Planet detection and characterisation

R-SCI-L0-01    PLATO shall detect and characterise hundreds of planets around dwarf and subgiant stars of spectral types from F5 to K7, orbiting at distances up to the stellar habitable zones.
Characterise means to determine the radius, mass, age and orbital parameters of the planet (see requirements below). Habitable zone is defined as the region around a star where liquid water can exist on a planetary surface. The stars that shall be observed to detect and characterise planets with the precision required in this section and section 3.4will constitute the PLATO core sample.

R-SCI-L0-03    PLATO shall provide photometric data for the detection of a planet orbiting a G0V star with an orbital period of one year.
According to the latest estimates from Kopparapu et al. (2013), the habitable zone around a G0V star for a planet of 1 M_Elays between 0.75 and 1.733 au, which corresponds to periods of 0.64 and 2.2 years, respectively. The choice of 1 year is driven by reaching a compromise between the longest periods detectable and the number of stars to be observed during the mission. For later type stars, this is already covered since the orbital period of habitable planets is less than 1 year, down to a few weeks for M dwarf stars.

R-SCI-L0-05    PLATO shall provide photometric data to determine the radius of a planet of the same size as the Earth and orbiting a G0V star of V=10 (goal V=11) with an accuracy better than 3%.

R-SCI-L0-07    PLATO shall provide photometric data to determine the ratio of planetary-to-stellar radius with an accuracy of 2%, for a planet of the same size as the Earth orbiting a G0V star of V=10 (goal V=11).
Typical current uncertainties for radius and mass determinations of small planets are around ±6% and ±20%, respectively, leading to uncertainties of 30 to 50% in mean density. The observational accuracy envisaged for PLATO will reduce the uncertainty in mean density to about 10%.

R-SCI-L0-10    PLATO shall provide photometric data to enable the determination of the stellar ages of the core sample planets defined in R-SCI-L0-01.

R-SCI-L0-12    PLATO shall determine the age of a G0V star of V= 10 (goal V = 11) with an accuracy of 10%.

R-SCI-L0-15    PLATO shall observe stars that are bright enough to allow for a determination through radial velocity measurements of the mass of a terrestrial planet orbiting a G0V star with an accuracy of 10% or better.
“Terrestrial planet” is defined as having R< 2 R_E and M< 10 M_E.
In requirements R-SCI-L0-05, -07, -12, -55 and -57, accuracies are specified for V=10, defining a sample of bright stars for which asteroseismology and the radial velocity follow-up may be carried out comfortably within the current expectations. To improve significantly the science return, however, the goal is set to V=11, which increases by a factor of ~2 the sample of stars and possible planets whose masses, radii and ages can still be accurately determined, although possibly with lower precision.

R-SCI-L0-25    PLATO shall detect planets orbiting at distances up to the star habitable zone in a large sample of dwarf and subgiant stars (> 100,000) of spectral types from F5 to K7. The characterisation of these planets may be possible, but with less accuracy than in the core sample. The aim is to provide enough detections for statistical studies of planetary systems properties.

R-SCi-L0-35    PLATO shall detect terrestrial planets which orbit M dwarf stars at distances that include the star habitable zone.

R-SCI-L0-40    PLATO shall be able to observe between 10 and 50% of the sky to allow for statistical studies of planetary formation under various conditions (e.g. clusters). The PLATO observing strategy and the amount of sky coverage may be subject to modification pending future developments and scientific priorities in the field.

R-SCI-L0-45    PLATO shall detect and characterise terrestrial planets in orbit around very bright (V<8) dwarf and subgiant stars of spectral types from F5 to K7 at distances up to the stellar habitable zones. The characterisation requirements are the same as for the core sample (R-SCI-L0-05, -10, -12, -15). These planets will be the main targets for detailed follow-up and atmospheric spectroscopic characterisation.

 

Stellar science

R-SCI-L0-55    PLATO shall provide photometric data to determine the radius of a G0V star of V=10 (goal V=11) with a precision of 1‒2%.

This requirement is directly derived from R-SCI-L0-05 and R-SCI-L0-07. In order to meet R-SCI-L0-05, and given R-SCI-L0-07, the radius of the star needs to be determined with the precision specified here.

R-SCI-L0-57    PLATO shall provide photometric data to determine the mass of a G0V star of V=10 (goal V=11) with a precision of 15%.

Planet mass uncertainty scales as . Accordingly, the requirement of 10% accuracy for the planet mass imposes 15% accuracy for the mass of the host star.

R-SCI-L0-60    PLATO shall provide photometric data to enable the measurement of frequencies of normal oscillation modes in main-sequence stars with precisions ∼0.1μHz for several mode frequencies below and above the frequency of the mode with the maximum amplitude.

PLATO must be able to measure modes with sufficient precision to allow separating solar-like oscillations.

R-SCI-L0-65    PLATO shall be able to observe between 10 and 50% of the sky to allow for asteroseismology analysis of several thousands of stars at different stages of their evolution and different locations in the sky.

The PLATO observing strategy and the amount of sky coverage may be subject to modification pending future developments and scientific priorities in the field.

R-SCI-L0-67    For asteroseismology measurements, the duration of the observations shall be at least two months.

For the asteroseismic analysis of the target stars, the total monitoring time must be sufficient since it translates directly into a relative precision for the measurement of individual mode frequencies. Based on CoRoT short-runs a duration of ~2 months is considered a minimum for good asteroseismology data. For solar-like stars an absolute precision of 0.2 to 0.1μHz is desirable, which translates into a monitoring time of 5 months for a reasonable SNR of 10 in the power spectrum.

 

References

PLATO – Revealing habitable worlds around solar-like stars
Definition Study Report, ESA-SCI(2017)1, April 2017