Tag Archives: Privileged Planet

What are galactic habitable zones and circumstellar habitable zones?

The Circumstellar Habitable Zone (CHZ)

What do you need in order to have a planet that supports complex life? First, you need liquid water at the surface of the planet. But there is only a narrow range of temperatures that can support liquid water. It turns out that the size of the star that your planet orbits around has a lot to do with whether you get liquid water or not. A heavy, metal-rich star allows you to have a habitable planet far enough from the star so  the planet can support liquid water on the planet’s surface while still being able to spin on its axis. The zone where a planet can have liquid water at the surface is called the circumstellar habitable zone (CHZ). A metal-rich star like our Sun is very massive, which moves the habitable zone out further away from the star. If our star were smaller, we would have to orbit much closer to the star in order to have liquid water at the surface. Unfortunately, if you go too close to the star, then your planet becomes tidally locked, like the moon is tidally locked to Earth. Tidally locked planets are inhospitable to life.

Circumstellar Habitable Zone
Circumstellar Habitable Zone

Here, watch a clip from The Privileged Planet: (Clip 4 of 12, full playlist here)

But there’s more.

The Galactic Habitable Zone (GHZ)

So, where do you get the heavy elements you need for your heavy metal-rich star?

You have to get the heavy elements for your star from supernova explosions – explosions that occur when certain types of stars die. That’s where heavy elements come from. But you can’t be TOO CLOSE to the dying stars, because you will get hit by nasty radiation and explosions. So to get the heavy elements from the dying stars, your solar system needs to be in the galactic habitable zone (GHZ) – the zone where you can pickup the heavy elements you need but not get hit by radiation and explosions. The GHZ lies between the spiral arms of a spiral galaxy. Not only do you have to be in between the arms of the spiral galaxy, but you also cannot be too close to the center of the galaxy. The center of the galaxy is too dense and you will get hit with massive radiation that will break down your life chemistry. But you also can’t be too far from the center, because you won’t get enough heavy elements because there are fewer dying stars the further out you go. You need to be in between the spiral arms, a medium distance from the center of the galaxy.

Like this:

Galactic Habitable Zone
Galactic Habitable Zone and Solar Habitable Zone

Here, watch a clip from The Privileged Planet: (Clip 10 of 12, full playlist here)

The GHZ is based on a discovery made by astronomer Guillermo Gonzalez, which made the front cover of Scientific American in 2001. That’s right, the cover of Scientific American. I actually stole the image above of the GHZ and CHZ (aka solar habitable zone) from his Scientific American article (linked above).

These are just a few of the things you need in order to get a planet that supports life.

Here are a few of the more well-known ones:

  • a solar system with a single massive Sun than can serve as a long-lived, stable source of energy
  • a terrestrial planet (non-gaseous)
  • the planet must be the right distance from the sun in order to preserve liquid water at the surface – if it’s too close, the water is burnt off in a runaway greenhouse effect, if it’s too far, the water is permanently frozen in a runaway glaciation
  • the solar system must be placed at the right place in the galaxy – not too near dangerous radiation, but close enough to other stars to be able to absorb heavy elements after neighboring stars die
  • a moon of sufficient mass to stabilize the tilt of the planet’s rotation
  • plate tectonics
  • an oxygen-rich atmosphere
  • a sweeper planet to deflect comets, etc.
  • planetary neighbors must have non-eccentric orbits

By the way, you can watch a lecture with Guillermo Gonzalez explaining his ideas further. This lecture was delivered at UC Davis in 2007. That link has a link to the playlist of the lecture, a bio of the speaker, and a summary of all the topics he discussed in the lecture. An excellent place to learn the requirements for a suitable habitat for life.

Guillermo Gonzalez lectures at UC Davis on the requirements for life

The 5 video clips that make up the full lecture.

The playlist for all 5 clips is here.

About the speaker

Guillermo Gonzalez is an Associate Professor of Physics at Grove City College. He received his Ph.D. in Astronomy in 1993 from the University of Washington. He has done post-doctoral work at the University of Texas, Austin and at the University of Washington and has received fellowships, grants and awards from such institutions as NASA, the University of Washington, the Templeton Foundation, Sigma Xi (scientific research society) and the National Science Foundation.

Learn more about the speaker here.

The lecture

Here’s part 1 of 5:

Habitability topics:

  • What is the Copernican Principle?
  • Is the Earth’s suitability for hosting life rare in the universe?
  • Does the Earth have to be the center of the universe to be special?
  • How similar to the Earth does a planet have to be to support life?
  • What is the definition of life?
  • What are the three minimal requirements for life of any kind?
  • Requirement 1: A molecule that can store information (carbon)
  • Requirement 2: A medium in which chemicals can interact (liquid water)
  • Requirement 3: A diverse set of chemical elements
  • What is the best environment for life to exist?
  • Our place in the solar system: the circumstellar habitable zone
  • Our place in the galaxy: the galactic habitable zones
  • Our time in the universe’s history: the cosmic habitable age
  • Other habitability requirements (e.g. – metal-rich star, massive moon, etc.)
  • The orchestration needed to create a habitable planet
  • How different factors depend on one another through time
  • How tweaking one factor can adversely affect other factors
  • How many possible places are there in the universe where life could emerge?
  • Given these probabilistic resources, should we expect that there is life elsewhere?
  • How to calculate probabilities using the “Product Rule”
  • Can we infer that there is a Designer just because life is rare? Or do we need more?

