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Philae comet lander eludes discovery

Artist's conceptionExcerpt from bbc.comEfforts to find Europe's lost comet lander, Philae, have come up blank. The most recent imaging search by the overflying Rosetta "mothership" can find no trace of the probe. Philae touched down on 67...

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Science Increasingly Makes the Case for God



Excerpt from  wsj.com
By Eric Metaxas


The odds of life existing on another planet grow ever longer. Intelligent design, anyone?


In 1966 Time magazine ran a cover story asking: Is God Dead? Many have accepted the cultural narrative that he’s obsolete—that as science progresses, there is less need for a “God” to explain the universe. Yet it turns out that the rumors of God’s death were premature. More amazing is that the relatively recent case for his existence comes from a surprising place—science itself.
Here’s the story: The same year Time featured the now-famous headline, the astronomer Carl Sagan announced that there were two important criteria for a planet to support life: The right kind of star, and a planet the right distance from that star. Given the roughly octillion—1 followed by 27 zeros—planets in the universe, there should have been about septillion—1 followed by 24 zeros—planets capable of supporting life.
With such spectacular odds, the Search for Extraterrestrial Intelligence, a large, expensive collection of private and publicly funded projects launched in the 1960s, was sure to turn up something soon. Scientists listened with a vast radio telescopic network for signals that resembled coded intelligence and were not merely random. But as years passed, the silence from the rest of the universe was deafening. Congress defunded SETI in 1993, but the search continues with private funds. As of 2014, researches have discovered precisely bubkis—0 followed by nothing.
What happened? As our knowledge of the universe increased, it became clear that there were far more factors necessary for life than Sagan supposed. His two parameters grew to 10 and then 20 and then 50, and so the number of potentially life-supporting planets decreased accordingly. The number dropped to a few thousand planets and kept on plummeting.
Even SETI proponents acknowledged the problem. Peter Schenkel wrote in a 2006 piece for Skeptical Inquirer magazine: “In light of new findings and insights, it seems appropriate to put excessive euphoria to rest . . . . We should quietly admit that the early estimates . . . may no longer be tenable.”
As factors continued to be discovered, the number of possible planets hit zero, and kept going. In other words, the odds turned against any planet in the universe supporting life, including this one. Probability said that even we shouldn’t be here.
Today there are more than 200 known parameters necessary for a planet to support life—every single one of which must be perfectly met, or the whole thing falls apart. Without a massive planet like Jupiter nearby, whose gravity will draw away asteroids, a thousand times as many would hit Earth’s surface. The odds against life in the universe are simply astonishing.
Yet here we are, not only existing, but talking about existing. What can account for it? Can every one of those many parameters have been perfect by accident? At what point is it fair to admit that science suggests that we cannot be the result of random forces? Doesn’t assuming that an intelligence created these perfect conditions require far less faith than believing that a life-sustaining Earth just happened to beat the inconceivable odds to come into being?
There’s more. The fine-tuning necessary for life to exist on a planet is nothing compared with the fine-tuning required for the universe to exist at all. For example, astrophysicists now know that the values of the four fundamental forces—gravity, the electromagnetic force, and the “strong” and “weak” nuclear forces—were determined less than one millionth of a second after the big bang. Alter any one value and the universe could not exist. For instance, if the ratio between the nuclear strong force and the electromagnetic force had been off by the tiniest fraction of the tiniest fraction—by even one part in 100,000,000,000,000,000—then no stars could have ever formed at all. Feel free to gulp.
Multiply that single parameter by all the other necessary conditions, and the odds against the universe existing are so heart-stoppingly astronomical that the notion that it all “just happened” defies common sense. It would be like tossing a coin and having it come up heads 10 quintillion times in a row. Really?
Fred Hoyle, the astronomer who coined the term “big bang,” said that his atheism was “greatly shaken” at these developments. He later wrote that “a common-sense interpretation of the facts suggests that a super-intellect has monkeyed with the physics, as well as with chemistry and biology . . . . The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question.”
Theoretical physicist Paul Davies has said that “the appearance of design is overwhelming” and Oxford professor Dr. John Lennox has said “the more we get to know about our universe, the more the hypothesis that there is a Creator . . . gains in credibility as the best explanation of why we are here.”
The greatest miracle of all time, without any close seconds, is the universe. It is the miracle of all miracles, one that ineluctably points with the combined brightness of every star to something—or Someone—beyond itself.

