The Holy Grail of Planetary Astronomy: The Search for Earth's Twin

Michio Kaku: One of the big stories of the last two months has been the discovery of the Holy Grail of planetary astronomy.  If you’re a planetary astronomer you’ve been chasing after earth-like twins in outer space and just recently we’ve bagged not one, but two of them, two planets that seem to have earth-like characteristics, though they’re more massive than the planet Earth.  One is Gliese 581g and the other one is Kepler 22b.  Now realize, first of all, that these planets are not gigantic Jupiter-size gas balls made out of lethal hydrogen gas.  They are small rocky planets like the earth and they may even have liquid oceans.  

Now police often say “follow the money” when they’re onto some kind of crime or some kind of big event.  Astronomers, on the other hand, say “follow the water.”  Liquid water is the most precious substance in the universe.  If a planet is too close to the sun, water boils and the oceans will boil off.  If a planet is too far from the sun, water freezes, so you have to be just right in the Goldilocks zone to have liquid oceans.  And why liquid water?  Liquid water is the universal solvent.  It dissolves most chemicals except for certain minerals and oils and it is the mixing bowl out of which the first DNA got off the ground.  That is why we say “follow the water,” and these two planets discovered right in our own backyard, practically, seem to be in the habitable zone of their sun, meaning they could very well have liquid oceans.  

So what’s the next step?  The next step beyond this is to focus in on these planets to discern if we can find out what their atmospheres are like.  Do they have oxygen?  Do they have H2O?  We want to find out the chemical composition of the atmospheres to see whether they’re earth-like.  And then the people involved in SETI that is eavesdropping for radio signals from intelligent life forms, they can zero in their radio telescopes to these planets to see whether or not there are any radio emissions from intelligent beings on these planets.  Realize that the SETI project in some sense so far has been a failure.  They have not picked up a single signal from an intelligent civilization in outer space, but hey, give them a break.  They’ve only scanned about 1,000 stars.  There are in the galaxy 100 billion stars right in our own Milky Way Galaxy, so they have a few billion more stars to go.  

So finding earth-like twins in outer space, either by telescope or by the Kepler Satellite, can really cut down the time necessary to zoom in on planets that have intelligent life forms on them.  Then the other question is, “Well, when can we meet them?”  Not any time soon.  A Saturn rocket traveling at 25,000 miles per hour would probably take a few hundred thousand years to reach the nearby planets.  So in other words, it is out of the question that we can use chemical rockets to reach these planets.  In fact, if we do find radio signals from one of these planets we can’t even make contact with them because if we send a reply back to them it will take 10, 20 years for light to race to these nearby planets and another 10, 20 years for the message to come back because you cannot go faster than the speed of light.

So forget all the Hollywood movies.  You’re not going to be able to have a two-way conversation.  But at night, at night when you look at the stars and you look at the constellations and you wonder “is anyone out there?” just realize that somebody out there could be looking back, looking back at us and wondering “Gee, is there any life on this solar system that we call our home?”  

Dr. Michio Kaku: At night when you look at the stars and you look at the constellations and you wonder "Is anyone out there?" just realize that somebody out there could be looking back at us and wondering "Gee, is there any life on this solar system that we call our home?"

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