How Venus and Mars Can Teach Us About the Past and Future of Earth

Moon and Mars From Space

On September 18, 2017, ESA astronaut Paolo Nespoli shot this image from the International Space Station showing the Moon rising above the Earth’s horizon together with Mercury, Mars, the star Regulus, and Venus. Credit: ESA/NASA

One has a thick poisonous atmosphere, one has hardly any atmosphere at all, and one is just right for life to flourish – but it wasn’t always that way. The atmospheres of our two neighbors Venus and Mars can teach us a lot about the past and future scenarios for our own planet.

Rewind 4.6 billion years from the present day to the planetary construction yard, and we see that all the planets share a common history: they were all born from the same swirling cloud of gas and dust, with the newborn Sun ignited at the center. Slowly but surely, with the help of gravity, dust accumulated into boulders, eventually snowballing into planet-sized entities.

Rocky material could withstand the heat closest to the Sun, while gassy, icy material could only survive further away, giving rise to the innermost terrestrial planets and the outermost gas and ice giants, respectively. The leftovers made asteroids and comets.

Comparison of Terrestrial Planets

The four terrestrial (meaning ‘Earth-like’) planets of our inner Solar System: Mercury, Venus, Earth, and Mars. These images were taken by the Mariner 10, Apollo 17, and Viking missions. Credit: ESA

The atmospheres of the rocky planets were formed as part of the very energetic building process, mostly by outgassing as they cooled down, with some small contributions from volcanic eruptions and minor delivery of water, gases, and other ingredients by comets and asteroids. Over time the atmospheres underwent a strong evolution thanks to an intricate combination of factors that ultimately led to the current status, with Earth being the only known planet to support life, and the only one with liquid water on its surface today.

We know from space missions such as ESA’s Venus Express, which observed Venus from orbit between 2006 and 2014, and Mars Express, investigating the Red Planet since 2003, that liquid water once flowed on our sister planets, too. While the water on Venus has long since boiled away, on Mars it is either buried underground or locked up in ice caps. Intimately linked to the story of water – and ultimately to the big question of whether life could have arisen beyond Earth – is the state of a planet’s atmosphere. And connected to that, the interplay and exchange of material between the atmosphere, oceans, and the planet’s rocky interior.

Planetary recycling

Back at our newly formed planets, from a ball of molten rock with a mantle surrounding a dense core, they started to cool down. Earth, Venus, and Mars all experienced outgassing activity in these early days, which formed the first young, hot, and dense atmospheres. As these atmospheres also cooled, the first oceans rained down from the skies.

Mars Horizon to Horizon

Mars from horizon to horizon. Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

At some stage, though, the characteristics of the geological activity of the three planets diverged. Earth’s solid lid cracked into plates, in some places diving below another plate in subduction zones, and in other places colliding to create vast mountain ranges or pulling apart to create giant rifts or new crust. Earth’s tectonic plates are still moving today, giving rise to volcanic eruptions or earthquakes at their boundaries.

Venus, which is only slightly smaller than Earth, may still have volcanic activity today, and its surface seems to have been resurfaced with lavas as recently as half a billion years ago. Today it has no discernable plate tectonics system; its volcanoes were likely powered by thermal plumes rising through the mantle – created in a process that can be likened to a ‘lava lamp’ but on a gigantic scale.

Mars, being a lot smaller, cooled off more quickly than Earth and Venus, and when its volcanoes became extinct it lost a key means of replenishing its atmosphere. But it still boasts the largest volcano in the entire Solar System, the 25-kilometer-high (16-mile-high) Olympus Mons, likely too the result of continuous vertical building of the crust from plumes rising from below. Even though there is evidence for tectonic activity within the last 10 million years, and even the occasional marsquake in present times, the planet is not believed to have an Earth-like tectonics system either.

It is not just global plate tectonics alone that make Earth special, but the unique combination with oceans. Today our oceans, which cover about two-thirds of Earth’s surface, absorb and store much of our planet’s heat, transporting it along currents around the globe. As a tectonic plate is dragged down into the mantle, it warms up and releases water and gases trapped in the rocks, which in turn percolate through hydrothermal vents on the ocean floor.

