Moon Shielding Was Critical to Earth’s Ability to Maintain Its Atmosphere

[flash13]

Moon Shielding Was Critical to Earth’s Ability to Maintain Its Atmosphere

The Earth and Moon, shown here in a composite of two images from the Galileo mission of the 1990s, have a long shared history. Billions of years ago, they had connected magnetic fields. Credit: NASA/JPL/USGS

 

Earth and Moon Once Shared a Magnetic Shield, Protecting Their Atmospheres

 

Four-and-a-half billion years ago, Earth’s surface was a menacing, hot mess. Long before the emergence

 

of life, temperatures were scorching, and the air was toxic. Plus, as a mere toddler, the Sun bombarded

 

our planet with violent outbursts of radiation called flares and coronal mass ejections. Streams of charged

 

particles called the solar wind threatened our atmosphere. Our planet was, in short, uninhabitable.

 

But a neighboring shield may have helped our planet retain its atmosphere and eventually go on to

 

develop life and habitable conditions. That shield was the Moon, says a NASA-led study in the journal

 

Science Advances.

 

This illustration shows magnetic field lines that Earth generates today. The Moon no longer has a magnetic field. Credit: NASA

 

“The Moon seems to have presented a substantial protective barrier against the solar wind for the Earth,

 

which was critical to Earth’s ability to maintain its atmosphere during this time,” said Jim Green, NASA’s

 

chief scientist and lead author of the new study. “We look forward to following up on these findings when

 

NASA sends astronauts to the Moon through the Artemis program, which will return critical samples of

 

the lunar South Pole.”

A brief history of the Moon

The Moon formed 4.5 billion years ago when a Mars-sized object called Theia slammed into the proto-

 

Earth when our planet was less than 100 million years old, according to leading theories. Debris from the

 

collision coalesced into the Moon, while other remnants reincorporated themselves into the Earth.

 

Because of gravity, the presence of the Moon stabilized the Earth’s spin axis. At that time, our planet was

 

spinning much faster, with one day lasting only 5 hours.

 

And in the early days, the Moon was a lot closer, too. As the Moon’s gravity pulls on our oceans, the water

 

is slightly heated, and that energy gets dissipated. This results in the Moon moving away from Earth at a

 

rate of 1.5 inches per year, or about the width of two adjacent dimes. Over time, that really adds up. By 4

 

billion years ago, the Moon was three times closer to Earth than it is today – about 80,000 miles away,

 

compared to the current 238,000 miles. At some point, the Moon also became “tidally locked,” meaning

 

Earth sees only one side of it.

 

When the Moon had a magnetic field, it would have been shielded from incoming solar wind, as shown in this illustration. Credit: NASA

 

Scientists once thought that the Moon never had a long-lasting global magnetic field because it has such

 

a small core. A magnetic field causes electrical charges to move along invisible lines, which bow down

 

toward the Moon at the poles. Scientists have long known about Earth’s magnetic field, which creates the

 

beautifully colored aurorae in the Arctic and Antarctic regions.

 

A magnetic field serves as a shield causing electrical charges to move along its invisible lines. Scientists

 

have long known about Earth’s magnetic field, which causes the beautifully colored aurorae in the Arctic

 

and Antarctic regions. The movement of liquid iron and nickel deep inside the Earth, still flowing because

 

of the heat left over from Earth’s formation, generates the magnetic fields that make up a protective

 

bubble surrounding Earth, the magnetosphere.

 

But thanks to studies of samples of the lunar surface from the Apollo missions, scientists figured out that

 

the Moon once had a magnetosphere, too. Evidence continues to mount from samples that were sealed

 

for decades and recently analyzed with modern technology.

 

Like Earth, the heat from the Moon’s formation would have kept iron flowing deep inside, although not for

 

nearly as long because of its size.

 

“It’s like baking a cake: You take it out of the oven, and it’s still cooling off,” Green said. “The bigger the

 

mass, the longer it takes to cool off.”

