What would happen if Mars and Venus switched orbits?
I don't know about you, but if I were God I would enjoy spending some of my eternity
experimenting with the things I just created.
Without harming anyone, of course, I would be there all the time trying to take away
curiosities like, "What if I put the lion in India and the tiger in Africa?
What if I move the white bear to Antarctica and the penguins to Greenland?
No, wait...I almost change the value of Pi…
No wait… what if I make the force of gravity vary with the cube of distance instead?
Um...I'm undecided."
Well, I mean...I think you get the picture...the game is one of "what if?"
And sooner or later, I'm sure, I would have started playing with the planets of the solar
system as well...constantly mixing their characteristics to create ever-changing planetary environments.
Which ones would I start with?
Well, I've always been very intrigued by the different fates of Venus and Mars, so I probably
would have wondered: what would happen if Mars and Venus switched places, that is, orbits?
Yeah, what would happen?
What do you guys think, would we have two better planets?
Or worse?
Venus and Mars are two planets that lie, one on either side, just outside the habitable
zone of our solar system.
It's a matter of luck-our Earth formed within the belt, and because of that, we are enjoying
a delightful planet; while our two neighbors the belt just missed it.
Thus, Venus is now too hot, and Mars is too cold.
At this point, the question envisioned by our game -or rather, our thought experiment
- is: what would happen if Mars and Venus switched places?
Could they, combining their other characteristics (size, mass, more or less dense atmosphere)
in the right way, turn into habitable Earth-like planets?
A planet's habitability, or ability to harbor life, results from a complex web of interactions
between the planet itself, the system of which it is a part, and the star on which it orbits.
The standard definition for a habitable planet can support life for a significant period.
As far as researchers know, this requires a planet to have liquid water, and the region
around a star where liquid surface water can exist on a planet's surface is called the
"habitable zone."
But what factors influence the composition of a planet's interior, surface, and atmosphere?
It is not easy to say.
Many different processes-physical, chemical, and geological-combine to produce the observable
characteristics...
Mars has a mass of only one-tenth that of Earth, with a thin atmosphere that is continually
stripped by the solar wind, which is particularly intense due to the absence of a magnetic field
capable of deflecting the flow of high-energy particles, which are thus free to attack and
disperse into space even the few remaining gaseous molecules.
The result?
Without a significant atmosphere capable of trapping heat, temperatures on the Martian
surface have settled at an average of -60°C (-80°F), much lower than they would be if
the red planet were a.bit more massive and thus endowed with an atmosphere.
In fact, Mars orbits near the upper boundary of the classic habitable zone -some say it
is even within it, albeit by a small margin - and it is precisely because of the virtually
absent atmosphere that the small planet is unable to adjust its temperature to values
that should compete with it at that distance.
Unlike Mars, Venus has almost the same mass as Earth.
However, the planet is suffused with an extremely dense atmosphere composed mainly of carbon
dioxide.
In contrast to Mars, Venus' gaseous blanket is so impenetrable to infrared radiation that
it triggers a greenhouse effect capable of raising average surface temperatures to a
hellish 460 °C (860 °F): values sufficient to melt lead…
"Hey, guys, just a moment before we continue...
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Two planets at antipodes, it seems...
So what if by magic Mars found itself orbiting the distance of Venus from the Sun?
Well, clearly, by increasing the average distance from the Sun from 228 to 108 million kilometers,
the amount of sunlight reaching its surface would increase by almost four times; but since
there would be no atmosphere to trigger the greenhouse effect, it has been estimated that
the average temperatures would rise to no more than about 90°F (32°C), similar then
to the very pleasant temperatures in our tropics.
However, we are talking about "average temperatures," and here the very thin atmosphere of Mars
also presents a problem.
Indeed, someone has calculated that with such a thin atmosphere the incoming heat would
not be able to distribute itself efficiently throughout the planet.
This would lead to extreme seasons and high-temperature differences between day and night.
Until recently it was also thought that such a conspicuous increase in temperature would
lead to the melting of the polar ice caps and the consequent release of huge amounts
of carbon dioxide gas.
In quantities that would give the planet a much denser atmosphere...
However, recent research suggests that there is not enough carbon dioxide in the ice to
form a true atmosphere on Mars, and according to some studies, the melting of the polar
ice caps would raise atmospheric pressure by only 15 millibars, bringing it to a total
of around 25 millibars And here it is well to remember that the average pressure at sea
level on Earth is 1,000 millibars.
