower of nanosized particles. The rain is mostly composed of molecular hydrogen, but also contain lots of icy water as well as carbon compounds, like butane and propane, reports Elizabeth Howell at Seeker.
The sheer volume of material was one of the biggest surprises; Cassini measured 22,000 pounds of material per second fall from the rings. Most of the chemical slurry is being purged from the ring closest to Saturn’s atmosphere, the D-ring. At the current pace, the ring could be fully depleted in about 100,000 years.
“Turns out, ring rain is more like a ring downpour,” says planetary scientist Hunter Waite of the Southwest Research Institute and lead author of the study in Science. “While [the ion and neutral mass spectrometer] was designed to investigate gases, we were able to measure the ring particles because they hit the spacecraft at such high velocities they vaporized. Water ice, along with the newly discovered organic compounds, is falling out of the rings way faster than anyone thought—as much as 10,000 kilograms of material per second.”
The finding changes what we know about Saturn’s rings and its atmosphere. Co-author Kelly Miller, also a planetary scientist at the Southwest Research Institute, tells Howell at Seeker that the massive amount of ring rains suggests that Saturn’s D-rings are being fed material from Saturn’s larger C-rings, a new discovery. The data also suggests that there is lots of material in the D-ring that is too small to be picked-up by remote sensors, meaning directly sampling it like Cassini has done is the only way to detect it.
In fact, another recent study using Cassini data indicates that Saturn’s rings are only about between 150 and 300 million years old, and may not last forever, especially if they are constantly losing material to the planet below. But not everyone agrees with that interpretation and the age of the rings is still debatable.
“Are we just lucky enough to be in the period of time when Saturn has these magnificent rings?” Sean Hsu of the University of Colorado Boulder asks Nadia Drake at National Geographic. “It’s also fascinating to think that if a massive ring could form recently, that has implications for the other icy moons of Saturn.”
All that dust entering Saturn’s upper atmosphere also has major effects on its ionosphere, perhaps heating it up or changing its atmosphere.
“This gunk coming in chews up a lot of the ionosphere, affects its composition and causes observable effects—that's what we're trying to understand now,” co-author Thomas Cravens of the University of Kansas says in a press release. “The data are clear, but explanations are still being modeled and that will take a while.”
This wasn’t the only finding from Cassini’s Grand Finale released recently. Several other papers based on the data also published in Science reveal a new electric current system connecting the rings and upper atmosphere and a newly discovered radiation belt around the planet. Another study shows that Saturn’s magnetic field is nearly aligned with its spin axis, unlike any other planet studied. Astronomers were also able to collect radio transmissions from the planet’s poles. It’s expected that the Grand Finale data will reveal even more of Saturn's secrets.
“Many mysteries remain, as we put together pieces of the puzzle,” says Linda Spilker, Cassini Project Scientist at the Jet Propulsion Laboratory in Pasadena. “Results from Cassini's final orbits turned out to be more interesting than we could have imagined.”
Digitization and preparation of these materials for online access has been funded through generous support from the Arcadia Fund.
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Dorsey number 90-J (part). Old number 1436 (part)
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Earlier this week, NASA released a stunning image of the so-called Fireworks galaxy, which certainly lives up to its nickname. In the frame, two blue beams and one large splash of green paint the already dazzling galaxy.
But don’t dust off your telescope lenses just yet. Those pops of color aren’t within the visible light spectrum. They’re extremely bright bursts of X-ray radiation—and the green glow vanished in the course of ten days.
At first, NASA’s NuSTAR space observatory, which was searching for supernovas, didn’t spot the green X-ray emission, known as an ultraluminous X-ray source (ULX), according to a NASA press release. But ten days later, another look at the Fireworks galaxy revealed that the source—dubbed ULX-4—had sparked to life. Another ten days after that, the Chandra X-ray Observatory failed to relocate ULX-4. The observations are detailed in The Astrophysical Journal.
