Astronomers will use the ELT to study the physical properties of asteroids, comets, and trans-Neptunian objects (TNOs) to characterise their nature and origin and refine the details of how the Solar System formed. This includes:

• Creating maps of the surfaces of large asteroids with a resolution of several kilometres, providing topography, chemical composition and geological information. 
• Determining the rotational periods, sizes, shapes and chemical compositions of medium-sized asteroids in the main Asteroid Belt. 
• Analysing the surface composition and outgassing processes for active asteroids in the Asteroid Belt, as well as determining the proportion of volatile elements, observing degassing processes, and even looking for the presence of atmospheres. 
• Studying the spatial distribution of chemical elements in the comas and tails of comets, looking at how these change with cometary activity, and monitoring jet activity, jet structure and fragmentation processes. 
• Measuring the dimensions, masses and densities of binary TNOs and Centaurs — objects that are similar to asteroids in size but to comets in chemical composition — as well as determining their thermal properties and the presence of volatiles and atmospheres. The largest of these objects can be spatially resolved using the ELT, and long-term spectroscopic monitoring will provide information on their surface evolution.  
• Searching and discovering moons and rings around all types of small bodies; over 400 asteroids and TNOs are known to host satellites, and rings have been detected around two of them, Chariklo (a Centaur object) and Haumea (a dwarf planet).  
• Long-term monitoring of Pluto and other dwarf planets to explore the evolution of atmospheres, temperatures and surface compositions (ices and mixtures). 
• Characterising possible interstellar objects such as ʻOumuamua and 2I/Borisov.   

The ELT will be able to take regular high-resolution images and spectra of moons orbiting other planets, allowing astronomers to better understand their evolving surfaces and atmospheres. Of particular interest are active moons that may be among the most likely places in the Solar System to host life, but the ELT will be used to follow the surface activity (ices and chemical contaminants) of a wide range of moons.

Jupiter has two moons that are especially interesting from an astrobiological point of view: volcanic Io and watery Europa. Astronomers will use the ELT to survey volcanic activity on Io, which releases sulphur dioxide that settles on the surface as a frost. The telescope will also be used to study Io’s atmospheric variability in response to this activity, as well as its influence on the neutral and plasma torus, which is a cloud of gas and plasma surrounding Io. Looking to Europa, the ELT will help us better understand the evolution of watery plumes that emanate from the moon’s surface, and the variability in its composition. 

Saturn also has two moons displaying conditions that could be suited to life. NASA’s Cassini spacecraft spotted geysers of frozen water shooting out of the surface of icy Enceladus; the ELT will provide us with the opportunity to study the evolution of these plumes. Massive Titan, another Saturn moon, is the only place in the Solar System — other than Earth — known to host liquid lakes. The ELT will be used to follow the seasonal cycle of high-altitude hazes, lower altitude methane clouds, and the "methane hydrology" on the moon, all of which are directly related to the formation of lakes and seas.

In short periods when Venus is furthest from the Sun, the ELT will enable astronomers to study the variability in atmospheric motions at different altitudes through cloud tracking and Doppler velocimetry of solar Fraunhofer lines. Astronomers will also use the telescope to map the intensity of oxygen airglow emission and track the motion of emissions, as well as to study the variability of chemical compounds.

When Earth passes between Mars and the Sun, the ELT will be able to support space missions by observing large-scale meteorological phenomena on the red planet (for example dust storms, orographic clouds and cyclones) and by mapping the seasonal evolution of key molecules (HDO, H₂O₂ and CH₄). 

The ELT will allow monitoring of atmospheric phenomena in specific regions of the giant planets Jupiter and Saturn. For example, with the ELT astronomers will be able to observe changes in the dynamics (winds) of Jupiter and Saturn, study the properties of their clouds, and monitor the variability and distribution of temperatures and chemical compounds as a function of height, in addition to the aurora phenomena in the gas giants' polar regions. The case of Saturn is particularly important since there is no scheduled space mission for the next few years. 

Since there aren't, to date, approved plans for space missions to Uranus and Neptune, and due to their enormous distances from the Sun, the ELT and its instruments will be fundamental to study these planets. Namely, the telescope will allow astronomers to study these planets' climate and meteorology (characterising winds, storms, vortices and waves), clouds and aerosol properties, the variability of their ionospheres and auroras, and the chemical composition and thermal structure of their atmospheres. 

The four outer planets have dynamic ring systems with very different characteristics and whose temporal changes could be accurately followed with ELT instruments.

The ELT will enable astronomers to take advantage of occultation events of Solar System bodies to study the structure of atmospheres at high spatial and spectral resolution, as well as to discover and characterise small satellites and rings.

The ELT will have a spatial resolution that will allow us to study different Solar System objects over a range of wavelengths. For comparison, we indicate below the resolution of the ELT at various wavelengths, as well as the diameter for various Solar System objects. 

Resolution in milliarc seconds (mas) at the indicated wavelength: 

• 3 (0.5 μm) 
• 10 (1.5 μm) 
• 16 (2.5 μm) 
• 32 (5 μm) 
• 65 (10 μm) 
• 130 (20 μm)