Introduction: Exoplanets and the Earth 2.0 trap.
Exoplanets, are simply planets outside our own solar system. Earth 2.0 is a label the gets applied to any number of planets that could be very similar to Earth, so there is no single ‘Earth 2.0’. It is kind of like a “Miss Galaxy” contest with several entrants, but no final winner.
The trap, is that the phrase “Earth 2.0”, can allow imagining the Earth we know today, and assuming that Earth 2.0 planets are something like the Earth as it is today. Wrong.
The assumption is only that they began like the lifeless Earth 4 billions years ago, which had no oxygen in the air, and radiation that would kill you on the surface.
That was Earth prior to 4 billion years of being transformed by life. Maybe some of these planets do have life, and have also been transformed, although it is highly unlikely the transformation has been identical. But being classified as an “Earth 2.0” does not assume there is life, and only if there is life, could such planets possibly allow anything like humans on the surface. Remember, for 4 billion years, Earth did not provide an environment where humans could survive.
The discovery of Earth like planets is significant, because we feel planets like Earth have the greatest chance of also containing life, and the question one of the biggest question is “how common is life?”.
We have no idea if we are all alone, or whether life is in fact quite common. It is true that one day, perhaps around 20 million years from now, humanity may need a new planet, but at this time, the search for Earth like planets, as explained by NASA, is part of the search for life elsewhere in the universe.
What is an exoplanet?
Nasa: What is an exoplanet? (see Nasa page for more details)
An exoplanet is any planet beyond our solar system. Most orbit other stars, but free-floating exoplanets, called rogue planets, orbit the galactic center and are untethered to any star.
Earth 2.0 is label given to any exoplanet that is thought may possibly be similar to Earth. In reality, from that distance, even Venus would be indistinguishable similar to Earth, despite Venus being an extremely hostile environment.
What stops an exoplanet being a potential new home?
The limitations of space travel.
The first problem, would be getting to a planet around another star.
Given the technology of today’s space craft, reaching even the nearest star could take over 16,000 years:
The nearby star Proxima Centauri will be the first passed by three of the explorers, as it is located around 4 light-years away in the Alpha Centauri system. That’s practically in our back yard, cosmically speaking. Voyager 1 will pass by Proxima Centauri within 16,000 years, while it will take 20,000 years for Voyager 2 to reach it, and 18,00 years for Pioneer 11 to meet our neighboring star.
Digital Trends: It will take 20,000 years for our earliest probes to reach Alpha Centauri
Popular mechanics also has a page on the same subject “Scientists Have Calculated How Long It’ll Take to Reach Distant Stars“, but the conclusion is basically the same.
But what about potential new technologies of the future?
Star Trek has ‘warp drive’, and Star Wars has ‘hyperspace’, and the movie ‘Interstellar’ uses ‘wormholes and an ‘anti-gravity drive’. All these science fiction solutions to travel to other stars, are based on speculation of what just might be possible. To quote NASA:
For the moment, sending humans to the edge of interstellar space, let alone across the cosmic void to other stars, remains firmly in the realm of science fiction.
But scientists and engineers are developing skills and technologies that might help us get there one day.
NASA: Going Interstellar
However, not that last sentence. There is work on trying to work out how to travel to the stars: the Tau Zero Foundation, with the stated mission:
The Tau Zero Foundation develops the technologies required for human flight to other star systems within a single lifetime. We see that interstellar flight is possible within physics we know now, and we work to make it practical.
We take an incremental approach, focusing on steps we can take today, to develop breakthrough propulsion physics, improve and lower costs for energy requirements, propulsion technologies for precursor missions, robotic probes and to participate in the near term developments of human space flight capabilities.
The Tau Zero Foundation.
NASA plans missions decades ahead, but does not foresee any such technologies having any practical applications in coming decades.
Certainly, bold and going when not even Elon Musk dares to dream in his plans to have humans colonize Mars this century. And, as seen with the self-driving, the Cybertruck, Tesla Semi, and new Tesla Roadster, Elon Must is not known for being conservative.
