Milky Way may bear 100 million life-giving planets

June 4, 2014 by Blaine Friedlander
Milky Way may bear 100 million life-giving planets
A new computation method to examine planets orbiting other stars suggests the Milky Way galaxy may house 100 million other places that could support complex life. Credit: Planetary Habitability Laboratory, University of Puerto Rico at Arecibo

( —There are some 100 million other places in the Milky Way galaxy that could support complex life, report a group of university astronomers in the journal Challenges. They have developed a new computation method to examine data from planets orbiting other stars in the universe.

Their study provides the first quantitative estimate of the number of worlds in our galaxy that could harbor life above the microbial level.

"This study does not indicate that complex life exists on that many planets. We're saying that there are planetary conditions that could support it. Origin of life questions are not addressed – only the conditions to support life," according to the paper's authors Alberto Fairén, Cornell research associate; Louis Irwin, University of Texas at El Paso (lead author); Abel Méndez, University of Puerto Rico at Arecibo; and Dirk Schulze-Makuch, Washington State University.

"Complex life doesn't mean intelligent life – though it doesn't rule it out or even animal life – but simply that organisms larger and more complex than microbes could exist in a number of different forms. For example, organisms that form stable food webs like those found in ecosystems on Earth," the researchers explain in an auxiliary statement.

The scientists surveyed more than 1,000 planets and used a formula that considers planet density, temperature, substrate (liquid, solid or gas), chemistry, distance from its central star and age. From this information, they developed and computed the Biological Complexity Index (BCI).

Milky Way may bear 100 million life-giving planets
Credit: Challenges 2014, 5(1), 159-174; doi:10.3390/challe5010159

The BCI calculation revealed that 1 to 2 percent of the planets showed a BCI rating higher than Europa, a moon of Jupiter thought to have a subsurface global ocean that may harbor forms of life. With about 10 billion stars in the Milky Way galaxy, the BCI yields 100 million plausible planets.

Despite the large number of planets that could harbor , the Milky Way is so vast that planets with high BCI values are very far apart, according to the scientists. One of the closest and most promising extrasolar systems, called Gliese 581, has two with the apparent, possible capacity to host complex biospheres. The distance from Earth to Gliese 581 is about 20 light years.

"It seems highly unlikely that we are alone," say the researchers. "We are likely so far away from life at our level of complexity that a meeting with such alien forms might be improbable for the foreseeable future."

The research, "Assessing the Possibility of Biological Complexity on Other Worlds, With an Estimate of the Occurrence of Complex Life in the Milky Way Galaxy," in Challenges, received no external funding.

Explore further: Image: The Milky Way's 100 billion planets

More information: The research paper is available online:

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4.3 / 5 (8) Jun 04, 2014
These number games are pretty pointless until we go out and take a look - and by that time the statistic will be doubley useless.

It IS interesting to look at the distribution of planet makeup, so the study isn't completely worthless. It gives us an indication where it would be most interesting to look first, given limited probe resources.

But currently our kowledge of where life can take a foothold/originate is just based on one data point. Extrapolating from this to the number of potentially life-bearing planets is nonsense.
5 / 5 (3) Jun 04, 2014
Yah, these kinds of stats extrapolations from minimal real data with huge unknowns are astro porn. Fun but unproductive.
Given reasonable advances we may not have to go out very far to take a look. Space based large interferometer telescopes in the later half of this century may give us spectroscopic evidence of active complex biospheres on rocky worlds, subsurface ocean Europa style bodies excepted. Then there's the 22nd century possibility of going out hundreds of AU and using the solar focal point for direct imaging over hundreds of LY.
1 / 5 (1) Jun 04, 2014
Wait, 10 billions stars in the Milky Way? Of a certain type then? I thought the number was around 300 billion?
2.3 / 5 (3) Jun 04, 2014
And still we don't have definitive proof of ONE habitable planet. Until this this numbers game is just academic.
2.5 / 5 (4) Jun 04, 2014
It is interesting that the estimates keep getting lower and lower over the decades.

I think I remember on an episode of Cosmos Carl Sagan saying there would be probably 50 billion. MSNBC said 8.8 billion last year, and now we're down to 100 million....

Works out to .03% of the stars in the galaxy if my math is correct.
3 / 5 (2) Jun 04, 2014
What is ESI?
4 / 5 (4) Jun 04, 2014
These number games are pretty pointless until we go out and take a look - and by that time the statistic will be doubley useless
But aa how will we know where to look if we dont start doing some meaningful extrapolation now? Of course considering potentials now helps us to learn more about them. And no, we arent 'going out' to take a look any time soon, if ever. And so we must be content with what astronomy we can do from here in the system.

"The final step in is to determine when humanity will have this kind of energy available for these kinds of missions. By extrapolation, Millis calculates that the required energy will not be available until at least the year 2196. "This study found that the first interstellar mission does not appear possible for another 2 centuries," he says."

-Not to mention solving the problems of interstellar dust, gas, and cosmic radiation.
3.7 / 5 (3) Jun 04, 2014
And still we don't have definitive proof of ONE habitable planet. Until this this numbers game is just academic.

I think you mean TWO ;-)
3.7 / 5 (3) Jun 04, 2014
What is ESI?
Earth similarity index
3 / 5 (4) Jun 05, 2014
8.7 million species on this planet and you guys still insist your the only ones in the universe. I think my species is reverting back to monkeys.
3 / 5 (2) Jun 05, 2014
8.7 million species on this planet and you guys still insist your the only ones in the universe. I think my species is reverting back to monkeys.

What does the number of species on this planet have to do with the likelihood that there is life elsewhere in the universe? You realize the two have nothing to do with each other....

Just like the number of coca cola cans in a particular location on this planet (a Wal-mart let's say) has nothing to do with how many are likely to be in a spot in the Gobi desert....

The conditions have to be right.
5 / 5 (3) Jun 05, 2014
8.7 million species on this planet and you guys still insist your the only ones in the universe.

Since they all stem from the same ur-organism - that's not an apt argument.
If a factory churns out a billion units that doesn't tell you how many other factories there are.
not rated yet Jun 08, 2014
I bet 100 million dollars they are wrong.

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