Page 28-29 - Magazine 136/137

The rate of discoveries is increasing. Even though news of
the detection of an extrasolar planet is far from being a sensa-
tion these days, it still enthuses planetary researchers. What can
such planets tell us? How did the Solar System evolve? How
different or similar are these planetary systems to our own?
Such questions are the concern of Head of the Extrasolar Planets
and Atmospheres Department at the DLR Institute of Planetary
Research Heike Rauer and her team.
In their quest, the scientists employ the transit method.
The principle is relatively straightforward – when an extrasolar
planet passes between its star and the observer, the perceived
brightness of the star diminishes. This effect can be thought of
as a kind of mini-solar eclipse. Transits within the Solar System,
like that of Venus on 6 June 2012, are more easily observed
from Earth because of their proximity. But observing the transit
of an exoplanet is much more challenging due to its distance
from Earth. The transit can only be inferred by measuring the
light curves of the host stars. Rauer’s team is investigating
precisely this – looking at more than 170,000 stars.
Rocky planet or gas giant?
While the detection of extrasolar planets is an endeavour
in itself, the real power of transit light curve analysis lies in the
wealth of information they provide about both the planet and
star. For example, they can give an indication of the size of the
planet. By measuring the decrease in the measured brightness
of a star as a planet transits its disk, it is possible to determine
the planet’s size relative to the star. The amount of starlight
blocked by the planet is proportional to its cross-sectional area.
As of 31 January 2013, 862 extrasolar planets have been discovered. In a circular polar orbit at an altitude of approximately
900 kilometres, CoRoT (Convection, Rotation and planetary Transits) has been searching for planets orbiting other stars.
The CoRoT space telescope has been in orbit since 2006, and has found 28 new planets using the transit method. The num-
ber of discoveries, however, is not the primary focus for the scientists in Berlin. Rather, it is the fascination of finding out
more about these distant worlds. Here, a key parameter is the planetary density.
Wanted – habitable, extrasolar planet
By Melanie-Konstanze Wiese
Finding Goldilocks zones
The CoRoT satellite
CoRoT is an astronomical satellite that measures
variations in the brightness of stars at optical
wavelengths. CoRoT was launched into its polar orbit
from the Baikonur Cosmodrome by a Russian Soyuz-
Fregat rocket on 27 December 2006. The CoRoT space
mission is operated by the French space agency CNES
with the participation of Austria, Belgium, Germany,
Spain, Brazil and the European Space Agency.
Researchers are on the lookout for planets within their star‘s Goldilocks
zone – not too cold and not too hot.
Planetary Research | DLR maGazıne 136 · 137 | 29