How Earth-like are the 8.8 billion Earth-like planets from a recent estimate?

Previously, I blogged about a few of the minimum requirements that a planet must satisfy in order to support complex life.

Here they are:

  • 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

Now what happens if we disregard all of that, and just classify an Earth-like planet as one which only has to potentially support liquid water at the surface? Well, you get a very high estimate of Earth-like planets.

Science journalist Denyse O’Leary responds to a recent estimate based on this questionable criterion, which placed the number of Earth-like planets at 8.8 billion.

Excerpt: (links removed)

A current official definition of habitable planets is “in the zone around the star where liquid water could exist,” but the ones discovered so far are unsuitable in many other ways.

Then a new cosmology term hit the media, “super-Earths.” It means “bigger than Earth,” but smaller than gas giant Neptune. Super-Earths could be the most numerous type of planet, in tight orbits around their star — which is actually bad news for life.Nonetheless, some insist, they may be more attractive to life than Earth is. Indeed, the Copernican Principle allows us to assume that some are inhabited already.

In reality, even the rocky exoplanets (known as of early 2013) that are Earth-sized are not Earth-like. For example, the Kepler mission’s first rocky planet find is described as follows: “Although similar in size to Earth, its orbit lasts just 0.84 days, making it likely that the planet is a scorched, waterless world with a sea of lava on its starlit side.” As space program physicist Rob Sheldon puts it, Earth is a rocky planet but so is a solid chunk of iron at 1300 degrees orbiting a few solar radii above the star. In any event, a planet may look Earth-like but have a very different internal structure and atmosphere.”

David Klinghoffer notes that the study is estimating that 8.8 billion number, but the actual number of Earth-like planets we can see is much lower.

He writes:

The study is supposed to be a major step forward because of its unprecedented accuracy:

For the first time, scientists calculated — not estimated — what percent of stars that are just like our sun have planets similar to Earth: 22 percent, with a margin of error of plus or minus 8 percentage points.

Oh! You see, they calculated. They didn’t just estimate.

Because there are probably hundreds of planets missed for every one found, the study did intricate extrapolations to come up with the 22 percent figure — a calculation that outside scientists say is fair.

Oh. They calculated in the sense of “extrapolating” to “come up” with a figure. In other words, they estimated. The figure of “8.8 billion stars with Earth-size planets in the habitable temperature zone” comes down a bit too when you talk about actual planets that have been observed instead of being merely conjectured and “calculated.”

Scientists at a Kepler science conference Monday said they have found 833 new candidate planets with the space telescope, bringing the total of planets they’ve spotted to 3,538, but most aren’t candidates for life.

Kepler has identified only 10 planets that are about Earth’s size circling sun-like stars and are in the habitable zone, including one called Kepler 69-c.

Ah hah. So from the initial, trumpets-blaring figure of 8.8 billion we’re down more realistically to 10. Not 10 billion, just 10. Meanwhile the silence from space continues absolutely unabated.

That’s the way it tends to go with stories like this, the blaring headline and the inevitable letdown.

One part of the AP press release makes the point that the estimate does not include all the minimum requirements for life. For example, you need an atmosphere, as I stated above. Do the estimated 8.8 billion Earth-like planets have an Earth-like atmosphere? How about an oxygen-rich atmosphere, do the 8.8 billion Earth-like planets have that?

NO:

The next step, scientists say, is to look for atmospheres on these planets with powerful space telescopes that have yet to be launched. That would yield further clues to whether any of these planets do, in fact, harbor life.

You know, after the whole global warming hoax, you would think that these headline writers would have learned their lesson about sensationalizing wild-assed guesses in order to scare up more research money. But a lot of true-believing naturalists are just going to read the headline and not the rest of the article, and they will never know that they’ve been had. Again. I love experimental science, but I don’t love the politicization of science. 

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