This question shows up from time to time whenever governmental budgets are discussed. Why do we need to go into space, and more specifically, why do we need to send humans into space? I’ll go ahead and give you what I think is the answer now: we send humans into space for survival of the human species. The next question I’ll answer later in the text; when?
If you surf the internet and read opinions of why we need human space flight you’ll get a variety of answers. Most of them discuss our need as humans to explore, benefiting Earth, that it is our destiny, or the need to find new natural resources. All of these are fine but are simply an equivalent counter to the arguments for human needs on Earth. However, there are some that get it right; that is, for us to survive as a human race we must eventually leave Earth. Does this mean that there is an immediate danger or catastrophe coming? Probably not, but we don’t really know.
In this article we’ll look briefly at mass extinction events in the Earth’s past, what may have caused them, whether or not these events could occur again, what other extinction events could occur in the future, and whether or not humans could prevent these events. The second part of this argument is how long we have before we need to leave. This is a “back of the envelope” calculation. I am not saying that I can tell you when a catastrophe will occur, just what might occur over a considered period of time. The values discussed below are guesses based on available information. First, let us start with the possibilities of extinction events. Then we should consider humans surviving one major catastrophic event but then spending years or millennia getting back to the same technological capability before the next event.
Potential Extinction Events
There are not as many rogue asteroids floating around from the early solar system since they have either settled into stable orbits or those in highly elliptical orbits have already impacted ours and other worlds. Earth tectonic plates and volcanism may have also settled into more stable geological conditions since the formation of the Earth. This does not, of course, eliminate the possibility of such events from occurring again. It also does not account for other calamitous events from relatively new conditions. To most researchers, we have five major extinction events that have occurred (source: Space.com):
• Ordovician-Silurian extinction – about 439 – 445 million years ago; the death toll: 25 percent of marine families and 60 percent of marine genera.
• Late Devonian extinction – about 364 – 365 million years ago; the death toll: 22 percent of marine families and 57 percent of marine genera.
• Permian-Triassic extinction – about 250 – 251 million years ago; the Permian-Triassic catastrophe is Earths worst mass extinction, killing 95 percent of all species, 53 percent of marine families, 84 percent of marine genera and an estimated 70 percent of land species such as plants, insects and vertebrate animals.
• End Triassic extinction – roughly 199 million to 214 million years ago; the death toll: 22 percent of marine families, 52 percent of marine genera. Vertebrate deaths are unclear.
• Cretaceous-Tertiary extinction – about 65 million years ago; the extinction killed 16 percent of marine families, 47 percent of marine genera and 18 percent of land vertebrate families, including the dinosaurs.
There are disagreements on what exactly caused these events so let us include many possibilities that have, or could, cause mass extinctions. We can classify them first into two major categories: 1) those events that are Earth caused; and 2) those events that are extra-terrestrially caused (please note that I am not referring to aliens in flying saucers, but anything that could affect Earth from space including asteroids, comets, gamma-ray bursts, etc.).
Earth Initiated Catastrophes
Of the categories of catastrophic events that are Earth caused, we can list them as:
1. Super volcanism
2. Natural climate change
3. Human created
Super volcanoes are real and exist today though the known super volcanoes of the world are dormant. A super volcanic eruption will deposit cubic miles of ash into the atmosphere as well as sulfur dioxide, carbon dioxide, hydrogen sulfide, and hydrochloric acid. In mass quantities, these gases and compounds could result in famine, climate changes, and possibly the extinction of humans. Super volcanoes are mostly scattered along the “ring of fire” surrounding the Pacific Ocean, Asia, and a few in the United States, notably, Yellowstone.
Eruptions of super volcanoes may have resulted in some extinction of human life that was present on the planet (source: Wikipedia and Discovery.com). The Toba, Sumatra, eruption occurring about 74,000 years ago and thousands of times more powerful than Mt. St. Helens or Pinatubo, is the largest known in the last 25 million years. Toba did not completely wipe out our ancestry but it probably came close. Other super volcanoes (there have been several in the geologically recent history of the world) could have similar results. Since Earth is a few billion years old, crusts and mantle have settled. The time between super volcano eruptions may get longer and longer, but it has only been 22,000 years since the last super eruption. Yellowstone has erupted a few times in the last 2.1 million years and extrapolating the data seems to indicate that we are due for a new major eruption, which is intuitively evident from all the geysers one sees when visiting the park. If we simply divide the number of geologically recent years by the number of major eruptions we get a value of one super eruption about every half million years over the last 4-5 million years. This is likely optimistic as the evidence indicates eruptions in the last 20 to 25 thousand years. With Yellowstone apparently overdue for an expected eruption, it may be safe to estimate the next super volcano erupts within the next twenty thousand years.
