Yahoo! News published an article today announcing that astronomers have discovered a planet approximately 120 trillion miles away that is "just like Earth." It is situated in what is called the "Goldilocks" zone, making it not too cold nor too hot, so it could contain liquid water. It is also neither too big nor too small for the proper surface, gravity and atmosphere to accomodate life.
If the conclusions stopped there, I would agree that this is a very exciting discovery. What disappointed me about the article, though, was the unwarranted speculation. I think this serves as a warning against the human nature to get overly excited about what we want to be true and start making all sorts of suggestions that go far beyond what is warranted by the evidence.
Penn State University's Jim Kasting said this planet is a "pretty prime candidate" for harboring life. It seems a bit premature to make statements like that. For example, the planet is so close to its sun that it orbits every 37 days. Therefore, it cannot have Earth's cycle of seasons as we orbit over a period of 365 days with one half tilted closer to the sun during part of the year, then tilted away during the other. The seasons are crucial to plant growth. With such a short year, I, for one, am skeptical whether any substantial plant life could exist on this planet.
The planet also does not rotate very much, so that one side is almost always bright, the other always dark. Temperatures on the planet range from up to 160 degrees farenheit on the bright side down to 25 degrees below zero on the cold side. Certainly, any area of the planet that is exposed to these temperature extremes is not conducive to any form of life of which we are aware. The article somewhat acknowledged this by saying that it would be "shirt-sleeve weather" in the "land of constant sunrise." What it glossed over, however, is that this would leave a much narrower habitable zone than we have on Earth. Besides, constant short-sleeve weather is not ideal for life either. If the climate always remained constant, you could not have the regular seasonal cycles that I mentioned above that are necessary for many forms of life.
Perhaps the most bold proclamation comes near the end of the article. Without even knowing whether liquid water actually exists on this planet, Steven Vogt of the University of California at Santa Cruz declares that "because conditions are ideal for liquid water, and because there always seems to be life on Earth where there is water, ... 'chances for life on this planet are 100 percent.'" Understand that Vogt is not talking necessarily about little green men, but at least single cell bacteria.
Vogt's statement could serve as a prime example for introductory logic students about common logical errors that people make. First of all, just because "conditions are ideal for liquid water" does not necessarily mean that water will exist. Consider the Large Hadron Collider, the particle accelerator that lies beneath the Franco-Swiss border near Geneva. Inside that collider, scientists have used large magnets to set up ideal conditions for particle beams to collide. Yet anyone who operates the collider could tell you that it often requires a good deal of patience before anything happens. Merely having ideal conditions for a collision does not necessarily mean that a collision will occur.
The bigger logical issue lies in the syllogism Vogt advances. It could be expressed in logical terms as follows:
P1: Conditions on this "Goldilocks" planet are ideal for liquid water.
P2: Wherever there is water on Earth there is also life.
C: Therefore, there is a 100% chance of life on the "Goldilocks" planet.
I already discussed the problems with premise 1. Ideal conditions for a result do not guarantee the actuality of that result. But even assuming premises 1 and 2 are both true, does that support the conclusion?
There are many hidden assumptions in Vogt's argument. First, he assumes that the alleged relationship between water and life on Earth will be mirrored on the "Goldilocks" planet. The mere fact that two things are correlated here does not mean, absent additional evidence, that they will necessarily be correlated elsewhere. Many other factors could come into play. But more importantly, Vogt's argument provides an excellent opportunity to illustrate to students of logic the danger of confusing correlation with causation.
"Correlation" refers to an observed relationship between phenomena. "Causation" refers to a cause-effect relationship between the two phenomena. However, a logical fallacy occurs when you confuse correlation with causation.
Take the following example. Suppose a researcher notices that in the same months that ice cream sales are at their highest, so are the number of deaths by drowning. When ice cream sales go down, drowning deaths likewise decrease. There is a definite correlation between these two phenomena. Is the researcher therefore warranted in concluding that eating ice cream causes us to drown? Leaving aside the obvious joke about waiting at least one hour before you swim, the researcher who rushed to this conclusion would be overlooking the obvious possibility that there is no direct causation between these two phenomena, but instead that they are both caused by some other 3rd factor, in this case the warm summer temperatures. More people buy ice cream in warmer weather than when it is colder outside. Likewise, warm weather inspires more people to swim, which in turn leads to more instances of drowning. The mere fact that we observed a correlation between ice cream sales and drowning does not mean that one caused the other.
Vogt made the same elementary logical mistake. He observed that there appears to be a correlation on Earth between the presence of water and the presence of life. But that does not mean that the presence of water causes the presence of life. In fact, there currently is no single theory of the origin of life that is accepted by even a simple majority of scientists in the field. Biologists, frankly, have no clue how the very first life occurred on Earth. Vogt's implication that the mere presence of water easily leads to the development of life is simplistic at best. Is water necessary? Most likely. Is it sufficient? Far from it. The number of other factors that go into building even the most basic single-cell organisms are mind-boggling.
The article concludes with Vogt stating, "It's pretty hard to stop life once you give it the right conditions." I understand that news agencies love the sensational. If you have two options to choose from, one that makes the story look novel and exciting and another that is more reserved, the exciting one generates more readers. And Vogt seems to have provided Yahoo! with that sensationalism. But the statement that "it's pretty hard to stop life once you give it the right conditions" is so far outside the warrant of the evidence that I can only encourage anyone to slow down, don't believe everything you hear, and evaluate the evidence for yourself. Life is actually remarkably easy to stop, even once it has begun. Just ask the dinosaurs or any of the species that have disappeared into extinction. But in the end Vogt doesn't even know how it began in the first place, let alone how difficult it is to keep it going.
This new discovery is exciting. But the evidence is a far reach from being able to support a "100% chance of life" on the "Goldilocks" planet. Let's not rush to judgment. Take it slow. Follow where the evidence leads, and try as hard as you can not to take that one extra step beyond what is justified. Otherwise you will end up stepping onto the wrong path, and before you know it you will be so lost in the woods that you won't be able to find your way back.