“Ten days is a really short amount of time for such a bright object to appear,” says the study’s lead author and Caltech astrophysicist Hannah Earnshaw in a statement. “Usually with NuSTAR, we observe more gradual changes over time, and we don’t often observe a source multiple times in quick succession. In this instance, we were fortunate to catch a source changing extremely quickly, which is very exciting.”
Most ULX’s are long lasting. Astronomers think they are created by super-dense objects—like black holes—feeding on nearby stars. The gravity of the black hole rips the star to pieces, creating a disk of debris. The material at the inner edge of the disk accelerates to speeds so fast that it heats up to millions of degrees and begins emitting powerful X-rays.
But that doesn’t explain how the mysterious green blob winked in and out of existence so quickly. The fact that no visible light was associated with the X-ray burst suggests that it was not a supernova, which usually shine brightly. The event was possibly a black hole gobbling up a very small star, which produced the short energetic burst.
Another possibility is that the event was created by a neutron star, the core of a giant star that collapsed in on itself during a supernova. Though they are only about 12.4 miles in diameter, these stars are super dense, with one teaspoon weighing a billion tons. Neutron stars' gravity is also about 2 billion times stronger than gravity on Earth.
These incredibly dense stars create debris fields like black holes. Typically, the strong magnetic field around a neutron star channels debris to the surface, where it produces a steady stream of X-rays as the material is heated up and obliterated. However, if a neutron star spins particularly fast, the study authors hypothesize, the magnetic field would block the material from reaching the surface.
“It would kind of be like trying to jump onto a carousel that’s spinning at thousands of miles per hour,” Earnshaw says.
If that magnetic barrier briefly wavered, allowing some debris through, it would cause the star to light up temporarily. The team hopes to watch the same spot to see if the green blob appears again, which would provide evidence for the neutron star theory.
ULXs were first catalogued in the 1980s, and until NuSTAR began investigating them in 2014, researchers thought they were all caused by black holes. New data, however, has led scientists to consider other possible sources of the bright X-rays. A study last year found that dips in the light spectrum of these ULXs were best explained if they were created by a neutron star, and researchers are beginning to find more and more ultraluminous X-ray sources that appear to be caused by neutron stars, not black holes.
“The discovery that these very bright objects, long thought to be black holes with masses up to 1,000 times that of the sun, are powered by much less massive neutron stars, was a huge scientific surprise,” says Caltech’s Fiona Harrison, principal investigator of the NuSTAR mission. “Now we might actually be getting firm physical clues as to how these small objects can be so mighty.”
From Whispering Galleries to Echo Chambers, These Five Architectural Structures Have Extraordinary Acoustics
From the gentle pitter-patter of raindrops on a bedroom window to the loud honking of horns in the city, noises are all around us. However, there are certain places around the world where acoustic anomalies occur that deserve a closer listen. Here are five manmade structures that demonstrate fascinating acoustic phenomena, transmitting whispers across a room or transforming sounds into unrecognizable new tones.
Hamilton Mausoleum, Hamilton, ScotlandHamilton Mausoleum, Scotland (iStock/jgshields )
One of the most iconic buildings in the town of Hamilton, located 15 miles southeast of Glasgow, is the Hamilton Mausoleum. But it’s what takes place inside its walls that makes it so intriguing. Built in the mid-1800s as a burial tomb for the 10th Duke of Hamilton, the 123-foot-tall Roman-style building was long billed as home of the “longest-lasting echo of any manmade structure in the world” thanks to its sheer size and shape. In fact, a single slam of its entrance door reverberates off the domed structure for a full 15 seconds. Unfortunately, it recently lost its title after a team of acoustic scientists successfully created an echo in an underground fuel depot that lasted an ear-splitting 112 seconds. But even despite thid defeat, the mausoleum still remains a popular draw and is likely one of the few places in the world where tour guides actually encourage visitors to slam doors. Listen here.