Mr. Metaxas is the author, most recently, of “Miracles: What They Are, Why They Happen, and How They Can Change Your Life” ( Dutton Adult, 2014).

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Opening of the Box

Ihave been contacted by a certain benefactor who is willing to donate considerable funds to sponsor projects that are supporting the Lightworkers and Light forces as we are approaching the planetary liberation. This charitable account is an ongoing fun...

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Top 6 tips for using ordinary binoculars for stargazing




Excerpt from earthsky.org


Admit it.  You’ve probably got a pair of binoculars lying around your house somewhere. They may be perfect – that’s right, perfect – for beginning stargazing. Follow the links below to learn more about the best deal around for people who want to get acquainted with the night sky: a pair of ordinary binoculars.
1. Binoculars are a better place to start than telescopes
2. Start with a small, easy-to-use size
3. First, view the moon with binoculars.
4. Move on to viewing planets with binoculars.
5. Use your binoculars to explore inside our Milky Way.
6. Use your binoculars to peer beyond the Milky Way.

1. Binoculars are a better place to start than telescopes. The fact is that most people who think they want to buy a telescope would be better off using binoculars for a year or so instead.  That’s because first-time telescope users often find themselves completely confused – and ultimately put off – by the dual tasks of learning the use a complicated piece of equipment (the ‘scope) while at the same time learning to navigate an unknown realm (the night sky).
Beginning stargazers often find that an ordinary pair of binoculars – available from any discount store – can give them the experience they’re looking for.  After all, in astronomy, magnification and light-gathering power let you see more of what’s up there.  Even a moderate form of power, like those provided by a pair of 7×50 binoculars, reveals 7 times as much information as the unaided eye can see.

You also need to know where to look. Many people start with a planisphere as they begin their journey making friends with the stars. You can purchase a planisphere at the EarthSky store. Also consider our Astronomy Kit, which has a booklet on what you can see with your binoculars.

2. Start with a small, easy-to-use size.  Don’t buy a huge pair of binoculars to start with! Unless you mount them on a tripod, they’ll shake and make your view of the heavens shakey, too. The video above – from ExpertVillage – does a good job summing up what you want. And in case you don’t want to watch the video, the answer is that 7X50 binoculars are optimum for budding astronomers.  You can see a lot, and you can hold them steadily enough that jitters don’t spoil your view of the sky.  Plus they’re very useful for daylight pursuits, like birdwatching. If 7X50s are too big for you – or if you want binoculars for a child – try 7X35s.

February 24, 2014 moon with earthshine by Greg Diesel Landscape Photography.
February 24, 2014 moon with earthshine by Greg Diesel Landscape Photography.

3. First, view the moon with binoculars. When you start to stargaze, you’ll want to watch the phase of the moon carefully. If you want to see deep-sky objects inside our Milky Way galaxy – or outside the galaxy – you’ll want to avoid the moon. But the moon itself is a perfect target for beginning astronomers, armed with binoculars. Hint: the best time to observe the moon is in twilight. Then the glare of the moon is not so great, and you’ll see more detail.

You’ll want to start your moon-gazing when the moon is just past new – and visible as a waxing crescent in the western sky after sunset. At such times, you’ll have a beautiful view of earthshine on the moon.  This eerie glow on the moon’s darkened portion is really light reflected from Earth onto the moon’s surface.  Be sure to turn your binoculars on the moon at these times to enhance the view. 
Each month, as the moon goes through its regular phases, you can see the line of sunrise and sunset on the moon progress across the moon’s face. That’s just the line between light and dark on the moon. This line between the day and night sides of the moon is called the terminator line.  The best place to look at the moon from Earth – using your binoculars – is along the terminator line. The sun angle is very low in this twilight zone, just as the sun is low in our sky around earthly twilight.  So, along the terminator on the moon, lunar features cast long shadows in sharp relief.

You can also look in on the gray blotches on the moon called maria, named when early astronomers thought these lunar features were seas.  The maria are not seas, of course, and instead they’re now thought to have formed 3.5 billion years ago when asteroid-sized rocks hit the moon so hard that lava percolated up through cracks in the lunar crust and flooded the impact basins. These lava plains cooled and eventually formed the gray seas we see today.

