Tag Archives: Habitable Zone

New study: Saturn’s orbit keeps Earth in the circumstellar habitable zone

Circumstellar Habitable Zone
Circumstellar Habitable Zone

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. So we need a star massive enough to give us a nice wide habitable zone far away from the Sun itself.

But even with the right size star, which we have in our solar sytem, we still have CHZ problems. Just because a planet starts off in the circumstellar habitable zone, it doesn’t mean that it will stay there.

Jay Richards tweeted about this new article from the New Scientist, which talks about that very problem.

Excerpt: (links removed)

Earth’s comfortable temperatures may be thanks to Saturn’s good behaviour. If the ringed giant’s orbit had been slightly different, Earth’s orbit could have been wildly elongated, like that of a long-period comet.

Our solar system is a tidy sort of place: planetary orbits here tend to be circular and lie in the same plane, unlike the highly eccentric orbits of many exoplanets. Elke Pilat-Lohinger of the University of Vienna, Austria, was interested in the idea that the combined influence of Jupiter and Saturn – the solar system’s heavyweights – could have shaped other planets’ orbits. She used computer models to study how changing the orbits of these two giant planets might affect the Earth.

Earth’s orbit is so nearly circular that its distance from the sun only varies between 147 and 152 million kilometres, or around 2 per cent about the average. Moving Saturn’s orbit just 10 percent closer in would disrupt that by creating a resonance – essentially a periodic tug – that would stretch out the Earth’s orbit by tens of millions of kilometres. That would result in the Earth spending part of each year outside the habitable zone, the ring around the sun where temperatures are right for liquid water.

Tilting Saturn’s orbit would also stretch out Earth’s orbit. According to a simple model that did not include other inner planets, the greater the tilt, the more the elongation increased. Adding Venus and Mars to the model stabilised the orbits of all three planets, but the elongation nonetheless rose as Saturn’s orbit got more tilted. Pilat-Lohinger says a 20-degree tilt would bring the innermost part of Earth’s orbit closer to the sun than Venus.

So the evidence for a our solar system being fine-tuned for life keeps piling up. It’s just another factor that has to be just right so that complex, embodied life could exist here. All of these factors need to be just right, not just the orbits of any other massive planets. And you need at least one massive planet to attract comets and other such unwelcome intruders away from the life-permitting planets.

Here’s a good clip explaining the circumstellar habitable zone:

The factor I blogged about today is just one 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

Here is a study that I wrote about recently about galactic habitable zones.

New study: Saturn’s orbit keeps Earth in the circumstellar habitable zone

Circumstellar Habitable Zone
Circumstellar Habitable Zone

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. So we need a star massive enough to give us a nice wide habitable zone far away from the Sun itself.

But even with the right size star, which we have in our solar sytem, we still have CHZ problems. Just because a planet starts off in the circumstellar habitable zone, it doesn’t mean that it will stay there.

Jay Richards tweeted about this new article from the New Scientist, which talks about that very problem.

Excerpt: (links removed)

Earth’s comfortable temperatures may be thanks to Saturn’s good behaviour. If the ringed giant’s orbit had been slightly different, Earth’s orbit could have been wildly elongated, like that of a long-period comet.

Our solar system is a tidy sort of place: planetary orbits here tend to be circular and lie in the same plane, unlike the highly eccentric orbits of many exoplanets. Elke Pilat-Lohinger of the University of Vienna, Austria, was interested in the idea that the combined influence of Jupiter and Saturn – the solar system’s heavyweights – could have shaped other planets’ orbits. She used computer models to study how changing the orbits of these two giant planets might affect the Earth.

Earth’s orbit is so nearly circular that its distance from the sun only varies between 147 and 152 million kilometres, or around 2 per cent about the average. Moving Saturn’s orbit just 10 percent closer in would disrupt that by creating a resonance – essentially a periodic tug – that would stretch out the Earth’s orbit by tens of millions of kilometres. That would result in the Earth spending part of each year outside the habitable zone, the ring around the sun where temperatures are right for liquid water.

