A Plethora of Planets: What does it all mean?

Before about 17 years ago astronomers knew of no other planets than the eight planets in our solar system (at the time is was nine but since then Pluto has be demoted, I think rightfully, from its ranking among the planets). Then in October 6, 1995, Michel Mayor and Didier Queloz announced in the journal Nature that they had discovered the first extra-solar planet orbiting 51 Pegasi. (I was only 14 at the time, but I remember this discovery and I was really excited about it. I thought I was going to be a professional astronomer one day and I was going to enter the field at a time where technology was advanced enough to study planets outside our solar system!) Since then, more than 800 other planets have been detected and confirmed using the radial velocity method, transit method, and other methods of detection. The first, easiest, and most widely used method of detection is the radial velocity method, but this method lends itself to discovering very massive planets like gas giant planets (planets like Jupiter), which means that, while they are valuable for their scientific data, they do not add anything to the search for a planet that could possibly host life. With the launching of the Kepler Mission and its use of the transit method, the number of potential planets has jumped by more than 2,000 (most of these still need to be confirmed/verified, which is why the above official number is still less than a thousand).

Since the launch of the Kepler Mission, you may have seen headlines like "NASA Finds Earth-size Planet Candidates in the Habitable Zone," "Newfound Alien Planet is Best Candidate Yet to Support Life," "NASA finds dozens of planets that might support life," and "Alien Planets: Billions Of Habitable Exoplanets In Milky Way Galaxy." Whenever scientists discover a planet that is similar in size to earth and in the liquid water habitable zone, excitement grows because they do add something to the search for a planet that could possibly host life. It is an exciting time to be an astronomer, to say the least, and the excitement has filtered down into the public because of the frenzy of news articles about the discovery of "earth-like" planets.

However, questions arise with all this excitement. With all the data pouring in from the Kepler Mission, how excited should we really get? Is NASA on the verge of discovering alien life or is that just media hype in order to sell a story? What does it really mean when an "earth-like" planet is discovered? How common or rare is Earth? Are the "habitable planets" really habitable? This last question is the most important because it brings up the possibility of life existing on other planets. Below we will cover these questions and do so with particular focus on the idea of "habitable planets." (Warning, by necessity this is going to get a bit technical. I have done my best to clearly explain these things but if something is not clear, comment and ask me about it.)

Let's talk for a few minutes about what it means to be "earth-like." As we all know, the term "like" is a very ambiguous term and in the astronomical business the situation is no different. There is no consensus on what it means for a planet to be "earth-like." How similar in mass and size does the planet have to be to earth in order to be considered "earth-like"? What kind of atmosphere does it need to have to be "earth-like"? What kind of star does it need to orbit to be "earth-like"? How far from its star does it need to be in order to be "earth-like"? What kind of orbital period (the time it takes for the planet to make one revolution around its star) is necessary for a planet to be "earth-like"? These are all good questions and there is no consensus on the answers. Now, do not be too quick to judge astronomers because they have not narrowed down a precise definition for "earth-like" planets. Think of how long it took to narrow down the definition of "planet" itself. Astronomers have known about most of the other planets in our solar system for hundreds of years, yet a formal definition for "planet" was not agreed upon until the IAU's meeting of 2006! "Why did it take so long?" one might ask. Well, let's use a little thought experiment to demonstrate why. Imagine for a moment that the only other humans you know about are those in your immediately family. For me, that would mean only five people (if I do not include my wife). Now, imagine your family wanted to define formally what it meant to be human. You could look at the family dog and say, "That is not a human." You could look at the family cat (though I cannot understand why anyone would want one) and say, "That is not human." Then you could look at each other, assess the common features of your family, and begin to define "human." But how accurate could you really be? Your sample size is so small that you would likely be tempted to be too narrow in your definition (e.g. perhaps including skin pigmentation or hair color in your definition) or too broad in your definition (e.g. perhaps including only the ability to walk erect in your definition). You need a much larger sample size and a lot of time to deliberate together even to begin to be able to create an accurate definition. The same goes for astronomers. In the case of the formal definition of "planet," astronomers needed a much large sampling of planets than those in our solar system to create an accurate, formal definition. In the case of "earth-like" planets, astronomers are just beginning to discover other planets that appear to them to look like earth. It is going to take a much larger sampling of planets and a lot more discussion for an accurate, formal definition to emerge. So, when you hear "earth-like" take it with a grain of salt and start asking other questions: What do you mean by "earth-like"? How large or small is the planet compared to earth? What kind of star does it orbit? How far is the planet from its star? What kind of atmosphere does it have (if that information is even available)? The answers to all these will be very important, especially when it comes to the possibility of the planet being habitable.

