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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!
2.
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.”
3.
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.
4.
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.
5.
The edge of the solar system is 1,000 times farther away than Pluto.
You might still think of the solar system as
extending out to the orbit of the much-loved dwarf planet 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.
6.
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.
7.
There are Mars rocks on Earth (and we didn’t bring here).
Chemical analysis of meteorites found in
Antarctica, the Sahara Desert, and elsewhere has 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.
8.
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!
9.
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.
10.
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.
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.
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