The white highlands, nestled between the maria, are older terrain pockmarked by thousands of craters that formed over the eons. Some of the larger craters are visible in binoculars. One of them, Tycho, at the six o’clock position on the moon, emanates long swatches of white rays for hundreds of miles over the adjacent highlands. This is material kicked out during the Tycho impact 2.5 million years ago.

View Larger. Photo of Jupiter's moons by Carl Galloway. Thank you Carl! The four major moons of Jupiter - Io, Europa, Ganymede and Callisto - are easily seen through a low-powered telescope. Click here for a chart of Jupiter's moons
Photo of Jupiter’s moons by Earthsky Facebook friend Carl Galloway. Thank you Carl! The four major moons of Jupiter are called Io, Europa, Ganymede and Callisto. This is a telescopic view, but you can glimpse one, two or more moons through your binoculars, too.


4. Move on to viewing planets with binoculars. Here’s the deal about planets.  They move around, apart from the fixed stars.  They are wanderers, right?

You can use our EarthSky Tonight page to locate planets visible around now.  Notice if any planets are mentioned in the calendar on the Tonight page, and if so click on that day’s link.  On our Tonight page, we feature planets on days when they’re easily identifiable for some reason – for example, when a planet is near the moon.  So our Tonight page calendar can help you come to know the planets, and, as you’re learning to identify them, keep your binoculars very handy. Binoculars will enhance your view of a planet near the moon, for example, or two planets near each other in the twilight sky. They add a lot to the fun!

Below, you’ll find some more simple ideas on how to view planets with your binoculars.

Mercury and Venus. These are both inner planets.  They orbit the sun closer than Earth’s orbit.  And for that reason, both Mercury and Venus show phases as seen from Earth at certain times in their orbit – a few days before or after the planet passes between the sun and Earth.  At such times,  turn your binoculars on Mercury or Venus. Good optical quality helps here, but you should be able to see them in a crescent phase. Tip: Venus is so bright that its glare will overwhelm the view. Try looking in twilight instead of true darkness.

Mars. Mars – the Red Planet – really does look red, and using binoculars will intensify the color of this object (or of any colored star). Mars also moves rapidly in front of the stars, and it’s fun to aim your binoculars in its direction when it’s passing near another bright star or planet.

Jupiter. Now on to the real action!  Jupiter is a great binocular target, even for beginners.   If you are sure to hold your binoculars steadily as you peer at this bright planet,  you should see four bright points of light near it.  These are the Galilean Satellites – four moons gleaned through one of the first telescopes ever made, by the Italian astronomer Galileo. Note how their relative positions change from night to night as each moon moves around Jupiter in its own orbit.

Saturn.Although a small telescope is needed to see Saturn’s rings, you can use your binoculars to see Saturn’s beautiful golden color.  Experienced observers sometimes glimpse Saturn’s largest moon Titan with binoculars.  Also, good-quality high-powered binoculars – mounted on a tripod – will show you that Saturn is not round.  The rings give it an elliptical shape.

Uranus and Neptune. Some planets are squarely binocular and telescope targets. If you’re armed with a finder chart, two of them, Uranus and Neptune, are easy to spot in binoculars. Uranus might even look greenish, thanks to methane in the planet’s atmosphere. Once a year, Uranus is barely bright enough to glimpse with the unaided eye . . . use binoculars to find it first. Distant Neptune will always look like a star, even though it has an atmosphere practically identical to Uranus.

There are still other denizens of the solar system you can capture through binocs. Look for the occasional comet, which appears as a fuzzy blob of light. Then there are the asteroids – fully 12 of them can be followed with binoculars when they are at their brightest. Because an asteroid looks star-like, the secret to confirming its presence is to sketch a star field through which it’s passing. Do this over subsequent nights; the star that changes position relative to the others is our solar system interloper.

Milky Way Galaxy arching over a Joshua tree

Pleiades star cluster, also known as the Seven Sisters
Pleiades star cluster, also known as the Seven Sisters





5. Use your binoculars to explore inside our Milky Way.  Binoculars can introduce you to many members of our home galaxy. A good place to start is with star clusters that are close to Earth. They cover a larger area of the sky than other, more distant clusters usually glimpsed through a telescope.