Natural Climate Change
In the Earth’s crust resides large deposits of methane hydrate, mostly frozen, that if released can result in major changes to the climate. Whether or not this will result in major extinctions is unclear but we can take some comfort that the changes are apparently over many thousands of years. Atmospheric hydrogen sulfide buildup has more to do with the depletion of oxygen and is the only historical climate event coinciding with the Permian-Triassic event of about 250 million years ago but this may also be due to volcanic activity. Monsoons, mega-tsunamis, and hypercanes are either on a relatively small scale or do not destroy the infrastructure sufficiently to set back a recovered capability to explore space very far.
Human created catastrophes
Humans could cause their own mass extinctions but can also can recognize some of these pending disasters and do something about it. In engineering we call that mitigating the risk with measures to preclude the event from occurring or exacerbating. This makes the event much less likely.
The only nuclear warfare ever waged was in World War II and in only 65 years we still have the possibility of some entity sending such destruction to a target nation. But with the current technology of oversight, it would be difficult for any set of enemies to begin and sustain a global nuclear war sufficient to result in mass extinction. Biological warfare may currently be the most likely scenario of unintended death of millions by pandemic beyond the intended target since the perpetrators would not only take the lives of their intended victims, but also stand a good chance of infecting themselves depending on the strain of infection. There may be only a few countries or radical groups bent on the use of biological weapons but other intervention may keep this scenario to a minimum risk.
Pandemics seem a little more sustainable than a nuclear war and have occurred many times in human history. The capability to move around globally enhances the possibility of spreading deadly communicable diseases. Smallpox, which killed an estimated hundreds of millions from the 18th to 20th centuries, has since, according to the World Health Organization, been eradicated. Given the mass communication in the world it would be difficult for a given pandemic to expand much farther than a continent before measures are taken to preclude the spread. Superbugs, or antibiotic resistant strains, are possible and some may spread by airborne means. Again, these potential pandemics are usually quickly identified and quarantined prior to their proliferation. Humans are capable of arresting such plagues.
Overpopulation, famine, and political turmoil are examples of havoc that can be prevented or curtailed. These measures would be another human intervention to reduce these events given a large population with a change in weather patterns resulting in drought, pestilence, and political unrest. Famines haven’t lasted longer than a century but there have been a large number of famines in human history. Such events would certainly divert resources from human space flight to simple human survival.
We could consider “Terminator” scenarios but most of these postulate a set of events that leave out important intermediate steps, much like the math student who begins the solution of a problem but gets stuck and writes: “then a miracle happens” resulting in the final solution. Sure, we could deposit nanotechnology into the ocean to clean up oil spills and then the synthetic “bugs” begin eating everybody because of some insidious runaway ecophagy (a term coined by Robert Freitas, that indicates an internal destruction of human life and commodities). I’m a little skeptical of such prospects but I suppose it could happen. I would hope that whoever invented such microbiology or technology would also include a means of killing any uncontrolled proliferation. Again, we would have humans intervening to preclude a catastrophe.
Some will question why I don’t mention human-caused global warming; sorry, I’m not a believer in this scenario.
Catastrophe from Space
Aside from super volcanoes, extraterrestrial catastrophes are probably our most hazardous and likely scenario that could utterly destroy the human species. Disaster movies mostly use asteroids or planetary collisions resulting in attempted mass evacuation or taking cover in caves. But there are other just as dangerous scenarios that could occur without warning. These possibilities would require us not only to leave the planet before they occurred, but travel to nearby stars to look for other planetary homes. This is technology that may require another thousand or so years of effort, restrained by Earthly priorities. We can classify catastrophes from space into three categories.
1. Impact events
2. Radiation from Space
3. Space bugs
Asteroids and comets impact Earth quite frequently but very large impacts resulting in mass human extinction may occur only once in many millions of years. As our disaster movies remind us, a rogue asteroid or comet could impact Earth tomorrow. The Tunguska Event, probably a small comet, impacted Earth on June 30, 1908 in Siberia. Despite the megaton explosion that destroyed a forest, there was no major human decimation. Asteroid and comet impending impact, if detected soon enough, are candidates for human intervention. But despite the movie portrayals, NASA might not be able to construct a manned or unmanned mission to get a device to deflect a comet or asteroid in time even given few months notice, we would have to have a defense measure already in place. We probably would not send a nuclear bomb, but a simple rocket motor to veer the asteroid away from Earth. As a guess, we’ll assume that there is a 50-50 chance of successfully diverting an asteroid. Verneshots (named for Jules Verne) are simply volcanoes that catapult a very large rock into a suborbital trajectory where it will impact Earth similar to a large meteoroid. We’ll assume that since it would take a super volcano to eject such a massive rock, that the Earth is already facing an extinction event.
