- 4537 -
SUN'S MYSTERIES ? - Our
understanding of the sun has come a long way in recent decades, but there are
still multiple outstanding mysteries that current and future missions hope to
solve.
--------------------- 1. The coronal heating problem
--------------------- 2. The sun's internal dynamo and the solar
cycle
--------------------- 3. Predicting solar flares and coronal mass
ejections
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----------------------------------- 4537
- SUN'S MYSTERIES ?
-
- What tools do we have to answer these
questions? Since we began sending
satellites to space, our knowledge of the sun has increased exponentially. We
saw the sun at new wavelengths, observing our local star in ultraviolet and
X-rays for the first time. These observations revealed many new unexplained
phenomena on the sun. Many of these early solar observations have been long
since explained, but there are still ongoing mysteries about the sun that
scientists are working to understand.
-
- Here, we outline three of the main
outstanding puzzles of our local star, although there are certainly others.
Most current and future projects to observe the sun, either from the ground or
in space, include one or more of these mysteries as a primary science goal.
---------------------- 1. The coronal heating problem
-
- The sun's outer atmosphere, called the
corona, has a temperature of around 1.8 million degrees Fahrenheit (1 million
degrees Celsius). However, the surface of the sun, called the photosphere, has
a much, much cooler temperature of 10,000 F (5,500 C). At a glance, this seems
puzzling. If the sun's atmosphere gets its energy from the sun, how can the
corona be hotter than the sun itself?
-
- In physics, temperature is defined as the
amount of energy within the atoms that make up a substance, for example, the
air around you. If air atoms are vibrating with a lot of energy, the air is
hot. If they are vibrating less, the air is cooler. But this definition doesn't
consider density. If the air is thicker with more atoms of the same
temperature, the air temperature doesn't change. What does change, however, is
the energy within the air around us.
-
- So, in the context of the sun, the corona
is far hotter — but far less dense — than the sun's surface. The surface, on
the other hand, is cooler but with much higher densities. The result is that
although the temperature of the photosphere is lower, the total energy is still
higher.
-
- But although we know the corona is hot
because of the higher energy in the photosphere, this still doesn't solve the
coronal heating problem. What remains a mystery is how the energy is
transported from the sun's surface to its atmosphere. There are multiple
theories, but our observations have not provided any conclusive evidence.
-
-------------------------- 2.
The sun's internal dynamo and the solar cycle.
-
- The sun follows an 11-year cycle of
increasing and decreasing activity. At the peak of this solar cycle — called
solar maximum — sunspots, solar flares and coronal mass ejections (CMEs) are
numerous. At solar minimum, the sun is inactive for months to years at a time.
The period of the 11-year cycle is fairly predictable, consistently falling
fairly close to this time span. What changes considerably from cycle to cycle,
however, is the magnitude of solar maximum. Some solar cycles have a peak over
twice that of others.
-
- In general terms, we understand what drives
the solar cycle. Because the sun rotates at different speeds at different
latitudes, the global magnetic field slowly winds up and becomes more
concentrated, producing more magnetic activity.
-
- Eventually, the magnetic field winds up so
much that it disappears below the sun's surface, revealing a basic solar
minimum magnetic field. Although we understand this at a top level, the
intricate physics driving the sun's magnetic field from inside the sun — called
the solar dynamo — and why that causes 11-year cycles with varying peaks are
not yet fully understood.
-
------------------------ 3. Predicting solar flares and coronal mass
ejections
-
- Solar flares and CMEs (eruptions from the
sun) are the primary drivers of space weather — the influence of the sun on the
near-Earth environment, with implications for our power grids, satellites and
radio communication. Around the world, dozens of space weather forecasters
release regular predictions to key stakeholders, informing them of any
potential disruption from the sun. These forecasters do a fantastic job, but
they are very limited by both available observations and our limited collective
knowledge about the drivers of solar flares and CMEs.
-
- Currently, our forecasting of flares and
CMEs is probabilistic and reactive. We can determine when they have a high
likelihood of occurring, but not specifically when one will erupt. For us to
get better at predicting these events, we must first understand the intricate
processes that trigger flares and CMEs on very small scales.
-
----------------- What tools do we have to answer these
questions?
-
- We are currently in a data-rich era of solar
physics research. In space, NASA has a host of heliophysics missions in Earth
orbit, including the Solar Dynamics Observatory and the Interface Region
Imaging Spectrograph. These will be joined later this decade by NASA's
Multi-slit Solar Explorer mission. Key Earth-orbit telescopes also include
Japan's Hinode, India's Aditya-L1 and China's Advanced Space-based Solar
Observatory.
-
- Orbiting the sun, we have the European
Space Agency's Solar Orbiter and NASA's Parker Solar Probe. And finally, we
have a host of solar telescopes on the ground, the largest of which is the
National Science Foundation's Inouye Solar Telescope. Together, these solar
physics missions, alongside others, are doing a fantastic job of providing the
data necessary to help solve the outstanding mysteries of the sun.
-
-
July 1, 2024 4537
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“Jim Detrick” -----------
--------------------- --- Sunday, August 18, 2024
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