Beginning each autumn and into the spring, look for a tiny dipper-like cluster of stars called the Pleiades.  The cluster – sometimes also called the Seven Sisters – is noticeable for being small yet distinctively dipper-like. While most people say they see only six stars here with the unaided eye, binoculars reveal many more stars, plus a dainty chain of stars extending off to one side. The Pleiades star cluster is looks big and distinctive because it’s relatively close – about 400 light years from Earth. This dipper-shaped cluster is a true cluster of stars in space.  Its members were born around the same time and are still bound by gravity.  These stars are very young, on the order of 20 million years old, in contrast to the roughly five billion years for our sun.

Stars in a cluster all formed from the same gas cloud. You can also see what the Pleiades might have like in a primordial state, by shifting your gaze to the prominent constellation Orion the Hunter. Look for Orion’s sword stars, just below his prominent belt stars. If the night is crisp and clear, and you’re away from urban streetlight glare, unaided eyes will show that the sword isn’t entirely composed of stars. Binoculars show a steady patch of glowing gas where, right at this moment, a star cluster is being born. It’s called the Orion Nebula. A summertime counterpart is the Lagoon Nebula, in Sagittarius the Archer.

With star factories like the Orion Nebula, we aren’t really seeing the young stars themselves. They are buried deep within the nebula, bathing the gas cloud with ultraviolet radiation and making it glow. In a few tens of thousands of years, stellar winds from these young, energetic stars will blow away their gaseous cocoons to reveal a newly minted star cluster.

Scan along the Milky Way to see still more sights that hint at our home galaxy’s complexity. First, there’s the Milky Way glow itself; just a casual glance through binoculars will reveal that it is still more stars we can’t resolve with our eyes . . . hundreds of thousands of them. Periodically, while scanning, you might sweep past what appears to be blob-like, black voids in the stellar sheen. These are dark, non-glowing pockets of gas and dust that we see silhouetted against the stellar backdrop. This is the stuff of future star and solar systems, just waiting around to coalesce into new suns.

Andromeda Galaxy from Chris Levitan Photography.
Andromeda Galaxy from Chris Levitan Photography.

Many people use the M- or W-shaped constellation Cassiopeia to find the Andromeda Galaxy.  See how the star Schedar points to the galaxy?  Click here to expand image.
Many people use the M- or W-shaped constellation Cassiopeia to find the Andromeda Galaxy. See how the star Schedar points to the galaxy?


6. Use your binoculars to view beyond the Milky Way.  Let’s leap out of our galaxy for the final stop in our binocular tour. Throughout fall and winter, she reigns high in the sky during northern hemisphere autumns and winters: Andromeda the Maiden. Centered in the star pattern is an oval patch of light, readily visible to the unaided eye away from urban lights. Binoculars will show it even better.

It’s a whole other galaxy like our own, shining across the vastness of intergalactic space. Light from the Andromeda Galaxy has traveled so far that it’s taken more than 2 million years to reach us.
Two smaller companions visible through binoculars on a dark, transparent night are the Andromeda Galaxy’s version of our Milky Way’s Magellanic Clouds. These small, orbiting, irregularly-shaped galaxies that will eventually be torn apart by their parent galaxy’s gravity.

Such sights, from lunar wastelands to the glow of a nearby island universe, are all within reach of a pair of handheld optics, really small telescopes in their own right: your binoculars.

John Shibley wrote the original draft of this article, years ago, and we’ve been expanding it and updating it ever since. Thanks, John!
Bottom line: For beginning stargazers, there’s no better tool than an ordinary pair of binoculars. This post tells you why, explains what size to get, and gives you a rundown on some of the coolest binoculars sights out there: the moon, the planets, inside the Milky Way, and beyond. Have fun!

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Ursid Meteor Shower Peaks: Here’s How to See It



Image: Geminid meteor shower
December is usually marked by a series of meteor showers. Geminid meteors (like the one seen in this picture of Florida) light up the skies at the beginning of the month, while the Ursids - which peak Monday night (Dec. 22) - put on a show just before Christmas.

Excerpt from space.com
 

The Ursid meteor shower peaks tonight, and it should be a great show. 

