184 Chapter 3 The Universe Was Born With a Big Bang
Outside of the solar system, there are two planetary systems that have stars similar to
our Sun. Tau Ceti, which is approximately 12 light-years away, and Epsilon Eridani, which is
approximately 10.5 light-years away, might have planets with environments similar to Earths.
Radio telescopes are being used to observe these stars on a continual basis, and the Search
for Extra-Terrestrial Intelligence (SETI) Institute, founded by Frank Drake, the creator of the
Drake equation, has projects established in Japan, the United States, and Europe. The day
when space aliens are detected may not be so far away.
NASAs Kepler spacecraft was launched in 2009 with the goal of finding Earth-sized
(and larger) planets in or near what astronomers call the habitable zone. Planets that orbit
their star in the habitable zone are the proper distance away from their star to sustain life on
their surface—that is, these planets are not too hot or too cold. Kepler continually observes
145,000 stars in a specific field of view for periodic changes in a star’s brightness. This dim-
ming indicates that one or more planets have moved in front of the star temporarily.
The Kepler mission announced in February 2011 that its initial data had found 1,235
planet candidates, 68 of them Earth sized. Of the total number of new candidates, 54 of
them were orbiting in the habitable zone, and 5 of those were less than twice the size
of Earth. From these results, mission scientists estimate that there are at least 50 billion
planets in the Milky Way and at least 500 million of those planets orbit their stars in the
habitable zone. Learn more at http://kepler.nasa.gov/.
Can We Contact an Extraterrestrial Civilization?
Let’s consider whether we have a method of contacting an extraterrestrial civilization if we
were to detect one.
If we were able to verify the existence of aliens who had some kind of advanced
civilization, detection would most likely occur via radio waves. Since radio waves for broad-
casts or communications clearly differ from naturally emitted electromagnetic waves, if we
happened to find such radio waves, we could try to contact the civilization producing those
radio waves by sending a message in its direction. However, the problem is that since even
stars in the Cetus or Eridanus constellations are more than 10 light-years away from Earth,
it would take more than 20 years to just exchange simple greetings like “Best wishes!” and
“Nice to meet you!”
More than 10 light-years
Cetus
Constellation
Earth
Best wishes!
Nice to meet you!
This simple exchange would take more than 20 years.

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