Skipping the first general question, let's take a look at the importance of the second: How large or small is the planet compared to earth? This is a crucial question when it comes to the planet's habitability. "Why is that?" one might ask. Because the size of the planet is related to its tectonic activity: the larger the planet the more tectonic activity; the smaller the planet the less tectonic activity. Tectonic activity is the movement of the tectonic plates on which the surface of a planet sits. This movement is what creates events like earthquakes and geological features like mountain ranges and volcanos. It has a much more important function for life, however. Tectonic activity is crucial for life because it recycles carbon dioxide, which helps regulate the planet's temperature. As plates move apart, slide under one another, and even crash into each other, they also recycle carbon dioxide. This regulation and recycling of this greenhouse gas acts as a thermostat to keep the planet warm (but not scorching) over large geological time scales. Without tectonic activity the earth would look like Venus. It is only slight smaller than earth but it is too small to have sustained tectonic activity (any activity after the planets initial formation), so carbon dioxide has built up to form a thick atmosphere and keep the surface temperature of the planet at about 800 degrees Fahrenheit (far too hot for life). So, being only slightly smaller than the earth is too small to support life because there will be no sustained tectonic activity. If a planet goes the other direction, larger than the earth, the possibility of life runs into another problem: too much tectonic activity. As a planet gets larger the tectonic plates become thinner, weaker, and more easily moved, so there is much more tectonic activity. Any larger than two to three times the size of the earth and the planet would have frequent and massive earthquakes, making it too geologically unstable for any type of advanced life. So, when someone says, "Scientists have found a habitable planet!" ask them how big it is compared to earth. If it is only slightly smaller, it will not be able to support any life, and if it is just a little larger, it also will not be able to support any type of advance life.

The second question, "What kind of star does it orbit?" I have discussed before here. This is important because of what is known as the planetary/circumstellar habitable zone. This zone is a band that circles around a star (circumstellar) which defines the minimum and maximum distance a planet can be from the star even to be considered "habitable." The type of star that a planet orbits is crucial to the circumstellar habitable zone because, as I discuss in my earlier post (please see it for more detailed information), there are really two zones around each star--a liquid water zone and a UV radiation zone--that must overlap for life to be possible. This overlap is a band around the star where liquid water could possibly exist and there will be enough UV radiation (but not too much) to give life the energy it needs. If the star has an effective temperature below 4,600 K or above 7,137 K, the zones will not overlap and life will not be possible. This rules out 80% of all stars as possible candidates for life-supporting planets! The Extrasolar Planet Encyclopedia has a list of all the confirmed and verified planets, and it gives you the effective temperature of the host star. When someone says, "This planet is habitable!" check it out. Go to the list, find the planet, click on its link, and check out its host star's effective temperature. If it is not within the above range, it will not be habitable.

The third question is "How far is the planet from its star?" This is crucial because distance from the star affects the planet's rotation (the planet's spinning on its axis). If the planet is too close to the star then it will be "tidally locked." A tidally locked planet is so close to its star that the star's gravity only allows it to rotate once per revolution, meaning the same side of the planet always faces the star. For example, the moon is tidally locked to the earth, i.e. the same side of the moon always faces the earth. This creates a serious problem for the possible habitability of a planet. No matter what kind of star the planet orbits, if it is tidally locked the side facing the star will become incredibly hot (well above boiling temperature) and the side facing away will become incredibly cold (well below freezing temperature). So, even if a planet is in the habitable zone (both the liquid water and UV radiation zones), a tidally locked planet could not support life. This is an important feature of the recent headline "Alien Planets: Billions Of Habitable Exoplanets In Milky Way Galaxy." This research claims that there could be billions of habitable planets orbiting M-dwarf stars in our galaxy (M-dwarf stars make up about 80% of our galaxy's total number of stars). (They have not, of course, detected that many planets; it is a statistical prediction.) The problem with this claim is that it is simply looking at whether or not the planet is in the liquid water habitable zone. What it does not point out is that M-dwarf stars are so dim/cool that any planet in the liquid water habitable zone will be tidally locked! Even though the star is dim, if one side is always facing it that side will be far too hot for life and the other side will be far too cold. Again, when someone says, "Scientists have discovered habitable planets!" ask how far it is from its star and whether or not it is tidally locked. If it is, then, while it may be in the habitable zone, the planet itself is in no way habitable.