The corelation between habitability and measurability.

  • Are the habitable places in the universe also the best places to do science?
  • Do the factors that make Earth habitable also make it good for doing science?
  • Some places and times in the history of the universe are more habitable than others
  • Those exact places and times also allow us to make scientific discoveries
  • Observing solar eclipses and structure of our star, the Sun
  • Observing stars and galaxies
  • Observing the cosmic microwave background radiation
  • Observing the acceleration of the universe caused by dark matter and energy
  • Observing the abundances of light elements like helium of hydrogen
  • These observations support the big bang and fine-tuning arguments for God’s existence
  • It is exactly like placing observatories on the tops of mountains
  • There are observers existing in the best places to observe things
  • This is EXACTLY how the universe has been designed for making scientific discoveries

This lecture was delivered by Guillermo Gonzalez in 2007 at the University of California at Davis.

What is intelligent design?

Related DVDs

Illustra also made two other great DVDs on intelligent design. The first two DVDs “Unlocking the Mystery of Life” and “The Privileged Planet” are must-buys, but you can watch them on youtube if you want, for free.

Here are the 2 playlists:

I also recommend Coldwater Media’s “Icons of Evolution”. All three of these are on sale from Amazon.com.

Related posts

Does God exist? Is there any scientific evidence to prove that God exists?

Since I haven’t talked about science in a while, I thought that now would be a good time to list some of the more common arguments for a Creator and Designer of the universe and/or intelligent life. I like to use arguments drawn from mainstream science that do not assume the Bible or inerrancy or anything specifically religious. The arguments below all show that the reality we live in exhibits effects in nature that are not explained by particles in motion, chance and the operation of natural laws.

First, here’s the list of a few of the better-known arguments:

The average knuckle-dragging atheist will not be familiar with any of these arguments, will have never seen them used in academic debates, and will not even click through to read about them. That’s atheism these days – it’s non-cognitive. Atheism is all about escaping from moral values and moral obligations, which are not even rationally grounded by atheism.

The point of being familiar with these arguments is to show that religion and science are virtually identical. Both are trying to explain the external world. Both are bound by the laws of logic. Both use evidence to verify and falsify claims. For example, the discovery of the origin of the universe falsifies Hinduism, Buddhism and Mormonism, but it leaves Christianity, Islam and Judaism unscathed. All religions make truth claims and those claims can be tested against what science tells us about the world.

What is the significance of scientific progress for Christians?

Some general points to know when presenting these arguments.

1. You need to emphasize that atheism is in full flight away from the progress of science. Each of these arguments has gotten stronger as the evidence grew and grew. For example, scientists had to be forced to turn away from the eternal universe as new discoveries arrived, such as the cosmic microwave background radiation measurements. Scientists had to turn away from the view that the cosmological constants are nothing special, as more and more fine-tuned quantities were discovered.

2. Christians need to pay attention in school and score top grades in mathematics and experimental sciences. Science is God-friendly, and we need to have Christians doing cutting edge research in the best labs at the universities. Think of the work done by Doug Axe at Cambridge University in which he was able to publish research showing that very few sequences of amino acids have biological function, so getting functional sequences at random is virtually impossible. One of Doug’s papers is here. We need more people like him.

3. Each of these arguments needs to be studied in the context of polemics and debates. The best way to present each of these arguments is by presenting them as a struggle against opposing forces. For example, when talking about the big bang, emphasize how atheists kept trying to come up with eternal universe speculations. When talking about the fine-tuning, talk about the unobservable multiverse. When talking about irreducible complexity, talk about the co-option fallacy. Don’t preach – teach the controversy.

4. Don’t make lazy excuses about how scientific evidence doesn’t persuade non-Christians. Science is absolutely the core of any argument for Christianity, along with the case for the resurrection of Jesus. Christianity is about knowledge. Christians who refuse to subject their faith to science are probably just trying to make sure that Christianity isn’t so true that it dictates how they should live. They like the uncertainty of blind faith, because it preserves their autonomy to disregard Christian moral teachings when it suits them.

5. The purpose of linking your Christian faith to scientific arguments is to demonstrate to non-Christians that Christianity is real. It is not a personal preference. It is not something you grew up with. It is not something you inherited from your parents. When you link your Christian faith with scientific facts in the external world, you are declaring to non-Christians that Christianity is testable and binding on everyone who shares the objective reality we live in. You can’t expect people to act Christianly without showing that Christianity is objectively true.

6. Scientific arguments are tremendously useful even for believing Christians, because sometimes it is difficult to act in a Christian way when your emotions are telling you not to. When your feelings make it hard for you to behave Christianly, that is when scientific evidence can come into play in order to rationally justify acts of self-denial and self-sacrifice. For example, scientific evidence for the existence of God is a helpful counterbalance to the problem of apparently gratuitous evil, which often discourages Christians.

My complete index of arguments for and against Christian theism is here.

UPDATE: I notice that in the popular culture, people are not really aware of these arguments, and are still arguing for religious faith based on pragmatism and personal experience, not on evidence. Using reason and evidence is much better, and it’s what the Bible teaches, too.