[attach id=650724 size="medium" align="right"]Jupiter’s south pole as seen by Juno. Photo: NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles[/attach]
On a winter night in January 1610, Galileo pointed a small refractor telescope at the largest planet in our solar system, Jupiter. What he saw forever changed our understanding of the universe. In observations he carried out between January and March of that year, he noted that there were 4 bodies clearly orbiting Jupiter, some changing their apparent position around the gas giant on the scale of a few hours. These are now known to be Io, Callisto, Ganymede and Europa, the four largest moons of Jupiter. At the time, the idea of any object in the solar system orbiting anything other than Earth was revolutionary, and eventually led to the heliocentric model of the solar system being accepted.
We have come a very long way since then. Much larger telescopes, of several different designs, have since been constructed. We now have the tools to learn more about the gas giant in our cosmic backyard than ever before, with even amateur-sized telescopes able to resolve a fair amount of detail on the gas giant.
The Great Red Spot, a massive persistent anticyclonic storm on Jupiter, can for example be seen with moderately sized amateur telescopes on clear nights. Io, Callisto, Europa and Ganymede are very easily discernible even with very small telescopes. Even though Earth-based observation has given us incredible insight into the gas giant’s behaviour, merely observing Jupiter from Earth was never going to be enough to answer some of the more fundamental questions concerning its formation.
Jupiter is believed to have been the first planet to form in the young solar system and understanding the processes that led to its formation could unlock the mysteries around the formation of the other planets, including Earth. In 2011, 401 years after Galileo’s ground-breaking observations, we launched the Juno space probe on a mission to observe Jupiter as never before.
After a five year journey, including a gravity assist manoeuvre with Earth itself in 2013, Juno reached Jupiter and entered in a polar orbit around it on July 5, 2016. Since then, its observations of Jupiter have completely changed the way we view the gas giant.
Several Earth-sized storms have been observed, particularly in the polar regions not easily visible from Earth, found in dense formations, with a significant variability between its two polar regions. Zones of unexpected high levels of radiation have also been found, some of which resulting from high-energy ions of hydrogen, oxygen and sulphur.
On a close approach of Jupiter in July 2017, Juno passed over the cloud-tops of the famous Great Red Spot and peered deep into its depths to gain a better understanding of what drives the giant anticyclone, and why it formed in the first place.
Juno is now nearing the end of its planned two year mission and will most likely enter a planned deorbit in July of this year, unless the mission receives further funding and a mission extension. Amateur astronomers can still contribute immensely during the final close approaches scheduled for Juno, as Earth-based observations of Jupiter during such close approaches, called perijoves, provide supporting data for the closer views of Jupiter’s atmosphere retrieved by Juno simultaneously. Thus, any amateur Maltese astronomers who would like to assist in the Juno mission with their observations can do so by recording observations of Jupiter over the next few days.
Josef Borg is currently a PhD student within the Institute of Space Sciences and Astronomy, University of Malta, and also the President of the Astronomical Society of Malta.
Did you know?
• Jupiter is thought to protect the inner solar system, including Earth, from some comets. It is theorized that the gas giant’s immense gravity can sometimes sling these fast-moving balls of ice and dust away from the inner solar system, and consequently reduce the frequency with which such comets would hit the Earth.
• A comet, named Shoemaker-Levy 9, was observed to collide with Jupiter in 1994. The comet broke up into several icy fragments prior to collision with Jupiter, which eventually tore through Jupiter’s atmosphere in July 1994. These caused easily discernible brown spots on Jupiter, even with small amateur telescopes from Earth. A similar brown spot was observed on Jupiter in 2009 by an amateur astronomer, Anthony Wesley.
• Apart from its four largest moons, 65 other smaller moons have now been discovered orbiting Jupiter. Most of these moons are too small to observe in any but the largest telescopes. The four Galilean moons, easily visible through telescopes, are by far the largest, together comprising 99.997 per cent of all the mass of objects orbiting Jupiter. A number of the outer, irregularly shaped moons are in fact thought to be captured asteroids.
For more trivia see: www.um.edu.mt/think
Sound bites
• An intriguing asteroid was spotted travelling backwards around Jupiter back in 2015. Now a team of researchers think it could have formed around another star. An asteroid found travelling backwards along Jupiter´s orbit has been puzzling astronomers since it was discovered in 2015. Most asteroids move around the Sun in the same direction as planets do, a motion inherited when the solar system formed from a swirling cloud of dust and gas. But asteroid 2015 BZ509 (or BZ for short) goes the wrong way, in a retrograde motion around the Sun. Now, a team of astronomers think they know why: It might have come from outside the solar system.
http://www.skyandtelescope.com/astronomy-news/wrong-way-asteroid/
• New observations suggest that stars began forming just 250 million years after the Big Bang - a record-breaker that will likely open a new line of cosmological inquiry. Astronomers peering back into time suggest that the cosmic dark ages, before the universe hosted its sea of twinkling lights, might have lasted no more than 250 million years. Takuya Hashimoto (Osaka Sangyo University, Japan) and his colleagues used the Atacama Large Millimetre/submillimetre Array (ALMA) to peer at a galaxy whose light was emitted 550 million years after the big bang, picking up a long-sought signal: oxygen. It’s the most distant galaxy for which astronomers have been able to detect individual elements, and that single element has a big story to tell.
http://www.skyandtelescope.com/astronomy-news/early-star-formation-presents-new-cosmic-mystery/
• To find out some more interesting science news, tune in Radju Malta on Saturday mornings at 11.05am and listen to Radio Mocha.