Sky & Telescope - March 2023 - 35

THE BLUE MARBLE by Javier Barbuzano
Tidal currents in the Sea of Okhotsk
(lower right) transition from smooth to
turbulent flows in this natural-color image
from the Landsat 8 satellite.
h's Wellspring
O
We live on a planet covered in water, but
where did this water come from?
n December 6, 2020, dozens of scientists and
technicians from the Japanese space agency, JAXA,
roamed the Australian outback, waiting for a sign
from the heavens. They were looking for a bright streak of
light that would cross the sky, bringing with it new knowledge
about the origins of our solar system. It arrived just
before dawn, accompanied by a radio signal that revealed
the location of the treasure left behind: a capsule filled with
about 5 grams of the near-Earth asteroid 162173 Ryugu,
recovered by the Hayabusa 2 robotic spacecraft more than
one year earlier and dropped as the craft whizzed by Earth.
Ryugu itself might only be 9 million years old, but it's
made of debris from a much older asteroid, a rocky remnant
from just after the solar system's formation about 4.6 billion
years ago. Asteroids and their icy cousins, the comets, act
as time capsules, preserving chemical details that can help
us understand how the planets came to be the way they are
(S&T: May 2020, p. 14). One of those details is where our
planet's water comes from.
Scientists have debated the origin of Earth's water for
0.2%
Fraction
of Earth's
mass that
is water
decades. While some think that water was embedded in
Earth's original building blocks, many more think it came
from elsewhere - for instance, from comets and asteroids
that collided with the young Earth when the solar system
was in its infancy. Others think the Sun itself might
have played a role. So far, none of these ideas can
provide an unequivocal answer.
The quest for water's origin is not just about
hydrogen and oxygen. It's part of the larger
mystery of how Earth got its volatile elements,
from the nitrogen that makes up 78% of our
atmosphere to the carbon that dominates
life's chemistry. The same mechanism most
likely furnished Earth with all of these elements,
the very things that make our blue
planet what it is.
sk yand tele scope .o r g * MARCH 2023 35
IMAGE: USGS / NASA EARTH OBSERVATORY; WATER DROPLET ICON: KAREEMOV1000 / THE NOUN PROJECT

Sky & Telescope - March 2023

Table of Contents for the Digital Edition of Sky & Telescope - March 2023

Contents
Sky & Telescope - March 2023 - Cover1
Sky & Telescope - March 2023 - Cover2
Sky & Telescope - March 2023 - 1
Sky & Telescope - March 2023 - Contents
Sky & Telescope - March 2023 - 3
Sky & Telescope - March 2023 - 4
Sky & Telescope - March 2023 - 5
Sky & Telescope - March 2023 - 6
Sky & Telescope - March 2023 - 7
Sky & Telescope - March 2023 - 8
Sky & Telescope - March 2023 - 9
Sky & Telescope - March 2023 - 10
Sky & Telescope - March 2023 - 11
Sky & Telescope - March 2023 - 12
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Sky & Telescope - March 2023 - 14
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Sky & Telescope - March 2023 - Cover3
Sky & Telescope - March 2023 - Cover4
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