Tag Archives: Exoplanet

News

Scientists discover that tides affect a planet’s habitability

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Circumstellar Habitable Zone
Circumstellar Habitable Zone

Science Daily reports on a new factor that affects planetary habitability: tides. Specifically, tides can affect the surface temperature of a planet, which has to be within a certain range in order to support liquid water – a requirement for life of any conceivable kind.

Excerpt:

Tides can render the so-called “habitable zone” around low-mass stars uninhabitable. This is the main result of a recently published study by a team of astronomers led by René Heller of the Astrophysical Institute Potsdam.

[…]Until now, the two main drivers thought to determine a planet’s temperature were the distance to the central star and the composition of the planet’s atmosphere. By studying the tides caused by low-mass stars on their potential earth-like companions, Heller and his colleagues have concluded that tidal effects modify the traditional concept of the habitable zone.

Heller deduced this from three different effects. Firstly, tides can cause the axis of a planet`s rotation to become perpendicular to its orbit in just a few million years. In comparison, Earth’s axis of rotation is inclined by 23.5 degrees — an effect which causes our seasons. Owing to this effect, there would be no seasonal variation on such Earth-like planets in the habitable zone of low-mass stars. These planets would have huge temperature differences between their poles, which would be in perpetual deep freeze, and their hot equators which in the long run would evaporate any atmosphere. This temperature difference would cause extreme winds and storms.

The second effect of these tides would be to heat up the exoplanet, similar to the tidal heating of Io, a moon of Jupiter that shows global vulcanism.

Finally, tides can cause the rotational period of the planet (the planet’s “day”) to synchronize with the orbital period (the planet’s “year”). This situation is identical to the Earth-moon setup: the moon only shows Earth one face, the other side being known as “the dark side of the moon.” As a result one half of the exoplanet receives extreme radiation from the star while the other half freezes in eternal darkness.

The habitable zone around low-mass stars is therefore not very comfortable — it may even be uninhabitable.

Here is my previous post on the factors needed for a habitable planet. Now we just have one more. I actually find this article sort of odd, because my understanding of stars was that only high-mass stars could support life at all. This is because if the mass of the planet was too low, the habitable zone wouldbe very close to the star. Being too close to the star causes tidal locking, which means that the planet doesn’t spin on its axis at all, and the same side faces the star. This is a life killer.

This astrophysicist who teaches at the University of Wisconsin explains it better than me.

Excerpt:

Higher-mass stars tend to be larger and luminous than their lower-mass counterparts. Therefore, their habitable zones are situated further out. In addition, however, their HZs are much broader. As an illustration,

  • a 0.2 solar-mass star’s HZ extends from 0.1 to 0.2 AU
  • a 1.0 solar-mass star’s HZ extends from 1 to 2 AU
  • a 40 solar-mass star’s HZ extends from 350 to 600 AU

On these grounds, it would seem that high-mass starts are the best candidates for finding planets within a habitable zone. However, these stars emit most of their radiation in the far ultraviolet (FUV), which can be highly damaging to life, and also contributes to photodissociation and the loss of water. Furthermore, the lifetimes of these stars is so short (around 10 million years) that there is not enough time for life to begin.

Very low mass stars have the longest lifetimes of all, but their HZs are very close in and very narrow. Therefore, the chances of a planet being formed within the HZ are small. Additionally, even if a planet did form within the HZ, it would become tidally locked, so that the same hemisphere always faced the star. Even though liquid water might exist on such a planet, the climactic conditions would probably be too severe to permit life.

In between the high- and low-mass stars lie those like our own Sun, which make up about 15% percent of the stars in the galaxy. These have reasonably-broad HZs, do not suffer from FUV irradiation, and have lifetimes of the order of 10 billion years. Therefore, they are the best candidates for harbouring planets where life might be able to begin.

This guy is just someone I found through a web search. He has a support-the-unions-sticker on his web page, so he’s a liberal crackpot. But he makes my point, anyway, so that’s good enough for me.

