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To Be Habitable, a Planet Needs Inhabitants

In a chicken-or-egg conundrum, astrobiologists are asking whether inhabitants are needed to make a planet habitable.

Astrobiology Hopes Dim with Exoplanet Findings

Harsh "space weather" around dim red dwarf stars may make planets uninhabitable. "Godzilla Earths" may not fare much better.

Carbon Cycle Keeps Earth from Fate of Venus, Mars

Another delicate balance making Earth habitable has been identified: the carbon cycle.

Cosmic Lottery: How Many Habitable Planets?

News media ran with a suggestion that one in five stars has a habitable planet, but they didn't read the fine print.

Planet Habitable Zone Cannot Be Too Windy

The "habitable zone" of a planet usually concerns its distance from the star such that it can support liquid water. But what if the star fries the surface with intense stellar winds?

Extrasolar Planets: Bigger and More Mortal

Many of the stars and planets found by the Kepler spacecraft are not earthlike. Also, astronomers have seen planets destroyed by their stars.

Star Chemistry Constrains Habitable Zone

The chemistry of a parent star can have drastic effects on the habitability of an earth-like planet.

Tilt-A-World: Another Constraint on Habitability

Did you ever ride a Tilt-A-Whirl, one of those cheap carnival rides that makes you dizzy and sick? Our planet would be like that if its inclination were out of control. Without tilt stability, a new study reveals, we wouldn't be sick, we'd be dead, or never alive in the first place. It's not enough to be in the Habitable Zone. Would-be inhabited planets need to avoid a new problem, called “tilt erosion.”

A Young Moon for Life

Our moon is unique in the solar system. Just the right size and just the right distance, it is positioned to stabilize the tilt of Earth’s axis, providing stable seasonal cycles. Science lacks data so far to know just how unique the Earth-moon relationship in a habitable zone is among other stellar systems. We know from the planets of our own solar system that moons come in all sizes, from tiny Deimos to massive Titan, and orbit in apparently arbitrary radii from their host planets. What astrophysicists can do is predict what would happen on earth if things were different. That’s what one scientist did. Another discovery could change the view of the moon’s surface being unaltered for billions of years.

Observations Upset Models of Stellar Evolution

Stellar evolution models go back decades. Ever since the Hertzsprung-Russell diagram came out in 1910 (graphing temperature against luminosity), showing most stars fell on a line called the “main sequence”, astrophysicists have sought to understand the life cycle of stars from birth to death. In general, the story goes, collapsing clouds of gas and dust produce main-sequence stars that burn nuclear fuel till they run out. Depending on their masses, they end up as supernovae, red giants or slowly-cooling cinders. While red dwarfs cool down slowly into the darkness, supernovae and red giants eject mass outward into space . Two new planets found close to a red giant are among new headaches for theorists.

Earth’s Twin: What Does “Potentially Habitable” Mean?

The Kepler spacecraft has found dozens of “potentially habitable” planets around other stars, but this week announced one that some news sources are calling “Earth’s twin.”

It’s Still a Rare Earth

Now that hundreds of extrasolar planets are known, how do they compare to ours? The Kepler spacecraft has found a varied assortment of all sizes and distances away from their parent stars. Only a few reside in their star’s habitable zones. But that’s only the first of many requirements for life. Two recent studies indicate that Earth remains a rare bird in the celestial aviary.

Science Without an Object: Astrobiology, Alien Science

Can science exist without an observable object? In recent years we have seen serious scientists ponder alternate universes and parallel universes, dark matter, dark energy and other imponderable entities. String theory has yet to rest on observable data, and physicists at CERN are getting worried about not finding the hypothetical Higgs boson. Sooner or later, these theories need to detect their subjects or lose credibility in the science club. Perhaps nowhere else has the disconnect between hype and observation reached the absurd limits of astrobiology and alien science.
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