www.harmoni-elt.eu

The Solar System: A new view of planetary systems close to home

The Solar System provides a unique laboratory to study planetary formation, evolution, and ongoing physical processes at a level of detail that cannot be achieved for extrasolar systems. Spatially resolved spectroscopy of planets, moons, asteroids, and comets reveals their surface composition, atmospheric structure, and temporal variability, linking present-day observations to the history of the Solar System.

With its exceptional angular resolution, sensitivity, and integral-field capabilities, HARMONI on the ELT will transform Solar System studies, enabling observations that bridge the gap between in-situ spacecraft measurements and unresolved remote sensing.

Spatially resolved spectroscopy of planetary surfaces

Many Solar System bodies exhibit strong spatial variability in composition and physical state. Understanding these variations requires spectroscopic mapping at high spatial resolution, particularly in the near-infrared where key diagnostic features are present.

HARMONI will enable:

  • Mapping of surface mineralogy and ices on asteroids, dwarf planets, and icy moons
  • Studies of space weathering, impact processes, and surface evolution
  • Investigation of compositional gradients linked to formation and thermal history

At ELT angular resolution, HARMONI will resolve surface features on nearby bodies at spatial scales previously accessible only to spacecraft, extending detailed compositional studies to a much broader range of objects.

Atmospheres of planets and moons

Near-infrared spectroscopy provides access to a rich set of molecular tracers that probe the structure and chemistry of planetary atmospheres.

Using HARMONI, astronomers will:

  • Characterise atmospheric composition and vertical structure of giant planets
  • Study weather patterns, circulation, and temporal variability
  • Investigate tenuous atmospheres and exospheres of moons and small bodies

Integral-field spectroscopy allows simultaneous measurement of spatial and spectral variations, enabling time-resolved studies of dynamic atmospheric processes.

Small bodies: asteroids, comets, and active objects

Small bodies preserve some of the most pristine material from the early Solar System and play a central role in models of planetary formation and volatile delivery.

HARMONI will provide:

  • Spatially resolved spectroscopy of asteroid surfaces, revealing heterogeneity and collisional history
  • Studies of cometary activity, including gas and dust release close to the nucleus
  • Observations of active asteroids and transitional objects, probing the boundary between asteroids and comets

These observations will help constrain the origin of water and organic material in the inner Solar System and provide context for sample-return missions.

Time-variable phenomena and non-sidereal tracking

Many Solar System targets are time-variable and move rapidly on the sky. HARMONI is designed to support non-sidereal tracking, enabling efficient observations of moving targets such as near-Earth objects and comets.

This capability is essential to:

  • Monitor short-timescale variability in atmospheres and comae
  • Respond rapidly to newly discovered objects
  • Track objects during close approaches, when spatial resolution and signal-to-noise are maximised

Such flexibility is critical for Solar System science in the era of large synoptic surveys.

Complementarity with space missions and other facilities

HARMONI observations will be highly complementary to:

  • Spacecraft missions, by providing global context for local measurements
  • JWST, through higher spatial resolution on bright Solar System targets
  • Large survey facilities, by enabling detailed follow-up of newly identified objects

Together, these synergies will place Solar System studies within a broader framework of planetary science, linking local observations to extrasolar planetary systems.

A cornerstone of comparative planetology

By delivering spatially resolved, high-quality spectroscopy of a wide range of Solar System bodies, HARMONI will:

  • Advance our understanding of planetary formation and evolution
  • Provide critical benchmarks for interpreting exoplanet observations
  • Enable comparative studies across planets, moons, and small bodies

Solar System science is therefore a key pillar of HARMONI’s scientific programme, demonstrating the power of ELT-class instrumentation to explore planetary systems both near and far