- 4209 -
ASTEROID - impacts and Earth's Interior ? An asteroid came uncomfortably close to
Earth in July. Could we have stopped it?
In July, 2023, an asteroid roughly 30 to 60 meters across passed Earth
to within one-quarter of the distance to the moon. If it had struck Earth it
would have created a blast three times greater than the 2013 Chelyabinsk
impact. And we only noticed it two days after it passed.
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--------------------- 4209 - ASTEROID - impacts and Earth's Interior
- This is a good
example of how sizable asteroids still miss detection. Not ones large enough to
threaten our extinction, but large enough to threaten millions of lives. If a
similar asteroid was detected just days before impact, could we stop it?
-
- Deflecting an
asteroid can be done, but only if we have a long lead time. So the question
really becomes whether we can launch a counter-offensive in time and whether
that counter-offensive would be enough to fragment the asteroid into harmless
bits.
-
- Surprisingly, the
answer to both of those questions seems to be yes. Given current launch
technology, we could launch a defense rocket within a day, assuming we were to
keep one on standby.
-
- To pulverize the
asteroid, they propose using a combination of kinetic and explosive impactors.
The rocket would release a cloud of impactors at a high relative speed to the
asteroid, shattering the body into fragments no more than 10 meters across.
Given a typical density and composition, even if the fragmentation occurred
just hours before Earth impact, the resulting debris cloud would pose limited
risk to us.
-
- This proposal is
still just a proof of concept. We have no rockets in place to launch, and no
impactor system for it to carry. If we detected an imminent asteroid tomorrow
we would have no way to counter it. We have the ability to build a planetary
defense rocket, but the question remains on whether we have the will to build
one.
-
- Impactors have
already hit us. A massive anomaly
within Earth's mantle may be remnant of collision that formed the Moon. The international research team has recently
discovered that a massive anomaly deep within the Earth's interior may be a
remnant of the collision about 4.5 billion years ago that formed the moon.
-
- The formation of
the moon has been a persistent enigma for several generations of scientists.
Prevailing theory has suggested that, during the late stages of Earth's growth
approximately 4.5 billion years ago, a massive collision occurred between
primordial Earth (Gaia) and a Mars-sized proto-planet known as “Theia”. The
moon is believed to have formed from the debris generated by this collision.
-
- Simulations have
indicated that the moon likely inherited material primarily from Theia, while
Gaia, due to its much larger mass, was only mildly contaminated by Theian
material.
-
- Since Gaia and
Theia were relatively independent formations and composed of different
materials, the theory suggested that the moon—being dominated by Theian
material—and the Earth—being dominated by Gaian material—should have distinct
compositions. However, high-precision isotope measurements have revealed that
the compositions of the Earth and moon are remarkably similar, thus challenging
the conventional theory of moon formation.
-
- While various
refined models of the giant impact have subsequently been proposed, they have
all faced challenges. After conducting
numerous simulations of the giant impact, scientists discovered that the early
Earth exhibited mantle stratification after the impact, with the upper and
lower mantle having different compositions.
-
- The upper mantle
featured a magma ocean, created through a thorough mixing of material from Gaia
and Theia, while the lower mantle remained largely solid and retained the
material composition of Gaia.
-
- This mantle
stratification may have persisted to the present day, corresponding to the
global seismic reflectors in the mid-mantle (located about 1,000 km beneath the
Earth's surface). The entire lower
mantle of the Earth may still be dominated by pre-impact Gaian material, which
has a different elemental composition (including higher silicon content) than
the upper mantle.
-
- An earlier theory
is the giant impact led to the “homogenization” of the early Earth. Instead the moon-forming giant impact appears
to be the origin of the early mantle's “heterogeneity” and marks the starting
point for the Earth's geological evolution over the course of 4.5 billion
years.
-
- Another example of
Earth's mantle heterogeneity is two anomalous regions—called Large Low Velocity
Provinces (LLVPs)—that stretch for thousands of kilometers at the base of the
mantle. One is located beneath the African tectonic plate and the other under
the Pacific tectonic plate. When seismic waves pass through these areas, wave
velocity is significantly reduced.
-
- LLVPs could have
evolved from a small amount of Theian material that entered Gaia's lower
mantle. Through in-depth analysis of
previous giant-impact simulations and by conducting higher-precision new
simulations, the research team found that a significant amount of Theian mantle
material, approximately 2% of Earth's mass, entered the lower mantle of Gaia.
-
- The research team
also calculated that this Theian mantle material, similar to lunar rocks, is
enriched with iron, making it denser than the surrounding Gaian material. As a
result, it rapidly sank to the bottom of the mantle and, over the course of
long-term mantle convection, formed two prominent LLVP regions. These LLVPs
have remained stable throughout 4.5 billion years of geological evolution.
-
- Heterogeneity in
the deep mantle, whether in the mid-mantle reflectors or the LLVPs at the base,
suggests that the Earth's interior is far from a uniform and "boring"
system. Small amounts of deep-seated heterogeneity can be brought to the
surface by mantle plumes—cylindrical upwelling thermal currents caused by
mantle convection—such as those that likely formed Hawaii and Iceland.
-
- Geochemists
studying isotope ratios of rare gases in samples of Icelandic basalt have
discovered that these samples contain components different from typical surface
materials. These components are remnants of heterogeneity in the deep mantle
dating back more than 4.5 billion years and serve as keys to understanding
Earth's initial state and even the formation of nearby planets.
-
- Through precise
analysis of a wider range of rock samples, combined with more refined giant
impact models and Earth evolution models, geologists can infer the material
composition and orbital dynamics of the primordial Earth, Gaia, and Theia.
This constrains the entire history of
the formation of the inner solar system.
How our home got started!
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-
November 4, 2023
ASTEROID - impacts and Earth's Interior 4209
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Sunday, November 5, 2023 ---------------------------------
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