2019-07-01_Discover

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60 DISCOVERMAGAZINE.COM

The Moon

THE MOON IS EARTH’S CLOSEST, albeit

inconstant, companion. Over the centuries,

humans have blamed the moon for tides,

fertility, werewolves and madness — mostly

incorrectly. It’s such an intrinsic part of our

night sky that we don’t even give it a proper

name, simply an article: the moon. Of course,

it’s had many names across many cultures,

some of which still linger. The study of the

moon is selenology, thanks to the Greek

goddess Selene; her Roman counterpart

was Luna. In China, the moon goddess was

Chang’e, a name now bestowed upon the

Chinese space agency’s lunar missions. It’s

only thanks to such exploration that we’ve

learned what we know about the moon.

Utter lunacy.

BY KOREY HAYNES

THE MOON’S HISTORY is a violent one, starting with its birth

when a Mars-sized object — dubbed Theia — smashed into the

young Earth billions of years ago. The resulting debris eventually

coalesced to form our satellite. This origin story arose because

lunar rock samples are molecularly pretty similar to samples

from Earth, implying the moon formed out of our planet. But

the impactor theory, as it’s known, suggests the moon should

have traces of both Earth and Theia — and we’ve never spotted

anything Theia-ish over there. It could be that the crash was more

of a glancing blow, with the bulk of Theia leaving the vicinity.

Scientists don’t really know how to explain this aspect of the

moon’s genesis, but they do know the origins of the biggest lunar

features. Over the eons, asteroids have pummeled the moon’s

surface, sometimes cracking it open to spill the molten rock

within, which hardened into the dark lunar spots, called maria.

The oldest and largest impact site, the South Pole’s Aitkin Basin,

covers nearly a quarter of the moon’s far side. (Like other old

features, it’s also covered with fresh craters.) The bright craters

dotting the moon’s near side, though, are the result of more recent

asteroid impacts.

A Loony Origin Story

The Moon and Water

Humans have long

associated oceans with

the moon, understanding

from observation that,

even before we knew

why, the moon influenced

the tides. We now know

the moon’s gravitational

pull tugs at Earth’s bodies

of water.

The association

goes both ways, too.

Scientists named the

moon’s dark areas

maria — meaning “seas”

in Latin — long before

telescopes revealed there

was no water on the

lunar surface. And while

the Apollo astronauts

hoped to find water

underground, all the soil

samples they returned

suggested the moon was

barren and dry.

The odds of a watery

moon have since

improved, however. The

Indian Chandrayaan-1

mission, and then

NASA’s LCROSS, hurled

probes into the satellite

to analyze the resulting

dust cloud. Both turned

up a surprising amount

of water. And last year,

researchers revealed

what many had long

suspected: Water ice

could and does hide in

permanently shadowed

craters near the lunar

poles.

Such stores of water

would be extremely

valuable, should we ever

get a moon-orbiting

space station (the closest

we’re likely to come to a

lunar settlement in the

near future).

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IMPACT DISK OF DEBRIS DEBRIS COALESCES

Moon

Low high

tide

High

high tide

Low tide

Low tide

Moon’s

gravitational

pull

Water ice

around

south

and north

poles