Tilting Saturn’s orbit would also stretch out Earth’s orbit. According to a simple model that did not include other inner planets, the greater the tilt, the more the elongation increased. Adding Venus and Mars to the model stabilised the orbits of all three planets, but the elongation nonetheless rose as Saturn’s orbit got more tilted. Pilat-Lohinger says a 20-degree tilt would bring the innermost part of Earth’s orbit closer to the sun than Venus.

So the evidence for a out solar system being fine-tuned for life keeps piling up. It’s just another factor that has to be just right so that complex, embodied life could exist here. All of these factors need to be just right, not just the orbits of any other massive planets. And you need at least one massive planet to attract comets and other such unwelcome intruders away from the life-permitting planets.

Here’s a good clip explaining the circumstellar habitable zone:

The factor I blogged about today is just one 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

Here is a study that I wrote about recently about galactic habitable zones.

Dr. Walter Bradley explains the requirements for life of any imaginable kind

I was talking to a friend of mine earlier this week about my experiences as an undergraduate in college, and it turns out that both of us relied on the same web site to get us through our late teens and early 20s. The web site is Leadership University, and it features articles on many different topics from Christian professors.

Here’s an article by famous mechanical engineering professor Walter Bradley to explain what it takes for a universe that supports complex, embodied life.

Excerpt:

We teach mechanical engineering students to begin the design process by specifying as clearly as possible the “needs statement” for their project. Then, the assignment for the semester is to develop a design solution that accomplishes the “need(s)” specified for the project. In similar fashion, the minimal needs to be satisfied for a universe to be capable of supporting life of any imaginable type, not just life as we know it, must be identified. Like our automobile illustration, many of the specifications will necessarily be interrelated to make a functional universe. From this essential “needs statement” we can then see how these needs (or design requirements) are met in our universe. We are essentially doing reverse engineering, constructing the blueprint backwards from the product (like an illicit manufacturing company copying a competitor’s product). Only then will we be ready to entertain Dawkins’ question, “Are there many ways in which these requirements could be satisfied within nature?” Or are the conditions so unique and interrelated that their collective satisfaction by accident would be a “miracle” in its own right? Let us then begin by drafting a “needs statement” for a habitable universe. Then we shall see how these requirements are satisfied in our universe.

Needs Statement for a Suitable Universe

An abbreviated list of requirements for a universe suitable to support life of any imaginable type must include the following items:

  • Order to provide the stable environment that is conducive to the development of life, but with just enough chaotic behavior to provide a driving force for change.
  • Sufficient chemical stability and elemental diversity to build the complex molecules necessary for essential life functions: processing energy, storing information, and replicating. A universe of just hydrogen and helium will not “work.”
  • Predictability in chemical reactions, allowing compounds to form from the various elements.
  • A “universal connector,” an element that is essential for the molecules of life. It must have the chemical property that permits it to react readily with almost all other elements, forming bonds that are stable, but not too stable, so disassembly is also possible. Carbon is the only element in our periodic chart that satisfies this requirement.
  • A “universal solvent” in which the chemistry of life can unfold. Since chemical reactions are too slow in the solid state, and complex life would not likely be sustained as a gas, there is a need for a liquid element or compound that readily dissolves both the reactants and the reaction products essential to living systems: namely, a liquid with the properties of water.
  • A stable source of energy to sustain living systems in which there must be photons from the sun with sufficient energy to drive organic, chemical reactions, but not so energetic as to destroy organic molecules (as in the case of highly energetic ultraviolet radiation).
  • A means of transporting the energy from the source (like our sun) to the place where chemical reactions occur in the solvent (like water on Earth) must be available. In the process, there must be minimal losses in transmission if the energy is to be utilized efficiently.

Unless ALL of these conditions and many more not included in this list are met, we would have a universe that would preclude the possibility of conscious, complex life forms. However, it is possible to meet all of these conditions for the universe and still not necessarily find a suitable habitat in the universe for complex, conscious life. Therefore, we might say that the above requirements for our universe are necessary, but not by themselves sufficient, conditions for a habitat suitable for complex human life. Next we try to identify the additional conditions within such a suitable universe that would provide a place of habitation for conscious, complex life.

