Callisto
Also known as Jupiter IV, is the outermost of the four large moons (Galilean satellites- Io, Europa, Ganymede, and Callisto) discovered around Jupiter
It’s Jupiter's second largest moon after Ganymede.
In the Solar System it is the third-largest moon after Ganymede and Saturn's largest moon Titan,
Despite being as big as the planet Mercury, it has less than half as much mass
Why in News
An international team of scientists, including from India, has discovered strong evidence indicating the presence of ozone on Callisto, shedding light on the complex chemical processes taking place on icy celestial bodies in the Solar System.
Researchers’ investigation into the chemical evolution of ‘SO2 astrochemical ice’, which is ice primarily composed of sulphur dioxide (SO2) in the presence of ultraviolet irradiation shed light on the chemical processes and composition of the surface of Callisto.
By analysing the data of the UV absorption spectra of the irradiated ice samples, the team was able to identify a distinct signature indicating the formation of ozone.
Importance of ozone
The earth has life not just because it found a way to originate here; it also has the resources to thrive, evolve, and diversify.
These resources include sunlight containing the “right” frequencies of radiation, water, a stable atmosphere providing a stable supply of the requisite gases at the right temperature, and various compounds required for the life-forms’ biochemical processes.
Not all emissions from the sun are good for organisms on earth. Ultraviolet radiation in particular is harmful to many species (but also useful to some others). Two of its components, called ultraviolet-B and ultraviolet-C, of wavelengths 290–320 nanometres and 100-280 nanometres respectively, can damage DNA, trigger mutations, and increase the risk of skin cancer and cataracts in humans.
Ultraviolet light has also been known to inhibit plant growth and have detrimental effects on various organisms.
This is why the ozone layer is a crucial part of the earth’s atmosphere: it completely absorbs ultraviolet-B and ultraviolet-C radiation.
Scientists are currently studying various celestial bodies in the Solar System that show signs of ozone, suggesting the existence of stable atmospheric conditions and, by extension, the possibility of their being able to host life.
Callisto and its unique environment
Callisto is primarily composed of water ice, rocky materials, sulphur dioxide, and some organic compounds.
These substances make the moon a potential candidate for supporting life in the solar system beyond the earth.
Callisto’s surface is heavily cratered, indicating a long history of being struck by asteroids and comets. (It may have the oldest surface in the Solar System, in fact.)
It also lacks the extensive seismic activity seen on some of Jupiter’s other moons, such as Io and Europa.
Its surface has likely been relatively stable for a long time.
This stability could be vital to preserve any subsurface ocean or potential habitats beneath the icy crust.
The discovery of ozone on Callisto suggests the presence of oxygen, which in turn is a fundamental ingredient required for the formation of complex molecules required for life (as we know it), such as amino acids, raising questions about the moon’s habitability.
This extends to other icy moons in our solar system, potentially informing our understanding of habitable conditions beyond Earth.
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