Milky Way may bear 100 million life-giving planets

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By Science Daily

 

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).

5 COMMENTS

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

    If Earth is anything to go by, most life in the universe will be at or below the microbial “level”. If cells have been around since about 4,000 million years ago on Earth, and an extremely early time for multicellular life forms to arise was 1,600 million years ago (roughly when genetic studies suggest the eukaryotes divided into their major groups), then about 60% of the history of life on our planet alone contained life that was exclusively microbial. This is before you realize that unicellular microbes still have the biosphere largely in their grip, and multicellular organisms are just interesting offshoots of them.

    This leads to four conclusions: the number of planets containing multicellular life will probably be dwarfed by the number of planets containing unicellular life; the number of planets containing multicellular life will therefore severely underestimate the number of planets with life on them at all; all planets containing life will have a good chunk of their prehistory strongly dominated by the exclusive presence of microbes; and the planets containing multicellular life will still be overwhelmingly dominated by microbes.

    • Or, it could be that earth is the oddity and that the vast majority of other planets life forms evolved into multicellular life much, much sooner. Considering we only have one solid planet’s life history to go on, we really cannot say in concrete terms what the norm really is.

  2. 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).

    Before we comment on these factors, we need to look at the other factors, such a which parts of the galaxy are hostile to life and therefore unlikely to support life bearing planets, or are in no position to support them for long enough for life to evolve.

    Galactic Habitable Zones – http://astro.unl.edu/naap/habitablezones/ghz.html

  3. I’m waiting for the estimate to change wildly by the end of the year. These estimates seem to be getting more sophisticated, but with equally bad assumptions. Someone wake me up when they find something concrete.

    And why are they calling it a biological complexity index? It’s no such thing. This survey doesn’t measure biological complexity, only the likelihood of a series of environmental parameters that are evidently important for life on Earth.

    Besides, there already is some compelling evidence for the presence of life on another planet. Mars may well actually harbour indigenous organisms, as Gilbert Levin, the chief designer of the Labelled Release experiment on the Viking space craft, has argued. NASA doesn’t want to send an equivalent experiment on their current batch of probes because they’re afraid that an ambiguous result would ”hurt their program”. Talk about political priorities.

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