When skywatchers think of meteor showers during the month of December, the Geminid shower (which peaked earlier this month) usually comes to mind. But the Ursid meteor shower — peaking tonight and into the wee hours of Tuesday (Dec. 23) morning — should also offer skywatchers a good view this year. 

Even if you can't see tonight's meteor shower due to light pollution or bad weather, you can still catch the Ursids online thanks to the Slooh Community Observatory. Tune in for Slooh's Ursid meteor shower webcast tonight starting at 8 p.m. EST (0100 Dec. 23 GMT) live on Space.com. You can also watch the webcast directly through Slooh.
The Ursids are so named because they appear to fan out from the vicinity of the bright orange star Kochab, in the constellation of Ursa Minor, the Little Bear. Kochab is the brighter of the two outer stars in the bowl of the Little Dipper (the other being Pherkad), that seem to march in a circle like sentries around the North Star, Polaris. These meteors are sometimes called the Umids, in a rather unsuccessful attempt to make clear that their radiant is in Ursa Minor, not Ursa Major. 

The fact that Kochab is positioned so near to the north pole of the sky means that this star almost never sets for most viewers in the Northern Hemisphere. And since the Ursids seem to fan out from this particular region of the sky, you have a reference point to look for these faint, medium-speed meteors all through the night if you care to. 

The fact that the shower peaks tonight is good news for observers braving the cold to see the display. The moon is just one day past its new phase, meaning that light reflected from Earth's natural satellite won't wash out the shower.

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The End of the Space Race?




Excerpt from
psmag.com

A far cry from the fierce Cold War Space Race between the U.S. and the Soviet Union, exploration in the 21st century is likely to be a much more globally collaborative project.

Today, NASA’s goal to put astronauts on Mars by the 2030s could be a similarly unifying project. And not only in the United States. A far cry from the fierce Cold War Space Race between the U.S. and the Soviet Union, exploration in the 21st century is likely to be a far more globally collaborative project.

Why has the idea of reaching Mars captured the world? A trip to Mars is a priority for many scientific reasons—some believe it’s the planet that most resembles our own, and one that could answer the age-old question of whether we’re alone in the universe—but there’s also been a long popular fascination with the planet, Stofan observed. Ever since Giovanni Virginio Schiaparelli first observed the canali on Mars in the 1800s or when H.G. Wells wrote about aliens from Mars in his 1898 science fiction novel, The War of the Worlds, the planet has loomed large in the public’s imagination.

NASA’s view is to turn over to the private sector those projects that in a sense have become routine so that it can focus its resources on getting to Mars.

This spirit of trans-border ownership and investment seems set to continue. One key part of this is the Global Exploration Roadmap, an effort between space agencies like NASA, France’s Centre National d’Etudes Spatiales, the Canadian Space Agency, and the Japan Aerospace Exploration Agency, among many others, that is intended to aid joint projects from the International Space Station to expeditions to the Moon and near-Earth asteroids—and to reach Mars. On a recent trip to India’s space agency, Stofan recounted to me, she met with many Indian engineers who were just as excited as the Americans to get scientists up there, not only to explore, but also to begin nailing down the question of whether there was ever life on the red planet.

It’s also clear that the next stage of space exploration will not only be more global, but will equally involve greater private and public partnerships.

This environment feels a lot different from the secretive and adversarial Space Race days, when the U.S. and Soviet Union battled to reach the moon first. What’s changed? The Cold War is over, of course, but with it, the funding commitment may also be missing this time around. Stofan mentioned, in response to an audience question, that at the time of the Apollo missions, NASA got up to about four percent of the federal budget, while now it’s only around 0.4 percent. The dollars are still large, but perhaps increased international and private cooperation can be seen as an efficient, clever way to do more with less.

So, what does the future hold? NASA is extremely focused on how to get to Mars and back again safely, Stofan told the audience, but the fun role of science fiction, she suggested, is to start envisioning what the steps after that might be. For example, what might it be like to live on Mars? After all, science often gets its inspiration from the creative world. Just look at how similar mobile phones are to the communicators from Star Trek, she pointed out, or the fact that MIT students made a real-life version of the robotic sphere that Luke Skywalker trains with in Star Wars. “Stories are a great counterpoint to science,” she said.