Finally, one must inquire as to the atmospheric characteristics of the planet, "What kind of atmosphere does it have?" Unfortunately, rarely can this question be answered. Our detection methods are not refined enough to give much information about an extra-solar planet's atmosphere. The point of asking the question, however, is to point out that even if all of the above qualifications are met (proper size, host star has a good temperature, and the planet is not tidally locked) the atmosphere could still easily rule the planet out as habitable. Since we have no idea what its atmosphere is like, it is dubious to claim it is habitable. Let's do another thought experiment. Say you were looking at our solar system from 100 light years away. You would see it has eight planets and, to your delight, you would discover that three of the eight are in the habitable zone (both liquid water and UV radiation)! Why? Because Venus, Earth, and Mars are all in that zone, yet we know that two out of the three cannot support life (Mars is debated, of course, but as it stands there is zero evidence for present or ancient life there). Why can't they? Venus' atmosphere is so thick that its surface temperature is about 800 degrees Fahrenheit. Mars' atmosphere is composed mostly of carbon dioxide, nitrogen, and argon and its atmosphere is so thin that it has lost all its liquid water. So, if you were looking at our solar system from far away you would think there were three habitable planets, yet when you got here you would only find one. The point is that being in the habitable zone, being the right size, orbiting the right kind of star, and being the right distance from the star does not at all mean the planet must be habitable.

So, what should we make of all this verbose (probably too verbose) explanation? How excited should we get? Are the planets really habitable? How common or rare is Earth? Well, in answer to the last question, Earth is still without an equal. Of all the claims for discovering habitable planets, none meet all the criteria I have named above. Furthermore, the criteria I have gone through above is a small sampling of the many characteristics necessary for life to exist on a planet (for a large working list, see this article by RTB), and all the planets discovered do not even meet the criteria on my small list. For more information on the rarity of Earth, check out this book (by two atheists!): Rare Earth. Are the planets really habitable? Most of the articles you will read in the popular media are just looking at whether or not liquid water could exist on the planet. Certainly liquid water is a necessary condition for life but it is in no way a sufficient condition for life. Furthermore, the list I linked above from RTB shows that there are dozens of necessary conditions for life and liquid water is only one of those. Finally, how excited should we get? I am very excited for two reasons: first, each new planet tells us a little more about how planets form, what most planets are like, and how solar systems form, all of which expand our knowledge of the universe; and second, each new planet shows us how fine-tuned our planet is for life, particularly for human life. It is no coincidence that no other planet is like ours. God chose to create humans, the apex of His creation, here on Earth and He made sure it was perfectly suited for our needs. No other planet even comes close. Far from showing God is not necessary or life is abundant throughout the universe, all the new planetary discoveries show that God's fine-tuning is absolutely necessary for life and life only exists where He wants it to be.

By His Grace,
Taylor

The Beginning of the Universe

"He asserts that the universe came from 'nothing' rather than from God. However, the different 'nothings' that Krauss appeals to for his explanations are really 'some things'—'some things' that demand nothing less than the existence and involvement of the biblical God." ~ Dr. Hugh Ross, "Universe from Nothing?: A Critique of Lawrence Krauss' Book, Part 1"

Another set of Big Bang news articles have hit the popular media. This time with headlines like "The Big Bang Didn't Need God to Start Universe, Researchers Say." This is similar to what Stephen Hawking wrote in his book The Grand Design, which I wrote about a while ago. The impetus behind such assertions is the desire to remove God from the equation when it comes to the origins of the universe. This has been a problem for naturalistic scientists ever since the first indications that the universe is expanding. So, let's talk about Big Bang cosmological theory and see if the above claims stand up within that framework.

Why is this such a big deal to Big Bang cosmologists? Well, it is often believed that "Big Bang" automatically means an atheistic world-view, but, while that may seem to be common now, that was not the original response to Big Bang cosmology. In fact, the Big Bang was originally seen by steady-state cosmologists as an inherently religious idea. Geoffrey Burbidge, for example, once lamented that his fellow scientists were running off to join the "First Church of Christ of the Big Bang." Sir Fred Hoyle first coined the phrase "Big Bang" in a 1949 BBC broadcast as a pejorative name because of its religious significance (though he did later recant). Why did they see it as religious? Because saying that the universe has a beginning means that it must have had a Beginner, and they did not want to admit the possibility of a Beginner.

