Juno’s tryst with Jupiter: A spacecraft’s data and the revelation of scientific truths

By Udita Shukla 

NASA’s spacecraft, Juno, was launched in 2011, carrying seven instruments into space. Since then, it has furnished our knowledge base with detailed images of Jupiter, the largest planet in the Solar system.

On May 19, 2017, Juno did its sixth fly-by near Jupiter. While sweeping through its polar elliptical orbit, Juno had a brief encounter with the upper atmosphere of the gaseous giant. It skimmed through its cloud-tops and imaged ever deeper into its atmospheric layers. As per NASA officials, the event occurred within a range of just 2,200 miles (3,500 kilometres) during Juno’s close approach, at 2 a.m. EDT-Eastern Daylight Time.

Juno’s primary task was to shed light on the origin, structure and atmosphere of Jupiter. This demanded an intensive study of the chemical and physical composition of its upper and lower atmospheric layers. The gaseous giant has long been a subject of scientific speculations. However, many of them now stand in the dock for their veracity as new findings from Juno flood in.

Jupiter’s cloud stripes

Jupiter’s cloud stripes are coloured bands of gas and dust which not only encircle the planet but also extend deep down into its atmosphere. This deep cloud cover came as a surprise to many scientists. This is because up till now scientists thought these stripes to be mere spots on top of the thin cloud cover.

Vastly different from the common belief of being just a “weather-layer”, this banded pattern has been found to stretch all the way down to two hundred and seventeen miles. Also, these structures become quite complex as one descends, because they adopt a circulatory pattern.

The ammonia belt and the Jovian weather system

The ability to peer through the overlying blanket of Jupiter’s clouds was one of Juno’s key strengths. This enabled the spacecraft to investigate the gases below the blanket. The cloud-forming substance, ammonia, has been found to be in much less concentration than expected.

The findings suggest that ammonia gathers up along the equatorial region. The gas rises up from the depths of Jupiter’s atmosphere from at least a couple of hundred miles down. It has been widely known that ammonia resides near the equatorial region but just how deep down this gas-column goes is a surprise. Also, the powerful force that pushes the gas upward stands unknown.

The aforementioned ammonia feature is similar to a weather phenomenon on Earth, where warm air at our equator swells upward and creates trade winds and hurricanes. Jupiter’s ammonia cycle looks similar, but the unknown upwelling force is hard to decipher because the gaseous giant lacks a solid surface. So, the force could be operating in an entirely different way from that on Earth.

The Polar Lights- Auroras

Auroras are beautiful aerial light shows that appear at or near a planet’s poles. Earth’s auroras are popularly known as the Northern and Southern Light. On Earth, auroral displays are due to charged particles that are given off by the Sun (solar wind). These particles are then deviated by the Earth’s magnetic field towards the poles which cause the light display.

Jupiter’s auroras are born much the same way. However, as far as the flux of charged particles is concerned, the planet exhibits an additional process completely reverse to the one found on Earth. The ultraviolet and infrared data from Juno shows beams of electrons being blasted out from the Jovian atmosphere into space.

According to the findings by Juno, the grandiloquent auroras over Jupiter’s poles are caused jointly by the sulphur emission from powerful volcanoes residing on Io (one of Jupiter’s moons), and over charged particles blasted off by the Sun.

Findings on Jupiter’s magnetic field

The behaviour of Jupiter’s magnetic field, originally considered uniform to the Earth, has come out quite differently. The data shows variations in magnetic field intensity with different areas having strong and weak magnitudes. The interior of the planet has been found to be alive with swirling electric currents which engender incredibly strong magnetic fields.

Jupiter boasts of one of the most intense magnetic fields in the planetary system. The data suggests that such extreme values of magnetic field magnitude can only be due to electric currents that circulate in the planet’s outer layers of hydrogen.

The mystery surrounding gravity

The gravitational field of any planet is responsible for the pull on its orbiting satellites and sustaining them in their orbits. Consequently, a slight variation in gravity’s strength can cause modifications in the inward force experienced by an orbiting object.

The values of gravity, as provided by Juno, indicate that Jupiter does not have a solid, compact core. It is much larger in size (than previously expected), and spread out thinly over a great area. This data on the planet’s gravity will be employed to investigate the structure and composition of its core, which is also believed to be the cause of the planet’s gravitational field.

A step closer to more radical discoveries

Juno arrived at Jupiter on July 4, 2016, and will have circled the planet thirty-two times before its mission ends in February 2018. It bears overarching significance in its scope. It is a key towards the understanding of other celestial rotating bodies such as neutron stars. It will provide data on the prevailing chemistry of gases in the Jovian atmosphere and shed light on the dynamics of the magnetic and gravitational fields. 

Juno offers information not only about the working of Jupiter but also on how gaseous planets evolve and behave in general. Jupiter is a standard of comparison for all gas giants and Jupiter-like planets that have been discovered in many other planetary systems. Hence, researchers can apply their understanding of Jupiter to some other planets as well. In an age when mortals have begun envisioning space colonies in the solar and the extra-solar realm, this takes the form of a profound and radical discovery.

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Featured image credits: NASA