Protoplanetary Disks

An artist impression of a protoplanetary disk in which planet formation is ongoing. Image credit: L. Calçada / ESO.

Disk Evolution with SPICA

The wavelength range of SPICA provides unique access to a large series of gas cooling lines from disks such as HD, H2, CO and water, to the far-IR water ice features and to a series of key dust features tracing the detailed mineralogy of refractory material.

Tracing gas, dust and ice evolution in planetary systems

  • SPICA will uniquely detect both the gas phase and water ice reservoirs in proto-planetary and debris disks.
  • SPICA will provide a direct link to the formation of the small bodies asteroids, comets and Trans Neptunian Objects that make up our own Solar System.
  • SPICA will derive the mineral properties, grain temperatures, and iron content of forming solar systems
  • SPICA will measure the dissipation and photo-evaporation of the gas and constrain the lifetimes of protoplanetary disks.

SPICA will study the mass evolution of the warm gas reservoir during the epoch of planet formation using the unique diagnostic lines of HD and OI in large statistical samples. SPICA’s highest spectral resolution modes will be used to quantify gas disk dispersal processes such as jets, winds and to link this to various disk geometries/structures such as gaps, holes and prominent asymmetries as inventorized by then through ALMA, scattered light imaging and JWST. SPICA will characterize at even later stages of debris disks the composition of the trace amount of gas and link it to its physical origin – left over primordial gas versus comets/asteroids.

Revealing the water trail

  • Hot water vapor up to a few ~1000K
  • Warm water down to 100K
  • Water ice features: crystalline and amorphous
  • Potential to follow water trail to mature planetary systems via ‘comet-water’

SPICA will establish how water – a key element for planet formation, and for the emergence of life – is brought to planets like our own. By observing a wide range of water lines, it will trace the transition from the gaseous to the icy phase – the so-called snow-line. The 40 and 60 μm thermal water ice emission features provide crucial insight into the role and processing of water ice during the planet formation process (crystalline versus amorphous). Given SPICA’s excellent sensitivity such studies can be done for statistically significant samples of objects, and as a results we will transition from discussing single cases to establishing the general trends from planet forming systems and putting this of disk sub-structure as revealed by ALMA. 

From pristine dust to planets

  • SPICA will make the link with our Solar System’s zodiacal emission and distant planet-forming disks and debris disks
  • Determine Fe/Mg ratio in olivine and pyrozene
  • Search for biomarkers like calcite and dolomite

Through broad band far-infrared spectroscopy, mineralogy beyond small micron-sized silicates becomes possible, and we can study the matter of which planets are eventually formed. SPICA will follow the evolution of mineralogy from pristine phases in protoplanetary disks all the way to debris disks and link this to the composition of asteroids in our own Solar System.

Setting the clock for planet formation

  • High sensitivity and resolution of SMI/HR allow for determination of accretion and disk winds from proto-planetary disks and set the lifetime of primordial gas in the disk.

Photoevaporation is a crucial process setting the lifetime of primordial gas in protoplanetary discs. Winds set the clock for planet formation and impact the architecture of planetary systems. SPICA’s SMI/HR, with its unique high spectral resolution access to atomic and molecular wind tracers like [Ne II], [Fe II], H2 and HD, can measure the dissipation and photoevaporation of the gas.

Further Reading