An illustration of the New Horizons spacecraft as it approaches Pluto and its largest moon, Charon. 
 
 Nine and a half years after it launched into space, a NASA probe is set to become the first spacecraft to fly by the dwarf planet Pluto. The New Horizons spacecraft is expected to make its closest approach tomorrow (July 14) at 7:49 a.m. EDT (1149 GMT), coming within 7,800 miles (12,500 kilometers) of Pluto's surface. But even 4.67 billion miles (7.5 billion km) away, the historic mission could help scientists learn more about planet Earth. This is because studying other objects in the solar system can provide clues about Earth's history. Here are five things researchers can learn about Earth by studying the dwarf planet Pluto. 
 
 How Earth formed 
 
 Earth and the other planets in this solar system were likely born after a bunch of smaller objects smashed into each other. In fact, early in Earth's history, a Mars-sized object nearly annihilated the planet, according to NASA.The resulting pieces of debris eventually coalesced into the moon we see today. [Photo Timeline: How the Earth Formed] 
 
 Artist's impression of a planetary system being formed. Credit: NASA 
 
 Roughly 4 billion years ago, the inner solar system was a billiard zone, partly because Jupiter's strong gravity served as a slingshot that sent asteroids and comets hurtling toward the sun. In the region of space where Pluto is found, called the Kuiper Belt, icy and rocky objects had a relatively tranquil environment. This means that observing Pluto (and similar objects in the Kuiper Belt) offers hints about what the solar system looked like early in its history. 
 
 Where Earth's water came from 
 
 Last year, scientists discovered that water from comets may not have seeded Earth with life-building molecules, as had previously been thought. Observations from the European Rosetta spacecraft showed a different type of water on Comet 67P/Churyumov-Gerasimenko. The molecules of water (specifically, the deuterium-to-hydrogen ratio) were different from the molecules found on Earth, according to a study published in the journal Science in December 2014. 
 
 There are many objects in the solar system that are icy, including moons, dwarf planets and even parts of the planet Mars. It's possible that there is ice on Pluto as well, scientists have said. Examining the ice on the dwarf planet could help researchers refine theories about how water spread through the solar system. 
 
 How life began on Earth 
 
 Life on Earth is full of carbon. This is why the potential discovery of organics (carbon-based molecules) in other parts of the solar system is such an exciting prospect. While not every organic chemical originated from something living, they are considered the building blocks of life. 
 
 Are there organics even on icy, hostile Pluto? There are some reasons to think there may be, given that organics have been found in similarly life-unfriendly environments such as Mercury and Comet 67P/Churyumov-Gerasimenko. Finding organic material — or even not finding them — could give scientists a better idea of how life first arose on Earth. 
 
 Earth's atmospheric structure 
 
 Earth's atmosphere, as seen from high above the surface. Credit: NASA 
 
 Pluto has something of a bizarre atmosphere. The dwarf planet's gravity is so low that its tenuous atmosphere extends much higher than Earth's atmosphere does. Some scientists think the dwarf planet's atmosphere collapses onto the surface when Pluto is colder. Because Pluto's orbit is taking it closer to the sun right now, gases in the atmosphere are heating up and expanding. [5 Strange Facts About Pluto] 
 
 By studying the atmospheres of other worlds, astronomers can learn more about how these same processes work on Earth. For example, Venus has a hothouse surface driven by a runaway greenhouse effect. Measurements of Venus' superhot, hellish atmosphere have helped scientists better understand global warming on Earth. 
 
 How the sun affects Earth 
 
 Life on Earth wouldn't survive for long without the sun. Most of the heat on Earth comes from its closest stellar neighbor. The sun even has effects high in the atmosphere, such as when solar flares belch gas (called coronal mass ejections) toward Earth and "excite" molecules in its atmosphere, causing stunning auroras (also known as the northern and southern lights). 
 
 While auroras are benign, the sun's radiation can also zap power lines or satellites during so-called geomagnetic storms. Scientists are interested in seeing how the sun interacts with atmospheres throughout the solar system, including at Pluto. These observations will help researchers better predict the effects of intense solar activity, ranging from what happens after a solar flare to how the sun affects Earth's climate. 
 
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 The moon is home to some of the most lyrically named bodies of water that never existed. The Sea of Tranquility is familiar enough, but what about the Ocean of Storms, the Sea of Nectar, the Lake of Forgetfulness, the Bay of Rainbows? Altogether, the lunar map features 20 seas, 14 bays, 20 lakes and one ocean. That’s both poetic and ironic, because a world that’s positively drenched in aquatic names has not a drop of actual water. 
 
 Or that’s what we always thought. In recent years, however, evidence for a watery moon has been mounting—particularly from NASA’s Lunar Reconnaissance Orbiter and its sister probe, the Lunar Crater Observation and Sensing Satellite. The moon is hardly a sodden place—it’s wetter than the Sahara Desert, but that’s about it. Still, that’s huge compared to what we once believed. Now, a paper in Science explains in greater detail than ever how water got to so unlikely a place and how it survived the fiery violence that gave birth to the moon in the first place. 
 
 The prevailing—and now all-but universally accepted—theory for how the Earth-moon system came to be was first proposed in 1975 and quickly became known as the Big Whack theory. About 4.5 billion years ago, a Mars-sized planetesimal careered through the solar system and collided with the infant Earth, sending up a massive cloud of molten and vaporous debris. The hit-and-run world sailed on its way and the cloud of debris slowly accreted into the moon, eventually retreating to a stable orbit roughly 239,000 mi. (385,000 km) away, where it has remained ever since. 
 