Needs Statement for a Habitat Place in the Suitable Universe for Complex, Conscious Life

An abbreviated, but illustrative, list of additional requirements must be specified for a place of habitation in this universe. First, we need a star that is located in a relatively “quiet” region of the universe (e.g., not too many neighbors that are producing high intensity, sterilizing radiation). This star needs to have its highest intensity of radiation in the range that is suitable to drive the chemical reactions essential to life without destroying the products of these reactions. Furthermore, this star needs to have a very special satellite within its solar system. A partial list of the requirements this satellite must meet include:

  • a planet or moon that is terrestrial–or, solid rather than gaseous;
  • a temperature range suitable to maintain the universal solvent as a liquid rather than a solid or gas;
  • just the right concentration of heavy (radioactive) elements to heat the core of the planet and provide the necessary energy to drive plate tectonics, to build up land mass in what would otherwise be a smooth, round planet completely covered with solvent;
  • just the right amount of solvent (carefully coupled to the plate tectonics activity) to provide a planet with similar proportions of its surfaces as oceans and land mass;
  • just the right protection from the destructive forces in nature such as radiation and asteroids over a reasonable amount of time; and
  • just the right stabilized axis tilt and angular velocity to give moderate, regular, and predictable seasons and moderate temperature fluctuations from day to night.

While one is temped to think that these requirements are easily met, given the large number of stars, it should be noted that there are few places in the universe sufficiently free of sterilizing radiation to provide a suitable solar system. The number of candidate “neighborhoods” is further reduced by the requirements of a sun with the right amount of mass to give the right electromagnetic radiation spectrum. Furthermore, the occurrence of a suitable satellite in conjunction with such a star is even more problematic. Only the earth in our solar system of sixty-two satellites meets the above requirements for a “home” (earth) in safe “neighborhood” like our sun and solar system, which are well placed in a quiet place in a suitable universe as described above.

In the next sections, we will see how these universal and local “needs” (or design requirements) are met by: the specific mathematical form encoded in nature, the exact values of the universal constants in our universe, and the remarkable “coincidence” that initial (or boundary) conditions are exactly what they must be. We will also see that the “evolutional” or developmental path that our universe navigated is consistently remarkable, making the origin of our “Garden of Eden” all the more wondrous and enigmatic.

If you want to see the next sections of his article, you can click here to read the rest.

Why is this important? It’s important because a lot of people on the other side want to dismiss the fine-tuning argument by saying that if the fundamental constants and quantities specified in the Big Bang had been different, then the results would be a universe that permits life of some other kind. That’s false. If you vary the constants and quantities, you lose things that are required for any conceivable kind of complex life. You can’t form stable, metal-rich stars. The universe recollapses into a hot fireball. You have only hydrogen. You have NO hydrogen. It’s not just that people have some ridges on their noses or maybe an extra pair of arms. It’s that there is no life, period.

This is important. There are minimum requirements for life of any conceivable kind, and messing with the fine-tuning of the universe destroys the ability of the universe to provide those minimal requirements. Naturalists can smirk and shrug this off, but this is the science that we have today and we have to deal with it.

Harvard astrophysicist backs the Rare Earth hypothesis

What is the Rare Earth hypothesis?

It’s the thesis of a recent book written by two scientists at the University of Washington.

Here’s the blurb:

What determines whether complex life will arise on a planet? How frequent is life in the Universe?

In this exciting new book, distinguished paleontologist Peter D. Ward and noted astronomer Donald Brownlee team up to give us a fascinating synthesis of what’s now known about the rise of life on Earth and how it sheds light on possibilities for organic life forms elsewhere in the Universe.

Life, Ward and Brownlee assert, is paradoxically both very common and almost nowhere. The conditions that foster the beginnings of life in our galaxy are plentiful. But contrary to the usual assumption that if alien life exists, it’s bound to be intelligent, the authors contend that the kind of complex life we find on Earth is unlikely to exist anywhere else; indeed it is probably unique to our planet.