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Is This What Really Killed the Dinosaurs?


Portrait of a killer: volcanoes were no friend to the dinos

Excerpt from time.com 

It wasn't just an asteroid

At the start of the 1980s, the question of what forced dinosaurs and huge numbers of other creatures to become extinct 65 million years ago was still a mystery. By the decade’s end, that mystery was solved: a comet or asteroid had slammed into Earth, throwing so much sun-blocking dust into the air that the planet plunged into a deep-freeze. The discovery of a massive impact crater off the coast of Mexico, of just the right age, pretty much sealed the deal in most scientists’ minds.

But a second global-scale catastrophe was happening at much the same time: a series of ongoing volcanic eruptions that dwarf anything humans have ever seen. They were so unimaginably powerful that they left nearly 200,000 square miles (518,000 sq. km) of what’s now India buried in volcanic basalt up to a mile and a half thick. And the gases and particulate matter spewed out by those eruptions, argue at least some scientists, could have played a big role in the dinosaurs’ doom as well.
How big a role, however, depends on exactly when the eruptions began and how long they lasted, and a new report in Science goes a long way toward answering that question. “We can now say with confidence,” says Blair Schoene, a Princeton geologist and lead author of the paper, “that the eruptions started 250,000 years before the extinction event, and lasted for a total of 750,000 years.” And that, he says, strengthens the idea that the eruptions could have contributed to the mass extinction of multiple species.

Schoene and his co-authors don’t claim volcanoes alone wiped out the dinosaurs; only that they changed the climate enough to put ecosystems under stress, setting them up for the final blow. “We don’t know the exact mechanism,” he admits. Volcanoes emit carbon dioxide, which could have triggered an intense burst of global warming, but they also emit sulfur dioxide, which could have caused global cooling. “What we do know,” Schoene says, “is that earlier mass extinctions were caused by volcanic eruptions alone.” The new dates, he and his co-authors believe, will help scientists understand what role these volcanoes played in the dinosaurs’ demise.

If there was such a role, that is, and despite this new analysis, plenty of paleontologists still doubt it seriously. The dating of the eruptions, based on widely accepted uranium-lead measurement techniques, is not an issue, says Brian Huber, of the Smithsonian Institution. “That part of the science is great,” he says. “It moves things forward.”

And those data, Huber says, make it clear that the extinction rate for the 250,000 years leading up to the asteroid impact wasn’t especially large. Then, at the time of the impact: whammo. The idea that volcanoes played a significant role in this extinction event keeps coming up every so often, and in Huber’s view, “the argument has gotten very tiresome. I no longer feel the need to put any energy into it. It’s from a minority arguing against overwhelming evidence.”

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Where does water actually come from? Comet evidence opening floodgates of mystery





Excerpt from slate.com

WE CALL Earth a water world, and that’s pretty fair: Our planet’s surface is 70 per cent covered in it, it makes up a percentage of our air, and there’s even a substantial amount of it mixed in to the planet’s mantle, deep underground. 

But where the heck did it come from?

This is no idle question. We have a lot of water here, and it must have come from somewhere. There are two obvious source — it formed here along with the Earth, or it was brought to Earth from space. Which is the dominant source has been a topic of long and heated debate among astronomers.

The first big science results have just been announced by the European science team working with the Rosetta probe, and, in my opinion, they throw more gasoline on the fire. Measurements made by the probe show that comets like 67P/Churyumov — Gerasimenko — the one Rosetta is orbiting — couldn’t have been the source of our water.

But that hardly helps answer the underlying question! Why not? Ah, the details …

When the Earth formed 4.55 billion years ago (give or take), there was a lot of water in the disk of material swirling around the Sun. Close in to the Sun, where it was warm, that water was a gas, and farther out it formed ice. We see that latter part echoed down through time now in the form of icy moons around the outer planets.

You’d expect water collected on Earth along with everything else (metals, silicates, and so on). When the Earth cooled, a lot of that water bubbled up from the interior or was outgassed by volcanism.

Where does water come from?
Where does water come from? Source: Getty Images
But we have another big source, too: comets. These are dirty snowballs, rock and dust held together by water frozen as ice. They formed farther out in the solar system, where ice was more plentiful. Long ago, just a few hundred million years after Earth formed and started to cool, there was a tremendous flood of comets sent down into the inner solar system, disturbed by the gravitational dance of the outer planets as they slowly settled down into their orbits. This Late Heavy Bombardment, as it’s called, could have supplied all of Earth’s water.

