- 4361 - EARTH MOON - dependency? Life appeared on Earth through a series of lucky coincidences, and that luck started with our Moon. None of the other planets of the inner solar system have significant moons. Space is lonely around Mercury and Venus.
------------------- 4361 - EARTH MOON - dependency?
- Mars does have two
small moons, Phobos and Deimos, but those are simply captured asteroids,
lassoed in the not-too-distant past and doomed to eventually come close enough
to their unloving parent to be torn to shreds by gravitational forces.
-
- In fact, no other
planet in the solar system, or any exoplanet known orbiting other stars, has a
moon quite like the Moon. With the exception of Pluto and its companion Charon,
no other planet has a satellite with the relative mass of our moon.
- The giant worlds
like Jupiter and Saturn have some moons large enough to be planets in their own
right, but they are insignificant next to the massive bulk of their parents.
The Moon is roughly 1% the mass of the Earth, a percentage unheard of in the
galaxy.
-
- Billions of years
ago, when our solar system was but a churning mass of gas and dust swirling
around a young star, the planets began to coalesce. But before they could
become planets, they were mere “planetesimals”, agglomerations of rock and ice,
dozens of them swarming in the chaos.
-
- In the orbit of
what would one day become the Earth, we were not alone. At some point, due to
some accident of trajectory and conceit of momentum, a planetesimal the size of
Mars struck us. The details of the collision and its aftermath are
muddied. The cosmic accident vaporized
part of the Earth and its “impactor”, creating a ring of superheated plasma
that looked more like a rage-filled doughnut than a proto-world.
-
- But with time the
fury ceased; the plasma cooled. The ring coalesced back into the shape of a
sphere, but now with an orbiting companion. The traces of the impactor are
almost lost to us, the evidence of its existence only slim. The Earth contains
more heavy metals in its core than it should for a planet its size, a
contribution from this interloper.
-
- The Moon itself,
when sampled to measure the composition of its fundamental elements, reveals
itself to be made of the exact same mixture as the Earth. A common origin then,
not an object formed elsewhere and captured by our gravity.
-
- Day to day, the
Moon doesn’t largely affect the Earth. It raises and lowers the tides in its
month-long orbit, sharing the duty with the gravitational pull of the Sun
itself. Some creatures, like dung beetles, use the polarized light of the Moon
to guide their way back home after a night of collecting.
-
- When we zoom our
perspective out over billions of years, the Earth wouldn’t be the same without
our sole friend. Our planet spins about its axis, but that spin is tilted with
respect to the movement of the Earth in orbit around the Sun by 23.5 degrees.
This tilt gives us our seasons, with half our year spent with the northern pole
facing the Sun, and the other half trading places with the southern pole.
-
- The other planets
have lesser and greater tilts, with Uranus tipped completely over on its side
and Venus rotating backwards. And there’s nothing to keep that tilt fixed over
cosmic time. Our planet was born spinning, but the internal arrangements of its
core, mantle, and crust, along with the ever-present gravitational machinations
of Jupiter, can cause the Earth to wobble, shifting its tilt ever so slightly.
-
- With every shift
in the tilt, the seasons would radically change. Instead of regular,
predictable changes year after year, we would experience ages with endless
summers, or ages with violent but short winters, or anything in between. The
rhythm of the seasons provides a pulse for life, which has the freedom to grow
and evolve without trying to overcome great climactic shifts caused by a
changing axis.
-
- The Moon acts as a
great gravitational counterweight, stabilizing the motion of the Earth. By
providing a source of gravity external to our planet, the Earth’s interior is
free to shift and reconfigure as it pleases.
-
- Every so often,
Earth's magnetic poles completely flip. What causes this to happen? And how do
these reversals affect life on Earth?
-
- Earth, our rocky,
watery oasis in the cosmos is the ideal place for life to flourish for a number
of reasons. We sit at just the right
distance from our home star for liquid water to exist on the planet's surface.
The gravitational pull of other large planets helps protect us from apocalyptic
collisions with wandering meteorites. And the planet's magnetic field encircles
Earth with a protective barrier that shields us from charged particles hurtling
through space.
