The Universe Within (8 page)

For thousands of years, humans have looked to the sky for answers about life, time, and our place in the universe.
Telescopes have enhanced our view, revealing
moons on distant planets and canals on Mars. For the past forty years, we’ve sent hundreds of craft to the moon,
asteroids, other planets and their moons, even deep space beyond the gravitational pull of our
sun.
Apollo 8
propelled the first humans beyond the gravitational pull of
Earth to enter one dominated by another celestial body. Circling the moon on Christmas Eve 1968,
William Anders captured the rise of Earth over the surface of the moon. About twenty-five years later, the unmanned
Voyager
spacecraft began to leave our solar system, departing from the gravitational pull of our sun to enter deep space. Engineers turned the cameras back to reveal Earth. What was for
Voyager
a single pixel in space, and for
Apollo 8
a globe, was a blue oasis of
water and air in a world unique among all known ones in the universe.

Even before
Project Apollo, observations of
Venus changed the way we see our place in the universe. The bright planet looks
like a sphere, but next time you have the opportunity, scan it with binoculars or a
telescope. What you will see is something that nearly got
Galileo executed when he first interpreted it in 1610. Venus, like our moon, has
phases that extend from crescent to full and back again. From these kinds of observations, Galileo was able to prove that the planets, including our own, rotate around the
sun rather than Earth.

Being near the size of Earth, and relatively close to the sun, Venus has long been thought to be our closest planetary relative—so much so that the earliest interplanetary missions were sent there in the hopes of finding life. Some scientists even thought that when we landed on Venus, we would discover a tropical world, almost like that of Earth during the age of the dinosaurs.

The first hint that something strange was happening on Venus came in the 1930s, when observers looked at the planet with a new kind of telescope. Rather than measure the intensity of light, this telescope, at the
Mount Wilson Observatory in California, deconstructed the light into its
electromagnetic
spectrum. The spectral pattern hinted that Venus’s
atmosphere was composed of 99 percent
carbon dioxide.

In 1962, Venus won the lottery as the first extraterrestrial planet to receive visitors from Earth when
NASA planners launched the first spacecraft of the
Mariner project. This mission was a huge undertaking; liftoffs are always dangerous, but in 1962 they were particularly so.
Mariner 1
’s liftoff went so awry that the destruct button had to be pushed to prevent a disaster for the towns of coastal Florida. The mission that followed,
Mariner 2
, only had the capability of carrying about forty pounds for all the scientific measurements it would perform. After a successful liftoff,
Mariner 2
’s trip to Venus took about three and a half months. The small number of instruments that the probe carried were to make some very large discoveries. They revealed that Venus has surface temperatures that were roiling hot, about
900 degrees Fahrenheit. Venus has surface pressures about ninety times those of Earth; you would need to go half a mile underwater to feel that kind of pressure. And the instruments confirmed that the
atmosphere is almost entirely
carbon dioxide.
Mariner 2
found that our close planetary relative, our near twin in size, is most similar to hell.

How could such a dead ringer for Earth in so many ways be so different? Part of the answer would come from new kinds of probes.

In the 1960s, while NASA was gunning for the moon, the Russians were developing machines to land on Venus. Getting a mission to actually visit and record data on Venus is a tricky business. These machines need to be lightweight so that they can be put aloft, but therein lies a huge trade-off: the immense pressures of the planet’s atmosphere give precious little time to make measurements before the probe is crushed like a beer can at a football game. Not surprisingly, the list of early missions reads like a list of calamities.
Venera 1
lost contact en route.
Venera 2
lost contact upon arrival.
Venera 3
crash-landed on the planet.
Venera 4
entered the atmosphere, sent a few signals, then was lost. But persistence paid off.
Venera 9
, launched fourteen years after
Venera 1
, landed on Venus and sent back the first grainy black-and-white photographs. Subsequent missions landed and were able to analyze soil samples and the environment. What did they find? Venus has thunder and lightning. Venus has lava rocks much like those of Earth. Venus may be a hot, high-pressure, and carbon-dioxide-rich world, but it is strangely similar to our own planet.

Then came NASA’s
Pioneer
mission, launched in 1978. This probe was a miniature science lab in space, carrying equipment that could measure the composition of the clouds and the chemical constituents of the atmosphere, among other things. When
Pioneer
entered a Venusian cloud, some of the sulfuric acid inside touched one of the devices. The device could then look at the
atoms inside, particularly the different kinds of
hydrogen. The ratio of different atoms of hydrogen in a sample of gas is influenced by the presence of
liquid water. In the measurement of these atoms came a surprise.
Venus is dry as a bone today, but at some point in the very distant past it had oceans.

Venus and Earth were born twins, but our fates have been completely different thus far—Venus lost its water, while our planet kept it. Venus’s relatively close position to the sun defines a world where liquid water cannot be maintained. The loss of water may be behind many of the differences between the two planets. On Earth, water facilitates the removal of
carbon dioxide from the atmosphere through a long chain of chemical interactions with rocks. These reactions are not possible on Venus. Having no liquid water, Venus is like a closed container being pumped with gas; with
volcanoes spewing carbon, and no way of removing it, pressure just builds over time. As a result, the planet gets hotter and hotter. Venus is in a runaway
greenhouse, set up by its loss of water.