A magnetic shield

The new study simulates how the magnetic fields of the Earth and Moon behaved about 4 billion years

 

ago. Scientists created a computer model to look at the behavior of the magnetic fields at two positions

 

in their respective orbits.

 

This illustration shows how Earth and its Moon both had magnetic fields that were connected billions of

 

years ago, helping to protect their atmospheres from streams of damaging solar particles, according to

 

new research. Credit: NASA

 

 

At certain times, the Moon’s magnetosphere would have served as a barrier to the harsh solar radiation

 

raining down on the Earth-Moon system, scientists write. That’s because, according to the model, the

 

magnetospheres of the Moon and Earth would have been magnetically connected in the polar regions of

 

each object. Importantly for the evolution of Earth, the high-energy solar wind particles could not

 

completely penetrate the coupled magnetic field and strip away the atmosphere.

 

But there was some atmospheric exchange, too. The extreme ultraviolet light from the Sun would have

 

stripped electrons from neutral particles in Earth’s uppermost atmosphere, making those particles

 

charged and enabling them to travel to the Moon along the lunar magnetic field lines. This may have

 

contributed to the Moon maintaining a thin atmosphere at that time, too. The discovery of nitrogen in

 

lunar rock samples support the idea that Earth’s atmosphere, which is dominated by nitrogen, contributed

 

to the Moon’s ancient atmosphere and its crust.

 

Scientists calculate that this shared magnetic field situation, with Earth and Moon’s magnetospheres

 

joined, could have persisted from 4.1 to 3.5 billion years ago.

 

“Understanding the history of the Moon’s magnetic field helps us understand not only possible early

 

atmospheres, but how the lunar interior evolved,” said David Draper, NASA’s deputy chief scientist and

 

study co-author. “It tells us about what the Moon’s core could have been like — probably a combination of

 

both liquid and solid metal at some point in its history — and that is a very important piece of the puzzle

 

for how the Moon works on the inside.”

 

Over time, as the Moon’s interior cooled, our nearest neighbor lost its magnetosphere, and eventually its

 

atmosphere. The field must have diminished significantly 3.2 billion years ago, and vanished by about 1.5

 

billion years ago. Without a magnetic field, the solar wind stripped the atmosphere away. This is also why

 

Mars lost its atmosphere: Solar radiation stripped it away.

 

If our Moon played a role in shielding our planet from harmful radiation during a critical early time, then in

 

a similar way, there may be other moons around terrestrial exoplanets in the galaxy that help preserve

 

atmospheres for their host planets, and even contribute to habitable conditions, scientists say. This would

 

be of interest to the field of astrobiology – the study of the origins of life and the search for life beyond

 

Earth.

 

Human exploration can tell us more

This modeling study presents ideas for how the ancient histories of Earth and Moon contributed to the

 

preservation of Earth’s early atmosphere. The mysterious and complex processes are difficult to figure

 

out, but new samples from the lunar surface will provide clues to the mysteries.

 

As NASA plans to establish a sustainable human presence on the Moon through the Artemis program,

 

there may be multiple opportunities to test out these ideas. When astronauts return the first samples

 

from the lunar South Pole, where the magnetic fields of the Earth and Moon connected most strongly,

 

scientists can look for chemical signatures of Earth’s ancient atmosphere, as well as the volatile

 

substances like water that were delivered by impacting meteors and asteroids. Scientists are especially

 

interested in areas of the lunar South Pole that have not seen any sunlight at all in billions of years — the

 

“permanently shadowed regions” – because the harsh solar particles would not have stripped away

 

volatiles.

 

Nitrogen and oxygen, for example, may have traveled from Earth to Moon along the magnetic field lines

 

and gotten trapped in those rocks.

 

“Significant samples from these permanently shadowed regions will be critical for us to be able to

 

untangle this early evolution of the Earth’s volatiles, testing our model assumptions,” Green said.

 

Source

[OrioNeXus]

Earth as Sister and Moon as Brother such cosmic relationship simplified with explanation 😄