- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
-
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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
-
“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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- “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.
-
-
“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.
-
-
“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.
-
- “Outer
Heliosheath”: The region just beyond the heliopause, which is still influenced
by the presence of the heliosphere, is called the outer heliosheath.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
March 24, 2023 SUN
- we still have mysteries to
solve?
3929
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------
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------ “Jim Detrick” -----------
---------------------
--- Sunday, March 26, 2023 ---------------------------
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