At this year's meeting of the General Assembly of the International Astronomical Union, at a panel titled "Solar and Stellar Variability ― impact on Earth and Planets," a multidisciplinary group of experts discussed the evolving research into the types of suns and planets that would be hospitable to the development of life.

Edward Guinan, a professor of astronomy at Villanova University, claims that our sun provided better conditions for the formation of life in its youth. Over four billion years ago, the sun rotated ten times faster than it does today, causing the sun to generate a stronger magnetic field and considerably more radiation than it does today. These conditions have aided the formation of life, but other stars exist that maintain such a rapid rotation for a much longer duration:

The Sun does not seem like the perfect star for a system where life might arise. Although it is hard to argue with the Sun's ‘success' as it so far is the only star known to host a planet with life, our studies indicate that the ideal stars to support planets suitable for life for tens of billions of years may be a smaller slower burning ‘orange dwarf' with a longer lifetime than the Sun ― about 20-40 billion years. These stars, also called K stars, are stable stars with a habitable zone that remains in the same place for tens of billions of years. They are 10 times more numerous than the Sun, and may provide the best potential habitat for life in the long run.

Jean-Mathias Grießmeier of ASTRON's research similarly suggests that the Earth may not be an ideal planet for the formation and development of life. Grießmeier examined planetary magnetic fields, finding that a planet with a stronger magnetic field is less likely to have its atmosphere blown away by cosmic debris and is also better able to shield its surface from cosmic radiation. Guinan suggests that planets larger than Earth might be better able to protect any burgeoning life forms:

On the more speculative side we have also found indications that planets like Earth are also not necessarily the best suited for life to thrive. Planets two to three times more massive than the Earth, with a higher gravity, can retain the atmosphere better. They may have a larger liquid iron core giving a stronger magnetic field that protects against the early onslaught of cosmic rays. Furthermore, a larger planet cools more slowly and maintains its magnetic protection. This kind of planet may be more likely to harbour life.

That K stars are relatively common may offer new hope for the possibility of extraterrestrial life, although astronomers are quick to note they don't fully understand how common or fragile life in the universe may be. But their findings do suggest that, on a cosmological scale, Earth can't support life much longer. Says Guinan:

The Earth's period of habitability is nearly over ― on a cosmological timescale. In a half to one billion years the Sun will start to be too luminous and warm for water to exist in liquid form on Earth, leading to a runaway greenhouse effect in less than 2 billion years.

[Science Daily]

The Kepler satellite will use the same planet-finding method that's already found a few hundred planets outside our solar system: looking for subtle dips in stellar brightness. But it'll use more sensitive methods, looking for smaller, cooler planets that are closer to Earth and more hospitable to life.

Boss, who's just written a new book called The Crowded Universe, argues that Earthlike planets should be quite common:

First, if you talk to astronomers who look at young stars, they will tell you that when stars form, they tend to have a little bit of angular momentum, which means that they can't accrete all of their matter and they end up having a disk around them. Such disks are what planetary systems form out of, basically the leftovers from the star-formation process. Essentially all young stars have these disks, so we expect that these young stars at least have the possibility of having planetary systems.

Second, those who worry about planet-formation processes find that it's very hard to stop Earth-like planets, or some sort of large, rocky object, from forming. Earths in some sense are easier to build than Jupiters, but we already know from our extrasolar planet census that Jupiters exist around at least 10 percent, and probably around 20 percent, of stars. So Earths should be even more common than that.

Finally, and even more directly, the planetary searches are already beginning to find a new class of planets called super-Earths with masses maybe five, 10 or 15 times the mass of Earth that orbit a little closer to their star than our planet does. These guys occur on roughly one third of nearby solar-type stars. And these are sort of the oddballs in some sense, which I think are very much just the tip of the iceberg of the spectrum of Earth-like planets. In any theoretical model of planet formation that people talk about, there should be a ton of Earths compared to these oddball super-Earths, so when we do a complete census we should find a lot of Earths. If these oddballs are there 30 percent of the time and the Jupiters are there 20 percent of the time, that means the ones we can't quite see should be there essentially all the time. So it's a very compelling story, and all the evidence from several different directions points toward Earths being quite common.

He also believes that life is quite tenacious and it's likely that many of these planets have water on them, and comets dumping amino acids and other prebiotic chemicals, making life pretty likely. So many of these Earthlike worlds could turn out to have our alien cousins on them. [Scientific American]

After digging up a few teaspoons of Martian soil, Phoenix ran some chemical analyses. It baked some soil to see what gases were given off, and found a puff of oxygen. That could mean a few different things, but one of the possibilities is that the soil contained perchlorate salts, which are made of oxygen and chlorine molecules. That's interesting because perchlorates can act as food for some microrganisms and are a byproduct of some plant life processes.

So why is NASA so ambivalent about this discovery? For one thing, they didn't detect any chlorine yet, so they aren't sure if they really found perchlorates at all. And even if they did, the presence of perchlorates is not evidence of prior living organisms, and neither does the it preclude prior living organisms. What is unusual is that NASA chose to reveal details of an ongoing scientific investigation before they had really confirmed anything. Are they just feeling the pressure from the public relations department, or are they stalling until they're ready for the big reveal? Image by: NASA.

Martian Life Or Not? NASA's Phoenix Team Analyzes Results. [Science Daily]