Communion Of Dreams

30 billion Earths.

How many Earth-like planets are there in our galaxy? Ones which are reasonably like ours, in terms of size, density, and location relative to their sun’s ‘habitable zone’? That’s one of the basic components of the Drake Equation, and until fairly recently all estimates were little more than speculation.

Enter Kepler:

Expanding our view from Kepler’s corner of the galaxy to show more of the Milky Way, the sky fills with billions of potentially life-bearing worlds. If we showed them all, the sky would be a mass of green. So now the green dots illustrate stars that might host such planets, visible with a good pair of binoculars on a dark night here on Earth.

From this perspective, the chances that we’re alone in the cosmos seem very slim, indeed.

The final answer? 15 – 30 billion Earth-like planets.

Of course, that doesn’t include the rest of the Drake equation values. Such as: what percentage of planets which could potentially develop life actually do so? Then what percentage of those planets develop intelligent, technologically sophisticated life? Then what percentage of such intelligent species develop interstellar communication capabilities? Then how long will such a civilization survive, out of the billions of years of history?

The last time I played with the numbers, the best guess from Phil Plait was that there were some 2.5 billion potentially habitable planets. Kepler indicates that number was too conservative, by something on the order of a factor of 10. Running the rest of the equation is largely just an experiment in gut feelings (since we don’t yet have any real data), but what is impressive is that at each stage as solid data has become available, we’ve had to adjust our “best guesstimate” numbers *upwards*. Meaning that the the total number of technologically sophisticated civilizations capable of interstellar communications out there at this point in time also goes up.

From Chapter 4 of Communion of Dreams:

“But in any event, as Arthur Bailey said this morning ‘where are they?’ Where are the aliens? That’s what’s bothering me.”

Where, indeed? I came up with my own answer, explained in Communion.

But I wonder what the real answer will be.

Jim Downey

Goldilocks and the three exoplanets.

As something of a follow-up to yesterday’s post, news today of the discovery (thanks to the Kepler mission) of three exoplanets which are very good candidates for harboring life. First, their size is within an order of magnitude of Earth’s — and, specifically, less than twice the size of Earth — meaning that they’re not gas giants such as Saturn or Jupiter. Secondly, and at least as importantly, they fall within the “habitable zone” in their star system. That’s the so-called “Goldilocks Zone” where liquid water can exist (it’s not too cold and not too hot).

This is exciting! As it is put in the article:

Two of the three detailed in the new findings in the journal Science are of particular interest: Kepler-62-e and Kepler-62-f. William Borucki, the chief scientist for NASA’s Kepler telescope, says the planets are slightly wider than Earth, but not too big. Kepler-62-e is a bit toasty, like a Hawaiian world and Kepler-62-f is a bit nippy, more Alaskan, Borucki tells the AP.

“This is the first one where I’m thinking, ‘Huh, Kepler-62-f really might have life on it,’ ” said study co-author David Charbonneau of Harvard. “This is a very important barrier that’s been crossed. Why wouldn’t it have life?”

Why, indeed?


Jim Downey

Is there anybody out there?*

From the opening pages of Communion of Dreams:

Jon sat there for a moment, trying to digest what Seth said. According to what pretty much everyone thought, it wasn’t possible. SETI, OSETI, META and BETA had pretty much settled that question for most scientists decades ago, and twenty years of settlement efforts throughout the solar system hadn’t changed anyone’s mind. Even with the Advanced Survey Array out at Titan Prime searching nearby systems for good settlement prospects, there had never been an indication that there was an intelligent, technologically advanced race anywhere within earshot.

It’s one of the very basic questions of space science: are we (sentient beings) unique? Rare? Common? There are a lot of ways to think about it, and here’s a nice piece on NPR discussing some of the relevant parts of the question and what we’re doing about it.  An excerpt:

So, to address the first part of the question we must find out how unique the Earth is. We then should figure out how unique life, and humans, are. Fortunately, thanks to NASA’s Kepler mission, we are making huge progress in the first part of the answer. A key finding is that the majority of stars (around 70 percent) have at least one planet orbiting around them. Based on the data so far (2,740 planet candidates and 115 confirmations), Kepler scientists estimate that some 17 percent of these are Earth-size, meaning with similar mass and rocky composition as the Earth, and possibly close enough to their parent star that water, if present, could be in its liquid state.

More good news arrived on this front earlier this month as NASA authorized the construction of Kepler’s successor, TESS (for Transit Exoplanet Survey Satellite). With launch scheduled for 2017, TESS will survey a much wider area of the sky than Kepler, while focusing mostly on stars that are closer. This way, it will use spectroscopy to resolve at least part of the atmospheric composition of the exoplanets. The goal is to find telling signs of life-related compounds such as ozone, water, carbon dioxide and, if we’re really lucky, even chlorophyll. Successful detection would be very exciting, as it’d point to what optimists expect, a few fairly close Earth-like planets with metabolizing beings.

I hope I live long enough that science is able to make a definitive affirmation of life, then intelligent life, outside our own planet.

Until then, well, there’s science fiction.


Jim Downey

*Seemed appropriate.