Friday, February 1, 2013

Redefining Habitable Zones

" 'Habitable Zone' for Alien Planets, and Possibly Life, Redefined"
Clara Moskowitz, Space.com (January 29, 2013)

" One of the most important characteristics of an alien planet is whether or not it falls into what's called the habitable zone ­- a Goldilocks-like range of not-too-close, not-too-far distances from the parent star that might allow the planet to host life.

"Now scientists have redefined the boundaries of the habitable zone for alien planets, potentially kicking out some exoplanaets that were thought to fall within it, and maybe allowing a few that had been excluded to squeeze in...."

This isn't the final word in how far a planet needs to be from its star, for it to have an atmosphere, liquid water, and - maybe - life. It's probably a better estimate than the last one, since at that time scientists had solid information on exactly no planets outside the Solar system. Today, the count is in the hundreds. Make that thousands.

Scientists have a big enough sample now, to make a pretty good estimate for how many planets in this galaxy are about about the same size as Earth, and rocky. Unless Earth just happens to be in a very crowded corner of this galaxy, there are about 17,000,000,000 planets that are sort of like the inner four here: Mercury, Venus, Earth, and Mars.

Statistics, Earth, and Neighbors

If only one in four of those 17,000,000,000 planets have life, which is the local percentage: that's a whole lot of worlds with life. That's a big "if," though: and that brings the Lemming back to the revised guesstimate on where habitable zones are.

Good news, by the way: Earth is, according to the new estimate, still inside Sol's habitable zone. If it wasn't, the Lemming would wonder about how reliable this new-and-improved definition was. After all, we know there's life here on Earth.

If life got started somewhere besides Earth, and if it's close enough to 'life as we know it' for humans to recognize it as "life," and if this extraterrestrial life is close enough for humans to find in the near future: that's a lot of "ifs."

The Lemming would be excited if the Curiosity Mars rover found a wrecked spaceship that hadn't come from Earth: or a bit of plastic that couldn't have come from the rover. Even if the extraterrestrial wreck didn't have a speck of life on it, its presence would be proof that humanity had company: at one time.

But the first evidence of extraterrestrial life might be a little ecosystem supporting one-celled critters. That would be exciting, too.

The Lemming Philosophizes

The Lemming is fairly sure that the familiar 'science fiction' universe isn't what we're really living in. There's nothing wrong with telling a story about a galaxy teeming with non-human people - who all just happen to be almost exactly as smart as humans; with almost exactly the same interests, needs, and goals; and using almost exactly the same technology.

The universe could be like that, but probably isn't. If humanity was one of a few billion almost-exactly-like-human civilizations; all of which were within a few thousand years of each other in terms of technology - humanity would probably be selling souvenirs to space alien tourists.

It seems hard to remember how old the universe is. A million years ago, humans were learning how to use fire without killing themselves. But a million years is only a tiny fraction of the time that stars and planets have been spinning around this galaxy's core.

In the Lemming's opinion, when or if humanity meets other people - they won't be very much like humans. And that, again in the Lemming's opinion, is a good thing. Humans do a pretty good job of being human, there may be many other ways of being people, and we all could learn by comparing notes.

Even if there aren't any other people in this vast universe, just finding life elsewhere would let humanity learn a great deal. And this, again in the Lemming's opinion, is a good thing.

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