A planet that happens to pass in front of its parent star along an observer’s line-of-sight will block a small fraction of the star’s light and cause a dip in the observed brightness of the star. As a result, planets can be detected around a star by precisely monitoring the star’s brightness to search for periodic dips in the star’s brightness that may signal the presence of a planet in orbit around the star. This method of planet detection is known as the transit method and it is used by space telescopes such as Kepler and Corot to search for planets around other stars. It becomes reasonable to consider that the transit method can also be employed to search for artificial planetary-sized objects in orbit around other stars.
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An artificial planetary-sized object can
take on any shape and should produce a transit light curve with a profile that
is different from one produced by a spherical object such as a planet. The
detection of an artificial transit can serve as definite proof for the
existence of an advanced technological civilization. Such a large object can be
constructed by an advanced civilization to communicate its existence or for an
entirely different purpose (e.g. a large collecting surface to harness energy
from its parent star). Artificial transits are an ideal method through which an
advanced civilization is likely to communicate its existence because such an
object is potentially able to last a lot longer than the lifetime of the
civilization itself.
Multiple artificial planetary-sized objects
in transit around a single star may turn out to be much more attention-grabbing
than the transit of a single object. To create multiple transits, the objects
involved do not need to have non-spherical shapes to communicate their
artificial nature. This is because the transit of each object can be
orchestrated in a remarkably regular fashion (e.g. grouped in prime numbers) to
create a series of transits whose artificial nature is obvious. As a result, a
technological civilization that wants to communicate its presence may find it
more appropriate to construct a series of smaller spherical objects than a
single large non-spherical object.
In October 2012, astronomer Geoff Marcy
was awarded a grant to search through data collected from the Kepler space telescope
with the aim of finding possible signatures of megastructures created by
advanced technological civilizations. This fits well with what astronomer Jill
Tarter mentioned in a paper published in 2001: “An advanced technology trying
to attract the attention of an emerging technology, such as we are, might do so
by producing signals that will be detected within the course of normal
astronomical explorations of the cosmos. Sooner or later the emerging
technology will build the proper instruments to observe their surroundings and
capture the signal.”
References:
1. Arnold L. (2005), “Transit
Light-Curve Signatures of Artificial Objects”, Astrophysical Journal, 627:534-539
2. Jill Tarter, “The Search for
Extraterrestrial Intelligence (SETI)”, Annual Review of Astronomy and
Astrophysics, Vol. 39: 511-548 (September 2001)