Recently, however, many noted scientists have begun theorizing how the universe could have created itself from nothing. That is, of course, the holy grail of a naturalistic world-view--if you can show that the universe did not need a Beginner, then God is not necessary (at least, that is the assumption). So, we get articles like the one list above and books like Hawking's The Grand Design. As I have already written about Hawking's work, I will make a few comments about the recent articles.

The basic premise of such arguments is that "the Big Bang could've occurred as a result of just the laws of physics being there. With the laws of physics, you can get universes." What I find most interesting about this is that the scientist quoted (Alex Filippenko of the University of California, Berkeley) admits that the laws of physics cannot explain themselves. He even admits that they would require a divine Creator, though he goes on to ask who created the divine Creator, which he believes leads to a never-ending chain of causes. But does it really? Basically, Filippenko is showing the validity and necessity of the Kalam Cosmological Argument, which is a classic argument for an uncaused Cause or a Creator. Eventually the chain of causality throughout the history of being has to have a beginning. String Theory posits a type of multiverse to explain the beginning of our universe. Filippenko and Hawking posit that the laws of physics cause the universe to create itself. Both of these simply push the need for a Creator back a step. They simply add another link to the chain of causality. Where did the multiverse come from? Where did the laws of physics come from? Believing they are simply "brute realities" takes as much faith as, if not more than it takes to believe in a Creator (I have written about this here, here, here, and here). Such theories do not solve the problem but are basically mathematical ways of skirting the question.

Furthermore, Filippenko positing quantum fluctuations as a creative event has problems. (Warning, this is going to get a little bit technical.) A consequence of the uncertainty principle in quantum mechanics is that quantum fluctuations in the fabric of space-time will generate particles out of "nothing" (it is not really nothing as we will soon see). Seth Shostack from SETI asserts, "Quantum mechanical fluctuations can produce the cosmos." In the article, Filippenko draws on this idea and says, "If you would just, in this room, just twist time and space the right way, you might create an entirely new universe. It's not clear you could get into that universe, but you would create it." The first problem with this, that is not mentioned in the articles, is that while the uncertainty principle allows for the random creation of particles, it also requires that these particles revert back to fluctuations before they can be observed. They will not stick around long enough to create anything, about a quintillionth of a second (that is 0.000000000000000001 seconds)! The second problem is even larger than the first. The article and the scientists call this creation from nothing but it is in no way creation from nothing. It is creation from other "some things" (as the quote from Dr. Hugh Ross above states). When he says, "If you would just, in this room, just twist time and space the right way..." Filippenko reveals a major problem in his theory: quantum fluctuations require space-time (which is something, not nothing) to already exist for any type of particles (or universes) to be created. Rather than coming from nothing, they come from pre-existent physical laws and pre-existent space-time. Space-time must already exist for quantum fluctuations to create anything. So, one must again ask, "Has the need for a divine Creator really been removed from the situation?" Not hardly. If the fabric of space-time is necessary for quantum fluctuations to create anything, then space-time first had to be created by something or Someone else. Again, this pushes the need for a Creator back a step but in no way rids us of that need.

For more on this topic, I would suggest you read Dr. Hugh Ross' review of Lawrence M. Krauss' book A Universe from Nothing. Krauss' book is a much more highly developed argument than the article I have been citing or even Hawking's book. Dr. Hugh Ross does a very good job of laying out the issues with it in part 1 and the theological explanations in part 2.

By His Grace,
Taylor

The Heavens Declare

¹The heavens declare the glory of God,
   and the sky above proclaims his handiwork.
²Day to day pours out speech,
   and night to night reveals knowledge.
³There is no speech, nor are there words,
   whose voice is not heard.
⁴Their voice goes out through all the earth,
   and their words to the end of the world.
~ Psalm 19:1-4

I just recently ran across this beautiful time-lapse video of the earth from the International Space Station. In it you can see the lights of our cities, lightning flashing in storms, the Aurora Borealis, and so much more. It is glorious reminder to me of the beautiful design in our universe and how the heavens truly do declare the glory of God.



If you want a reservoir of images, check out my Space Images Picasa Web Album. I have collected images and captions from all over the web. I add to it anytime I come across an image I find particularly striking.

Also, one of my most popular posts has been "Mote of Dust in a Sunbeam," which is a size comparison to show you just how small you really are in this universe of God's handiwork.

By His Grace,
Taylor