Page 12 - COSMOS & H -Health - Science

THEIA IMPACT THEORY

Since the beginning of modern astronomy, there have
Since the beginning of modern astronomy, there have
been at least four hypotheses for the origin of the Moon:
been at least four hypotheses for the origin of the Moon:
1. A single body, split into Earth and Moon
1. A single body, split into Earth and Moon
2. The Moon was captured by Earth's gravity (as most of
2. The Moon was captured by Earth's gravity (as most of
the outer planets' smaller moons were captured)
the outer planets' smaller moons were captured)
3. The Earth and Moon formed at the same time when
3. The Earth and Moon formed at the same time when
the protoplanetary disk accreted
the protoplanetary disk accreted
4. The Giant Impact Hypothesis (also called Theia impact)
4. The Giant Impact Hypothesis (also called Theia impact)

The lunar rock samples retrieved by Apollo astronauts were found to
The lunar rock samples retrieved by Apollo astronauts were found to
be very similar in composition to Earth's crust, and so were likely
be very similar in composition to Earth's crust, and so were likely
removed from the Earth in some violent event.
removed from the Earth in some violent event.
The most popular theory (Theia Impact) says that about 4.5 billion
The most popular theory (Theia Impact) says that about 4.5 billion
years ago, a Mars-sized protoplanet, Theia orbited the Sun, nearly
years ago, a Mars-sized protoplanet, Theia orbited the Sun, nearly
along the orbit of the proto-Earth, by staying close to one or the other
along the orbit of the proto-Earth, by staying close to one or the other
of the Sun-Earth system's two more stable Lagrangian points (L4 or
of the Sun-Earth system's two more stable Lagrangian points (L4 or
L5).
L5).

Initially, the hypothesis was that Theia had struck Earth
Initially, the hypothesis was that Theia had struck Earth
with a glancing blow and ejected many pieces of both the
with a glancing blow and ejected many pieces of both the
proto-Earth and Theia, those pieces either forming one body
proto-Earth and Theia, those pieces either forming one body
that either developed into the Moon or into two moons that
that either developed into the Moon or into two moons that
eventually combined to create the Moon. Such accounts
eventually combined to create the Moon. Such accounts
assumed that a head-on impact would have destroyed both
assumed that a head-on impact would have destroyed both
planets, creating a short-lived second asteroid belt between
planets, creating a short-lived second asteroid belt between
the orbits of Venus and Mars.
the orbits of Venus and Mars.