вторник, 9 февраля 2016 г.

Pluto’s cutest geological feature, heart-shaped Sputnik Planitia, may have reoriented the whole planet.

Pluto’s cutest geological feature, heart-shaped Sputnik Planitia, may have reoriented the whole planet.
Pluto’s cutest geological feature, heart-shaped Sputnik Planitia, may have reoriented the whole planet.

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But that doesn’t solve everything. “The problem is it’s a hole in the ground. You’d expect less mass, not more,” says Francis Nimmo, a planetary scientist at the University of California, Santa Cruz, and author of the second paper. “So you have to come up with a way to hide that extra mass.” A subsurface ocean would certainly hide plenty of mass.

Nimmo sees Keane’s theory about the seasonal volatile creep, and raises some watery oceanic activity: When something big smacks into your icy crust, it’s going to make a dent. Sputnik Planitium’s mass might get heavier if whatever was hanging out below the surface was denser than nitrogen or water ice. Nimmo’s theory is that liquid water—which is denser than water ice—would provide enough mass to solve the riddle. So you’d have a double whammy of extra mass, from above and below.

So how do you get water on a dwarf planet—Pluto—that is famously an ice ball? “Temperature and pressure are linked,” Stern says. “Every time you go to deeper, the temperature rises. As you go deeper and deeper down into the water ice crust, and the pressure and temperature increases, eventually it turns to liquid water.”

From New Horizons, scientists learned that Pluto’s ice is pretty evenly distributed. When Pluto and Charon were younger and spun a little more rambunctiously, the angular momentum would have pushed the dwarf planet’s mass toward the equator, creating a bulge. But Pluto doesn’t have that kind of bulge, which according to Nimmo, makes sense if there is a subsurface ocean.

Pluto is also laced with these funky extensional faults, which suggests that its surface was forced outward—maybe by a water ocean expanding as it froze into less dense water ice, maybe by Cthulhu having a bad dream … just asking questions here. Anyway, this is why Sputnik Planitia factors in. “If you’re just freezing out an ocean, the orientations of the faults are random,” says Keane. “When you include this reorientation of Pluto, that also builds up stress, and a preferred orientation.” Result: Pluto’s faults radiate outward from Sputnik Planitia: reorientation ground zero.

So why does it matter that Pluto’s heavy heart dragged it onto a tidal axis? Well, by supplying a bit more proof of Pluto’s water ocean, it gives Plutonian researchers a bit more leverage to push for sending an orbiter out to confirm its existence. But also, it gives scientists another reason to keep looking further and further outward. “This is another piece of evidence suggesting the more Kuiper belt objects we visit, the more we’ll find they’re dramatically active,” Keane says. Geologically speaking, Pluto and its heart may be cold and icy, but they’re certainly not dead.

Original article and pictures take https://www.wired.com/2016/11/plutos-icy-heart-broke-pluto/ site

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