Extrasolar Moons as Gravitational Microlenses Christine Liebig

Chapter 1
Introduction
Astronomy, and in particular the search for planets outside our solar system, begins
to touch what has long been a question reserved for philosophers to ponder about:
Do other worlds exist?
After centuries of speculation and research, it was less than two decades ago
when it was confirmed for the first time that planets exist in the universe that circle
stars other than our sun. By now hundreds have been detected with five different
techniques that are described in the overview below. For all we know, none of
these extrasolar planets offer physical conditions permitting any form of life. But
the search for planets potentially harbouring life and the search for indicators of
habitability is ongoing. One of these indicators might be the presence of a large
natural satellite – a moon – which stabilises the rotation axis of the planet and
thereby the surface climate.
This work sets out to simulate and evaluate the success rate of one of the most
promising techniques for detecting extrasolar moons. This technique is gravitational
lensing. The deflection of light by massive bodies is a consequence of the theory of
general relativity and has been experimentally verified since 1919. It is now the
basis for diverse areas of research in astronomy, because of its ability to work as a
magnifying glass to make distant or small objects visible that could not be detected
otherwise. Even small-mass objects like planets can leave a detectable mark in
Galactic gravitational lensing events. While a lensing star passing in front of a
background source star can be detected as a transient brightening of the source,
the gravitational influence of a planet in orbit around the star can be detected as
an irregularity in this brightening. The method is sensitive to masses as low as an
Earth mass. From theoretical works about planet formation we know that massive
moons can exist in stable orbits around giant planets. Therefore it is promising to
apply the technique of gravitational lensing to the search for extrasolar moons.
Overview of different methods for finding extrasolar planets. . .
The following list provides a brief overview of the various techniques that have
successfully discovered extrasolar planets in the last years, with a reference to the
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