With broad expertise and wonderful descriptive imagery, the authors give us a compelling argument, a splendid introduction to the emerging field of astrobiology, and a lively discussion of the remarkable findings that are being generated by new research. We learn not only about the extraordinary creatures living in conditions once though inimical to life and the latest evidence of early life on Earth, but also about the discoveries of extrasolar planets, the parts Jupiter and the Moon have played in our survival, and even the crucial role of continental drift in our existence.

Insightful, well-written, and at the cutting edge of modern scientific investigation, Rare Earth should interest anyone who wants to know about life elsewhere and gain a fresh perspective on life at home which, if the authors are right, is even more precious than we may ever have imagined.

And here’s a review by Library Journal:

“Renowned paleontologist Ward (Univ. of Washington), who has authored numerous books and articles, and Brownlee, a noted astronomer who has also researched extraterrestrial materials, combine their interests, research, and collaborative thoughts to present a startling new hypothesis: bacterial life forms may be in many galaxies, but complex life forms, like those that have evolved on Earth, are rare in the universe. Ward and Brownlee attribute Earth’s evolutionary achievements to the following critical factors: our optimal distance from the sun, the positive effects of the moon’s gravity on our climate, plate tectonics and continental drift, the right types of metals and elements, ample liquid water, maintainance of the correct amount of internal heat to keep surface temperatures within a habitable range, and a gaseous planet the size of Jupiter to shield Earth from catastrophic meteoric bombardment. Arguing that complex life is a rare event in the universe, this compelling book magnifies the significance — and tragedy — of species extinction. Highly recommended for all public and academic libraries.”

Note that Peter Ward is a militant atheist (he has debated against Stephen C. Meyer), and Donald Brownlee is an agnostic. These are not Christians, nor are they even theists. However, I have the book, I have read the book, and I recommend the book. I usually have this book on my shelf at work for show-and-tell.

Now for the latest news about the hypothesis of the book. (H/T Brian Auten of Apologetics 315)

There are always going to be optimistic predictions by scientists who need to attract research funding, but those are hopes and speculations. The data we have today says Earth is rare. The number of conditions required for complex life of any kind is too high for us to be optimistic about alien life in this galaxy, at least. And as the number of requirements for life roll in, the odds of finding alien life that can contact us get slimmer and slimmer.

From the UK Daily Mail. (H/T Peter S. Williams)

Excerpt:

Dr Howard Smith, a senior astrophysicist at Harvard University, believes there is very little hope of discovering aliens and, even if we did, it would be almost impossible to make contact.

So far astronomers have discovered a total of 500 planets in distant solar systems – known as extrasolar systems – although they believe billions of others exist.

But Dr Smith points out that many of these planets are either too close to their sun or too far away, meaning their surface temperatures are so extreme they could not support life.

Others have unusual orbits which cause vast temperature variations making it impossible for water to exist as a liquid – an essential element for life.

Dr Smith said: ‘We have found that most other planets and solar systems are wildly different from our own.

‘They are very hostile to life as we know it.’

‘The new information we are getting suggests we could effectively be alone in the universe.

‘There are very few solar systems or planets like ours. It means it is highly unlikely there are any planets with intelligent life close enough for us to make contact.’ But his controversial suggestions contradict other leading scientists – who have claimed aliens almost certainly exist.

These arguments are actually quite useful, and I include them in my standard list of scientific arguments for theism. (See below) You have to know this stuff cold. Most people believe in aliens because they watched movies made by artists. As a result, they think that humans are nothing special and that God is not interested in us in particular. Which is very convenient for them, because it means they can do whatever they want and not care what God thinks about what they are doing. If you want to defend against the idea that humans are nothing special, and that we were not placed here for a purpose, and that we are not accountable and obligated to seek and know the Creator/Designer, then you’ll need more than feelings. You’ll need science. You’ll need the best science available.

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.