Grand Central Terminal Whispering Gallery, New York CityGrand Central Terminal's Whispering Gallery in New York City (<ahref="flickr url"="">David Hsu - Flickr/Creative Commons)
Throughout the day, Grand Central Terminal in Midtown Manhattan comes alive with bustling activity as commuters rush to catch their trains inside one of the city’s major transit hubs. Amid the noise, though, there’s one spot within the hundred-year-old building where it pays to be quiet. Located on the lower level near the Grand Central Oyster Bar, the “Whispering Gallery” has become a popular spot for visitors to engage in a moment of conversation that needn’t be at a shouting level. Thanks to the rotunda’s arched Guastavino tile work, two people can stand on opposite sides of the arch and, facing away from each other and towards each wall, hold a conversation at a muted tone despite being 30 feet apart. No one knows for sure if architects intentionally created the phenomenon, but it’s believed that the thin and tightly set terracotta tiles coupled with the ceiling’s curvature creates the ideal environment for this anomaly to occur. Listen here.
Temple of Heaven, Beijing, ChinaTemple of Heaven, Beijing, China (iStock/zhaojiankang )
Built in 1420 for the Yongle Emperor of the Ming dynasty, the Temple of Heaven in Beijing is a sprawling complex that encompasses 675 acres. The grounds are home to a number of ornate buildings, including the Hall of Prayer for Good Harvests, a massive triple-gabled structure set on a multi-tiered marble base. While impressive in its own right, one aspect of the complex that causes visitors to scratch their heads in wonder is the “Echo Wall” that encircles the iconic structure. It’s believed that a number of factors are at play for creating this echoing phenomenon, including the 12-foot-tall, 213-foot diameter wall’s curvature, its tightly constructed stonework and the eaves that run along its top, making it the ideal avenue for the transmission of sounds between two points along the wall. Listen here.
Whispering Gallery, National Statuary Hall, U.S. Capitol, Washington, D.C.Whispering Gallery inside the U.S. Capitol, Washington, D.C. (iStock/dkfielding )
There are a number of rotundas around the world where similar acoustic anomalies occur, including the Texas Capitol—but perhaps the most heavily trafficked one is the Whispering Gallery located inside the National Statuary Hall, a chamber within the U.S. Capitol. For years, echoes had been the bane of the Greek Revival structure’s existence due, in large part, to its tile floor and domed shape, which together helped to carry sounds throughout the chamber with little interruption. Although beautifully designed, it was problematic as it was frequently too loud for politicians to hold debates. Thus, over time, curtains and statuary were added to the interior. Despite this, one acoustic phenomenon still remains: if you stand directly in the center of the room while another person stands in the periphery, you can clearly hear his or her voice. Listen here.
El Castillo, Chichen Itza, Yucatan, MexicoEl Castillo in Chichen Itza, Yucatan, Mexico (<ahref="flickr url"="">Paul Simpson - Flickr/Creative Commons)
Perhaps among the strangest sound anomalies in the world is the one heard at El Castillo, also known as the Temple of Kukulcan, located in Chichen Itza, a city within the Yucatán state of Mexico. Built by the Maya civilization sometime between the 9th and 12th centuries, the ancient Mesoamerican step pyramid is part of a larger complex that includes a ball court, temples and various other buildings. While archaeologists are continually learning more about the complex and the Maya people every day, one aspect that remains a mystery is the strange sound that occurs when you clap your hands. All you have to do is stand in the field facing the exterior steps of El Castillo and do a single clap and you’ll immediately hear an echo that sounds eerily similar to a bird chirp. Listen here.
Although a lot of people are excited about wind energy, few are excited about the pinwheel-shaped machines that often produce it. Branded as noisy, blamed for spoiling bucolic views and proven deadly to some bats and migrating birds, the giant, white-bladed horizontal axis wind turbines that now dot the landscape of the American West have earned a fair number of detractors—even among environmentalists who generally favor renewable power.
