Sunday, March 26, 2023

3929 - SUN - we still have mysteries to solve?

 

-   3929 -    SUN  -  we still have mysteries to solve?    Our Sun is a star like billions of other stars in the universe. Some of those stars also have astrospheres, like the heliosphere, but this is the only astrosphere we are actually inside of and can study closely.  We need to start from our neighborhood to learn so much more about the rest of the universe.


-----------------  3929  -  SUN  -  we still have mysteries to solve?

-    The “aurora borealis”  known as the “northern lights”  is a vivid demonstration of the Earth's magnetic field interacting with charged particles from the sun.

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-    Auroras are centered on the Earth's magnetic poles, visible in a roughly circular region around them. Since the magnetic and geographic poles aren't the same, sometimes the auroras are visible farther south than one might expect, while in other places it's farther north.

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-   In the Northern Hemisphere, the auroral zone runs along the northern coast of Siberia, Scandinavia, Iceland, the southern tip of Greenland and northern Canada and Alaska.

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-    Aurora displays are created when protons and electrons stream out from the solar surface and slam into the Earth's magnetic field. Since the particles are charged they move in spirals along the magnetic field lines, the protons in one direction and the electrons in the other.

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-     Those particles in turn hit the atmosphere. Since they follow the magnetic field lines, most of them enter the atmospheric gases in a ring around the magnetic poles, where the magnetic field lines come together.

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-  The air is made up largely of nitrogen and oxygen atoms, with oxygen becoming a bigger component at the altitudes auroras happen, starting about 60 miles up and going all the way up to 600 miles. When the charged particles hit them, they gain energy. Eventually they relax, giving up the energy and releasing photons of specific wavelengths. Oxygen atoms emit green and sometimes red light, while nitrogen is more orange or red.

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-    The International Space Station's orbit is inclined enough that it even plows through the heavenly lights. Most of the time nobody notices, as the density of charged particles is so low.   The only time it matters is during particularly intense solar storms, when radiation levels are high. At that point all the astronauts have to do is move to a more protected area of the station.

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-    Voyagers 1 and 2 were the first probes to bring back pictures of auroras on Jupiter and Saturn, and later Uranus and Neptune. Since then, the Hubble Space Telescope has taken pictures of them as well. Auroras on either Jupiter or Saturn are much larger and more powerful than on Earth, because those planets' magnetic fields are orders of magnitude more intense.

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-    On Uranus, auroras get weirder, because the planet's magnetic field is oriented roughly vertically, but the planet rotates on its side. That means instead of the bright rings you see on other worlds, Uranus' auroras look more like single bright spots, at least when spied by the Hubble Space Telescope in 2011. But it's not clear that's always the case, because no spacecraft has seen the planet up-close since 1986.

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-    Occasionally the auroras are visible farther from the poles than usual. In times of high solar activity, the southern limit for seeing auroras can go as far south as Oklahoma and Atlanta, as it did in October 2011.

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-   A record was probably set at the Battle of Fredericksburg in Virginia in 1862, during the Civil War, when the northern lights appeared. Many soldiers noted it in their diaries.

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-      The northern lights look like fire, but they wouldn't feel like one. Even though the temperature of the upper atmosphere can reach thousands of degrees Fahrenheit, the heat is based on the average speed of the molecules. That's what temperature is. But feeling heat is another matter, the density of the air is so low at 60 miles up that a thermometer would register temperatures far below zero where aurora displays occur.

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-    One of the most difficult problems in solar physics is knowing the shape of a magnetic field in a coronal mass ejection (CME), which is basically a huge blob of charged particles ejected from the sun. Such CMEs have their own magnetic fields.

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-    The problem is, it is impossible to tell in what direction the CME field is pointing until it hits. A hit creates either a spectacular magnetic storm and dazzling aurora with it, or a fizzle. Currently there's no way to know ahead of time.

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-    Our corner of the universe, the solar system, is nestled inside the Milky Way galaxy, home to more than 100 billion stars. The solar system is encased in a bubble called the heliosphere, which separates us from the vast galaxy beyond and some of its harsh space radiation.

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-  We’re protected from that radiation by the heliosphere, which itself is created by another source of radiation: the Sun. The Sun constantly spews charged particles, called the solar wind, from its surface. The solar wind flings out to about four times the distance of Neptune, carrying with it the magnetic field from the Sun.

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-    Magnetic fields tend to push up against each other, but not mix.   Inside the bubble of the heliosphere are pretty much all particles and magnetic fields from the Sun. Outside are those from the galaxy.

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-    “Heliosphere” is the combination of two words: “Helios,” the Greek word for the Sun, and “sphere,” a broad region of influence ,though, to be clear, scientists aren’t sure of the heliosphere’s exact shape.

