Venus, Earth, and Mars - The Untold Story

Mercury, Venus, Earth, and Mars are the terrestrial planets which form the inner part of the Solar System. Born some 4.6 billion years ago in the planetary nebula, centre of which formed the Sun, the latter three planets shared something common back there in their distant past.

Some scientists speculate that the three planets, Venus, Earth, and Mars, shared approximately similar geology at the time of their cooling from their molten newly-born states. These three planets may have started to evolve along similar lines, and it is thought that their atmospheres were very similar as well as their geology. Their may have been liquid water on their surfaces, with favourable conditions for life to get a foothold. Keeping this in view that life is thought to evolve on Earth some 3.5 Billion years ago, which is a very distant past, and covers a considerable fraction of the expected age of the Universe itself, there is every possibility that if life could have started on Earth, it could have on Venus and Mars too.

At present, Venus and Mars are present at the two poles of environmental extremes. Studies reveal that Venus, except for its size, has got no other similarity with Earth, its closest neighbour. The whole planet Venus is shrouded with thick clouds and mysteries. The atmosphere is composed of extremely poisonous mixture of Carbon Dioxide, Sulfur Dioxide, and Sulfuric Acid. Added with it is the extreme surface atmospheric temperature (480°C, hotter than a self-cleaning oven), and extreme pressure (exceeding 90times the pressure of our atmosphere, equal to the pressure nearly 1 km under ocean surface). Moreover, the temperature and the pressure is equally hellish throughout the surface, all over the day and night side, and on the poles. The atmosphere retains a major fraction of heat it receives from the Sun, and is under a runaway green-house effect. The day on Venus lasts about 116 Earth days, because Venus rotates at its axis once every 243 Earth days, and that, in a retrograde motion (in opposite direction than other planets).

On the other hand, Mars, which is nearly one-tenth as heavy as Earth, has a little more similarities than Earth. Its day is almost as long as that of Earth, as well as its axial tilt, therefore Mars experiences seasons like on Earth. However, Mars is also a very different world. It perhaps lies on the other extreme of environmental conditions than Venus. Mars has a very thin atmosphere (6 millibars, only 0.6 % of Earth). The atmosphere is nearly entirely made up of Carbon Dioxide. Because of its very thin atmosphere, Mars experiences wide fluctuations of temperatures on its surface, from day to night, and from pole to equator, just opposite to that of Venus. There are no traces of liquid water on Mars, except for the polar ice caps, which may have water ice in it. However, closely studying the surface of Mars reveals that it had a considerably aquatic distant past, with dried water channels all over surface, which used to flow billions of years ago. The surface is almost devoid of any cloud cover, and the atmosphere hardly retains any solar heat.

The conditions on Earth, however, lie in between the two extremes we see on Venus and Mars. The atmospheric pressure is standard 1 bar, nearly one hundredth of Venusian atmosphere, and one hundred times that of Martian atmosphere. The temperature variations are intermediate as compared to that of its sibling planets (Venus and Mars). There is abundant water on the surface, and the atmosphere retains just sufficient heat to maintain the perfect average temperature to sustain life. The Earth is in the most perfect equilibrium one can think of, for the survival of life.

In short, we see that the three planets, which are thought to start as similar worlds, took on to very different paths and are very different worlds with opposite extremes.


WHAT WENT WRONG?

Studies suggest that about 4 billion years ago, the Sun was 40% cooler than it is now. Venus, which is closer to the Sun than Earth and Mars, may have started to evolve earlier along the line on which Earth and Mars started millions of years later. Nothing can be stated with certainty, but if life began on Earth, it may have started on Venus too. Venus may have been covered with vast oceans just like Earth. Over the course of millions of years, the Sun started to get hotter. The Surface of Venus started to get hotter too. The oceans may have evaporated. The carbon dioxide, which was trapped in the rocks in the form of carbonates must have started to escape at higher temperatures. The amount of carbon dioxide in the atmosphere thus rose sharply, making the atmosphere more dense, thus capturing and retaining more solar heat, leading to a self-sustained green-house effect. As it may have happened in the early era of planetary evolutions, when volcanic activities were many magnitudes greater than now, they may have added to the rising temperatures too. Moreover, the ejecting compounds of sulphur from the volcanoes may have reacted with water vapours to form huge amount of sulphuric acid we see in the Venusian clouds today, thus depriving it of water in any form. This led the Venus in its current state, most inhospitable place on can think of, for the life to sustain. The most important fact to remember is that Venus is the closest neighbour of our own planet, the Earth. Any life that may have got foothold on Venus must have been ruthlessly destroyed.

