Tag Archives: Exoplanet

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. 

What makes a planet suitable for supporting complex life?

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.

New paper finds that mass of asteroid belts affect habitability of planets

Science Daily reports. (H/T Evolution News via ECM)

Excerpt:

They suggest that the size and location of an asteroid belt, shaped by the evolution of the Sun’s protoplanetary disk and by the gravitational influence of a nearby giant Jupiter-like planet, may determine whether complex life will evolve on an Earth-like planet.

This might sound surprising because asteroids are considered a nuisance due to their potential to impact Earth and trigger mass extinctions. But an emerging view proposes that asteroid collisions with planets may provide a boost to the birth and evolution of complex life.

Asteroids may have delivered water and organic compounds to the early Earth. According to the theory of punctuated equilibrium, occasional asteroid impacts might accelerate the rate of biological evolution by disrupting a planet’s environment to the point where species must try new adaptation strategies.

The astronomers based their conclusion on an analysis of theoretical models and archival observations of extrasolar Jupiter-sized planets and debris disks around young stars. “Our study shows that only a tiny fraction of planetary systems observed to date seem to have giant planets in the right location to produce an asteroid belt of the appropriate size, offering the potential for life on a nearby rocky planet,” said Martin, the study’s lead author. “Our study suggests that our solar system may be rather special.”

There’s a long list of factors that have to be present for a planet to support life – and more keep appearing every day. Here’s another recent one from the journal Nature.

Related posts

What conditions support the minimum requirements for complex life?

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.

New study on tidal heating strengthens stellar habitability argument

Circumstellar Habitable Zone
Circumstellar Habitable Zone

Note: If you need a refresher on the habitability argument, click here.

Here’s an article entitled “Tidal heating shrinks the ‘goldilocks zone’: Overlooked factor suggests fewer habitable planets than thought”. It appeared in Nature, the most prestigious peer-reviewed science journal.

The gist of it is that tidal forces can alter orbits so that planets don’t spend all of their orbit in the habitable zone. If planets go outside the habitable zone, it damages their supply of liquid water, and any life chemistry going on in there is disrupted.

Excerpt:

A previously little-considered heating effect could shrink estimates of the habitable zone of the Milky Way’s most numerous class of stars — ‘M’ or red dwarfs — by up to one half, says Rory Barnes, an astrobiologist at the University of Washington in Seattle. That factor — gravitational heating via tides — suggests a menagerie of previously undreamt-of planets, on which tidal heating is a major source of internal heat. Barnes presented the work yesterday at a meeting of the American Astronomical Society’s Division on Dynamical Astronomy in Timberline Lodge, Oregon.

The habitable zone is the orbital region close enough to a star for a planet to have liquid water, but not so close that all of the water evaporates. For our Sun, the zone extends roughly from the inner edge of the orbit of Mars to the outer edge of that of Venus. For smaller, cooler stars, such as M-class dwarfs, the zone can be considerably closer to the star than Mercury is to the Sun. And because close-in planets are easier to spot than more distant ones, such stars have been a major target for planet hunters seeking Earth-like worlds.

There’s just one problem with finding habitable planets around such stars, says Barnes. Because tidal forces vary dramatically with the distance between a planet and its star, closer orbits also result in massively larger tidal forces.

Since planets do not have perfectly circular orbits, these tidal forces cause the planet to flex and unflex each time it moves closer to or further from its star; kneading its interior to produce massive quantities of frictional heat. Substantial heat can be produced, he added, with even slight deviations from a perfectly circular orbit. And, Barnes notes, other factors — such as the rate of the planet’s rotation and its axial tilt — can also influence heat production.

A similar tidal process makes Jupiter’s moon Io the most volcanic body in the Solar System. “I’m just scaling that Io–Jupiter system up by a factor of 1,000 in mass,” Barnes said at the meeting. “It’s the same process, on steroids.”

So, stars that are smaller and cooler will have a habitable zone that is closer to the star, exposing them to more tidal forces. More tidal forces makes their orbits less likely to stay circular – within the habitable zone around the star. These variations cause an increase in heat production on the planet. Too much heat means that the planet is unable to support liquid water on the surface, making it inhospitable for life. Therefore, solar systems with less massive stars can be ruled out as possible sites for life, because of these tidal forces.