Comparison of performances of CoRoT,
Kepler and PLATO
These previous space missions will
leave a strong needfor a further mission aiming at establishing a
complete and unbiased statistical knowledge of exoplanetary systems.
Such is the goal of PLATO.
In particular, in its survey of more than 100,000 stars brighter than mV=11,
PLATO will bring us the essential capability to characterize
completely the stars orbited by the detected planets. This
characterization will involve ground-based follow-up observations, but
also asteroseismic analysis of these stars, using PLATO data. Such
characterization will allow us to measure accurately the radii and
masses of the detected planets, and will provide a reliable estimate of
their ages.This is one of the most important advances of PLATO compared
to CoRoT and Kepler, whose
observing strategies are such that they will find planets mainly around
faint and distant objects, making it very challenging -- if not
impossible -- to study in detail the characteristics of the exoplanet's
host stars. Also, due to the large distances to these stars, there is
no hope for future direct imaging and spectroscopic investigation of
the planets discovered by these missions, whereas PLATO should identify
potential targets for future interferometric and coronographic space-
and ground-based instruments.
Moreover, for this sample of 100,000 stars, similar in size as that of Kepler, PLATO will reach a noise
level at least three times lower than the average level of noise of Kepler, and will therefore allow us
to detect smaller planets in front of cool dwarf stars, or terrestrial
planets in front of hotter and larger stars, thus significantly
extending our knowledge of the statistics of exoplanetary systems.
In addition, PLATO is designed to detect terrestrial planets in the
habitable zone down to about mV = 14, a performance very
similar to that of Kepler.
Due to the larger size of the surveyed field, PLATO will monitor about
400,000 stars down to this magnitude, extending by approximately a
factor of four the sample of detected planetary systems over Kepler.
Also, the seismological observations of the proposed concept will give
us the possibility to study stellar oscillations down to solar-like
level for more than 100,000 stars, of all masses and ages. This is a
considerable step forward compared to currently planned missions: it
represents 1,000 times the stellar sample monitored by CoRoT, about 200
times that planned for the seismology programme of Kepler, and more than five times
the sample that was planned for the
This star sample represents a significant fraction of the targets to be
observed by Gaia/RVS, and for
which PLATO will provide an estimate of their age. The age
determination, missing from the Gaia/RVS
science, will nicely complete the space and velocity-space coordinates
provided by Gaia, and
bring us a full characterization of the surveyed galactic populations.
PLATO, by largely extending the results of CoRoT and Kepler in the area of exoplanet
search and characterization, and in that of stellar structure and
evolution, represents a natural step in our investigation of stellar
and planetary system evolution. Filling and extending the important
place in the European strategy that was left vacant by the cancellation
of Eddington, PLATO will
complete our knowledge of the statistics of extrasolar systems and
stellar evolution. Hence, flying a mission like PLATO after CoRoT, Kepler and Gaia is a requirement for our
understanding of stellar and planetary formation and evolution.
Finally, PLATO observation of bright and nearby stars will make the
well-known problem of false alarms for planetary transit search
techniques less severe. For instance, background eclipsing binaries,
which usually dominate the false alarm problem, will constitute a much
smaller difficulty: an eclipsing binary mimicking a planetary transit
in front of a star with mV = 11 will need to be 100
times brighter than that mimicking a transit with the same depth for a mV
= 16 star, and it can be shown that the probability of false alarm due
to such an event will be 100 times lower.