Our neighbor on the opposite side of our planet’s
orbit from the sun, Mars, tells a different story. On Mars, we have yet to find active volcanoes spewing gases, lava floes, or a moving crust. Canyons and canals carry the signature of having been sculpted by flowing water. Dormant volcanoes dot the surface. If there was liquid water, then there needed to be temperatures in the ranges we experience here on Earth. The surfaces that reveal extensive flowing water are scarred by time, often pockmarked by small and large impacts that may have happened billions of years ago. Recent probes reveal seasonal flowing water on Mars today, but these flows are a far cry from those that created the deep canyons that exist on the planet. Mars’s vigorous and aquatic past is largely frozen in time.

Many of the differences between Venus and Mars derive from the
heat balance of the planets. Venus lost its water because, being close to the sun, its water evaporated and set off a runaway chain
reaction of ever-increasing heat. Since Mars is relatively far from the sun, it likely did not receive enough heat to sustain liquid water. Mars’s relatively small size also contributed to its loss of heat. All else being equal, small entities have more surface area for their size than do big ones. For example, children have relatively more surface than adults. More surface area means more loss of heat, so children start to shiver in a cold pool quicker than adults do. Planets are no different. Mars’s shivers led it to lose its heat and much of its geological activity.

In the planet business, being in the right place, at the right size, with the right materials, at the right time is everything. We live on a planet that is
habitable because it formed at just the right distance from the sun, in a gravitational balance with its neighbors, with just the right amount of material to support a world with liquid water, recycling crust, and an atmosphere. What can we thank for being the lucky recipients of such an inheritance?

For the
Romans,
Jupiter was the god who oversaw oaths and laws and thereby defined the social balance that maintains a just society. The planet Jupiter plays an analogous role in the physical and biological worlds.

Jupiter has two and a half times the
mass of the rest of the planets in our
solar system combined. Its mass is over three hundred times that of Earth; more than eleven hundred Earths could fit inside Jupiter. This colossus exerts, through its gravitational pull, an enormous effect on its neighbors. It sucks
asteroids and
comets into its field. As for the planets, Jupiter competes with the sun to pull them into its
orbital plane. This cosmic tug-of-war defines our own orbit and has guided much of our history.

Over 4.6 billion years ago, as dust swirled the star that would become our sun, clumps of debris formed, as Swedenborg,
Kant, and
Laplace envisioned. Jupiter was the equivalent of the two-ton gorilla in the crowd: being the most massive planet in the solar system, it had a profound impact on its neighbors. The gravitational attraction that produced the planets made them, in
effect, compete and interact with one another. Imagine the tugs felt on the forming
Earth everywhere from the
sun, from other planets, and from the center of attraction inside the young planet itself. A huge planet, such as Jupiter, with a proportionally large gravitational field around it, influenced how much material was available for Earth to form and where it would lie relative to the sun.

Computer simulations of the origin of the solar system suggest that Jupiter formed before Earth. Competition with Jupiter for debris meant that the position
of Jupiter defined the shape of the rest of the solar system. If Jupiter formed closer to the sun, it would have led to fewer but larger
rocky planets in the interior of the solar system. If Jupiter formed farther from the sun, there would likely have been a larger number of smaller planets. Our planet’s mass and its distance from the sun—the benevolent conditions that have supported liquid water and life—are due in no small part to the influence of Jupiter.

Our dependence on Jupiter lies in every part of our being, from the presence of liquid water on the planet to the size, shape, and workings of our bodies. The formation of Jupiter defined the size of Earth and, in so doing, the pull of gravity on all things on its surface. A simple thought experiment reveals the web of interconnections. If Jupiter had formed closer to the sun, then Earth would have been larger and heavier and the pull of gravity experienced by Earth’s denizens greater. Even in the unlikely event that such a strange Earth managed to hold liquid water, life on the planet would be very different. As every engineer knows, if you want to make a beam resistant to bending with the same material, just make it relatively wider. All else being equal, a heavier Earth means fat and wide bodies to cope with the greater
tug of gravity. Conversely, a smaller
Earth would have meant less tug of gravity on evolving bodies; hence, their proportions would need to be longer and lighter. The mass of Earth defines the gravity we experience and, in so doing, controls virtually every aspect of our lives, from our size and shape to how we move about, feed, and interact with the planet.

From the imbalance of matter over
antimatter in the moments after the
big bang, and the formation of
Jupiter that defined our livable planet, to the way a single sperm out of millions fertilized the egg that defined our genes, it is easy to celebrate the lottery each of us has won to be here on a habitable planet. But it is a virtual certainty that within the next billion years the
sun will run through its
hydrogen fuel, expand, and become superhot. In the process, Earth will almost certainly lose its
water. The subsequent loss of water will cause a runaway
greenhouse
effect, superheating the surface of our planet. Earth will become like
Venus. The next planet with liquid
water, and the conditions for life, will likely lie farther from the sun. Perhaps it will be a more distant body in our solar system that currently has ice—one of the
moons of Jupiter such as
Europa, or
Enceladus, a moon of Saturn. Our good fortune, the perfection of circumstances that have defined our existence, is just a moment in time.