Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff,
Speaker 1: Christian Sager Here. The Milky Way is thought to hold
Speaker 1: at least a hundred billion planets. About seventeen billion of
Speaker 1: those are roughly the size of Earth. And check this out.
Speaker 1: One in every six of our galaxy stars have planets
Speaker 1: revolving around them. As far as confirmed planets go, though,
Speaker 1: as of this recording, NASA has confirmed nine hundred and
Speaker 1: sixty two of those one hundred billion planets. We used
Speaker 1: to think that they were rare, but since we launched
Speaker 1: the Kepler Space Telescope, we're finding more planets every day,
Speaker 1: especially ones with water on them. And what we've also
Speaker 1: learned is that these planets don't need to be as
Speaker 1: perfect as we once thought to sustain life here at home.
Speaker 1: We've learned that life is a lot hardier and exists
Speaker 1: in some extremely hard environments. All of this adds up
Speaker 1: to a lot more evidence that we aren't alone in
Speaker 1: the galaxy. While Earth is still the only planet that's
Speaker 1: proven to support life, we're actively searching for other worlds
Speaker 1: to join us. But to do that, first, we have
Speaker 1: to define what life actually means. And not everyone agrees
Speaker 1: on this topic, but let's try this one out. Life
Speaker 1: requires an organized cellular structure that functions in a relatively
Speaker 1: unchanging state. It's capable of reproduction, growing, taking in energy
Speaker 1: from its environment, and responding to stimuli, and it can
Speaker 1: adapt to the environment it lives in. Okay, and per
Speaker 1: Darwinian evolution, we know that similar organisms produce similar organisms,
Speaker 1: so for instance, a dog reproduces another dog, not a dandelion.
Speaker 1: And while there's variation from one generation to the next,
Speaker 1: some are more favorable than there's, leading to natural selection,
Speaker 1: which leads us to how tough we've discovered life can
Speaker 1: survive to be. Until around thirty years ago, we thought
Speaker 1: all life on Earth needed energy from the sun and
Speaker 1: couldn't survive in extreme temperatures. But we were so wrong.
Speaker 1: When we explored hydrothermal vents on the ocean floor, we
Speaker 1: discovered clams, crabs, and giant tube worms. The latter survived
Speaker 1: through bacteria in their tissue that helped them derive energy
Speaker 1: from the water, subsequently feeding the other animals. What this
Speaker 1: potentially means is that life could exist in similar extreme
Speaker 1: environments on other planets or moons. In other words, big
Speaker 1: things have small beginnings. Now we're taking a huge leap
Speaker 1: in the likelihood of alien life, and while people like
Speaker 1: Frank Drake and Carl Sagan have speculated how many civilizations
Speaker 1: could evolve out there, we still don't know the basics
Speaker 1: of what extraterrestrials require to exist. Yes, we can work
Speaker 1: from variable traits were familiar with from natural selection, but
Speaker 1: would they be bilaterally symmetrical like humans or more like
Speaker 1: bacteria or viruses. Scientists in the field of astrobiology have
Speaker 1: drawn a few guidelines to how aliens might work. They'd
Speaker 1: be governed by the laws of physics and chemistry. Their
Speaker 1: bodies would also require solvency, temperature, pressure, and energy. In addition,
Speaker 1: they would probably be comprised of complex molecules, including informational
Speaker 1: molecules like DNA that carry their genetic information. So, armed
Speaker 1: with these assumptions about alien biology, to next find alien life,
Speaker 1: we've got to go planet hunting. Traditionally, we've looked for
Speaker 1: something like Earth, rocky, watery, and orbiting a star and
Speaker 1: what is called the gold Delock zone because it's not
Speaker 1: too hot and it's not too cold. It's got to
Speaker 1: be just right. But we've discovered three things about planets
Speaker 1: that make it much more likely that there's life out there. First,
Speaker 1: of all, water is not as rare as we thought.
