SRON_Spectrum_2016

Artist impression van PLATO-missie (illustratie: ESA - C.Carreau).
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Distant planets shed light on earth
SRON Spectrum
Are we alone in the universe? Since the discovery of the first exoplanets
in 1991 astronomers have feverishly been looking for habitable planets
outside of our solar system. About 2000 exoplanets have already been
identified and many thousands more will follow in the coming years.
So you would expect to find a second earth among all those planets.
Or is the earth actually quite unique? Recent
discoveries have revealed that other planetary
systems can be quite different from our solar
system. “The statistics so far indicate that the
most common planet in the universe is two
to three times as big as earth. Interestingly
we do not have such a super earth in our
own solar system,” says Michiel Min, research
leader of the exoplanets group at SRON. So it
could well be the case that our solar system
and the earth are utterly unique. Of course
that would be a considerable setback in the
search for life similar to that on earth.
However, astronomers currently know too
little about exoplanets to give an answer to
that. Of the 2000 planets found we often
know only the period it takes the planet
to revolve around its star. In some cases
astro nomers have an indication about the
size or the mass but that is also not enough
to state how similar they are to earth.
Furthermore, the exoplanets found so far
give a distorted picture. “Some of those
planets have been found by observing
wobbles of the star the planets orbit. However
that phenomenon is only visible in the
case of heavy planets,” says Min. “Other
planets have been found because we saw
them move in front of the star. Using this
method you mainly find planets located
close to the star.”
To resolve the statistical shortcoming more
exoplanets need to be found and character
ised. SRON is therefore collaborating in
two future missions of the European Space
Agency ESA, in which space telescopes will
be used to study exoplanets in detail.
Dips in brightness
The first is the PLATO mission (Planetary
Transits and Oscillations of stars), which will
be launched in 2024. During this mission a
space probe with 34 telescopes onboard will
search in the vicinity of about one million
stars for exoplanets. It will do this by record -
ing so-called transits. These are the regular
dips in the brightness of a star, which can