Is Our Solar System Unique Or Rare?

As I became older, I developed a rule of thumb for formulating hypotheses about things I was studying—what's the worst case? I would then come to some subjective conclusion about what the worst case was, and use that as my initial hypothesis about what's going on, subject to revision in the direction of less worse (but still bad) outcomes. This habit of mind has served me well. This is not my natural disposition; earlier in my life, I had the same hopes and optimism I ridicule today on this blog. Life taught me to think this way. This was one of the painful lessons of experience.

What is the worst outcome when it comes to "intelligent" technologically advanced life on Earth? Quite simply, it is that Earth life is unique or fleetingly rare, that species with the same abilities humans have are unique or fleetingly rare, and so on. That's been my hypothesis for a long time now. No new data has forced me revise it.

And why is that the worst outcome? Quite simply, it means that when Homo sapiens brings about its own destruction and another mass extinction, that might be all she wrote for "intelligent" life in the Milky Way, or even the observable Universe. This astonishing natural experiment on Earth in which the Universe became (very briefly) self-aware and capable of observing itself would  be over, and that's that.

2012 was another big year in the discovery of exoplanets, which are planets revolving around other suns. If you had followed this news the way I do, you would have marveled at all the discoveries of either "Earth-like" planets or planets which potentially host life because they are in the "habitable zones" of their parent stars, meaning that liquid water might exist there.

The only problem with all these happy announcements was that the "Earth-like" planets were not "Earth-like" and planets in the "habitable zone" were actually planets orbiting dwarf-stars in very tight orbits. For example, let's look at Earth-like planet discovered next to our solar system.

It is the type of planet they've been searching for across the Milky Way galaxy and they found it circling a star right next door — 25 trillion miles away. But the Earth-like planet is so hot its surface may be like molten lava.

Life cannot survive the 2,200 degree heat of the planet, so close to its star that it circles it every few days.

Needless to say, a planet whose surface temperature is 2,200 degrees is not Earth-like

That did not curb the enthusiasm of the planet hunters.

The astronomers who found it say it's likely there are other planets circling the same star, a little farther away where it may be cool enough for water and life. And those planets might fit the not-too-hot, not-too-cold description sometimes call the Goldilocks Zone.

That means that in the star system Alpha Centauri B, a just-right planet could be closer than astronomers had once imagined.

It's so close that from some southern places on Earth, you can see Alpha Centauri B in the night sky without a telescope. But it's still so far that a trip there using current technology would take tens of thousands of years.

But the wow factor of finding such a planet so close has some astronomers already talking about how to speed up a 25 trillion-mile rocket trip there. Scientists have already started pressuring NASA and the European Space Agency to come up with missions to send something out that way to get a look at least...

And one of the European team's main competitors, Geoff Marcy of the University of California Berkeley, gushed even more about the scientific significance.

"This is a historic discovery," he wrote in an email. "There could well be an Earth-size planet in that Goldilocks sweet spot, not too cold and not too hot, making Alpha Centauri a compelling target to search for intelligent life."

Harvard planet-hunter David Charbonneau and others used the same word to describe the discovery: "Wow."

Isn't it satisfying to discover that hard-core scientists, especially planet-hunting astronomers, are just as delusional as everybody else? (They're much like economists in this regard.)

The proliferation of exoplanet discoveries (other solar systems) has literally forced some astronomers to admit that the systems they are finding, which are populated with "Super-Earths" and "Hot Jupiters", are very strange, and not at all what they expected to find, given our own solar system. Consider Tau Ceti has habitable planet, just 12 light years away.

One of the closest stars to our own, Tau Ceti, appears to have five planets, including one that's in the so-called habitable zone and could be suitable for life.

Not only is Tau Ceti a near neighbor, at 12 light years away, it has the same spectral classification as our sun. Previously, the nearest planet believed to be capable of supporting life — found just last month  — was 42 light years away.

The new-found planets are estimated to have masses between two and six times the mass of the Earth, making this the lowest-mass planetary system yet detected.

The planet that lies in its habitable zone has a mass around five times that of Earth, making it the smallest planet found in the habitable zone of any sun-like star.

OK, here's the money quote.

"This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets," says Steve Vogt, a professor of astronomy and astrophysics at UC Santa Cruz.

"We are now beginning to understand that nature seems to overwhelmingly prefer systems that have multiple planets with orbits of less than 100 days. This is quite unlike our own solar system, where there is nothing with an orbit inside that of Mercury.

So our solar system is, in some sense, a bit of a freak and not the most typical kind of system that Nature cooks up"

The international team made the discovery using a new method that, they say, can detect signals half the size previously thought possible.

"We pioneered new data modeling techniques by adding artificial signals to the data and testing our recovery of the signals with a variety of different approaches," says first author Mikko Tuomi of the University of Hertfordshire.

"This significantly improved our noise modeling techniques and increased our ability to find low-mass planets."

While over 800 exoplanets have been discovered so far, most couldn't possibly host Earthlike life, and most are at very great distances. Discovering planets — and particularly one that might be suitable for life — so close to home will open up a vast range of new research possibilities.

Is our solar system unique? Or are solar systems like ours quite rare? If so, we might conclude once again that we humans "got lucky" in yet another important respect. But it is too early to provide definitive answers to these questions. As the Tau Ceti article implies, what we can observe is heavily constrained by the technology we are able to bring to bear. Mikko Tuomi notes that we "have increased our ability to find low-mass planets." "Super-Earths," which are thought to be rocky planets, have a mass several times that of our Earth.

But as we wait for better observational techniques and better data to settle these questions, it remains true that of the 800 exoplanets discovered so far, most couldn't possibly host Earth-like life. It's a pity that we self-absorbed humans have so little appreciation of our perhaps rare, privileged (and perhaps unique) place in our galaxy and the observable Universe.

Comments

[John Ennis]

I don't know guy, the idea that we are alone just is not one that I prefer.

Though I do remember a science fiction story once that was premised on the a scientific mission going to the last unexplored solar system and finding it empty. I still remember how that movie depressed me.

Naw, I will continue to believe (without proof), because the alternative (again without proof) is just not to my liking. I don't expect the space aliens to save us, but I would like to think that they are there.

[J. Drew]

Earth like planets are rare? No biggie. We can just send a few Internet millionaire "Pioneers" Up there to build a few man made ones once their done putting the finishing touches on their floating cities. They can get the energy they need from harvesting moon-beams and maybe a few solar wind farms.

[Phil]

If we could visit them, they could visit us.

Speculations on Betty Hill's 'star map':

http://www.yaridanjo.warmkessel.com/hilalien.html

Remeber, the universe is stranger than we can imagine.

Merry Christmas!

[Phil]

And, on a similar note, Alpha Centauri in fiction:

http://en.wikipedia.org/wiki/Alpha_Centauri_in_fiction

Phil

[ABSolute Vapors]

What makes people think that we are alone and that earth is a rarety for that is nieve in thinking? Evidence proves otherwise and I don't think there are other planets out there that our just like earth, but we are not the only life forms that exist.