 “The angular momentum, the distance, the size of the moon,” says Brown University geochemist Alberto Saal, the lead author of the Science paper, “there is no other model that can explain the physics of the Earth-Moon system than the Big Whack.” 
 
 (MORE: The Universe’s Biggest, Baddest Gamma Ray Burst Ever) 
 
 Physics isn’t chemistry, however, and none of this explained with any precision the elements and compounds—particularly water—that would have survived aboard the early moon. The inner solar system as a whole ought to be a very dry place. When the planets and moons that orbit the sun were first accreting, it took a very particular environment for water molecules to form. Anything too close to the sun would simply be too hot and energetic for H2O molecules to assemble themselves. You’d have to get about 3 astronomical units away (1 AU is the distance from the sun to the Earth) to reach what Saal calls the “snow line,” the place water could form. That boundary is roughly between Mars and Jupiter. 
 
 Nothing, however, would prevent water from being imported from the wet zone into the dry zone aboard comets or water-rich meteors known as carbonaceous chondrites. In recent years, comets have gained traction as the source of Earthly water. They’re mostly made of water ice and rock after all, and we now understand just how many billions—perhaps trillions—of them there are surrounding the solar system in the formations known as the Kuiper Belt and the Oort Cloud. 
 
 But there’s a good case to make for the carbonaceous chondrites too. They’re hardly the sodden snowballs comets are, and the little bit of water they do contain is integrated deep in their matrices. But there are a great, great many of the meteors flying around out there, and there’s nothing to say a downpour of rocks, rather than two or three comets, could not have watered us too. The growing study of exoplanets is helping to explain just how this could happen. 
 
 (MORE: Hopeful New Signs of Duplicate Earths) 
 
 “In 2011,” Saal says, “there were observations in other solar systems of large planets like Jupiter that probably migrated in towards their suns and then migrated back out, due to gravitational resonance. This would affect overall gravitational fields causing materials from deeper out to move in.” That material would likely include meteors. That same scenario could have played out here too, and there’s a relatively straightforward way to prove it. 
 
 Water comes in more than one form. So-called heavy water is not simple H2O, but 2H2O, containing a hydrogen isotope, known as deuterium. Unlike ordinary hydrogen, with just a proton in its nucleus, deuterium also contains a neutron. Heavy water and ordinary water are present on comets, carbonaceous chondrite meteors and Earth, but in different ratios, known as their deuterium/hydrogen, or D/H ratio. Studies since 1998 have shown that Earth’s D/H ratio is more similar to that of the meteors than of the comets, making a strong case for meteoric origins for Earth’s water. That case is not closed: a 2011 study of Comet Hartley 2 drew the opposite conclusion. Still, at the moment, the meteor camp is winning. 
 
 (PHOTOS: Windows on Infinity: Pictures from Space) 
 
 What Saal and his colleagues succeeded in doing was analyzing the D/H ratios in tiny beads of volcanically cooked glass in lunar samples brought back by Apollo 15 and Apollo 17 to see how closely they parallel Earth’s. The answer: exceedingly closely. “The moon’s D/H rations are similar to Earth’s and they’re both similar to the chondrites’,” says Saal. “What difference there is is probably due to the impact.” 
 
 So the moon’s water came from the Earth and maybe the impactor. But the fact that any water at all survived that collision is something of a surprise, since water’s extreme volatility should have caused it simply to vanish into space. Saal, however, cites research by Caltech astrophysicist David Stevenson and others that the blast might have created a sort of envelope of hot gasses, protecting the water while the moon accreted. 
 
 Of course, just as the Earth and moon drew apart in distance over time, so too did they part ways developmentally. The Earth’s greater gravity allowed it to retain an atmosphere, protecting the water that was there, as well as any that barreled in later. The moon could keep enough only to achieve its decidedly humbler wetter-than-the-Sahara status. Lunar gravity may turn the tides in our distant oceans, but the moon’s own seas and lakes and bays were—and always will be—mere phantasms. 
 
 (FROM THE ARCHIVES: Moon: From the Good Earth to the Sea of Rains)
– If you live and die by food and beverage expiration dates, you might not want to know how old some of our drinking water is. A study finds that 30% to 50% of the water found in our taps and oceans contains molecules created more than 4.5 billion years ago—making them older than our solar system and the sun, the Los Angeles Times reports. The findings from the study, published in Science, indicate that certain water molecules contain a deuterium atom instead of a hydrogen atom (making what's called "heavy water"), which could only be created under very cold, energy-replete conditions—specific conditions that didn't exist before the Earth, sun, and solar system were formed. Earth was actually "born dry," in an extremely hot environment, according to the Times. Scientists believe we eventually received water via comets or asteroids that crashed down on Earth's surface. Figuring out where the water in the comets and asteroids came from, however, is another story, though researchers think they've narrowed it down to two possibilities: that the heavy deuterium water was dispersed among bodies in the solar system during the "violent" process of our sun's birth, or that the heavy water originated from ice found in the gas cloud from which our sun and solar system were born. Either way, researchers say this could indicate that young planets all around the universe contain water: According to scientists, there are up to 11 billion planets outside our own system that could house liquid water and, possibly, life, notes Time. (The amount of water found on Mars surprised scientists around the world.)