Maybe the new discovery is talking about this, but I already knew about it because I watched The Privileged Planet DVD. Actually that whole video is online, and the clip that talks about the habitable zone and water is linked in this blog post I wrote before.

Atheism hates science

Theism loves science

Podcasts

Brian Auten interviews Jay Richards about Christian apologetics

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Dr. Jay Richards
Dr. Jay Richards

Christian scholar Jay Richards was interviewed by Brian Auten of Apologetics 315.

The MP3 file is here.

Topics:

  • What is intelligent design (ID)?
  • Is ID specifically Christian?
  • How does ID helpful to Christian apologetics?
  • What does ID prove?
  • Is it OK to use an argument that doesn’t prove Christianity specifically?
  • What is the difference between deism and theism?
  • Do ID arguments get you to deism or theism?
  • What is materialism, and how can you challenge it?
  • How do opponents of ID define ID?
  • What factors do you need to make a habitable planet?
  • Are habitable planets common or rare in the universe?
  • What is “The Privileged Planet” hypothesis?
  • Is there an overlap between habitability and suitability for making scientific discoveries?
  • What is the “Copernican Principle”?
  • Has the progress of science made Earth seem common and ordinary?
  • What is the most Earth-like planet that we’ve ever discovered?
  • How should ID proponents respond to the objection that creatures aren’t perfect?
  • Does having a big moon make a planet more or less habitable?
  • Does a planet’s distance to the Sun make that planet more or less habitable?
  • How do these two habitability factors affect the observability of solar eclipses?
  • What does co-relation between habitability and “discoverability” tell us about God?
  • How important is training in philosophy to Christian apologetics?
  • What one thing should a Christian apologist work on to be more effective?

I’m hoping that Brian will do a follow-up interview with Jay on Jay’s new book on theistic evolution.

Here’s the description from Amazon.com:

What does it mean to say that God “used evolution” to create the world? Is Darwin’s theory of evolution compatible with belief in God? And even if Darwin’s theory could be reconciled with religious belief, do we need to do so? Is the theory well established scientifically? Is it true?

In the century and a half since Charles Darwin first proposed his theory of evolution, Christians, Jews, and other religious believers have grappled with how to make sense of it. Most have understood that Darwin’s theory has profound theological implications, but their responses have varied dramatically.

Some religious believers have rejected it outright; others, often called “theistic evolutionists,” have sought to reconcile Darwin’s theory with their religious beliefs, but often at the cost of clarity, orthodoxy, or both. Too few have carefully teased out the various scientific, philosophical, and theological claims at stake, and separated the chaff from the wheat. As a result, the whole subject of God and evolution has been an enigma wrapped in a shroud of fuzz and surrounded by blanket of fog.

The purpose of this anthology of essays is to clear away the fog, the fuzz, and the enigma. Contributing authors to the volume include Jay Richards, co-author of The Privileged Planet: How Our Place in the Cosmos Is Designed for Discovery; Stephen Meyer, author of Signature in the Cell: DNA and the Evidence for Intelligent Design; William Dembski, author of The Design Revolution; Jonathan Witt, co-author of A Meaningful World: How the Arts and Sciences Reveal the Genius of Nature; Denyse O’Leary, author of By Design, or by Chance?; and David Klinghoffer, author of Shattered Tablets.

Those authors are some of my favorite people to read in the whole world. I think this group will be mostly fed up with theistic evolutionists, like I am, although they may not go as far as I do when I label theistic evolutionists “functional atheists” or “theistic atheists”.

Jay Richards is probably my favorite all-round Christian scholar, because he also writes a lot on policy and economics, and was interviewed on those topics by Frank Turek. He has a complete, well-rounded worldview.

Posts featuring Jay Richards

Interviews by Jay Richards

Related posts

Commentary

What are galactic habitable zones and circumstellar habitable zones?

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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.