Tag Archives: Astronomy

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How tidal effects improve the habitability of a planet

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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 now, but I already knew about the tides and habitability, 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.

Polemics

The connection between our moon, plate tectonics and habitability

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Apologetics and the progress of science
Apologetics and the progress of science

I found an interview with Peter Ward (atheist) and Donald Brownlee (agnostic) discussing astrobiology in Forbes magazine. They were asked about how important plate tectonics are for a planet to be able to support complex life.

Excerpt:

Astrobiologists often cite the sheer numbers of stars and galaxies as evidence that complex life elsewhere must surely have evolved somewhere. But is probability enough?

Without a moon, we don’t have any idea of how commonly a planet could have the long-term stability needed for complex life. Until we “get” that, going to the sheer numbers argument is useless. Without that moon-forming collision, we wouldn’t have plate tectonics. Without plate tectonics, we might have microbes but we’d never get to animals.

What about the rarity of earth’s crustal dichotomy of oceans and continents?

If you can’t make granite, you’re not going to have continents. But granite formation is a consequence of our moon-forming collision. That scrambled the entire density of our crust. Mars doesn’t have granite; all it’s got is this volcanic basalt. To build granite you need a planetary subduction [or plate tectonic] process.

In triggering complex life, how important were plate tectonics’ role in the continual recycling of earth’s atmosphere?

It’s this recycling that allows for a very rich planetary atmosphere with an extended life. Photosynthesis gets you oxygen, but how do you get enough photosynthesis to get oxygen at 10 to 20 percent? You’ve got to have a shoreline next to a rich sea with rocks eroding into it in order to provide the nitrogen and phosphates for [plant] photosynthesis.

This article from Astrobiology explains more about the importance of plate tectonics.

Excerpt:

Plate tectonics is the process of continents on the Earth drifting and colliding, rock grinding and scraping, mountain ranges being formed, and earthquakes tearing land apart. It makes our world dynamic and ever-changing. But should it factor into our search for life elsewhere in the universe?

Tilman Spohn believes so. As director of the German Space Research Centre Institute of Planetary Research, and chairman of ESA’s scientific advisory committee, he studies worlds beyond our Earth. When looking into the relationship between habitability and plate tectonics, some fascinating possibilities emerged.

It is thought that the best places to search for life in the Universe are on planets situated in “habitable zones” around other stars. These are orbital paths where the temperature is suitable for liquid water; not so close to the star that it boils away, and not so far that it freezes. Spohn believes that this view may be outdated. He elaborates, “you could have habitats outside those, for instance in the oceans beneath ice covers on the Galilean satellites, like Europa. But not every icy satellite would be habitable. Take Ganymede, where the ocean is trapped between two layers of ice. You are missing a fresh supply of nutrition and energy.”

So planets and moons that lie beyond habitable zones could host life, so long as the habitat, such as an ocean, is not isolated. It needs access to the key ingredients of life, including hydrogen, oxygen, nitrogen, phosphorous and sulphur. These elements support the basic chemistry of life as we know it, and the material, Spohn argues, must be regularly replenished. Nature’s method of achieving this on the Earth appears to be plate tectonics.

Spohn found that the further he delved into the issue, the more important plate tectonics seemed to be for life. For example, it is believed that life developed by moving from the ocean to the kind of strong and stable rock formations that are the result of tectonic action. Plate tectonics is also involved in the generation of a magnetic field by convection of Earth’s partially molten core. This magnetic field protects life on Earth by deflecting the solar wind. Not only would an unimpeded solar wind erode our planet’s atmosphere, but it also carries highly energetic particles that could damage DNA.

Another factor is the recycling of carbon, which is needed to stabilize the temperature here on Earth. Spohn explains, “plate tectonics is known to recycle carbon that is washed out of the atmosphere and digested by bacteria in the soil into the interior of the planet from where it can be outcast through volcanic activity. Now, if you have a planet without plate tectonics, you may have parts of this cycle, but it is broken because you do not have the recycling link.”

It has also been speculated that the lack of tectonic action on Venus contributed to its runaway greenhouse effect, which resulted in the immense temperatures it has today.

Most planets don’t have a moon as massive as ours is, and the collision that formed the moon is very fine-tuned for life. This is just one of the many factors that needs to be present in order to have a planet that supports complex, carbon-based life.

If you want to learn more about this data, I recommend watching “The Privileged Planet” DVD, and someone posted it on YouTube:

If you haven’t seen it, and have 90 minutes, this is time well-spent.

News

Atheist gets her PhD in astronomy and astrophysics and finds evidence for God

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Sherlock Holmes and John Watson
Sherlock Holmes and John Watson

Christian apologist Terrell Clemmons tweeted this testimony by Sarah Salviander, a research scientist in astronomy and astrophysics at the prestigious University of Texas at Austin.

Dr. Salviander writes:

I was born in the U.S., but grew up in Canada. My parents were socialists and political activists who thought British Columbia would be a better place for us to live, since it had the only socialist government in North America at the time. My parents were also atheists, though they eschewed that label in favor of “agnostic.” They were kind, loving, and moral, but religion played no part in my life. Instead, my childhood revolved around education, particularly science. I remember how important it was to my parents that my brother and I did well in school.

