Detecting and sizing the Earth with PLATO: A feasibility study based on solar data

• Main Authors: Krenn, A. F, Lendl, M, Sulis, S, Deleuil, M, Hofmeister, S. J, Jannsen, N, Fossati, L, De Ridder, J, Seynaeve, D, Jarolim, R, Veronig, A. M
• Format: Journal Article
• Language: English
• Published: 26-10-2024
• Subjects: Physics - Earth and Planetary Astrophysics; Physics - Instrumentation and Methods for Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2410.20077

Context. The PLAnetary Transits and Oscillations of stars (PLATO) mission
will observe the same area of the sky continuously for at least two years in an
effort to detect transit signals of an Earth-like planet orbiting a solar-like
star.
Aims. We aim to study how short-term solar-like variability caused by
oscillations and granulation would affect PLATO's ability to detect and size
Earth if PLATO were to observe the Solar System itself.
Methods. We injected Earth-like transit signals onto real solar data taken by
the Helioseismic and Magnetic Imager (HMI) instrument. We isolated short-term
stellar variability by removing any variability with characteristic timescales
longer than five hours. We then added a noise model for a variety of different
stellar magnitudes computed by PlatoSim assuming an observation by all 24
normal cameras. We first compared four different commonly used treatments of
correlated noise in the time domain. We then tried to recover pairs of transit
signals. Finally, we performed transit fits using realistic priors on planetary
and stellar parameters.
Results. We find that short-term solar-like variability affects the correct
retrieval of Earth-like transit signals in PLATO data. Variability models
accounting for variations with typical timescales at the order of one hour are
sufficient to mitigate these effects. For bright targets (8.5 - 10.5 mag), the
transit signal of an Earth analogue can reliably be detected in PLATO data. For
faint targets the results of transit search algorithms have to be verified by
transit-fitting algorithms to avoid false positive detections being flagged.
For bright targets (V-mag $\leq$ 9.5), the radius of an Earth-like planet
orbiting a solar-like star can be correctly determined at a precision of 3% or
less, assuming that at least two transit events are observed and the
characteristics of the host star are well understood.