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-     Some radiation surrounds us every day. When we sunbathe, we’re basking in radiation from the Sun. We use radiation to warm leftovers in our kitchen microwaves and rely on it for medical imaging.  Space radiation, however, is more similar to the radiation released by radioactive elements like uranium.

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            -    The space radiation that comes at us from other stars is called galactic cosmic radiation. Active areas in the galaxy, like supernovae, black holes, and neutron stars, can strip the electrons from atoms and accelerate the nuclei to almost the speed of light, producing galactic cosmic radiation.

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            -    On Earth, we have three layers of protection from space radiation. The first is the heliosphere, which helps block galactic cosmic radiation from reaching the major planets in the solar system.

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            -     Earth’s magnetic field produces a shield called the magnetosphere, which keeps galactic cosmic radiation out away from Earth and low-orbiting satellites like the International Space Station. Finally, the gases of Earth’s atmosphere absorb radiati-on.

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-   When astronauts head to the Moon or to Mars, they won’t have the same protection we have on Earth. They’ll only have the protection of the heliosphere, which fluctuates in size throughout the Sun’s 11-year cycle.

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-   In each solar cycle, the Sun goes through periods of intense activity and powerful solar winds, and quieter periods. Like a balloon, when the wind calms down, the heliosphere deflates. When it picks up, the heliosphere expands.

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-    The effect the heliosphere has on cosmic rays allows for human exploration missions with longer duration. In a way, it allows humans to reach Mars.    The challenge for us is to better understand the interaction of cosmic rays with the heliosphere and its boundaries.

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-    “Termination shock”: All of the major planets in our solar system are located in the heliosphere’s innermost layer. Here, the solar wind emanates out from the Sun at full speed, about a million miles per hour, for billions of miles, unaffected by the pressure from the galaxy. The outer boundary of this core layer is called the termination shock.

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-    “Heliosheath”: Beyond the termination shock is the heliosheath. Here, the solar wind moves more slowly and deflects as it faces the pressure of the interstellar medium outside.

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-    “Heliopause”: The heliopause marks the sharp, final plasma boundary between the Sun and the rest of the galaxy. Here, the magnetic fields of the solar and interstellar winds push up against each other, and the inside and outside pressures are in balance.

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-    “Outer Heliosheath”: The region just beyond the heliopause, which is still influenced by the presence of the heliosphere, is called the outer heliosheath.

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-    Many NASA missions study the Sun and the innermost parts of the heliosphere. But only two human-made objects have crossed the boundary of the solar system and entered interstellar space.

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-   In 1977, NASA launched Voyager 1 and Voyager 2. Each spacecraft is equipped with tools to measure the magnetic fields and the particles it is directly passing through. After swinging past the outer planets on a grand tour, they exited the heliopause in 2012 and 2018 respectively and are currently in the outer heliosheath. They discovered that cosmic rays are about three times more intense outside the heliopause than deep inside the heliosphere.

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-    The Voyagers work with the Interstellar Boundary Explorer (IBEX) to study the heliosphere. IBEX is a 176-pound, suitcase-sized satellite launched by NASA in 2008. Since then, IBEX has orbited Earth, equipped with telescopes observing the outer boundary of the heliosphere. IBEX captures and analyzes a class of particle called “energetic neutral atoms”, or ENAs, that cross its path. ENAs form where the interstellar medium and the solar wind meet. Some ENAs stream back toward the center of the solar system and IBEX.

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-    Every time you collect one of those ENAs, you know what direction it came from.    By collecting a lot of those individual atoms, you’re able to make this inside out image of our heliosphere.

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-   In 2025, NASA will launch the Interstellar Mapping and Acceleration Probe (IMAP). IMAP’s ENA cameras are higher resolution and more sensitive than IBEX’s. 

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-    In 2009, IBEX returned a finding so shocking that researchers initially wondered if the instrument may have malfunctioned. That discovery became known as the IBEX Ribbon, a band across the sky where ENA emissions are two or three times brighter than the rest of the sky.

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-    The Ribbon was totally unexpected and not anticipated by any theories before we flew the mission. It’s still not entirely clear what causes it, but it is a clear example of the mysteries of the heliosphere that remain to be discovered.

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-    Our Sun is a star like billions of other stars in the universe. Some of those stars also have astrospheres, like the heliosphere, but this is the only astrosphere we are actually inside of and can study closely.  We need to start from our neighborhood to learn so much more about the rest of the universe.

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                   March 24, 2023       SUN  -  we still have mysteries to solve?            3929                                                                                                                         

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