However, even Tau Zero are not claiming the steps needed for interstellar flight will all be taken before 2100.
How many spaceships to move even 1 billion lucky survivors?
One criticism of the plan of Elon Musk to colonise Mars with 1 million people, is that we may be close to being able to create ships for a one-way journey, but we are not close to being able to make ships large enough to carry even 100 people. If we did have ships capable of carrying 100 people, we would need to build 10,000 of those ships to transport 1 million people, which if we could build 10 per year would take 1,000 years. However, this is assuming as most do that even the craft would be on a one-way trip, as Mars could use those materials or the ship as a home, and the cost of sending ships back would be more than that of building a new ship. However, that is not the Elon Musk plan.
Entrepreneur Elon Musk has claimed he’s confident there will be a city of 1 million on Mars by 2050, transported there by 1000 Starships proposed by his SpaceX venture, with plans for up to three rocket launches per day.
Mars settlement likely by 2050 says UNSW expert – but not at levels predicted by Elon Musk
This does not seem well thought out. Assuming there are 1,000 starships, then 3 launches per day would require the return trip to be completed and each craft ready for relaunch in 333 days. Except when you look at the orbits of the two planets, it becomes clear there is only one in time every over 1 year when the planets are int the right alignment to begin the trip, and a round trip takes over 1 year to complete.
The distance between Earth and Mars varies from 54.6 million kilometres to over 400 million kilometres.
If you launched at other times of year, trips would take between “way longer” and “way, way longer”. Forgetting those problems for a moment and assuming the ships have a new warp drive, 3 ships per day is around 1,000 launches per year if you can launch every day of the year irrespective of the relative positions of Earth and Mars and with no regard weather at the launch site. Over 20 years of this would produce 20,000 trips between 2030 and 2050 and thus 500 people per ship. So, these spaceships would carry more passengers each than any Boeing 747, plus it would be reasonable to expect these passenger may need more baggage than the average airline passenger.
Just the logistics of the spaceport would be challenging without considering how to produce the fuel to launch 3 such craft beyond Earth’s orbit every day.
Now imagine trying to move 8 billion people to a planet in another solar system.
It takes billions of years of life to create a breathable atmosphere.
A planet itself may be ‘Earthlike’, but it is easy to forget the first life on Earth did not breath air, or was able to survive on land on the young Earth.
The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe the Oxygen Revolution, and the Oxygen Crisis, was a time interval when the Earth’s atmosphere and the shallow ocean first experienced a rise in the amount of oxygen. This occurred approximately 2.4–2.0 Ga (billion years) ago, during the Paleoproterozoic era.
Wikiepedia: The Great Oxygenation event.
Earth did not start ready for us to live on. For at least the first 2 billion years, there was basically no oxygen in the air. Even then, radiation levels were too strong for life on the Earths’ surface, due to the lack of a ‘mature’ atmosphere with an ozone layer.
Life on Land: Ozone Was Key
Prior to this time in Earth’s history, early life on Earth began and lived in the oceans. So, what changed to allow life to move from the ocean to colonize the land?
Two factors were important to allow colonization of the land: oxygen and ozone in the Earth’s atmosphere. A special type of ocean bacteria, called blue-green algae, worked hard over the initial 4 billion years of Earth history to produce enough oxygen that the Earth’s oceans became oxygenated and the atmosphere become breathable by about 600 to 500 million years ago.
Ontario Beneath Our Feet: First Life on Land.
It took 4 billion years of life to make Earth into the planet we can survive on, which means 4 billion years of evolution. Any Earth like planet with an oxygen atmosphere will have had billions of years with its own evolution, and will logically be full of life. This means to live on such a planet humans would need to colonize and displace some of the locals.
Even on a planet identical to Earth, odds are we still can’t live there!
