Could Earth Have Livelier Twins?

Exo-EarthsNote:  I apologize un-Romney-like for the apparent tardiness of this posting, but I just returned to home and the internet from a month-long refuge in Brooklyn after evacuating the Rockaways from Hurricane Sandy.  I survived, safe and sound, but the same cannot be said of what was — aside from several books and a laptop — my only other worldly possession: a 30″ flat-screen HDTV that was summarily sequestrated, not by Congress but equally criminal post-storm looters who rampaged unmolested in the storm’s lawless wake.   Oh, well….  Above, artist’s rendition of exo-Earths orbiting a sun-like star.  More on superstorm Sandy will follow soon, but now, having paid my personal Pearl Harbor tribute earlier today, more news from space:
From Ohio State University Research News:

Search for Life Suggests Solar Systems More Habitable than Ours

SAN FRANCISCO—Scattered around the Milky Way are stars that resemble our own sun—but a new study is finding that any planets orbiting those stars may very well be hotter and more dynamic than Earth.

That’s because the interiors of any terrestrial planets in these systems are likely warmer than Earth—up to 25 percent warmer, which would make them more geologically active and more likely to retain enough liquid water to support life, at least in its microbial form.

Panero

Panero

Wendy Panero

The preliminary finding comes from geologists and astronomers at Ohio State University who have teamed up to search for alien life in a new way.

They studied eight “solar twins” of our sun—stars that very closely match the sun in size, age, and overall composition—in order to measure the amounts of radioactive elements they contain. Those stars came from a dataset recorded by the High Accuracy Radial Velocity Planet Searcher spectrometer at the European Southern Observatory in Chile.

They searched the solar twins for elements such as thorium and uranium, which are essential to Earth’s plate tectonics because they warm our planet’s interior.  Plate tectonics helps maintain water on the surface of the Earth, so the existence of plate tectonics is sometimes taken as an indicator of a planet’s hospitality to life.

Unterborn

Unterborn

Cayman Unterborn

Of the eight solar twins they’ve studied so far, seven appear to contain much more thorium than our sun—which suggests that any planets orbiting those stars probably contain more thorium, too. That, in turn, means that the interior of the planets are probably warmer than ours.

For example, one star in the survey contains 2.5 times more thorium than our sun, said Ohio State doctoral student Cayman Unterborn. According to his measurements, terrestrial planets that formed around that star probably generate 25 percent more internal heat than Earth does, allowing for plate tectonics to persist longer through a planet’s history, giving more time for live to arise.

“If it turns out that these planets are warmer than we previously thought, then we can effectively increase the size of the habitable zone around these stars by pushing the habitable zone farther from the host star, and consider more of those planets hospitable to microbial life,” said Unterborn, who presented the results at the American Geophysical Union meeting in San Francisco this week.

Unterborn:

“If it turns out that these planets are warmer than we previously thought, then we can effectively increase the size of the habitable zone around these stars…”


“At this point, all we can say for sure is that there is some natural variation in the amount of radioactive elements inside stars like ours,” he added. “With only nine samples including the sun, we can’t say much about the full extent of that variation throughout the galaxy. But from what we know about planet formation, we do know that the planets around those stars probably exhibit the same variation, which has implications for the possibility of life.”

His advisor, Wendy Panero, associate professor in the School of Earth Sciences at Ohio State, explained that radioactive elements such as thorium, uranium, and potassium are present within Earth’s mantle. These elements heat the planet from the inside, in a way that is completely separate from the heat emanating from Earth’s core.

“The core is hot because it started out hot,” Panero said. “But the core isn’t our only heat source. A comparable contributor is the slow radioactive decay of elements that were here when the Earth formed. Without radioactivity, there wouldn’t be enough heat to drive the plate tectonics that maintains surface oceans on Earth.”

The relationship between plate tectonics and surface water is complex and not completely understood. Panero called it “one of the great mysteries in the geosciences.” But researchers are beginning to suspect that the same forces of heat convection in the mantle that move Earth’s crust somehow regulate the amount of water in the oceans, too.

“It seems that if a planet is to retain an ocean over geologic timescales, it needs some kind of crust ‘recycling system,’ and for us that’s mantle convection,” Unterborn said.

In particular, microbial life on Earth benefits from subsurface heat. Scores of microbes known as archaea do not rely on the sun for energy, but instead live directly off of heat arising from deep inside the Earth.

On Earth, most of the heat from radioactive decay comes from uranium. Planets rich in thorium, which is more energetic than uranium and has a longer half-life, would “run” hotter and remain hot longer, he said, which gives them more time to develop life.

As to why our solar system has less thorium, Unterborn said it’s likely the luck of the draw.

“It all starts with supernovae. The elements created in a supernova determine the materials that are available for new stars and planets to form. The solar twins we studied are scattered around the galaxy, so they all formed from different supernovae. It just so happens that they had more thorium available when they formed than we did.”

Jennifer Johnson, associate professor of astronomy at Ohio State and co-author of the study, cautioned that the results are preliminary. “All signs are pointing to yes—that there is a difference in the abundance of radioactive elements in these stars, but we need to see how robust the result is,” she said.

Next, Unterborn wants to do a detailed statistical analysis of noise in the HARPS data to improve the accuracy of his computer models. Then he will seek telescope time to look for more solar twins.

This research was funded by Panero’s CAREER award from the National Science Foundation.

— Pam Frost Gorder

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McArtichoke’s Theory of Interstellar Stuff

n11lmc_noaoRecent developments beyond the world, or rather the lack of them, have  intrigued me.  As a curious peripheral observer of the UFO phenomenon, I have detected a stellar dis-economy of scale: a cosmological counterpoint to the economic law of diminishing returns.  I often wonder, with the technological capabilities humans possess and the array of devices scanning the sky, why have we not by now made contact with an extra-terrestrial or two?  It certainly is not for lack of effort.  Or of manpower, on our side.  We have several quasi-governmental bodies (SETI, e.g.) devoted solely to the task.

It got me thinking….  There are countless – let’s say thousands and stay on the conservative side for argument’s sake – of earth-similar, life supportable, rocky planets orbiting sun-like stars that we know about in the universe.  It seems to me the likelihood that advanced biological life has arisen on a small percentage of them is large.  Of those planets where life has flourished, a small percentage would develop beings with advanced intelligence, similar to human.

Given that the time period in question is roughly 13.75 billion years (literally, all the time in the world), and taking into account the minute percentages involved, it would seem to me that, by now, we on earth should have experienced incontestable evidence of “communion” much more significant than has been reported to date in popular media.

I have a theory — that I hope is not as close to truth as other theories, the Theory of Gravity or of Evolution come to mind for example – a hypothesis that suggests one  explanation for this Space Age dichotomy.  That is, that intelligence itself poses an existential threat to the species that it (science) is not able to solve, sufficiently to pose a timely solution – a chilling prospect if it applies to our species.

Briefly, my point is that we earthlings have not communed with extra-terrestrial civilizations simply because those civilizations do not exist… long enough for communion to occur before they annihilate themselves; that by the time they reach the capacity to contact, they have progressed to the extent of developing nuclear or other equally destructive technology or weaponry, and they – being human-esque, and thus genetically predisposed to conflict, destroy themselves before they make contact with us.   It is no secret that intelligence – particularly, lesser instances of it – is a dangerous thing.  The ancient Greeks recognized this, millennia ago, and gave us the word sophomore  – roughly, wise fool.

(Break Time – Popcorn in the Lobby)