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Friday, February 24, 2017

SETI: Part 2: How Many ExoPlanets Are There Out There?

The Search for Extraterrestrial Intelligence (SETI) is a field with which I have been associated for nearly half a century.  Back in those days we had not confirmed another planet outside our solar system.  Part 1 came last week.

The next few postings will further review the history, status and future of this challenge.  I'll even speculate on what an ET might look like, and it, assuredly, will not take the form to the left.

How rational is it for Humanity to establish colonies on Mars over the next decade, as proposed by Elon Musk?  What about flying saucers?  One-third of Americans think they are real.  Considering all our spending priorities, how much of your tax dollars should be applied to major space projects?

There recently has been a swarm of articles touting to have found the next Planet Earth.  One group using the Spitzer Space Telescope, found seven potential candidates only 40 light years (LY) away.  Remember, though, that the closest star, Proxima Centauri, one of the three in the Alpha Centauri system, is 4.25 LYs away:
  • Light takes 4.25 years to get there from here.
  • Voyager is tooling along at 38,000 miles/hour, and if headed that way, would take 76,000 years to reach Proxima Centauri.
  • How big is our Milky Way Galaxy?  Light would take 100,000 years from one end to the other.
  • Space is very large, and our technology to survive outer space for any length of time is rudimentary.
As we'll learn, these announcements are based on good science, with a lot of creative word smithing.  But first, some early history.

Indian astronomer Aryabhata 1500 years ago visualized heliiocentricism (Earth revolves around the Sun), Dominican Monk Giordano Bruno, was burnt at the stake in 1600 for suggesting that there were an infinite number of suns with inhabited planets.

Frank Drake of Cornell in 1960 actually searched for extraterrestrial signals from Tau Ceti and Epsilon Eridani...  He failed to find anything.

Then, along came Carl Sagan, who was denied tenure at Harvard in 1968 and was at Cal-Berkely when I was attending school at Stanford.  Sagan joined Drake at Cornell and remained on the faculty until his death in 1996, already more than two decades ago.  I had several interactions with him, including assisting in initial funding for SETI.

Official U.S. government interest in SETI began in the early '70s when the Ames Research Center suggested searching the Water Hole.  Frankly, this is where all went wrong, for the focus since then has largely remained in the microwave region of the spectrum, limiting the information gathering potential of optical laser frequencies searches.

I had an office at Ames close to the secret Blackbird (the black  one below--although normally kept well hidden), which was easily accessible to anyone who wanted to take a look.  I went up and touched it.


  • At a distance of ten light years, a Jupiter-size planet cannot be seen revolving around a Sun-size star.
  • That is because the star is so much brighter, from 5-10 magnitudes, or, at best, the planet is 1/100,000 as bright.
  • However, if the extrasolar planet had an atmosphere, the starlight would cause lasing of the gases, resulting in spikes of discrete frequencies which could be detected and tracked.
  • That was the theory suggested by Nobel Laureate Charles Townes, who I went to see at Cal-Berkeley in 1976 when I worked at Ames.
  • Knowing the colors of the various monochromatic light  sources, you would then be able to determine the atmospheric content.
  • The result was the Planetary Abstracting Trinterferometer (or PAT), where my proposal on the cover quoted Miguel de Cervantes:  
          To Man, the Don Quixote of the universe
          May be succeed in his impossible dream

The problem was that NASA eliminated optical  searches with a limited budget and turned down this pathway.  As a result, all the found exo-Earths are determined by the wobble of the star or the diminution of light across the face of the star when the planet passes across.  Chapter 4 of SIMPLE SOLUTIONS for Humanity was for good reason entitled:  SEEKING THE LIGHT--SETI.

The European CoRoT space observatory (now out of commission) and American Hubble, Spitzer and Kepler Space Telescopes have found most of the exoplanets.  Hubble went up in 1990 and seems still to be working.  Kepler flew in 2009, ran into problems in 2013, but, apparently has been fixed and is supposedly again functioning.

As of Wednesday, scientists have confirmed 3,583 exoplanets in 2,688 planetary systems.  These numbers keep changing, getting higher and higher, but there are probably 200 billion planets in our Milky Way.  Except that this article says the number should be closer to ten trillion planets, just in our galaxy.  Further, as there are at least 200 billion galaxies out there (and probably many more), one estimate is that there are 10 to the 24th power, that is, the number 1 followed by 24 zeros, planets in our Universe.

But SETI is all about detecting signals from outer space, so at least one of those septillion planets had to have evolved into an intelligent civilization.  But they have had a 10 billion-year head start, so the chances got to be good.

Part 3 will take a closer look at the wisdom of interplanetary travel.

The Dow Jones Industrial Average edged up 11 more points to 20,822, the 11th consecutive record-setting day.

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