Extremely hardy lifeforms have been found in such environments at the bottom of Earth’s oceans, providing clues as to how early life may have begun, and giving scientists pointers on where to look elsewhere in the Solar System: Jupiter’s moon Europa, or Saturn’s icy moon Enceladus for example, which conceal oceans of liquid water beneath their icy crusts, with evidence from space missions like Cassini suggesting hydrothermal activity may be present.

Moreover, plate tectonics helps to modulate our atmosphere, regulating the amount of carbon dioxide on our planet over long timescales. When atmospheric carbon dioxide combines with water, carbonic acid is formed, which in turn dissolves rocks. Rain brings the carbonic acid and calcium to the oceans – carbon dioxide is also dissolved directly in oceans – where it is cycled back into the ocean floor. For almost half of Earth’s history the atmosphere contained very little oxygen. Oceanic cyanobacteria were the first to use the Sun’s energy to convert carbon dioxide into oxygen, a turning point in providing the atmosphere that much further down the line allowed complex life to flourish. Without the planetary recycling and regulation between the mantle, oceans, and atmosphere, Earth may have ended up more like Venus.

Extreme greenhouse effect

Venus is sometimes referred to as Earth’s evil twin on account of it being almost the same size but plagued with a thick noxious atmosphere and a sweltering 470ºC (880ºF) surface. Its high pressure and temperature is hot enough to melt lead – and destroy the spacecraft that dare to land on it. Thanks to its dense atmosphere, it is even hotter than planet Mercury, which orbits closer to the Sun. Its dramatic deviation from an Earth-like environment is often used as an example of what happens in a runaway greenhouse effect.

Earth's Evil Twin

Appearances can be deceiving. This thick, cloud-rich atmosphere rains sulphuric acid and below lie not oceans but a baked and barren lava-strewn surface. Welcome to Venus. Credit: ESA/MPS/DLR-PF/IDA

The main source of heat in the Solar System is the Sun’s energy, which warms a planet’s surface up, and then the planet radiates energy back into space. An atmosphere traps some of the outgoing energy, retaining heat – the so-called greenhouse effect. It is a natural phenomenon that helps regulate a planet’s temperature. If it weren’t for greenhouse gases like water vapor, carbon dioxide, methane, and ozone, Earth’s surface temperature would be about 30 degrees cooler than its present +15ºC (59ºF) average.

Over the past centuries, humans have altered this natural balance on Earth, strengthening the greenhouse effect since the dawn of industrial activity by contributing additional carbon dioxide along with nitrogen oxides, sulfates, and other trace gases and dust and smoke particles into the air. The long-term effects on our planet include global warming, acid rain, and the depletion of the ozone layer. The consequences of a warming climate are far-reaching, potentially affecting freshwater resources, global food production and sea level, and triggering an increase in extreme-weather events.

There is no human activity on Venus, but studying its atmosphere provides a natural laboratory to better understand a runaway greenhouse effect. At some point in its history, Venus began trapping too much heat. It was once thought to host oceans like Earth, but the added heat turned water into steam, and in turn, additional water vapor in the atmosphere trapped more and more heat until entire oceans completely evaporated. Venus Express even showed that water vapor is still escaping from Venus’ atmosphere and into space today.

Venus Express also discovered a mysterious layer of high-altitude sulfur dioxide in the planet’s atmosphere. Sulfur dioxide is expected from the emission of volcanoes – over the mission’s duration Venus Express recorded large changes in the sulfur dioxide content of the atmosphere. This leads to sulphuric acid clouds and droplets at altitudes of about 50-70 km (31-43 mi) – any remaining sulphur dioxide should be destroyed by intense solar radiation. So it was a surprise for Venus Express to discover a layer of the gas at around 100 km (62 mi). It was determined that evaporating sulphuric acid droplets free gaseous sulphuric acid that is then broken apart by sunlight, releasing the sulfur dioxide gas.

