10 ) The hottest planet isn’t closest to the sun
Many people know that Mercury is the closest planet to the sun, well
less than half of the Earth’s distance. It is no mystery, therefore, why
people would assume that Mercury is the hottest planet. We know that
Venus, the second planet away from the sun, is on the average 30 million
miles farther from the sun than Mercury. The natural assumption is that
being farther away, it must be cooler. But assumptions can be
dangerous. For practical consideration, Mercury has no atmosphere, no
warming blanket to help it maintain the sun’s heat. Venus, on the other
hand, is shrouded by an unexpectedly thick atmosphere, about 100 times
thicker than our own on Earth. This in itself would normally serve to
prevent some of the sun’s energy from escaping back into space and thus
raise the overall temperature of the planet. But in addition to the
atmosphere’s thickness, it is composed almost entirely of carbon
dioxide, a potent greenhouse gas. The carbon dioxide freely lets solar
energy in, but is far less transparent to the longer wavelength
radiation emitted by the heated surface. Thus the temperature rises to a
level far above what would be expected, making it the hottest planet.
In fact the average temperature on Venus is about 875 degrees F, hot
enough to melt tin and lead. The maximum temperature on Mercury, the
planet closer to the sun, is about 800 degrees F. In addition, the lack
of atmosphere causes Mercury’s surface temperature to vary by hundreds
of degrees, whereas the thick mantle of carbon dioxide keeps the surface
temperature of Venus steady, hardly varying at all, anywhere on the
planet or any time of day or night!
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9 ) Pluto is smaller than the USA
The greatest distance across the contiguous United States is nearly
2,900 miles (from Northern California to Maine). By the best current
estimates, Pluto is just over 1400 miles across, less than half the
width of the U.S. Certainly in size it is much smaller than any major
planet, perhaps making it a bit easier to understand why a few years ago
it was “demoted” from full planet status. It is now known as a “dwarf
planet.”
8 ) George Lucas doesn’t know much about “Asteroid Fields”
In many science fiction movies, spacecraft are often endangered by pesky
asteroid fields. In actuality, the only asteroid belt we are aware of
exists between Mars and Jupiter, and although there are tens of
thousands of asteroids in it (perhaps more), they are quite widely
spaced and the likelihood of colliding with one is small. In fact,
spacecraft must be deliberately and carefully guided to asteroids to
have a chance of even photographing one. Given the presumed manner of
creation, it is highly unlikely that spacefarers will ever encounter
asteroid swarms or fields in deep space.
7 ) You can make volcanoes using water as magma
Mention volcanoes and everyone immediately thinks of Mount St. Helens,
Mount Vesuvius, or maybe the lava caldera of Mauna Loa in Hawaii.
Volcanoes require molten rock called lava (or “magma” when still
underground), right? Not really. A volcano forms when an underground
reservoir of a hot, fluid mineral or gas erupts onto the surface of a
planet or other non-stellar astronomical body. The exact composition of
the mineral can vary greatly. On Earth, most volcanoes sport lava (or
magma) that has silicon, iron, magnesium, sodium, and a host of
complicated minerals. The volcanoes of Jupiter’s moon Io appear to be
composed mostly of sulfur and sulfur dioxide. But it can be simpler than
that. On Saturn’s moon Enceladus, Neptune’s moon Triton, and others,
the driving force is ice, good old frozen H20! Water expands
when it freezes and enormous pressures can build up, just as in a
“normal” volcano on Earth. When the ice erupts, a “cryovolcano” is
formed. So volcanoes can operate on water as well as molten rock. By the
way, we have relatively small scale eruptions of water on Earth called
geysers. They are associated with superheated water that has come into
contact with a hot reservoir of magma.
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6 ) The “edge” of the Solar System is 1,000 times farther away than Pluto
Most people have been taught that the solar system just goes out to the
orbit of Pluto. Today we don’t even consider Pluto a full-fledged
planet, but the impression remains. Still, we have discovered numerous
objects orbiting the sun that are considerably farther than Pluto. These
are “Trans-Neptunian Objects” (TNOs), or “Kuiper Belt Objects” (KBOs).
The Kuiper Belt, the first of the sun’s two reservoirs of cometary
material, is thought to extend to 50 or 60 astronomical units (AU, or
the average distance of the Earth from the sun). An even farther part of
the solar system, the huge but tenuous Oort comet cloud, may extend to
50,000 AU from the sun, or about half a light year – more than a
thousand times farther than Pluto.
5 ) Almost everything on Earth is a rare element
The elemental composition of planet Earth is mostly iron, oxygen,
silicon, magnesium, sulfur, nickel, calcium, sodium, and aluminum. While
such elements have been detected in locations throughout the universe,
they are merely trace elements, vastly overshadowed by the much greater
abundances of hydrogen and helium. Thus Earth, for the most part, is
composed of rare elements. This does not signify any special place for
Earth, however. The cloud from which the Earth formed had a much higher
abundance of hydrogen and helium, but being light gases, they were
driven away into space by the sun’s heat as the Earth formed.
4 ) There are Mars rocks on Earth (and we didn’t bring here)
Chemical analysis of meteorites found in Antarctica, the Sahara Desert,
and elsewhere have been shown by various means to have originated on
Mars. For example, some contain pockets of gas that is chemically
identical to the martian atmosphere. These meteorites may have been
blasted away from Mars due to a larger meteoroid or asteroid impact on
Mars, or by a huge volcanic eruption, and later collided with Earth.
3 ) Jupiter has the biggest ocean of any planet
Orbiting in cold space five times farther from the sun than Earth,
Jupiter retained much higher levels of hydrogen and helium when it
formed than did our planet. In fact, Jupiter is mostly hydrogen and
helium. Given the planet’s mass and chemical composition, physics
demands that way down under the cold cloud tops, pressures rise to the
point that the hydrogen must turn to liquid. In fact there should be a
deep planetary ocean of liquid hydrogen. Computer models show that not
only is this the largest ocean known in the solar system, but that it is
about 40,000 km deep – roughly as deep as the Earth is around!
2 ) Even really small bodies can have moons
It was once thought that only objects as large as planets could have
natural satellites or moons. In fact the existence of moons, or the
capability of a planet to gravitationally control a moon in orbit, was
sometimes used as part of the definition of what a planet truly is. It
just didn’t seem reasonable that smaller celestial bodies had enough
gravity to hold a moon. After all, Mercury and Venus have none at all,
and Mars has only tiny moons. But in 1993, the Galileo probe passed the
20-mile wide asteroid Ida and discovered its one-mile wide moon, Dactyl.
Since then moons have been discovered orbiting nearly 200 other minor
planets, further complicating the definition of a “true” planet.
1 ) We live inside the sun
Normally we think of the sun as being that big, hot ball of light 93
million miles away. But actually, the sun’s outer atmosphere extends far
beyond its visible surface. Our planet orbits within this tenuous
atmosphere, and we see evidence of this when gusts of the solar wind
generate the Northern and Southern Lights. In that sense, we definitely
live “inside” the sun. But the solar atmosphere doesn’t end at Earth.
Auroras have been observed on Jupiter, Saturn, Uranus, and even distant
Neptune. In fact, the outer solar atmosphere, called the “heliosphere,”
is thought to extend at least 100 A.U. That’s nearly 10 billion miles.
In fact the atmosphere is likely teardrop shaped due to the sun’s motion
in space, with the “tail” extending tens to hundreds of billions of
miles downwind.
