Abstract
The transit method is presently the most successful planet discovery and
characterization tool at our disposal. Other advanced civilizations would
surely be aware of this technique and appreciate that their home planet's
existence and habitability is essentially broadcast to all stars lying along
their ecliptic plane. We suggest that advanced civilizations could cloak their
presence, or deliberately broadcast it, through controlled laser emission. Such
emission could distort the apparent shape of their transit light curves with
relatively little energy, due to the collimated beam and relatively infrequent
nature of transits. We estimate that humanity could cloak the Earth from
Kepler-like broadband surveys using an optical monochromatic laser array
emitting a peak power of about 30 MW for roughly 10 hours per year. A chromatic
cloak, effective at all wavelengths, is more challenging requiring a large
array of tunable lasers with a total power of approximately 250 MW.
Alternatively, a civilization could cloak only the atmospheric signatures
associated with biological activity on their world, such as oxygen, which is
achievable with a peak laser power of just around 160 kW per transit. Finally,
we suggest that the time of transit for optical SETI is analogous to the
water-hole in radio SETI, providing a clear window in which observers may
expect to communicate. Accordingly, we propose that a civilization may
deliberately broadcast their technological capabilities by distorting their
transit to an artificial shape, which serves as both a SETI beacon and a medium
for data transmission. Such signatures could be readily searched in the
archival data of transit surveys.
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