Of the 4.5 billion years of the Earth so far, for the first 4.0 billion years, even as oxygen levels rose, there was still too much radiation for life on the surface. Then finally, around 0.4 billions years ago, life could exist on land. But now, there is only another 0.1 billion years before natural climate change turn the Earth into something like Venus, where conditions are too hot for live as we know it.
Earth, The Sun And CO2: What Really Determines Our Climate?
This means even on the real Earth, if aliens arrived at random, they would have a 5% chance of landing on a planet we could live on. This is explained in more depth in the Earth, The Sun And CO2. But, it gets worse. Because most likely no other planet would ever have the exact conditions as those during human evolution, so we would either have to evolve to the planet, to transform a whole planet, potentially kill most if no all existing life.
Even on the actual Earth, life on land was not possible for the first 4 billion years. The process of plants turning the atmospheric CO2 into oxygen not only made the planet liveable for us, it also reduced greenhouse gasses, cooling the planet as the star inevitably heats up, keeping the temperature under control. In fact plants can only survive in the correct numbers to keep the temperature stable. They all circle stars with a wide range of sizes and thus lifespans, resulting in varying levels of plant life, and thus a variable stable oxygen level.
It turns out, we humans are very particular about oxygen level, and need oxygen to be within a specific range. Plus, too much oxygen, and everything catches fire, so getting the balance right for us human becomes quite very specific. We can adjust a little, and even people from high altitudes on Earth can get by with a little less, but the range is still narrow. We evolved for a very specific environment.
Life on Earth can evolve for different environments, but it takes thousands of year! Life evolved to survive the oxygen event and other major changes. But it is not that same life before and after the changes. Most life from before was killed by the oxygen event. There have been several mass extinctions where most species die, and in fact the small changes introduced by humans now is creating another mass extinction. The point is, we evolved for a very specific environment, unlike to ever be exactly matched on another planet.
We would either have to evolve, which would take thousands of years, or change the planet, which would not be good for current occupants and on the scale of a planet, could also take thousands of years.
The Search For Life: Why we look for Earth like planets.
The three Searches looking to answer “Is there life elsewhere?”.
I would suggest there are really at least three large scale searches going on:
- Searching data for evidence for advanced alien civilisation (The Seti Institute)
- The search for hospitable planets, or planets with hospitable moons(The NASA Kepler mission)
- Probes to planets (and/or moons) in our own solar system
Is there someone like us out there? (SETI)
This search is the easiest to fund, as it is mostly analysing data from existing telescopes for signals that could indicate life. the problem is, we don’t know what such a civilisation will look like.
The search for advanced alien civilisations generally assumes that if such a civilisation is all like ours, then all we have to is look for the same type of signals as those our civilisation is broadcasting from earth as a by-product of our hi-tech way of life. If they live in any similar to the way we live we should be able to detect their existence with radio telescopes. SETI has already searched most likely every single target for the Kepler mission and found no evidence of civilisations like ours. The universe does seem to be very empty of civilisations like ours, what do not yet know is just how empty.
The Search for hospitable planets and/or moons. (Kepler Mission)
Kepler was a space telescope designed to survey a portion of the Milky Way galaxy in search of exoplanets, which are planets outside our solar system.
Using data from the Kepler mission and the extended K2 mission, scientists have identified more than 2,800 candidate exoplanets and have confirmed more than 2,600 of these as bona fide planets (as of 2015). A handful of planets are thought to be rocky like Earth (but a bit bigger), and orbit in the habitable zone of their stars, where liquid water – an essential ingredient of life as we know it – might exist.
Read the brief from the NASA website, and would assume we are looking for planets just like earth. Places perhaps where, at some future time, we could land and establish colonies? The catch is that no planet like the earth we live on can exist without already having life. We live on planet that has been totally changed by the life on our planet. Early Earth had an atmosphere poisonous to modern humans with no oxygen to breath nor an ozone layer block life destroying radiation before plants and other life completely changed the atmosphere. In fact free oxygen never exists naturally anywhere in the universe without plants to separate that oxygen from compounds with other chemical elements.