-
- Earth's magnetic
field is generated by the complex flow of molten metallic material in the outer
core of the planet. The flow of this material is affected both by the rotation
of Earth and the presence of a solid iron core, which results in a dipolar
magnetic field where the axis roughly aligns with the rotational axis of the
planet.
-
- Hidden in the
chemical composition of ancient rocks are clues that Earth's magnetic field is
a dynamic, shifting phenomena. Cooling magma rich in iron minerals is pulled
into alignment with Earth's magnetic field, similar to how a needle is pulled
to point towards north on a compass. The study of ancient geomagnetic fields
recorded in rocks is the subject of a discipline known as
"paleomagnetism."
-
- Paleomagnetic
research has provided scientists with the knowledge that Earth's magnetic field
has shifted and even reversed in polarity many times in the geological
past. What causes the magnetic poles to
flip?
-
- Earth's magnetic
field varies at very short timescales and extremely long ones, ranging from
milliseconds to millions of years. The interaction of the magnetic field with
charged particles in space can alter it at short timescales, while
perturbations in the magnetic field at longer timescales are caused by internal
processes unfolding in the outer liquid core of the Earth.
-
- Variation of the
magnetic field results from the effect of advection of the magnetic field by
the flow in the fluid outer core and from effects of magnetic field diffusion
in the core and the mantle.
-
- Fluctuations in
the magnetic field caused by the movement of metallic material in the outer
core have brought about full reversals of the magnetic field's polarity in
Earth's past.
-
- Studies of
previous states of the magnetic field have shown there are two possible states
of polarity, the current 'normal' state, where the lines of force of the field
enter towards the center of the Earth in the northern hemisphere and exit
towards the outside of the Earth in the southern hemisphere. The inverse, or
'reverse' polarity is also equally as probable and stable.
-
- Studies have shown
that polarity reversals of Earth's magnetic field are not periodic and cannot
be predicted. This is largely because of the behavior of the mechanisms that
are responsible for it.
-
- The flow of the
metallic fluid (mostly molten iron) in the outer core of the Earth is chaotic
and turbulent. Polarity reversals occur during periods of low geomagnetic field
intensity, during which the intensity of the dipolar component drastically
decreases, and the structure of the field is unstable.
-
- The transitory
period of polarity reversal appears as a geologically instantaneous with a
duration spanning up to a few thousand years.
When the magnetic field is prone to flipping, it is in a state of
reduced intensity, resulting in a greater exposure of Earth's atmosphere to
solar wind and cosmic rays in the form of charged particles.
-
- A study showed that
during the “Laschamps excursion”, a recent period of low magnetic field
intensity which occurred only 41,000 years ago, the global cosmic ray flux
reaching the Earth's atmosphere was up to three times higher than today's
value.
-
- Currently, there
is no significant evidence of a correlation between mass extinctions of life on
Earth and geomagnetic polarity reversals. However, linking rates of species
extinction and speciation with periods of low magnetic field intensity is
hindered by uncertainties in the known timescale of these magnetic
'flips'. Magnetic reversals happen
frequently on geological timescales (several hundred times in the past 160 million
years), while recorded mass extinction events occur every hundred million years
or so (much less frequently).
-
- The risks to which
our planet and civilization is exposed could have significant impacts on civil
society, how we do commerce, security, communications, power infrastructure,
satellites and the lives of people in low Earth orbit. Unfortunately, the
sporadic nature of magnetic variations and reversals means we cannot predict
when exactly this will happen, all we know is that it will happen.
-
- We want to learn
more about our Moon. Japan’s SLIM moon
lander has gone dormant once more at the start of a 14-day-long lunar night.
The upended robot sent back a stream of data and imagery while its solar cells
were in position to soak up sunlight, and its handlers hope they can get SLIM
to wake up again and resume its work after lunar sunrise in mid-February.
-
- The car-sized robot
accomplished its primary mission on January 20, 2022 when it landed within 100
meters of its target point near Shioli Crater. SLIM, “Smart Lander for Investigating Moon”, was
designed to demonstrate a precision landing technique that Japan hopes to use
for future missions to the moon and Mars.
-
- Unfortunately, the
lander ended up in an upside-down position, with its solar cells pointing off
to the side. Mission managers were able to get some data and pictures back ,
including a photo captured by a mini-robot that documented the lander’s
predicament.
