Tag Archives: Science

News

Scientists discover that tides affect a planet’s habitability

Leave a comment
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

William Lane Craig on Sam Harris’ attempt to ground morality with science

55 Comments

William Lane Craig is going to be debating atheist Sam Harris in April, so I thought that I would link to a couple of resources in which Craig assesses Harris’ views. Harris thinks that you can use science to discover an objective morality. Does his view make sense?

Here’s an audio clip from Youtube:

And in this MP3 file, Craig assesses Harris’ attempt to grounded morality on naturalism.

Topics:

  • Harris opposes ground moral values and moral duties on a theistic worldview
  • Harris thinks that the factual statements made by science can ground moral values and moral duties
  • Harris thinks that these findings of science lead to an objective morality
  • Harris’ view is that what is “good” is what contributes to “human well-being”
  • Human happiness and flourishing is “good” and human unhappiness and decline is “evil”
  • Craig agrees that science can show what factors contribute to human flourishing
  • On atheism, there is no reason to select the fourishing of human beings as “good”
  • Craig asks: why say that human well-being and flourishing is a moral good?
  • there are non-moral uses of the word “good” and moral uses of the word “good”
  • the moral sense of “good” refers to the “good life” and what we ought to do to be good
  • Harris equivocates between different uses of the word good
  • in chess, there are good moves and bad moves with respect to winning the game – but that’s not moral good
  • similarly, someone who cleans your yard can do a good job or a bad job – but that’s not moral good
  • what is the explanation, on atheism, for human flourishing having the moral dimension of being “good”?
  • how does Harris deal with the fact-value divide? (the fallacy of deriving an ought from an is)
  • how does Harris leap from facts about brains to the moral property of “goodness”?
  • what scientific experiments does Harris propose to show that human flourishing is the “good”?
  • is Harris’ view just utilitarianism? (the view that the good is whatever makes the most number of people happy)
  • can Harris ground human rights like the right to life on his view?
  • Can human rights be overridden if it makes lots of people happy, on Harris’ view?
  • does Harris’ view lead to eugenics? how could Harris oppose the elimination of the weak or undesirables?

I think the question that Sam Harris has to answer is this: on atheism, why should a person limit their own pursuit of happiness when they can be more happy by being selfish and spurning the “flourishing of humans”? Why should any individual atheist care about the flourishing of humans when self-sacrificial actions to improve the flourishing of others diminishes his own happiness?

You can hear even more about Harris’ views from New Zealand philosopher Glenn Peoples.

Commentary

Who is right about snow and global warming? Al Gore or the IPCC?

2 Comments

From the Daily Caller.

Excerpt:

Al Gore took to his blog earlier this month to respond to Bill O’Reilly’s question: “Why has southern New York turned into the tundra?”

Gore happily typed away, blaming global warming for the snow and quoting Chicago Tribune columnist Clarence Page as his scientific authority.

“As it turns out, the scientific community has been addressing this particular question for some time now and they say that increased heavy snowfalls are completely consistent with what they have been predicting as a consequence of man-made global warming,” Gore wrote.

Unfortunately for Gore and others who have claimed that the snow this winter is a global warming byproduct, their own authorities have said climate change will result in less snow.

Both the Intergovernmental Panel on Climate Change (IPCC) and the Environmental Protection Agency (EPA) have predicted warmer, less snowy winters.

A sampling:

  • “Snow season length and snow depth are very likely to decrease in most of North America … except in the northernmost part of Canada where maximum snow depth is likely to increase (Christensen et al., 2007).” (EPA)
  • “Decreases in snowcover and increases in winter rain on bare soil will likely lengthen the erosion season and enhance erosion intensity.” (EPA)
  • “Rising temperatures have generally resulted in rain rather than snow in locations and seasons where climatological average temperatures for 1961 to 1990 were close to freezing (0 °C).” (EPA)
  • “As temperatures rise, the likelihood of precipitation falling as rain rather than snow increases, especially in autumn and spring at the beginning and end of the snow season, and in areas where temperatures are near freezing. Such changes are observed in many places, especially over land in middle and high latitudes of the Northern Hemisphere, leading to increased rains but reduced snowpacks.” (IPCC)

Some, such as University of East Anglia senior climate researcher, Dr. David Viner, have said that in a few years snow will be scarce, and “children just aren’t going to know what snow is.”

How can global warming be scientific if more snow and less snow both mean that global warming is happening?

More contradictory global warming predictions at Marginalized Action Dinosaur.