Earth, Atmospheric and Planetary Physics
The physics of the Earth, its atmosphere and climate, and of other planets and moons.
arXiv: physics.geo-ph, physics.ao-ph, astro-ph.EP
18 topics
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The Atlantic overturning circulation carries warm water north, and the West Antarctic ice sheet rests on bedrock below sea level. Both may have thresholds beyond which they change abruptly and do not recover.
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Thunderclouds make lightning even though their electric fields seem too weak to break down air, and they sometimes shoot out bursts of gamma rays. Ball lightning, glowing spheres seen after storms, still has no accepted explanation.
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Climate sensitivity is how much Earth eventually warms if the CO2 in the air doubles. The answer is uncertain mostly because nobody knows well how clouds will change as the planet warms.
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Origin of the Moon and of Earth's water
6 problemsThe Moon probably formed when a Mars-sized body hit the young Earth, yet Moon rocks are chemically almost identical to Earth rocks, which the simple version of that story does not predict. Where Earth's oceans came from is likewise unsettled.
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Earthquakes happen when stressed faults suddenly slip, but how a slip starts, how fast friction collapses, and why it stops are poorly understood. As a result no one can reliably predict when a large earthquake will occur.
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Geodynamo and geomagnetic polarity reversals
7 problemsEarth's magnetic field is made by churning liquid iron in the outer core, and every so often the north and south magnetic poles swap places. Nobody can yet say what triggers a swap or what kept the field alive for billions of years.
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Giant planet interiors and Saturn's ring age
7 problemsJuno and Cassini showed that Jupiter and Saturn do not have a small, sharp rocky core; heavy material is smeared over a large fraction of the planet. Cassini also measured Saturn's rings in a way that suggests they are young, which is now hotly disputed.
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Inner core age, anisotropy and rotation
6 problemsAt the center of Earth is a solid iron ball about 1220 km in radius, growing as the liquid core around it freezes. How old it is, why seismic waves cross it faster in some directions, and how it turns relative to the rest of the planet are all disputed.
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Earth's rocky mantle flows slowly like very thick syrup, carrying heat from the core to the surface. Seismic images show two continent-sized odd regions at its base and columns that may rise to volcanic hotspots, but what they are is debated.
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Icy-moon oceans and ice-shell interiors
5 problemsSeveral moons of Jupiter and Saturn hide liquid-water oceans under shells of ice. How thick the ice is, what heats the oceans and how material moves between surface and ocean decide whether they could support life.
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Deep-time and glacial paleoclimate puzzles
6 problemsRocks, ice cores and seafloor mud record climates very different from today, from a warm early Earth under a dim Sun to planet-wide ice ages and sudden jumps in temperature. Several of these episodes still have no agreed explanation.
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Planetary magnetic fields beyond Earth
6 problemsMercury, Ganymede and the giant planets make magnetic fields with a dynamo (flowing electrically conducting fluid deep inside that generates and sustains a field), and the Moon and Mars once did, but several of these fields do not fit simple theory. Saturn's field is too symmetric, Mercury's too weak, and the young Moon's too strong.
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Onset and cause of plate tectonics
4 problemsEarth's surface is broken into moving plates that sink back into the mantle, while Venus, its near twin, has a single unbroken shell. When Earth's plates started moving and what made that possible are open.
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Dynamical history of the Solar System
6 problemsThe planets did not always orbit where they do now: the giant planets moved, and their movements scattered smaller bodies and shaped the inner planets. Reconstructing this history explains the present layout of the Solar System.
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Radiation belts and space weather prediction
5 problemsEarth's magnetic field traps high-energy particles and connects to storms of magnetized gas thrown out by the Sun. How these particles are energized and lost, and how solar storms affect the upper atmosphere, decides how well damage to satellites and power grids can be forecast.
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Tropical thunderstorms organize into patterns thousands of kilometers across that travel, oscillate and generate hurricanes. Several of these patterns, and how they will change with warming, are not explained by theory.
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Divergence of Venus and Earth
5 problemsVenus has almost the same size and mass as Earth, yet it has a crushing carbon dioxide atmosphere, a surface hot enough to melt lead, no oceans and no magnetic field. Why two similar planets ended so differently is not settled.
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Some volcanoes release lava slowly while others throw ash into the stratosphere, and many restless volcanoes never erupt. The physics deciding these outcomes happens deep underground where it cannot be watched directly.