Webb telescope points indicate that Eris and Makemake are geologically active

Active geology—and the large-scale chemistry that can catalyze it—requires large amounts of heat. Dwarf planets near the far edges of the solar system, such as Pluto and other Kuiper Belt objects, were formed from extremely cold icy material and never transited close enough to the sun to heat up significantly. Any heat remaining from its formation has likely been lost to space long ago.

However, Pluto turned out to be a world rich in geological features, some of which implied the dwarf planet's surface was being constantly reshaped. Last week, researchers reported that the same may be true for other dwarf planets in the Kuiper Belt. The indications come thanks to the capabilities of the Webb telescope, which was able to resolve differences in hydrogen isotopes present in the chemicals that fill the surface of Eris and Makemake.

Cold and distant

Kuiper belt objects are objects native to the distant solar system, forming at a sufficient distance from the Sun's warmth that many of the gaseous materials in the inner planets — things like nitrogen, methane and carbon dioxide — are solid ice. Many of these objects formed so far beyond the gravitational influence of the eight major planets that they never made the journey to the warmer inner solar system. In addition, because there is much less material farther away from the Sun, most objects are very small.

Although they start out hot due to the process by which they were formed, their small size means they have a large surface-to-volume ratio, allowing internal heat to spread out into space relatively quickly. Since then, any heat comes from rare collision events or the decay of radioactive isotopes.

However, New Horizons' visit to Pluto has shown that it doesn't take much heat to drive active geology, although seasonal variations in sunlight are likely responsible for some of its features. Sunlight is unlikely to have an effect on worlds like… Makemakewhich orbits at a distance of one and a half times the closest distance of Pluto to the Sun. IrisIt is approximately the size of Pluto, and orbits twice as close as Pluto.

A mission to any of these planets would take decades, and none of them are currently under development, so we can't know what their surfaces look like. But this does not mean that we know nothing about them. The James Webb Space Telescope has added significantly to what we know.

Webb was used to photograph sunlight reflecting off these objects, obtaining the infrared spectrum – the amount of reflected light at different wavelengths. The spectrum is affected by the chemical composition of the surfaces of dwarf planets. Some chemicals can absorb specific wavelengths of infrared light, ensuring that it is not reflected. By noting where the spectrum drops, it is possible to see what chemicals are present.

Some of this work has already been done. But Webb is able to image parts of the spectrum that were previously inaccessible, and his instruments are able to identify the different isotopes of atoms that make up each chemical. For example, some methane molecules (CH₄) One of the hydrogen atoms will, randomly, be replaced by its heavier isotope, deuterium, to form CH₃Dr.. These isotopes potentially act as tracers, telling us things about where the chemicals originally came from.