Speaker 1: Take Mars, for example, scientists found water there inn or
Speaker 1: Jupiter's moon. Europa it's a freezing atmosphere, less mess bombarded
Speaker 1: by radiation. But we also think it has a deep
Speaker 1: ocean under its icy exterior that could have hydrothermal vents
Speaker 1: similar to the ones on Earth, spewing chemicals and nurturing
Speaker 1: strange marine life. If we stick with the assumption that
Speaker 1: water is essential to life, then the necessary materials are
Speaker 1: all over the galaxy, and Europa could also prove the
Speaker 1: second thing we know about the possibility of planetary life
Speaker 1: that life is way more flexible than we originally thought.
Speaker 1: We found strains of bacteria surviving under miles of ice
Speaker 1: in Antarctica for thousands of years. Could similar microbes be
Speaker 1: on Europa or somewhere outside our solar system. If that's
Speaker 1: the case, then do we discard the notion of that
Speaker 1: Goldilocks habitable zone near the Sun. And the third thing
Speaker 1: we now know about planets is what we said at
Speaker 1: the top of the episode. There are billions of them.
Speaker 1: By measuring the light coming from each star and then
Speaker 1: waiting for it to temporarily dim, we pose it that
Speaker 1: there's a planet there eclipsing the star's view. Now, how
Speaker 1: do we see this? Well? With the Kepler Telescope spacecraft
Speaker 1: launched in two thousand nine, Kepler orbits our Sun using
Speaker 1: a photometer light meter to monitor more than a hundred
Speaker 1: and fifty thousand stars, looking for any changes in their
Speaker 1: brightness to identify an eclipse. That's where we get the
Speaker 1: potential number of seventeen billion planets from Scientists then compare
Speaker 1: Kepler's findings with spectroscopic data from ground based observatories to
Speaker 1: confirm planetary candidates. And soon there will be two new
Speaker 1: space instruments to bolster Kepler's findings. The Transiting Exoplanet Survey
Speaker 1: Satellite or TESTS will launch in scanning for nearby exoplanets,
Speaker 1: and the James Web Telescope, scheduled to launch in eighteen,
Speaker 1: is so powerful it could analyze these planets atmospheres for
Speaker 1: signs of life. Kepler's already discovered several planets with inhabitable
Speaker 1: Goldilocks zones, but they're not at all like Earth. Instead
Speaker 1: of water and rocks, they seem to be small cores
Speaker 1: surrounded by atmospheres of hydrogen and helium, which doesn't sound
Speaker 1: life supporting at all. But don't forget there are still
Speaker 1: several ways life could exist on planets we used to
Speaker 1: consider inhabitable. There could be life deep under a planets subsurface,
Speaker 1: like the bacteria in Antarctica or the nematode worms discovered
Speaker 1: three point six kilometers below South Africa's deepest gold wine.
Speaker 1: Or what if a planet had shifting habitable zones attributing
Speaker 1: to a wobbling planet. Moving clouds could reflect radiation back
Speaker 1: into space, or temperatures could rise and fall dramatically, but
Speaker 1: at certain latitudes heat would dissipate, allowing for liquid water
Speaker 1: to resist boiling. It's hard to know if photosynthetic life
Speaker 1: could survive such drastic changes, but maybe it's possible. I mean,
Speaker 1: then diesel survived on such a planet in the Chronicles
Speaker 1: of Riddicks, so you know, I'd say anything's possible. Even
Speaker 1: moons orbiting exoplanets could be habitable if they were large
Speaker 1: enough to hold onto an atmosphere. For instance, even if
Speaker 1: a planet within a habitable zone didn't have the right
Speaker 1: composition for life, its moon might have rocky, watery settings
Speaker 1: like Earth kind of like end or in the Return
Speaker 1: of the Jetta, you know, the one with the Ewoks.
Speaker 1: As we've seen, the previously established rules for life sustaining
Speaker 1: planets are diminishing as we gather more and more information
Speaker 1: about the universe. However, this brings up the Fermi paradox,
Speaker 1: established by Enrico Fermi in nineteen fifty. If alien life
Speaker 1: or even civilizations exist in the Milky Way Galaxy, why
Speaker 1: haven't we detected them yet? Check out the Brainstuff channel
Speaker 1: on YouTube, and for more on this and thousands of
Speaker 1: other topics, visit how stuff works dot com.