I just want to point out that I hope that all you Christian parents are taking seriously the obligation to make your kids do well in school, because even if they start out as atheists when they are young, they can still find their way back to God through study, as Sarah did.

She had a bad start, that’s for sure:

I grew up in the 1970s and 1980s, a time when science fiction was enjoying a renaissance, thanks largely to the popularity of Star Wars. I remember how fascinated I was by the original Star Wars trilogy. It had almost nothing to do with science—it’s more properly characterized as space opera—but it got me thinking about space in a big way. I also loved the original Star Trek, which was more science fiction. The stoic and logical character of Mr. Spock was particularly appealing to me. Popular science was also experiencing a renaissance at that time, which had a lot to do with Carl Sagan’s television show, Cosmos, which I adored. The combination of these influences led to such an intense wonder about outer space and the universe, that by the time I was nine years old I knew I would be a space scientist someday.

Canada was already post-Christian by the 1970s, so I grew up with no religion. In retrospect, it’s amazing that for the first 25 years of my life, I met only three people who identified as Christian. My view of Christianity was negative from an early age, and by the time I was in my twenties, I was actively hostile toward Christianity. Looking back, I realized a lot of this was the unconscious absorption of the general hostility toward Christianity that is common in places like Canada and Europe; my hostility certainly wasn’t based on actually knowing anything about Christianity. I had come to believe that Christianity made people weak and foolish; I thought it was philosophically trivial. I was ignorant not only of the Bible, but also of the deep philosophy of Christianity and the scientific discoveries that shed new light on the origins of the universe and life on Earth.

She documents a phase of following Ayn Rand and embracing “Objectivism”, but eventually she rejects it for failing to answer the big questions of life.

More:

I began to focus all of my energy on my studies, and became very dedicated to my physics and math courses. I joined campus clubs, started to make friends, and, for the first time in my life, I was meeting Christians. They weren’t like Objectivists—they were joyous and content. And, they were smart, too. I was astonished to find that my physics professors, whom I admired, were Christian. Their personal example began to have an influence on me, and I found myself growing less hostile to Christianity.

This is why I think it is so important for Christian parents to raise their children to get advanced degrees… either to become professors themselves, or to finance others (e.g. – our own children) to do advanced degrees. It is so important for university students to see Christian professors on campus. And failing that, it’s important that we bring Christian speakers in to debate non-Christian speakers on the important issues. This will not happen unless we recognize how important it is, and then make a plan to achieve it.

More:

I had joined a group in the Center for Astrophysics and Space Sciences (CASS) that was researching evidence for the big bang. The cosmic background radiation—the leftover radiation from the big bang—provides the strongest evidence for the theory, but cosmologists need other, independent lines of evidence to confirm it. My group was studying deuterium abundances in the early universe. Deuterium is an isotope of hydrogen, and its abundance in the early universe is sensitive to the amount of ordinary mass contained in the entire universe. Believe it or not, this one measurement tells us whether the big bang model is correct.

If anyone is interested in how this works, I’ll describe it, but for now I’ll spare you the gruesome details. Suffice it to say that an amazing convergence of physical properties is necessary in order to study deuterium abundances in the early universe, and yet this convergence is exactly what we get. I remember being astounded by this, blown away, completely and utterly awed. It seemed incredible to me that there was a way to find the answer to this question we had about the universe. In fact, it seems that every question we have about the universe is answerable. There’s no reason it has to be this way, and it made me think of Einstein’s observation that the most incomprehensible thing about the world is that it’s comprehensible. I started to sense an underlying order to the universe. Without knowing it, I was awakening to what Psalm 19 tells us so clearly, “The heavens declare the glory of God; the skies proclaim the work of his hands.”

That summer, I’d picked up a copy of The Count of Monte Cristo by Alexandre Dumas and was reading it in my off hours. Previous to this, I’d only known it as an exciting story of revenge, since that’s what the countless movie and TV adaptations always focused on. But it’s more than just a revenge story, it’s a philosophically deep examination of forgiveness and God’s role in giving justice. I was surprised by this, and was starting to realize that the concept of God and religion was not as philosophically trivial as I had thought.

All of this culminated one day, as I was walking across that beautiful La Jolla campus. I stopped in my tracks when it hit me—I believed in God! I was so happy; it was like a weight had been lifted from my heart. I realized that most of the pain I’d experienced in my life was of my own making, but that God had used it to make me wiser and more compassionate. It was a great relief to discover that there was a reason for suffering, and that it was because God was loving and just. God could not be perfectly just unless I—just like everyone else—was made to suffer for the bad things I’d done.

The Count of Monte Cristo is one of my favorite, favorite books as well, and had the same impact on me as it did on her.

OK, that’s enough for this post. Go read the rest, and please share it. This woman is an expert Christian apologist and her life will have an influence. Are you going to be like her? Will you mentor others to be like her? Will you marry someone like her? Will you raise children who are like her (which is my plan)? We really need everyone to pull their weight now, because everywhere you look, the truth of Christianity is under attack.

Positive arguments for Christian theism