But what if you turned the idea sideways, and created a turbine that could spin like a carousel? And what if you made a turbine small enough to sit on top of a building or inside an urban park? Could the result produce enough power to really matter?
The idea isn’t a new one—people have been playing with windmill designs and experimenting with alternatives to the horizontal axis turbine for almost a century now. But in the last two decades, a flurry of interest in expanding renewable energy in cities has attracted the attention of a large number of inventors and artists, many of whom see the vertical axis wind turbine as promising.
There is no single design for these upended wind catchers, but all share one key aspect: the blades turn around an axis that points skyward. And unlike their horizontal brethren, the components and associated generators of a vertical turbine are placed at its base, giving it a lower center of gravity. Most are also relatively small, and unlike horizontal units, they can be grouped very closely together to optimize efficiency.
In many large cities, including New York, San Francisco, Boston and Chicago, city officials and scientists have been studying vertical axis turbines and contemplating their use. Paris has embraced the notion with enthusiasm, even allowing two giant turbines of this type to be installed within the steel latticework of the Eiffel Tower, which might someday generate enough electricity to power the ground floor of the tourist attraction. Some private firms worldwide have begun integrating vertical axis turbines into architectural plans for commercial buildings.
But vertical turbines have also attracted a sizable number of skeptics and naysayers.
“You can make a [vertical axis wind turbine] that will produce electricity,” says Robert Preus, a researcher at the National Renewable Energy Laboratory in Colorado who helped develop certification criteria for small wind turbines in the U.S. “The question is whether or not you can do so competitively.”
There hasn’t been enough research to make vertical turbines durable and affordable, Preus points out. Not enough is known yet about how long the equipment will last, and there’s not always a solid guarantee of return on investment. There also aren’t enough of these machines being produced commercially to bring down the price, which remains stubbornly high—in some cases running into tens of thousands of dollars per unit. Many questions remain unanswered about how much energy a small vertical turbine on top of a building can produce. And although enthusiasts claim that the smaller vertical turbines don’t kill flying animals such as birds, there has not been a great deal of data gathered yet about their overall impact on wildlife.
There is, however, an abundance of people willing to experiment, sometimes via shaky financial backing, with the emerging turbine technology. The Internet is littered with websites for now-bankrupt companies, proclaiming the glory of these machines and their capabilities, as well as an almost endless list of enthusiastic articles, often full of myths about them. In some cases, those stories may be overstating their potential, or using outdated information to present an inaccurate portrait of them.
One of the most popular misconceptions, says engineer Richard Cochrane from Exeter University in the UK, is that all vertical axis wind turbines are silent, or at least less noisy than all of their horizontal counterparts on large wind farms.
“There are some vertical axis machines that are very noisy, because they didn’t put into so much effort into the aerodynamics of the machine,” Cochrane says. There are also some newly developed horizontal axis turbines that are incredibly quiet.
For several years, Cochrane was part of a team working on a machine called the Quiet Revolution. His research team placed prototypes in more than 200 different locations throughout the UK, including on the top of school buildings, in suburban parks and on the edge of shopping center parking lots, all the while measuring both performance and energy production and gathering feedback on issues like noise and aesthetics. He was able to gather an enormous amount of information about the potential of small vertical turbines before pulling out of the project after becoming frustrated by an investor’s push to take the turbine to market quickly.
Some engineers have voiced skepticism, for example, about the potential of harnessing wind power in built-up areas. Buildings and trees tend to cause turbulence and reduce steady currents, especially at ground level or on rooftops. But there were several locations on the outskirts of towns and near the seaside where Cochrane and his team were able to get strong, steady, reliable wind, even on top of buildings.
“We ended up kind of jokingly referring to it as the machine for suburban wind, rather than urban wind,” Cochrane says.
Either way, the vertical design seems to inspire a lot of sculptural engineering. Horizontal blades turning toward a person on the ground may set off a subconsciously intimidating feel. But vertical blades, by contrast, are often said to be mesmerizing, peaceful and relaxing to watch. They are often mistaken for public art.