Now let us see what may have gone wrong on Mars. Mars is comparably very small then Venus and Earth. It however lies in nearly the same temperature zone in the Solar System. It means that had the Earth been in place of Mars, and vice-versa, conditions may have been nearly the same on both planets. Many known similarities between Earth and Mars, as concluded by the results of the data gathered by the probes sent there, reveal that the Earth and Mars shared a similar past…even more similar than it is thought regarding Venus. However Earth is far more massive than Mars, and therefore it remained molten for a much longer time, allowing sufficient time for iron to sink down. This was not the case with Mars, which cooled much quickly and possibly solidified completely leaving enough iron on the surface. Because of solidification, it also lost its magnetic field, if there was any. The presence of traces of water channels reveal that there was abundant water on Mars too. It may have harboured life in abundance. Just as it is thought that the oxygen in our atmosphere is a result of photosynthesis by bacteria in oceans over a very long period of time, the oxygen may have been produced on Mars too. But photosynthesis consumes carbon dioxide and releases oxygen. The same may have happened on Mars. As Mars has much weaker gravity than Earth, its atmosphere may have been thin (yet thicker than it is now). Consumption of atmospheric carbon dioxide and releasing oxygen must have been a bad trade-off.

Oxygen is highly reactive gas, which may have reacted with the abundant iron on the surface. As a result, nearly all the oxygen may have been consumed by iron, forming red coloured oxides of iron, which give this planet its red colour. This could have caused plummeting of atmospheric pressure. As a result, the oceans may have evaporated. Because of the low gravity of Mars, the water vapours simply escaped into space, leaving out a desert behind. The thinned atmosphere, along with extremely weak magnetic field could not stop the solar radiation from reaching the surface. The heavy bombardment of solar radiations, along with lack of water, and extreme temperature fluctuations, may have wiped out all life, in a way opposite to that of Venus.


CAN THINGS GO WRONG ON EARTH?

Carbon dioxide constitutes nearly 0.03 – 0.04% of Earth’s atmosphere. On one hand, this is nearly the total amount of carbon dioxide on Mars. On the other hand, huge quantity of carbon dioxide is also trapped in rocks in the form of carbonates and other compounds. There is a huge amount of carbon dioxide dissolved in the oceans as well. This is perhaps equal to (or more than) the amount of carbon dioxide in the Venusian atmosphere. It is worth noting that the TOTAL amount (NOT the percentage) of nitrogen in atmosphere of Venus is almost equal to that in Earth’s atmosphere, a very important clue to the similar distant past of the two planets.

The planet Venus is the best, and the worst example of a green-house effect. The level of carbon dioxide is steadily rising in Earth’s atmosphere as result of emission from factories, cars, aviation industry, and many other sources. To add to the effect, the area of forests is decreasing at an ever increasing rate. The plants help to keep the level of carbon dioxide low by consuming them and releasing oxygen. The increasing carbon dioxide is already taking its toll on the environment by increasing the average global temperature. The resulting melting of glaciers would further contribute to the warming effect of sunlight because of reduced reflective surfaces of glaciers.

The worst fear of this global warming is the threat that it may get self-sustained after a period of time. It means that rising temperature due to increasing carbon dioxide will increase the temperature of the oceans, which would start to release dissolve carbon dioxide too, further increasing the temperature, and repeat this cycle in a sustained fashion. The carbon dioxide trapped in rocks will also start to be released further augmenting this vicious cycle. The high atmospheric temperature would in turn accelerate the process of carbon dioxide release from oceans and rocks. A runaway greenhouse effect would take place, that can be unimaginably difficult to control than it can be controlled now. When this breaking point would occur is not known, but once it happens, the Earth may end up as a second Venus.


LESSON LEARNED

What actually went wrong on Venus is its high gravity and its proximity to the Sun. And what led Mars to its present condition is its small size and low gravity. Had there been a flip-flop of the positions of Venus and Mars in the Solar System, their conditions would have been different. Despite being closer to Sun, had Mars been in position of Venus, it could never sustain a thick atmosphere because of low surface gravity, thus harbouring an atmosphere at a much lower temperature than Venus. On the other hand, Venus, at the current position of Mars, could possibly be somewhat Earth-like.

The perfect balance of nature on Earth is precious. Our two neighbours are there to tell us that it is not always necessary for a planet to have such perfect conditions as we have on Earth. Who knows, that an intelligent life may have evolved on Venus in distant past, even more ‘intelligent’ than us, who might have ruined the natural balance on their planet in the name of progress, modernity, ‘21st Century’, and so on, and brought forth wrath upon themselves. It is not an illogical guess, because there is another intelligent life already present on Earth, busy in destroying the equilibrium.