No plants can ever at all like the earth we live on without being changed by plants over billions of years. So the search for a true hospitable planet, means the search for a planet that actually has already been transformed by living organisms to become liveable, just as happened on Earth.
Probes to planets (and/or moons) in our own solar system.
This includes Mars missions, Venus missions, and probes to the moons of Jupiter and Saturn.
Supporting Life vs Supporting Humans.
The vastly different odds of live, vs support for human life.
A very common mistake is to forget that even though the Earth has supported life in the sea for almost 4 billion years, it has supported life on land for more like 0.5 billion years. The Earth has supported life 8x longer than it has supported human life. Then there is Venus, which is also believed to have been able to support life for perhaps as much as 3 billion years, but never had the oxygen atmosphere humans needed. Mars, also is believed to have had liquid water and other conditions necessary for life at one time, but never had an oxygen atmosphere.
The four rocky planets in our solar system have existed for a total of over 4 billion years each, or a total of 16 billion years.
Scores:
- Of 4 planets, 3 supported life in some at some point.
- An estimated total of 8 billion years out of 16 with support for support life in some form.
- A total of 0.5 billion years of 16 totally billion years support oxygen based life on land.
Summary not only do more planets potentially support life in some form than specifically support human life, even the one planet that has ever supported human life, only supports human life for a narrow window.
Search for oxygen?
The reality is that to find a planet actually like the earth as we know it, we need to find a planet with life. If we could detect oxygen molecules in a planet’s atmosphere then we would be almost certain we had found life. Free oxygen, as opposed to oxygen as a compound like water or iron oxide etc, would almost certainly only be present because life of some type, had separated that oxygen to produce food. So oxygen would mean life, but so far, we have no way of detecting oxygen in the atmosphere of a planet orbiting a distant star.
So how can we find life? Reality is that all we can do is try and somewhere which mimics as closely as possible the conditions of the only place where we know complex life does exist: earth.
The excitement of Kepler 452b: maybe there is life!
The space news in July 2015 was of the discovery of a potentially very earth like planet, around a relatively earth-like star. The planet is named Kepler 452b, because the star the planet orbits a star named Kepler 452. The star being the 452nd previously unnamed star investigated by the Kepler mission telescope. The Kepler mission is to search for habitable planets and this is not quite the most habitable exoplanet found so far, but the first ‘very habitable’ planet around a star like our own star, the sun.
452b is a planet that is not just around the right size, and in the somewhat mythical ‘goldilocks zone’ where the temperature is right. It is also circling a star similar to our own sun, and as been circling that star for even longer than we have been circling our sun, giving life a chance to have evolved.
That is the excitement. Or, more accurately, the excitement is this confirms that such planets do exist, and if there is one, given the size of the universe, there is a countless number. This suggests somewhere, all the huge number of variables, will have all the right values, and there must be life elsewhere.
Conclusion.
The search for Earth like exoplanets is done to answer the big questions about the universe, and about our existence. An Earth 2.0 is not a backup location for people, because we have evolved very specifically to live in our environment which has been shaped by billions of years of life on Earth.
Despite the science fiction, even our Earth only supports humans for 5% of the life of the Earth, and we evolved to live on Earth at one specific point in the evolution of an ever changing planet, as transformed by life as we have in on Earth over billions.
A true ‘carbon copy’ requires not just an Earth like planet, but that planet to be at the exact right point of its evolution, and transformed in the same way life has transformed the Earth. If, despite the extremely low probability such a planet does exist, it is likely to already to have life quite like us.
For more likely would be that we find many planets, like Mars and the Earth’s moon, where we can live in artificial environments. Perhaps even one day we will learn how to transform such a place into an artificial Earth, but it will to a lot easier to learn that in our own solar system.
Updates.
- 2022 July 24: Rewrite, updated to fully clarify why ‘no alternate home’. I learnt a lot in 7 years.
- 2015 July 26: Version 1.0, following reporting of the discovery of Kepler 452b.
Planned Future updates.
- What the sci-fi gets right, and wrong.