“The noise of the old machine might have put people off,” Cochrane says. But to him it seemed like more of a subconscious thing. “They liked to see the vertical one turning.”
As two of the oldest Ivy League schools in the country, both Yale and Harvard possess some serious academic cred—and some seriously bitter rivalries. This weekend, the two schools will face off in a football game that dates back to 1875 and is so famous, it’s merely referred to as “The Game.” Still, the universities do have some unexpected commonalities, including their most popular class. As the Boston Globe’s Steve Annear writes, the most popular course at Yale is now CS50, an intro to computer science course taught by a Harvard University professor.
David Malan, a Harvard computer scientist, has drummed up quite the following—both within and outside of his employer's halls. His course has been ranked as one of Harvard’s hardest, writes Michael Farrell for the Boston Globe, but it’s also one of the university’s most popular, garnering immense enrollment and cult status on campus.
Malan took the course on the road in this fall, including a pilot program he created for teaching it at Yale. Annear writes that it’s the first time that Yale and Harvard students are classmates—they watch live-streamed or archived lectures and work with a Yale-based team for sections and office hours. At Yale, the course is called CPSC100, but Malan tells Annear that the experience is “nearly identical on both campuses.”
So what’s so special about the class? CS50/CPSC 100’s website explains that the class, which is designed for computer science majors and non-majors alike, “teaches you how to think more methodically and how to solve problems more efficiently. As such, its lessons are applicable well beyond the boundaries of computer science itself.” More practically, some students may be drawn to the class given the fact that software developers are now some of the most sought after and well paid employees in the nation.
But Yale might want to draw on some of the class' more lofty lessons during The Game this weekend—as Paul Doyle reports for The Hartford Courant, a Yale win could mean that Harvard loses its chance at the Ivy League title. In both sports and academics, turnabout is fair play.
The South Carolina Aquarium marked an important milestone on May 27, 2017 when it opened the doors to its new Zucker Family Sea Turtle Recovery facility. Located alongside the banks of the Charleston Harbor and housed within the aquarium, the recovery center is a state-of-the-art facility that will serve both as a hospital for sick or injured sea turtles and an educational facility offering the public a glimpse into the rescue, rehabilitation and release of these aquatic reptiles.
Since opening 17 years ago, more than 200 sea turtle patients have passed through the aquarium’s doors—but it didn’t originally set out to become a world-class turtle hospital. In fact, it took the unexpected arrival of one severely dehydrated loggerhead named Stinky to inspire the creation of the aquarium’s current Sea Turtle Care Center, South Carolina’s main hub for sea turtle rehabilitation.
Located inside the building’s basement, the hospital has grown in size over the years, going from a slapdash facility comprised of kiddie pools subbing in for tanks, to a facility equipped with the latest technology to help diagnose and treat patients. However, over the years it became apparent that the hospital was outgrowing its facility, especially if it wanted to involve the community with its mission to help save sea turtles in ways that went beyond simply inviting them to releases back to the ocean.
The new facility significantly expands both the patient and the visitor areas. The new, upgrade tanks nearly double the hospital's previous patient capacity, and can accommodate larger turtles, including adult loggerheads that are known to reach sizes of more than 300 pounds. The new tanks were designed in such a way as to keep turtles’ health and wellbeing at the forefront—meaning tanks are equipped with one-way glass so that visitors can peer in but turtles can’t see them. The glass also lets veterinarians and volunteers do visual examinations of the turtles at all angles, thus minimizing the need for physical human interaction, which can prove stressful to patients. The tanks are also set behind a glass wall to minimize any human disturbances such as tapping on the glass.
“As architects were designing the tanks, we had animal-care experts in the meetings to ensure that the final designs would be best for our patients,” says Kelly Thorvalson, sea turtle rescue program manager. “Each tank will be equipped with a tablet where visitors can swipe through and learn about each patient’s medical situation, what it looked like ... upon admission and more.”