The observation adds to the discussion what might happen if large quantities of sulfur dioxide are injected into Earth’s atmosphere – a proposal made for how to mitigate the effects of the changing climate on Earth. The concept was demonstrated from the 1991 volcanic eruption of Mount Pinatubo in the Philippines, when sulfur dioxide ejected from the eruption created small droplets of concentrated sulphuric acid – like those found in Venus’ clouds – at about 20 km (12 mi) altitude. This generated a haze layer and cooled our planet globally by about 0.5ºC (0.9ºF) for several years. Because this haze reflects heat it has been proposed that one way to reduce global temperatures would be to inject artificially large quantities of sulfur dioxide into our atmosphere. However, the natural effects of Mt Pinatubo only offered a temporary cooling effect. Studying the enormous layer of sulphuric acid cloud droplets at Venus offers a natural way to study the longer-term effects; an initially protective haze at higher altitude would eventually be converted back into gaseous sulphuric acid, which is transparent and allows all the Sun’s rays through. Not to mention the side-effect of acid rain, which on Earth can cause harmful effects on soils, plant life, and water.

Global freezing

Our other neighbor, Mars, lies at another extreme: although its atmosphere is also predominantly carbon dioxide, today it hardly has any at all, with a total atmospheric volume less than 1% of Earth’s.

Terrestrial Planet Magnetospheres

Artist impression (not to scale) idealizing how the solar wind shapes the magnetospheres of Venus (top), Earth (middle) and Mars (bottom). Credit: ESA

Mars’ existing atmosphere is so thin that although carbon dioxide condenses into clouds, it cannot retain sufficient energy from the Sun to maintain surface water – it vaporizes instantly at the surface. But with its low pressure and relatively balmy temperatures of -55ºC/-67ºF (ranging from -133ºC/-207ºF at the winter pole to +27ºC/81ºF during summer), spacecraft don’t melt on its surface, allowing us greater access to uncover its secrets. Furthermore, thanks to the lack of recycling plate tectonics on the planet, four billion-year-old rocks are directly accessible to our landers and rovers exploring its surface. Meanwhile our orbiters, including Mars Express, which has been surveying the planet for more than 15 years, are constantly finding evidence for its once flowing waters, oceans and lakes, giving a tantalizing hope that it might have once supported life.

The Red Planet too would have started out with a thicker atmosphere thanks to the delivery of volatiles from asteroids and comets, and volcanic outgassing from the planet as its rocky interior cooled down. It simply couldn’t hold on to its atmosphere most likely because of its smaller mass and lower gravity. In addition, its initial higher temperature would have given more energy to gas molecules in the atmosphere, allowing them to escape more easily. And, having also lost its global magnetic field early in its history, the remaining atmosphere was subsequently exposed to the solar wind – a continuous flow of charged particles from the Sun – that, just as on Venus, continues to strip away the atmosphere even today.

With a decreased atmosphere, the surface water moved underground, released as vast flash-floods only when impacts heated the ground and released the subsurface water and ice. It is also locked up in the polar ice caps. Mars Express also recently detected a pool of liquid water buried within two kilometers of the surface. Could evidence of life also be underground? This question is at the heart of Europe’s ExoMars rover, scheduled to launch in 2020 and land in 2021 to drill up to two meters below the surface to retrieve and analyze samples in search for biomarkers.

Mars Dried Out River Valley Network

This image from ESA’s Mars Express shows a network of dried-up valleys on Mars, and comprises data gathered on 19 November 2018 during Mars Express orbit 18831. Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Mars is thought to be currently coming out of an ice age. Like Earth, Mars is sensitive to changes in factors such as the tilt of its rotational axis as it orbits the Sun; it is thought that the stability of water at the surface has varied over thousands to millions of years as the axial tilt of the planet and its distance from the Sun undergo cyclical changes. The ExoMars Trace Gas Orbiter, currently investigating the Red Planet from orbit, recently detected hydrated material in equatorial regions that could represent former locations of the planet’s poles in the past.

The Trace Gas Orbiter’s primary mission is to conduct a precise inventory of the planet’s atmosphere, in particular the trace gases which make up less than 1% of the planet’s total volume of atmosphere. Of particular interest is methane, which on Earth is produced largely by biological activity, and also by natural and geological processes. Hints of methane have previously been reported by Mars Express, and later by NASA’s Curiosity rover on the surface of the planet, but the Trace Gas Orbiter’s highly sensitive instruments have so far reported a general absence of the gas, deepening the mystery. In order to corroborate the different results, scientists are not only investigating how methane might be created, but also how it might be destroyed close to the surface. Not all lifeforms generate methane, however, and the rover with its underground drill will hopefully be able to tell us more. Certainly, the continued exploration of the Red Planet will help us understand how and why Mars’ habitability potential has changed over time.