Planetoids – There are theories (source: space.com) regarding a nemesis or planetoid orbiting our sun in a highly elliptical orbit every 25-26 million years resulting in the recurring extinction events. Gliese 710, a dwarf star is heading toward our solar system and will pass within 1.1 light years from the sun in about 1.4 million years. Though not a direct collision, this object may disturb comets and asteroids in the Oort cloud and send a comet and asteroid shower to the inner solar system. Barnard’s star will pass within 3.8 light years in the year 11,700 possibly with the same effects (source: Wikipedia). For this calculation, with all the possibilities mentioned, we’ll guess a large comet or asteroid shower will occur due to other stars and planetoids every ten million years.
Black Holes and Anti-matter – these are exotic objects and there are no historical accounts of a black hole or piece of anti-matter passing into or nearby our solar system. The gravitational influence of a black hole could be felt well beyond our solar system and if one came within our planetary orbits, we would be destroyed. Anti-matter, the opposite of matter, has a very short life and could only be created under extraordinary collisions. A piece of anti-matter large enough to inflict damage on Earth would probably not last very long as it floated through space. Even though space is a vacuum, there is still matter in the form of dust, hydrogen molecules, and solar ejected matter; anti-matter would be annihilated quite soon. Even with these conditions, we will still include these events since we humans probably could not preclude the effects of the impact, though in this calculation we’ll apply a very rare probability of occurrence, say 1 in 5 billion years.
Radiation from Space
Satellites launched in the 1960’s to look for clandestine nuclear explosions on Earth found instead gamma rays bursting from everywhere else except Earth. These bursts are apparently from other galaxies and dissipate before they reach our own galaxy. Supernovae are sources for gamma rays and X-rays but could also radiate Earth with other high energy particles. For example, Eta Carinae (the seventh brightest star in the constellation Carina) is a very massive and unstable star about 7500 to 8000 light years from our sun. Astronomers have shown interest in this star because it is the nearest star scientists believe could become a supernova (source: Wikipedia). In the 1840’s this star was a typical low magnitude star but in a few years became the second brightest star in the sky. It eventually dimmed and became a low magnitude star, again. Even so, Eta Carinae is still expected to explode some time within the next million years or so, or within our lifetime depending on whose studies you read. The contradictory opinions are due to the uncertainty of how long Eta Carinae has been unstable. Should Eta Carinae explode, gamma rays could arrive to Earth with varying consequences ranging from damaging the upper atmosphere, satellites, and any astronauts in orbit, or, if the poles of Eta Carinae are pointed toward Earth, completely destroy all life on the hemisphere exposed to the burst. Most astronomers believe this resulting gamma ray burst will point away from our solar system (source: Wikipedia). Some researchers say a supernova within 8 parsecs (one parsec is about 3.26 light years) is considered close enough to cause severe damage on Earth depending on the type of explosion (Michael Richmond Dec 5, 2009). There is also no direct evidence of mass extinctions due to supernovas but there are several nearby stars that could become a supernova though none are within the postulated 8 parsecs. For our calculation, we’ll use extinction due to a gamma ray burst or X-rays from a supernova as one in a billion years.
A recent publication from the American Physical Society describes the possibility of cosmic radiation resulting from the exposure of our solar system to the leading edge of the Milky Way galaxy as our galaxy moves through intergalactic space. As the galaxy rotates, our solar system moves in and out of a protective cloud of material that shields us from the exposure to cosmic rays created by the shockwave of the galaxy’s face-on movement. This exposure is purported to occur every 62 million years. There is not much that humans could do under such a scenario other than to move to a star that is still within the protective material.
Our own sun emits massive amounts of material every day and from time to time discharges solar protons toward Earth but we are protected by the magnetosphere. Any common solar event is only harmful to astronauts or satellites, but can cause power outages, electronics failures, and other technical equipment problems. We are told that the sun will survive another 5 billion years in its current state so for our sun we will consider one in 5 billion years.
Alien life forms arriving on Earth causing havoc similar to the movie Andromeda Strain is another possible reason for mass extinction, but this assumes that any bug that arrives is inexorably lethal. An extraterrestrial virus or bacteria arriving on Earth may also be faced with the billions of bacteria and other microbial competition and could be itself obliterated. The other side of the argument is that the space bug would have to be pretty hardy to survive long space transits and entry through the atmosphere. Of course we have no way of knowing a data point for this occurrence but as a guess, we’ll use 1 in a billion years.
