Direct imaging of molten protoplanets in nearby young stellar associations

Abstract

During their formation and early evolution, rocky planets undergo multiple global melting events due to accretionary collisions with other protoplanets. The detection and characterization of their post-collision afterglows (magma oceans) can yield important clues about the origin and evolution of the solar and extrasolar planet population. Here, we quantitatively assess the observational prospects to detect the radiative signature of forming planets covered by such collision-induced magma oceans in nearby young stellar associations with future direct imaging facilities. We have compared performance estimates for near-and mid-infrared instruments to be installed at ESO's Extremely Large Telescope (ELT), and a potential space-based mission called Large Interferometer for Exoplanets (LIFE). We modelled the frequency and timing of energetic collisions using N-body models of planet formation for different stellar types, and determine the cooling of the resulting magma oceans with an insulating atmosphere. We find that the probability of detecting at least one magma ocean planet depends on the observing duration and the distribution of atmospheric properties among rocky protoplanets. However, the prospects for detection significantly increase for young and close stellar targets, which show the highest frequencies of giant impacts. For intensive reconnaissance with a K band (2.2 µm) ELT filter or a 5.6 µm LIFE filter, the β Pictoris, Columba, TW Hydrae, and Tucana-Horologium associations represent promising candidates for detecting a molten protoplanet. Our results motivate the exploration of magma ocean planets using the ELT and underline the importance of space-based direct imaging facilities to investigate and characterize planet formation and evolution in the solar vicinity. Direct imaging of magma oceans will advance our understanding of the early interior, surface and atmospheric properties of terrestrial worlds.

Linking the evolution of terrestrial interiors and an early outgassed atmosphere to astrophysical observations

“…Magma oceans have also garnered interest from the perspective of observing planet formation in process, notably the giant impact stage, which may be amiable to direct detection using the next generation of ground-based facilities (Miller-Ricci et al 2009;Lupu et al 2014;Bonati et al 2019). The planet may emit strongly in the infra-red and have an outgassing atmosphere that is preferable for atmospheric characterisation.…”

Evolution and Spectral Response of a Steam Atmosphere for Early Earth with a Coupled Climate–Interior Model

“…β Pictoris having an age of 23 Myr) leading to the formation of MOs have a higher probability for detection of magma oceans. For a steam atmosphere, only a few planets with a flux density of the order 10 −2 − 10 −3 (µ Jy) would be detectable in the β Pictoris stellar association with an observation time of 50 hrs with E-ELT through direct imaging (Bonati et al 2019). The PLATO 3 mission, on the other hand will provide accurate ages to a precision of 10% and radii to a precision of 2% for a large sample of planetary systems (Rauer et al 2014) which will lead to better characterization of young magma ocean planets.…”

Exoplanet Detection and Its Dependence on Stochastic Sampling of the Stellar Initial Mass Function

“…In this section we describe our Monte Carlo simulations to sample from the stellar initial mass function (IMF) and the procedure to calculate the probability of detecting magma ocean planets in nearby young moving groups (YMGs) following Bonati et al (2019).…”

“…Future telescopes and instrumentation may even be able to detect the formation signatures of terrestrial planets. For example, Bonati et al (2019) recently calculated the probability of detecting magma ocean planets in nearby YMGs with the Extremely Large Telescope (ELT). Magma ocean planets are forming protoplanets with a molten surface, caused by collisions with planetessimals in the protoplanetary disk (e.g., Benz & Cameron 1990;Tonks & Melosh 1993;Canup & Asphaug 2001;Nakajima & Stevenson 2015;Nakajima et al 2020), and hence directly trace terrestrial planet formation.…”

“…In this paper, we determine whether stochastic sampling of the IMF can explain the observed deficit of low-mass M-stars in some nearby YMGs, and then use the calculations in Bonati et al (2019) to determine the probability of detecting magma ocean planets in these YMGs based on updated observational membership data. We then calculate the range of possible magma ocean detection probabilities assuming a stochastically sampled IMF, for hypothetical YMGs at similar distances to those observed.…”