Exploring farther

Despite starting with the same ingredients, Earth’s neighbors suffered devastating climate catastrophes and could not hold on to their water for long. Venus became too hot and Mars too cold; only Earth became the ‘Goldilocks’ planet with the just-right conditions. Did we come close to becoming Mars-like in a previous ice age? How close are we to the runaway greenhouse effect that plagues Venus? Understanding the evolution of these planets and the role of their atmospheres is tremendously important for understanding climatic changes on our own planet as ultimately the same laws of physics govern all. The data returned from our orbiting spacecraft provide natural reminders that climate stability is not something to be taken for granted.

In any case, in the very long term – billions of years into the future – a greenhouse Earth is an inevitable outcome at the hands of the aging Sun. Our once life-giving star will eventually swell and brighten, injecting enough heat into Earth’s delicate system to boil our oceans, sending it down the same pathway as its evil twin.

6 Comments on "How Venus and Mars Can Teach Us About the Past and Future of Earth"

    . It’s time all of us take a realistic look at global warming so that we can fiqure out what is causing it and how to stop global warming. Back in 1960’s jet engine airplanes starting replacing propeller airplanes. Also at the time period China started it’s massive industrial buildup which led to massive pollution and heat being emitted into the atmosphere. Then at that time in the 1960’s air conditioning world wide started up in mass production. Add to the global warming problem automobiles which was also being used worldwide in mass quantities. This all added up to more heat being put into this bubble we humans live in called Earth’s atmosphere. We humans and the rest of life on Earth have been living in this bubble quite well for millions of years. However when you mess with this bubble we live in then just take a look around and see if you can find another floating rock in the universe where there is a life system that we humans and all other life can live on. There isn’t any and if you were to find one it would be impossible for us humans to live on because it is impossible for us humans to transport our bodies through space for long periods of time. We don’t have the body to survive in weightlessness and we don’t possess the intelligence or ability to make all the equipment that will be needed to create machines that let us get to and live on another planet. And then the cost alone and the amount of people it would take to achieve that goal of living on other planets would be too much for all of us on Earth to do! So we better take care of what rock in space we live on because no matter what NASA and others say as they try to pick your pocket for more money for their pie in the sky dreams about space travel this is the only place in the universe we are going to be able to live so wake up and face reality! The combination of all the things I mentioned above that started happening in the 1960’s started a chain reaction that resulted in the catastrophe we are in today. All that heat released into this bubble we live in resulted in the unbalancing of the hot and cold molecules that are everywhere from the ground up to the most outer part of the bubble we all live in called Earth’s atmosphere. Now this balancing of hot and cold molecules are very important to maintaining life on Earth. For great things happen like clouds and rain when these molecules are balanced just right. And I say history shows that we humans and all other life on this rock we call Earth didn’t have any problems living on this rock we call Earth for billions of years. But now we so called intelligent people have decided that we can do what we want and think we can live on this planet with no problem after we do what we do! Well I hate to burst your bubble and wake you from the dream world you all live in make you face reality but you are in very deep trouble. You see since the 1960’s when us humans started flying jet engine airplanes and rockets and weaponized rockets as well as driving all those combustion engine cars and running all these air conditioners we have in effect unbalanced the balance of hot and cold molecules in the bubble we live in and that resulted in the Earth’s weather systems to be changed in such a way that now with the hot molecules overpowering the cold molecules in this bubble we live in the battle between the Earth and the Sun for existence of life on Earth will be won by the Sun as it cooks our paradise we call Earth into another one of the billions lifeless planets in the universe. Yes folks, there is a battle between the Earth and the Sun. The Earth is trying to do things that allow us humans and all other life to live here. The Earth can create clouds that shield the Sun’s hot rays from cooking the Earth into areas that like deserts or other planets. In fact clouds are Earth’s only shield from the Sun’s hot rays. Without the clouds there is no rain. Without rain there would be no water. Without the clouds constantly raining somewhere on Earth then the Earth’s waters would all evaporate from the rays of the Sun. Without the right amount of moisture in the atmosphere there would be no rain. When you see clouds that yield no rain you are looking at water being evaporated and disappearing forever from the Earth forever by the Sun’s hot heat waves. It’s not good for the Earth to lose water when it is not producing rain! And all the things we humans have been doing since the 1960’s with jet planes, rockets, combustion engine vehicles and air conditioning it has resulted in much more heat in our bubble we call Earth’s atmosphere. This resulted in the Earth’s temperature to rise which affected the cold and hot ballance of molecules and the hot molecules started overpowering the Earth’s cold molecules. The earth’s temperature started rising in the 1960’s and the first chain of disastrous events started unfolding in the Russian part of the Earth in it’s permafrost region. Folk,s permafrost is the easiest form of ice to melt. And when the earth’s temperature rose just a little it was enough to start the melting of all that ice in the area in Russia where the permafrost was. Well when that permafrost melted it turned to water and all that water started draining into the seas and ocean around that part of Russia. Ever since the 1960’s when this melting of Russia’s permafrost started happening this melted permafrost water was draining into the North Pole region and slowly year after year has been melting the ice in the North Pole. There are photos that I have seen that were posted on the internet by some gov’t or someone that showed that this was happening from the 1960’s to modern time! As the warmer melted permafrost water melted the North Pole’s waters that water traveled through the water current travelling around the world and warmed up the waters of the South Pole area. This caused the waters of the Earth to become warmer which then