-
- But within hours,
the lander’s batteries ran down to the point that SLIM had to go into
hibernation. The mission team could only hope that as the sun moved westward in
the lunar sky, enough light would eventually hit the panels to allow for a
reawakening.
-
- That’s what
happened on January 28: They re-established contact with the charged-up SLIM
and commanded the lander to transmit a set of multispectral images showing the
area around the landing site.
-
- SLIM’s recent
science-gathering session was limited to just a few days due to the moon’s
day-night cycle. By the time the lander’s solar cells soaked up enough
sunlight, it was the equivalent of late afternoon on the moon. Sunset came on
February 1, and once again, SLIM went into hibernation.
-
- Temperatures were
expected to fall to somewhere around 200 degrees below zero Fahrenheit during
the lunar night. JAXA initially had planned to let the lander go dead when the
sun went down, but in light of the unlucky lander’s recent resilience, those
plans could change.
-
- India’s Moon
mission also had a moon lander. In just
two weeks, the Indian mission has made some surprising discoveries about the
composition of the Moon. The Indian
Space Research Organisation’s (ISRO) Moon lander Vikram and robotic rover
Pragyan have now been told to go to sleep. ISRO hopes to awaken them at lunar
dawn on 22 September.
-
- But in their
two-week sojourn around the Moon’s south pole, they provided insights that have
planetary scientists abuzz. A probe
onboard Vikram made the first measurements of the density and temperature of
Moon’s ionosphere. ISRO reports a “relatively sparse” mix of ions and electrons
in the 100-kilometer-thick layer of electrically charged plasma that surrounds
the Moon’s surface near the south pole.
-
- Initial
measurements of the plasma indicate a density of about 5 million to 30 million
electrons per cubic meter. And the density seems to vary as the lunar day
progresses. The peak density of a similar layer in Earth’s upper atmosphere is
one million electrons per cubic centimeter.
-
- The density of the
ionosphere would affect lunar communication and navigation systems if humans
were to inhabit the Moon, the higher the electron density, the longer radio
signals take to travel through the ionosphere.
-
- Understanding
lunar soil, including its temperature and conductivity, will be important when
considering settlement on the Moon. The
lander is fitted with a temperature probe containing 10 sensors and able to
reach 10 centimeters below the surface of the Moon. Its preliminary data show
that during the day, the temperature 8 cm down is around 60 ºC lower than at
the surface.
-
- A steep decline in
temperature is expected during the lunar daytime, because the heat does not
conduct downward from the warm sunlit surface. This is similar to the effect
one experiences when visiting a beach on a hot day. Dig down just a few centimeters and the sand
is much cooler.
-
- Measurements so
far have found that the temperature at the surface is significantly warmer than
recorded by NASA’s 2009 Lunar Reconnaissance Orbiter. It far too warm for water ice to be
stable. Water converts from solid to
gas at a very low temperature in the vacuum of space, at about −160 ºC.
Chandrayaan-3’s data indicate temperatures warmer than −10 ºC at all depths
sampled. Further down "we expect temperatures to flatten out at close to
the average surface temperature of about −80 ºC”.
-
- Among many
vibrations recorded by the lander’s seismograph, one in particular caught the
attention of scientists. The instrument recorded a very small seismic event
that decayed to background in about 4 seconds.
Scientists suspect it was a small moonquake or the impact of a tiny
meteorite.
-
- Such perturbations
are expected on the Moon. Small impacts and local tectonic adjustments related
to tidal forces are common on the Moon.
-
- Testing by the
rover unambiguously confirms the presence of sulfur in the lunar surface near
the south pole. It also found aluminum, silicon, calcium and iron, among other
elements.
-
- Sulfur, being
volatile, is not generally expected.
Sulfur is a key element of molten rock, and researchers think that the
primitive Moon was covered with a thick layer of hot molten rock, which
crystallized to form the Moon’s surface. Measurements of sulfur concentrations
can provide insight into that process.
-
- However, it’s
also possible that the sulfur came from asteroids that bombard the Moon’s
surface. The scientist says they hope to add their findings to those of the US
Apollo missions to better understand the Moon’s geochemistry.
-
-
February 20, 2024
EARTH MOON
- dependency? 4361
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Tuesday, February 20, 2024 ---------------------------------
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