Departure from Earth
Delays in Departure
Because of human initiated events, we as a nation or planet populace will divert resources to resolve terrestrial issues before we continue exploring space and finding new places for our species to live. Famine, pandemics, war, and political events tend to impede progress. It appears that at least fifty years will pass before we continue exploring space beyond low Earth orbit. The world has seen some famine and pandemics since 1970. Resources diverted to war or the potential for war, instead of space flight, have been on-going the last few decades. (This is not to say that these diversions are not important; the first order of business is human survival here on Earth). The best advancement we have achieved is the experience of long term space flight (space station) and landing on another planet (the moon). So it does not take much to stifle human exploration of space when there is no indication of an imminent threat. After the moon landings, there wasn’t a drive to go farther and with economic problems of the late 1970’s and energy issues. Even with movies depicting catastrophes and extinction events, the perceived need to explore and populate other worlds seems tepid. Of course the detection of a large asteroid on a collision course with Earth would indeed quickly change our priorities.
Delays in human spaceflight can be calculated based on our first-hand experience. When the first man journeyed into space in 1961, it was only 10 years later before man landed on the moon even with a cold war, Viet Nam war, and massive social spending sapping resources. Current plans of a first landing on Mars may be anywhere from 60 to 80 years from the first lunar landing. But given the possible delays due to other priorities, that time could be 100 years. If an extinction event is not imminent, then we only have our abiding need to explore for economic reasons or natural curiosity to drive our programs. To get to the nearest habitable planet in a nearby star system, I’m guessing we may need 500 to 1000 years.
Moving populace to other planets within our solar system may save our species from Earth catastrophes and asteroid impacts where humans could not prevent the threat. Candidates for terra-forming planets in our own solar system include Mars, Venus, the Jovian moons (probably Europa, Ganymede, and Callisto), and possibly Saturn’s moon, Titan. Such engineering feats could take centuries and would require daunting programs in today’s technology, but maybe not for technology 300 years from now. Mars is the obvious candidate with its thin atmosphere, water, and a nearly 24 hour day. Visionaries sometimes will speculate on how long it would take to terra-form a planet. These seem to average out from a few centuries to a millennia before the planet, like Mars, are habitable enough to walk around without breathing apparatus. When Earth inhabitants do finally land on Mars, the success of the moment may dissipate the sense of need to continue the expansion of habitation of humans. So, in 2030 or so, the first Mars landing may be the last until 2100. After that, we may not see a terraformed Mars until 2500 or later.
To escape solar system catastrophic events we must travel to new star systems. The nearest star system, Alpha, Beta, and Proxima Centauri, is about 4.3 light years from our sun. Current technology will not allow us to get there but ideas for interstellar travel have been proposed over the past few decades. Within the next two centuries, propulsion technology should be sufficiently developed to travel at a few percent the speed of light or millions of miles per hour. Even at such speeds, it would take a few to several decades to get to the nearest star so such human ventures will likely be one-way. We could, and would, send unmanned probes first possibly at greater speeds though responses from these probes from nearby stars would take years or decades after arrival and require major advances in communication. Nearby solar systems with habitable planets would not really be known for many decades after the probes departed. To be efficient, we would catalogue all of the possible livable nearby (say within 30 light years) star systems and send scout probes for candidate planets. This may require thirty or so probes and a century to complete. Imagine the differences in technology over a hundred years. Designers would consider these technology changes when developing spacecraft. We may also be able to, given thousands of years, construct protection around our planet.
Overall Calculation for When We Need to Begin Sending Humans to Space
This calculation, a very rough calculation, has quite a bit of uncertainty and in no way predicts when the next catastrophic event will occur. It simply sums up the probabilities of the hypothesized catastrophic events. Very low probabilities of extinction including the effects of black holes, anti-matter, gamma ray bursts, planetoids, and massive solar events are events we could not prevent. Hypercanes, tsunamis, and natural climate changes may cause havoc and massive loss of life, but will likely not totally destroy the human species. Man-made catastrophes could be devastating, but also would likely not completely destroy the human race, either; however, these events would give more time for more devastating catastrophes to occur. With all of the possibilities, I’m guessing that we have somewhere between 5 thousand and 200 thousand years to begin leaving Earth permanently before the next catastrophe obliterates us; with the single point estimate of a catastrophic event occurring around 16,000 years or so from now. I’ll leave it at that until others wish to carry this analysis further. Probably our biggest threat for extinction of the human species comes with super volcanoes, a large asteroid or comet impact, and nearby supernovae. Can we get to another planet or solar system by then? Sure, given the apparent need, but I believe we may need a foreboding event to nudge us along.
One post script: In my motto, it says “do not be anxious about tomorrow, for tomorrow will be anxious for itself” which seems counterintuitive to the article. My motto refers to little things.