put the Earth into new weather patterns which are dictated by environmental conditions. That is the condition that our Earth is in today. If we continue on the way we are going then in about 10-15 years all or most of the ice in the North Pole will be melted. In about 15-20 years all or most of the ice in the South Pole will be melted. In 5-15 years all the ice glaciers and snow covered mountains will disappear. The Earth will then produce less cold molecules and the Sun will produce more hot molecules. Us humans produce massive amounts of hot molecules daily from these jet engine airplanes and rockets! Go to to see how many of these jet planes are flying at any moment worldwide. There use to be about 9,000 daily worldwide by these jet planes worldwide before the days of the coronavirus epidemic but I’m sure that there is at least 7,000 flights or more on the average a day now. And doesn’t even include any military planes of any nation on it’s radar system. Now bear in mind that these jet engine planes create massive amounts of hot molecules and pollution. The passenger jet planes exhaust temperature ranges from 800 degrees for small jet planes to 1200 degrees for large passenger jet planes. Military jet planes exhaust temperatures range from 1200 to 2500 degrees. Rockets are much hotter. The Space Shuttle was as hot as the Sun! All this heat is emitted daily into our atmosphere and has been since the 1960’s by these jets and rockets! Then to top it off these jet planes are also gigantic vacuum machines that are sucking up, heating up and polluting enough air and moisture out of our atmosphere to fill an enclosed Super Dome Stadium every 2 minutes! Google search all the pollutants that these passenger flying cigar shape vacuum and polluting machines we call jet planes emit and you will see that it is very difficult for nature to produce clouds from all the pollutants and heat that we humans emit into our atmosphere! Folks, we have got to stop flying rockets and jet engine airplanes of all kinds. We have to go back to flying propeller airplanes because they don’t pollute or heat up our atmosphere. we have to stop driving combustion engine cars and start driving electric cars or even better devise a new transportation system that doesn’t involve any or very little pollution or heat. Then we have to redesign our buildings and dwellings so that we don’t need air conditioning or very little air conditioning. We have to do these things now before anymore ice or snow melts anywhere on the Earth. If we bring down Earth’s temperature to the point it was in about 1875 then the Earth will stop experiencing global warming and start rebuilding it’s ice and snow covered areas of the Earth. If you wait too long and the ice and snow covered areas of the earth are lessen drastically then it will be very hard and most likely impossible to stop the Sun’s hot rays from creating more hot molecules which then will overpower the cold molecules which will then lead to less clouds which will then lead to less water which will then lead to massive worldwide droughts, starvations, deaths by thirst, chaos, riots, break down of law and order worldwide, rapes, murders and all kinds of violence and diseases as world order comes to an end! That’s what you folks have to face very soon! I am an old man who won’t be around to witness your future you are building for yourselves. But I thought you ought to know so that maybe just by chance you decided to do something about it and change your way of living so that you are not killing your only place to live called Earth! But if no one listens to me and in 20-30 years you see that the Sun is going to win the battle that it fights with every planet in the universe as it bakes each planet with it’s heat waves remember that you have one more thing that you can do to stop global warming and that is to somehow put as much volcano ash into the upper atmosphere
    worldwide so that the ash blocks the Sun’s rays from reaching the surface of the Earth. Doing this will cool down the Earth. Nature has done exactly the same over the years and it worked. Massive volcano eruptions have cooled the Earth before and can do it again anytime! It will be your only chance to save the Earth. Perhaps start doing it now to help cool the Earth! But do something quick folks because time is running out. Every year the earth’s weather patterns are going to be affected by this global warming. We can’t let political parties nonsense stand in the way to success. we have to have politicians in office who know how to fix our problems and care to fix our problems. This is no longer the time to deny that global warming is happening, this is the time to do something about or our planet and all live on Earth dies! Read for more info about this topic as well as many other topics.
    Water. Weight. Gravity. Slabs of humongous rocks assembled together to form Earth. Earthquakes. Global warming. More water. More gravity. More quakes that are also more serious. What happens when the North and South Pole melt in about 15-25 years? Can anyone out there please answer this? NASA? ANYONE!
    has something to say about this that all of you should read because all hell is going to break out on Earth in about 20-30 years as the Earth takes a very quick spin into a whole new climate era that will very quickly lead to a weather pattern that will lead to the death of this planet! I’m warning you! You better all wake up and save this planet or you can all kiss your butts goodbye because in 20-30 years you all will be fighting for your lives as you try to survive on a planet that will be daily cooked by the Sun and all water will evaporate, in land first and then the oceans. Then people and animals will use up whatever water there is on the planet but there will be no more rain and very few clouds worldwide to create more water. Then as no more water is available most of the people and animals will die from thirst or lack of food farming will end. Mass starvation, chous, riots, breakdown in social order, collapse of all nations and law and order will follow! On
    is why global warming is happening and how to stop it. More info is being added periodically. Good Luck everyone because of my health I won’t be around much longer to try to save all of you from the future that awaits you. And remember what I say before you vote because our next president is going to have to start laying out a plan and getting it initiated before this global warming gets worse and harder to solve which it will if Trump is re-elected. So everyone PLEASE join together and save yourselves by electing Joe Biden as your next president. Put away your feelings about why you may not want to vote for Biden and remember that it’s either Biden or Trump that is going to save you from this global warming problem as well as this coronavirus epidemic. Trump has shown us what an idiot he is! Trump only makes our problems worse! Joe Biden will unite all of us Americans on a path to recovery from the disasters that Trump has caused us and all other problems of ours!