How to tell? Well, it turns out that in this one case, hipsters are right: Locally sourced is measurably different than stuff trucked in.
Water is made up of one oxygen atom and two hydrogen atoms. Hydrogen atoms, it so happens, come in two flavours: The normal kind that has single proton in its nucleus, and a heavier kind called deuterium that has a proton and a neutron (there’s also tritium, with two neutrons, but that’s exceedingly rare). Deuterium is far more rare than the normal kind of hydrogen, but how rare depends on what you look at. The ratio of deuterium to hydrogen in Earth’s water can be different than, say, water in comets, or on Mars.
Note I said, “can be”. We know the ratio differs across the solar system. But suppose we find the same ratio in comets as we do on Earth. That would be powerful evidence that water here began out there. Astronomers have looked at a lot of comets trying to pin down the ratio, and what they’ve found is maddening: Some comets have a ratio very different from Earth’s, and only one (103P/Hartley 2) has a ratio similar to ours.

Jets of material — including water — emanate from comet 67P/Churyumov — Gerasimenko.
Jets of material — including water — emanate from comet 67P/Churyumov — Gerasimenko. Source: AP
Now that’s interesting: 103/P is a Jupiter-family comet, meaning it used to orbit the Sun far out, but dropped into the inner solar system, got its orbit modified by Jupiter, and now has a much shorter path that keeps it in the inner solar system.
Rosetta’s comet, 67/P, is also a Jupiter-family comet. You’d expect them to have roughly similar deuterium/hydrogen ratios.

They don’t. 67/P, according to Rosetta, has three times the deuterium per hydrogen atom as Earth (and 103/P).
What does that mean? It’s not clear, which is why this is maddening. It could be simply that not all Jupiter-family comets have the same ratio; they may all have different origins (born scattered across the solar system, so with different D/H ratios), but now belong to the same family. Or it could mean that 67/P is an oddball, with a much higher ratio than most other comets like it. That would seem unlikely, though, since we’ve studied so few you wouldn’t expect an oddball to be found so easily.

Making things more complicated, some asteroids in the main belt between Mars and Jupiter have water on them, and it appears to have an Earth-like D/H ratio. But we think they have so little water that it would take a lot more of them impacting the early Earth to give us our water than it would comets. That’s possible, but we know lots of comets hit us back then, so it’s still weird that the D/H ratios don’t seem to work out. Still, it’s nice that there could be another potential source to study, and this new Rosetta result does lend credence to the idea that asteroids did the wet work.

So what do comets have to do with it?
So what do comets have to do with it? Source: Getty Images
So if you ask where Earth’s water come from, the answer is: We still don’t know...

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Warning: file_put_contents(/homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-content/cache/comet-cache/cache/http/dimensionalbliss-com/tag/clear/page/21.html-587ee983da132819866680-tmp): failed to open stream: Disk quota exceeded in /homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-content/plugins/comet-cache/src/includes/traits/Ac/ObUtils.php on line 409

Fatal error: Uncaught exception 'Exception' with message 'Comet Cache: failed to write cache file for: `/tag/clear/page/21/`; possible permissions issue (or race condition), please check your cache directory: `/homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-content/cache/comet-cache/cache`.' in /homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-content/plugins/comet-cache/src/includes/traits/Ac/ObUtils.php:414 Stack trace: #0 [internal function]: WebSharks\CometCache\Classes\AdvancedCache->outputBufferCallbackHandler('<!DOCTYPE html>...', 9) #1 /homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-includes/functions.php(3673): ob_end_flush() #2 [internal function]: wp_ob_end_flush_all('') #3 /homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-includes/class-wp-hook.php(298): call_user_func_array('wp_ob_end_flush...', Array) #4 /homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters('', Array) #5 /homepages/37/d125350870/htdocs/dimensionalbliss-www/ in /homepages/37/d125350870/htdocs/dimensionalbliss-www/wp-content/plugins/comet-cache/src/includes/traits/Ac/ObUtils.php on line 414