The new facility also gives visitors visual access into an operating room and a CT scan room, where they can see chief veterinarian Shane Boylan and his team working on patients whose injuries can range from boating accidents to entanglements with fishing lines to digesting plastic.Visitors can practice mock surgeries using VR. (South Carolina Aquarium)
“Just like in a typical hospital, we triage patients,” Boylan says. “This can mean stopping any bleeding, assessing injuries, conducting supportive therapy such as oxygen and administering drugs or vitamins. Nine times out of ten, we can save patients, even those with catastrophic wounds.”
In addition, the new facility features mock medical stations using augmented reality technology where visitors can perform triage steps on mock sea turtle patients, like checking vital signs just as Boylan does. Finally, the new care center features a 40-seat classroom and theater that features daily programs and videos showcasing a sea turtle’s journey from being a patient to his or her return to the ocean.
“Education is a major part of the recovery plan,” Thorvalson says. “[The new facility] will allow us to educate guests in a more powerful and meaningful way.”
When should babies stop breastfeeding? Given the explosive response to a 2012 TIME cover of a woman breastfeeding a three-year-old child, that question is a controversial one at best. But when it comes to primates, orangutans, it seems, have all other species beat, reports Austa Somvichian-Clausen for National Geographic. They breastfeed their young for up to eight years.
Studying orangutan nursing habits, however, is far from easy. Orangutans like to climb and nurse at night, clasping their babies close, making it almost impossible to make direct observations of how everything works in the wild—or how long they nurse.
But it turns out there’s a clue to when orangutans wean: their babies’ teeth. The teeth and other bones of orangutans that drink mothers’ milk contain the element barium. So researchers decided to analyze the barium levels in orangutan teeth in the hopes it would serve as a kind of backdoor to their nursing habits.
They detail their findings in a paper in the journal Science Advances. The team studied four immature orangutans that were shot in the wild and their bones housed in zoological museums.
Since teeth grow outwards, kind of like trees, they’re like time capsules of different growth periods. Using a mass spectrometer, the team analyzed the layers of each of the orangutan’s teeth, measuring barium as an indicator of times during which they drank a lot of their mothers’ milk.
They found that though barium levels fell after a year—when the babies presumably started eating solid foods—it was still present years later. Though the barium levels varied among the animals, they showed much longer periods of breastfeeding than previously expected. One of the orangutans was shot when it was nearly nine years old, and still had barium in the outer layers of its teeth.
That’s significant for two reasons. Not only does it mean that orangutans nurse longer than any known primate, but it could reveal important information about how breastfeeding evolved in humans. The team hypothesizes that during food shortages, orangutans breastfed their older kids instead. In turn, that could help other researchers figure out times of environmental variation for early humans or even when they started living longer and needing less breast milk.
Barium has already revealed clues about prehistoric humans: In 2013, researchers found that one Neanderthal breastfed continuously for about seven months and stopped intermittent feeding by 1.2 years of age. Perhaps information about how orangutans breastfeed—and how that milk benefits their young—could one day influence how long their human cousins nurse their babies.
A new theory about how the moon formed might also tweak our understanding of early life on Earth.
The presence of gold and platinum in Earth's mantle has previously been assumed to be the result of a heavy shower of meteors raining down on early Earth, but new research suggests another source—one enormous impact with the object that crashed into the planet to create the moon.
Around 4 billion years ago the Earth was under constant attack, according to geophysicists. Asteroids and meteors continuously smashed into the planet for about 100 million years, a period known as the Late Heavy Bombardment. Any life on the planet at that time would be in constant peril.
We know about these impacts not because of the craters they left—erosion and plate tectonics have long spirited those away—but because of the presence of certain metals in the Earth's mantle. The pockmarked surface of the moon, which is not tectonically active, also helps bolster this theory.
