Headline: Why caring for the Earth depends on space Earth Day is about where we live -- our home world.
And it is about its condition, how we care for it, what we do with it. It seems ironic, therefore, that in many ways Earth Day depends on space travel, because to learn much of what we know about our planet, we've had to leave it.
Looking back down
The history of our presence in space is mostly the history of looking back at the Earth and trying to understand it. Even the earliest satellites revolutionized our knowledge and understanding of the Earth.
An example of this is TIROS 1, one of the very first working satellites, launched in April 1960. What TIROS 1 did seems trivial today, but at the time it was an enormous advance: TIROS (Television Infrared Observation Satellite) was the first weather satellite. It allowed us to see weather, and indeed our whole planet, in a new perspective. For the first time we could see patterns of clouds moving across Earth's face, and see weather as a single global system instead of disconnected local phenomena.
Those first photos from TIROS 1, beamed back day after day, also did something else: For the first time we saw Earth as an isolated world in the vastness of space. But we also saw it as a rotating sphere -- and each new image revealed a living, dynamic planet. Many remarked on the prominence of Earth's oceans, continents and atmosphere -- and also how national boundaries were completely invisible. Coming at the peak of the Cold War, the TIROS images provided an enlightening, as well as sobering perspective.
TIROS 1s first image of the Earth from space.
More than weather
Weather satellites are the best-known Earth-monitoring satellites, but in many ways other, lesser-known satellites and space probes have had just as much impact on our understanding of Earth.
Possibly the best example of this is a program now called Landsat, which started with something called the Earth Resources Monitoring Satellite, or ERTS. In 1972 ERTS 1 carried aloft sensors that allowed imaging of Earth in both visible and infrared light, and it sent back over 300,000 images of deserts, forests, crops and other landforms from all over the world. Spy satellites had taken such photos before, but the ERTS photos were available to anyone, and what they revealed changed forever how Earth science is studied.
It wasn't just the clarity and resolution of the photos that was startling, but what ERTS' multi-wavelength "eye" revealed: Photographed in infrared light, diseased portions of forests and crops stood out in bright colors, making it easy to see from space what was difficult to see even upon close inspection on the surface.
Large geologic formations, impossible to see on Earth, stood out in stark relief from space. The satellite photos revealed water flows, circulation patterns and pollution effects never before detected. ERTS 1 had a design life span of only one year, but in that time it launched a revolution in what we now call remote sensing. Its successors -- the Landsat satellites -- continue to this day, often providing the reference data from which we gather much of our knowledge about the state of our world and the impact we are having on it.
Wiring the wild
But large, complex spacecraft such as Landsats are not the only ones that have changed how we monitor Earth; sometimes very simple ideas are the ones that make a difference. A good illustration of that is the ARGOS platforms, first launched in 1978, operated jointly by the U.S. and France.
ARGOS is a set of data-collection platforms that fly aboard other spacecraft and collect data from the ground. However, they themselves carry no sensors of any kind; instead they receive their data from ground-based sensors, which can be almost anything: temperature sensors on glaciers, wind and wave sensors on remote ocean buoys, transmitters strapped to migrating animals, underwater sensors with floating antennas, and so on.
The beauty of the ARGOS system is that for more than two decades it has provided a very simple means for scientists to devise new instruments and put them anywhere in the world, without having to worry about going back to get the data. ARGOS sensor platforms are commonly dropped from airplanes onto remote locations, deployed by submarines on the polar ice cap, or set adrift on the oceans. With the advent of microelectronics it's now possible for an ARGOS ground station to weigh as little as one ounce, making it possible to attach one to something as small as a bird and track its migration.
A simple metal ball
ARGOS was conceived and remains very simple in concept, but for sheer simplicity and ingenuity it would be hard to top LAGEOS (Laser Geodynamics Satellites). LAGEOS satellites are probably the simplest satellites every launched, containing no electronics or even batteries, but they have made possible large strides in geology and other forms of Earth study. To understand how a simple metal ball in space can make such a big difference, see the
sidebar.Exploring worlds to study Earth
Satellites are not the only space application for the study of Earth. Many of the programs undertaken to study other worlds, even our own moon, were conceived to help us better understand this planet.
The Apollo program measured the chemical and tectonic composition of the moon for clues about Earth's formation; the Viking landers analyzed martian rocks for possible information about early terrestrial life; the Voyager and Galileo space probes have studied Jupiter's moons for what clues they give about Earth's tectonic activity.
In addition, solar probes such as SOHO and Ulysses watch the sun to understand and predict its effects on Earth, while remote probes such as the NEAR spacecraft examine asteroids to help us understand and perhaps avoid them. Future programs, such as upcoming probes to Mars, have direct application to how we understand Earth, its climate and its formation.
Journey to ourselves
It's often said that the purpose of space exploration is to satisfy our need to explore what lies beyond. And while satellites and space probes have taught us much about the universe, by far their biggest effect has been what they have taught us about Earth -- and about ourselves. In that sense, most space exploration is really Earth exploration carried on from another point of view.
Some of that exploration will continue with satellites designed explicitly to study Earth, such as the new Terra satellite that is the most powerful platform ever launched for the study of our world and its inhabitants. Some of that exploration will also be via space telescopes and space probes that gather information about the cosmos that we apply in turn to understanding terrestrial science.
But in just about every way, the history of space exploration will continue to be mostly a journey to understand our home planet, to understand ourselves and perhaps most importantly, to understand the dynamic relationship of our species to our home world. It is in that goal -- not only in understanding but in helping us preserve our environment -- that space exploration is satisfying not just our curiosity but some of our most basic practical needs as well.
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