Cosmic Spectacles: Exploring Extra-terrestrial Auroras

The beauty and wonder of auroras have captivated humanity for centuries, with Earth's mesmerizing displays of shimmering lights dancing across the night sky. However, beyond our own planet lies universe of celestial phenomena, including auroras in other planets. So, let’s explore the captivating auroras found on Extra-terrestrial planets of our solar system, shedding light on their unique characteristics and into the diversity of our cosmic neighborhood.

 

Image credit - NASA

King of auroras - Jupiter, the largest planet in our solar system, boasts some of the most awe-inspiring auroras ever observed. Its magnetic field interacts with electrically charged particles from its moon Io and the solar wind to create powerful and dynamic displays. The auroras on Jupiter are so immense that they can span an area larger than the Earth itself, with ultraviolet and infrared observations revealing complex patterns and structures. These phenomena show the sheer power of Jupiter's magnetosphere and its ability to generate mesmerizing light shows.

 

 

Image credit - NASA

 

Serenade of Colors - Saturn, famous for its mesmerizing rings, also possesses its own unique auroras. Unlike Jupiter's auroras, which primarily emit ultraviolet light, Saturn's auroras emit a variety of colors, including infrared, ultraviolet, and visible light. Scientists believe that Saturn's auroras are caused by its interaction with charged particles originating from the Sun, similar to Earth's auroras. These colorful displays add to the otherworldly charm of the ringed planet, painting the night sky with ethereal hues.

 

 

 

 

Ice Giants with Subtle Lights - Uranus and Neptune, known as the ice giants, are lesser-known but equally fascinating worlds that possess their own auroras. These icy planets have a distinct composition and magnetic field, leading to unique auroral phenomena. Due to their extreme axial tilts, the auroras on Uranus and Neptune are unusual in that they appear as subtle, faint glows. Observations from spacecraft missions, Voyager 2 have revealed intermittent bursts of auroras on Uranus and Neptune.

Image credit - NASA's Goddard Space Flight Center/Jenny Hottle

A Hint of Auroral Magic - While not as pronounced as those on Jupiter or Saturn, Mars also experiences its own version of auroras. Unlike the other planets mentioned, Mars does not possess a global magnetic field. However, localized magnetic fields are found in specific regions of its crust. During intense solar activity, these magnetic fields can interact with the solar wind, generating faint auroral glows near the planet's surface. Although the Martian auroras may be elusive, they serve as a reminder of the dynamic interplay between a planet's magnetic field and its surrounding environment. 

Animation showing proton aurora at Mars. Credits: NASA/MAVEN/Goddard Space Flight Center/Dan Gallagher

 

Auroras occurs not only on Earth but also across our cosmic neighborhood. From the colossal displays on Jupiter and the multicolored symphonies on Saturn, to the subtle glows on Uranus and Neptune, each planet's auroras offer a glimpse into the unique characteristics of their magnetospheres. As we continue to explore the wonders of our solar system, these extraterrestrial auroras serve as a reminder of the vast diversity and awe-inspiring beauty that lies beyond our home planet.

Earth’s atmosphere – From a hot cloud of dust and gas to life nurturing environment

 

The early atmosphere –

History of earth – 4.6 billion years. 

Evidences - Oldest occurring rock – Faux Amphibolites of the Nuvvuagittuq greenstone belt - found in Quebec Canada with age of 4.28 billion years. Isotopic analysis of meteorites, soil, rock samples of moon.

Faux Ambibolites (Nuvvuagittuq Greenstone Belt, Eoarchean, 4.28 Ga; western Ungava Peninsula, eastern side of Hudson Bay, Quebec, Canada) James St. John, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

 The continuous collisions between primordial solar nebula particles (interstellar gas and dust) is mainly considered responsible for the most rudimentary form of earth. This continued for some 150 million years until eventually clumped into a rock form. The mass of earth had very high temperature due to terrestrial accretion heat generated through –

o   Decay of radioactive isotopes

o   Gravitational energy of sinking metals

o   Impact of small planetary bodies bombarding into earth.

 ·         Eventually, rock material started melting bringing about sinking of heavier material rich in iron and nickel, to core and rising of lighter elements to top. The maximum amount of lighter primordial gases like hydrogen and helium escaped during this phase.

 ·      The light molten material crystallized to build initial thin crust. This thin and unstable crust collapsed again formed many times to ultimately form a thicker crust as a result of large scale convection current inside earth. At the same time, outgassing of gases from surface volcanic activity led to oceanic evolution and secondary atmosphere.

Oceanic evolution -

H2O particles were already present in the Earth mass during the planetary accretion phase of formation of earth. During outgassing temporary steam atmosphere was created which precipitated during the subsequent cooling phases of the earth.

Secondary atmosphere –

·         Volcanism was the major route through which degassing of volatile material from the inner Earth took place. Volcanic activity produces water vapor, Carbon dioxide, Carbon monoxide methane gas, nitrogen in substantial quantities but no oxygen.

Decrease in CO2 –

·         Carbon dioxide was the main gas providing heat in the early atmosphere as the early solar system was illuminated by a weak, young Sun that only delivered ∼75% of the present day energy.

According to a climate model, at 2.75 Ga, CO2 level was 500 times present atmospheric levels. However, by the Cambrian, CO2 levels were close to present atmospheric levels.

The main reason for the extraction of CO2 out of the atmosphere was the development of life forms in the ocean that seized carbon in organic and later inorganic (calcium carbonate) forms and buried it in sedimentary formations on the sea floor.

Evidence -  presence of early carbonated sediments,

        Increase in O2 –

·         The secondary atmosphere formed by outgassing was anoxygenic. Amount of oxygen in the atmosphere increased gradually through

• Solar radiation - UV rays break H2O into hydrogen and oxygen
• Organic photosynthesis by earliest form of life - Blue-green algae (Cyanobacteria) uses CO2 and H2O for photosynthesis and release free oxygen.

 ·         Oxygen production continued for 2.2 billion years and did not achieve considerable levels until 2 Ga and only approached present-day levels by 1.5 Ga. Due to chemical action with the material deposited through lava eruptions, such as iron and evaporite formations.

Evidence - Iron rock formation in earliest sediments at Isua in western Greenland aged 3.8 billion years ago. Barite gypsum bearing evaporite found in Pilbara region of western Australia. 3.5 billion years ago.

·         O2 level rose in atmosphere occurred with decrease in the iron deposition.

Evidence – Earliest form of life i.e. Eukaryotes which were present 1.4 billion years ago, require O2 content of about 0.02 present atmospheric level. Similarly, soft life forms like jelly fish, worms developed about 650 million years ago, which require the minimum oxygen level of 0.1 present atmospheric level. Plants first appeared 400 million years ago.

·         The evolution of more complex form of plants and animals extract more CO2 from the atmosphere and provide an additional source of O2.

·         Once O2 started to accumulate in the atmosphere, the production of ozone (O3) could occur, shielding the Earth’s surface from ultra violet (UV) radiation. 

 References –

• Neil C. Wells - The atmosphere and ocean: a physical introduction, 3rd Edition, Wiley Blackwell
• Essentials of Meteorology – An Invitation to the Atmosphere, Eighth Edition 2018, C. Donald Ahrens and Robert Henson, Cengage Learning.
• Brian Frederick Windley (2016) Geologic history of Earth, Encyclopædia Britannica. Available at https://www.britannica.com/science/geologic-history-of-Earth.  Accessed on November 23, 2020