New study: the Milky Way contains at least 100 billion planets.

A new study puts the number of planets in our galaxy at at least 100 billion – and this is a conservative calculation.

The Milky Way contains at least 100 billion planets, or enough to have one for each of its stars, and many of them are likely to be capable of supporting conditions favorable to life, according to a new estimate from scientists at the California Institute of Technology in Pasadena, California (Caltech).

That specific figure of 100 billion planets has been suggested by earlier, separate studies, but the new analysis corroborates the earlier numbers and may even add to them, as it was conducted on a single star system — Kepler 32 — which contains five planets and is located some 1,000 light years away from Earth in between the patch of sky found between the constellations Cygnus and Lyra, where NASA’s planet-hunting Kepler Space Telescope is pointed.

In fact, the new star census estimate, which came after scientists verified three of the five planets around the star Kepler 32, is strictly conservative, according to the Caltech astronomers who developed it after studying the Kepler 32 system.

“There’s room for these numbers to really grow,” said Jonathan Swift, a Caltech astronomer who is the lead author on a paper on the new findings, in a phone interview with TPM. “They’re not going to shrink. Our calculation is new in the sense that we are making the calculation of planets in compact systems around the most populous type of stars in the galaxy.”

This should be taped to the forehead of every Christian who, in defense of god, talks about how incredibly improbable it would be for a planet to wind up inside a star’s habitable zone.  For one, that zone is not as small as they think.  In the 1990s, James Kasting determined the limits of the habitable zone for a Sun-like main-sequence star (the zone that would remain habitable for the first 4.6 billion years of the star’s main-sequence lifetime).  The boundary closest to the Sun is where liquid water would be broken down to hydrogen and oxygen by photolysis.  Get closer than that to the Sun and you get no life as we know it (this is an important distinction, as life as we do not know it may exist).  The inside boundary is at .95 AU (or about 4,650,000 miles closer to the Sun).

Kasting gave two different figures for the outer boundary of a Sun-like star’s habitable zone.  One gives the point at which carbon dioxide starts to condense out of the atmosphere.  That occurs at 1.37 AU.  The other boundary point is where there could still be enough water vapor and carbon dioxide in the atmosphere to make an Earth-like planet habitable by means of the greenhouse effect.  That boundary stretches out to 1.67 AU, or to the aphelion of Mars’ orbit, 62,310,000 miles toward the backside of Earth.

This amounts to a habitable zone 66,960,000 miles wide.  But even that huge-ass zone is not set in celestial stone, as there are exceptions for celestial bodies like Europa, which could contain liquid water beneath an icy surface.

But those figures are just for one star, and that star is not even the type most-likely to house life.  That honor, in our galaxy, belongs to red dwarfs.

Red dwarfs like Kepler 32 are thought to make up about 75 percent of the total stars in the entire galaxy, but can’t be seen by the naked eye here on Earth or most telescopes because they are so faint.

“You can think of them as the ‘Silent Majority’ of the galaxy,” said John Johnson, an assistant professor of astronomy at Caltech who also participated in the study and was a co-author on the paper.

Red dwarfs are cooler, less massive, and less luminous stars than our own Sun. The specific star Swift looked at, Kepler 32, is about half the mass and half the radius of the Sun.

But that turns out to be a bonus when it comes to the capacity for Kepler 32 and other red dwarf systems to have conditions favorable to life. Because the stars are so much smaller and cooler than the Sun, the habitable zone — the area where any orbiting planets have surface temperatures amenable to liquid water — is much closer than in our own Solar System.

“The outermost planet in the Kepler 32 system is just a tenth distance Earth to our Sun,” noted Swift. “But it could still be amenable to liquid water because it is just inside edge of habitable zone.”

100 billion stars in our galaxy, and at least that many planets.  To find a planet in a habitable zone, it turns out, is not rare at all.  In terms of probability, there is all-but-certainly gaggles of planets in habitable zones in our galaxy alone, and then there are trillions of other galaxies out there.  It does not take divine influence to plop a planet into a habitable zone.  In fact, in a universe without a god that also bears life, this is precisely what we’d expect to see: a very big universe with lots of opportunities for life to arise naturally, and a very old universe with lots of time for it to take place.

Compare that to a universe we’d expect with a god, who could make one special planet without all the superfluous immensity of the cosmos; or who could snap life into existence in a blink, rather than allowing it to develop naturally over billions of years of pain and suffering (with all the garnishing of cancer, predators, and other suffering god designed).  Humans look precisely as we’d expect us to look in a godless universe: a tiny blip, our strife, happiness, and even our existence as significant to the universe as any random, floating piece of debris.  The wonder of it is that the universe does not give us significance, but from our tiny rock in the cosmic ocean, we give significance to the universe.  It is we who care about life, beauty, and other humans, even if the universe doesn’t.  At least we do until the religions we conceive tell us which humans to hate, which sufferings are deemed righteous by god, and what art to keep from the eyes of those who find it beautiful.

I am so very grateful to scientists for giving us a real picture of the universe.  I equally loathe religions for slowing the process, and for insisting that they can achieve equal or greater revelations about the nature of the universe without hard work, introspection, or experiments, but by insisting that god told them things he then hid from our telescopes.

  • invivoMark

    Actually, I gotta burst yer bubble here, sorry.

    Those planets are generally not suitable for life, even within the “habitable zone”, because they will generally not accumulate enough volatiles (which includes water). Linky: http://iopscience.iop.org/1538-4357/660/2/L149/fulltext/21115.text.html

    It isn’t impossible for life to form on a planet orbiting an M dwarf, as the paper I linked explains. But due to the expected extremely low accumulation of volatiles, we’re still a lot more likely to find life on a planet orbiting a star much more similar to ours.

    There’s still almost certainly tons of life out there, but this new study probably shouldn’t significantly affect our estimate of how much.

    • LeftWingFox

      Two other possibilities in the other direction:

      One is that habitable zones might also include moons of gas giants, which we now consider possible on Europa and Enceladus.

      The second is that we don’t know if there are alternative chemistries that can create biochemical reactions recognizable otherwise as being life, (hydrocarbon-based life perhaps?) which might evolve in other favourable environments.

      • invivoMark

        True on both counts.

        However, my spidey sense tells me that both of the above are unlikely. Water-based systems just work for living organisms, for a lot of reasons (spontaneous creation of lipid membranes, a water is a chemically useful solvent for redox, etc.), whereas other solvents don’t have those benefits. And planet size, as well as location in a stellar system, makes a big difference in how much water can accumulate.

        I wouldn’t say either scenario is impossible, but I will say that I think it’s likely that most life in the universe exists around Earth-like planets orbiting sun-like stars.

  • advent-gred

    the universe can be meaningful to ourselves, but I don’t quite think that gives the universe meaning. maybe just the wording sounds to me like you are saying that if the universe were sentient, it would be glad we made it’s existence meaningful lol.

    • invivoMark

      Universe don’t give a shit! (I want that on a t-shirt.)

      • Artor

        Universe just takes what it wants!

  • Volizden

    You should clarify something JT

    “Kasting gave two different figures for the outer boundary of a Sun-like star’s habitable zone (OR A G-Type Star). One gives the point at which carbon dioxide starts to condense out of the atmosphere. That occurs at 1.37 AU (again this is for a G-Type Star Like ours).”


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