Then there would also be carbon dioxide imprisoned in Martian rocks to consider, but to release
it would require temperatures of at least 300°C, a value fortunately unattainable for
Mars moved into the orbit of Venus.
And there's more.
Not only would Mars have no benefit from the temperature rise, but it would also end up
losing its already skimpy atmosphere much faster than before.
In fact, even the pressure exerted by the solar wind at the distance from the Sun of
108 million kilometers would be about four times greater than that experienced by the
planet when it was in its original orbit.
So that in a short time (a few tens of thousands of years), Mars would find itself transformed
into a desolate rocky planet, increasingly hotter and completely stripped of its gases,
ice caps, and water ...
.
OK.
While Mars seems to be doing no better in Venus' position, what would happen if Venus
were towed outward into Mars' current orbit?
Brought to the upper boundary of the habitable zone, would this Earth-sized planet be able
to cool down and become a habitable second world?
Surprisingly, cooling Venus may not be so simple.
In fact, Venus has a very high albedo, which means that the upper layer of whitish clouds
surrounding it reflects back into space about 75 percent of the radiation it receives (Earth,
by comparison, reflects 30 percent).
The sweltering temperatures on the planet's surface are thus due not only to the heat
received from the Sun but largely to the greenhouse effect triggered by the thickness and density
of the atmosphere.
The planet's conditions might therefore not be immediately affected by the reduced amount
of incoming light if Venus were to orbit at the distance of Mars.
In theory, the temperature of Venus should drop as low as 70°C (156°F), but because
of what we have just said, it is much more likely that for a very long time it will not
be able to drop below 260°C (506°F).
This is too high for carbon dioxide to condense and thus stop fueling the greenhouse effect.
Apparently, computer simulations show that decisive cooling could only occur if Venus
were brought to a distance from the Sun of at least 260 million kilometers...
In short, it certainly seems that simply swapping the orbits of present-day Venus and Mars would
fail to produce at least a second habitable world...
There are, in fact, other factors that would prevent Venus and Mars from becoming habitable--at
whatever distance to the Sun, we put them.
The first, most important for Mars, is the lack of a magnetosphere, which is necessary
to prevent the solar wind from reaching the planet's surface and dispersing its gaseous
elements.
And we had already discussed this.
The second concerns both Mars and Venus.
Both, in fact, lack the extraordinary geological process that we here on Earth call "plate
tectonics..."
Plate tectonics, also colloquially referred to as Continental drift, is one of the most
important theories formulated last century that can explain how the lithosphere, composed
of the Earth's crust and the upper part of the mantle (which is rigid, while the lower
part is plastic), is made up of huge solid plates that float on the molten interior of
the planet and move slowly, colliding with each other.
Such movements are responsible for earthquakes and the formation of most of Earth's volcanoes
and mountain ranges.
Our Planet is the only one among those we know of that currently has active tectonics.
But plate tectonics is more than earthquakes and eruptions.
A wave of new research increasingly indicates that the movements of Earth's outermost part
may be crucial to its other defining characteristic: life.
Indeed, tectonic activity plays an essential role in maintaining the long-term stability
of Earth's thermostat.
Consider the case of carbon dioxide.
A planet with too much carbon dioxide could end up becoming like Venus, a planetary blast
furnace.
In contrast, plate activity has helped regulate the level of carbon dioxide on Earth for billions
of years, thus ensuring its thermal and environmental stability.
The Earth is uniquely blessed with this privilege--we have said that before--but where does this
great gift of nature come from?
Until now, scientists have always said that plate motion would be attributable to convection
currents in the Earth's mantle.
For the past few years, however, more and more planetologists have been pointing to
the presence of a large natural satellite such as the Moon as the real driving force
behind this process.
This would mean only one thing: to get to the point of changing one's planetary environment,
it is not enough to change the "distance from the Sun" factor.
Apparently, without the presence of a large moon capable of triggering the crust-crushing
process, both Mars and Venus will never be able to turn on the engine of their magnetic
field and regulate their surface temperature.
Can we do anything about it?
Well, definitely not!
Although some people believe it is possible that in the distant future it will be possible
to change the orbit of other planets at will by altering their orbital velocity, it would
be a feat bordering on impossible to provide them with a satellite as massive as our Moon.
What do you guys think?