But new research suggests that the bombardment may have been milder than expected, because the metals found in Earth's mantle could instead be from the moon-forming impact, about 500 million years earlier.
Early in the life of the solar system, a growing world known to scientists as Theia collided with the young Earth. The violent impact liquefied Earth's outer layers and pulverized Theia, creating a ring of debris that swirled around the scarred world. Iron from Theia's core drew together to form the heart of the moon. The remaining heavy material rained back down on Earth, and gravity drew the lighter components together to create the moon.
But new research suggests not all of Theia's iron built the lunar core. Instead, some may have settled on Earth's crust, and was later drawn into the mantle through plate tectonics. Elements such as gold and platinum, which are drawn to iron, may have been pulled into the mantle along with it. Such elements are sparse in the lunar mantle, presumably because all of the iron delivered to the moon created its core while Earth's original core remained intact after the collision.
That could mean good news for life on the early Earth. If Theia's core brought in traces of iron that attracted scarcer, iron-loving elements, the rain of asteroids and meteors couldn't have been as heavy as previously estimated.
"The Earth is not going to be completely unhabitable for a long period of time because the bombardment is relatively benign," says Norman Sleep, a geophysicist at Stanford University. Sleep investigated the idea that Theia could have brought platinum and similar elements to Earth's mantle, comparing it with previous suggestions that meteors delivered the material. In a recent paper published in the journal Geochemistry, Geophysics, Geosystems, he found that Theia could have brought in enough iron-loving elements to suggest later bombardment was milder than previously considered.
"It was certainly not anything we would survive, but we're dealing with microbes," he says.
However, without a heavy bombardment of meteorites, a new problem arises. The collision between Theia and the young Earth would have vaporized any water on the planet. The leading theory for how Earth got its water back is via collisions with water-carrying meteorites, but meteorites would also have delivered more iron-loving elements along with iron, leaving behind too much gold and platinum than measured. That means Sleep's calculations would require another method of bringing water to the planet.
That doesn't make the theory a deal-breaker. "There's no guarantee that there's one event that solves every problem," says Tim Swindle, who studies planetary materials at the University of Arizona. Water could have come from another source unrelated to Theia.
Figuring out exactly what happened in the early life of Earth and its moon may require a return to our satellite. "We've got to go back to the moon and get a better handle on the age of the basins," Swindle says, especially those on the back side of the moon. "We might be able to get an age with a rover that could answer the questions, but I think we'd do better to bring the samples back." That doesn’t necessarily mean humans have to be onboard the lunar mission, but, as Swindle points out, people do a great job.
Sleep agrees, calling for a visit to the South Pole Aiken basin, the largest and oldest of those on the moon. That basin has never been sampled, and should provide insight into the timing of the bombardment, which would give clues into how much material rained down on Earth.
According to Edward Young, a planetary scientist at the University of California at Los Angeles, the biggest result of Sleep's research is the mental shift it requires for the scientists studying Earth and the moon. "I think what he's doing is exposing the soft underbelly of what we do," Young says, adding that geochemical arguments are filled with basic assumptions of the processes that go into building the Earth and moon. "He's challenging some of those assumptions."
Portland Head Light (Portland)
As Maine's first and most famous lighthouse, Portland is located near the entrance to Portland Harbor at Fort Williams Park in Cape Elizabeth. Commissioned by George Washington, it was built in 1791. It is visited by thousands of people each year, and today is one of the most photographed lighthouses in the country.
The Fort Knox State Historic Site (Prospect)
One of the best-preserved Civil War era forts in the country. This massive granite fortification overlooks the Penobscot River and features several interpretive displays. Guided and self-guided tours are available. During the summer there is a special event each weekend, ranging from Civil War encampments to blacksmith demonstrations.
The Maine Lighthouse Museum (Rockland)
The museum displays a large exhibit of items relating to lighthouses and is home of the largest collection of lighthouse lenses, and one of the most important landmark collections of lighthouse artifacts and Coast Guard memorabilia in the United States.