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There are a few ways to think about the edge of the solar system.

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One is with the extent of the solar wind.

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This is the constant flow of charged particles gushing out of the Sun

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at a million miles per hour

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and bathing the planets.

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The wind forms a giant, protective bubble around our solar system

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known as the heliosphere.

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This huge region surfs through the Milky Way, shielding us from interstellar radiation

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and creating an environment that helps life on Earth to flourish.

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But its borders aren’t fixed.

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Around 11 billion miles from Earth, far past the planets,

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solar wind pushes against interstellar space.

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Scientists have been monitoring this boundary over the past decade

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and they’re seeing it change with the Sun’s activity.

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Roughly every 11 years, the Sun’s magnetic field ramps up.

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This is known as the solar cycle and at the peak,

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the Sun’s magnetic poles flip — north becomes south and vice versa. 

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This cycle causes the Sun’s activity to sway from calm to turbulent

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with an abundance of flares and eruptions,

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which in turn affects the solar wind.

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Changes from the Sun can make the solar wind gust hard.

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When it does, the heliosphere expands like a balloon.

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Over the past solar cycle, scientists mapped what that looked like.

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To understand these maps, you need to know how we observe the edge of the solar system.

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Scientists use NASA’s Interstellar Boundary Explorer, or IBEX.

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About the size of a bus tire and in orbit around Earth,

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IBEX maps the heliosphere with a process similar to sonar.

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But instead of using sound to detect objects,

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it uses the echo of solar wind variations.

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For example, starting in 2014,

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there was a huge and prolonged increase in solar wind pressure.

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NASA spacecraft near Earth detected solar wind gusting 50% harder than previous years.

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After traveling outward for a year, solar wind hit the edge of the heliosphere

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— first the termination shock and then it entered the heliosheath

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that’s encased by the heliopause.

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Solar wind particles spent another year or so in this region.    

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Some collided with interstellar gases in the heliosheath

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and turned into energetic neutral atoms, or ENAs.                                               

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ENAs travel in all directions,

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some even back toward Earth.

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And between 2017 and 2019, a few of the returning ENAs reached IBEX,

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 an echo of where the boundary is and what it looks like.

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If you cut into the heliosphere and laid it out onto a flat surface,

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this is what you would see.

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This is the nose and this is the tail.

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The nose shows high ENA fluxes,

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which indicate a strong gust of wind and the heliosphere ballooning.

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From tracking this expansion,

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scientists found that the nose and tail were not symmetrical.

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If we compare the maps,

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ENAs from that big 2014 solar wind increase have returned from the nose,

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but they haven’t returned from the tail yet

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suggesting that the tail is much farther away from the Sun than the nose. 

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This indicates that the heliosphere looks more like a comet rather than a round bubble.

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Having a full solar cycle of observations of the heliosphere opens doors to understanding

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the only environment we so far know can support life.

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And there have been a few surprises.

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Beyond the heliosphere, near the nose,

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there was one region that took two years longer to respond to the 2014 increase  of solar wind.

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Scientists think these ENAs bounced out of the heliopause

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and into interstellar space before heading back toward Earth.

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These are signs that we’re still learning about the quirks of our solar system.

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But one thing’s for sure,

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these characteristics could tell us about the key ingredients for life around a star.

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