    • whatchimacallit | August 8, 2020 at 3:44 am | Reply

      Do you know what a paragraph is and how it is used to make your words easier to comprehend?

    • if you look at the bible.. it does not say that people have been living on earth for millions of years. if you don’t look at the bible.. you can think all sorts of things that are not true.

  2. A day in Venus equals 243 Earth days, Venus orbit is almost circular with a 3 degree tilt so it experience no seasonal changes, It has no Magnetic field, has no moon to help in tectonic activity and rotation stability , the planet is closer to the Sun than Earth outside the habitable zone. Mars is also outside the habitable zone, it’s gravity and lack of a strong gravity and magnetic field contributed to atmospheric loss, no tectonic activity and so on and so on, these planets will not teach Earth nothing because they are far extreme, scientists need to stop dreaming and get to reality millions are spent sending probes to Mars to find nothing, it’s a dead toxic waste of time and money. The Earth is too resilient to be destroyed that easily, only a nuclear proliferation threatens th planet.

  3. i don’t know about venus teaching us about the past and future of earth.. but i know the bible has a lot to say about these topics.. and i know it is the word of God that is entirely trustworthy. some know these things right now. everyone will know them eventually.

  4. “In any case, in the very long term – billions of years into the future – a greenhouse Earth is an inevitable outcome at the hands of the aging Sun.”

    If left to nature, yes–but whoever’s running the Solar System then may well know how to fix such circumstances.

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