Author: Irene Park
Editors: Ada Hagan, Alisha John, Shweta Ramdas, Scott Barolo
On July 4th 2016, NASA announced that the spacecraft Juno arrived at Jupiter after traveling two billion miles over five years. Juno was designed to investigate the origin of Jupiter, our solar system’s largest planet.
NASA’s name for the spacecraft, a reference to the wife of the Roman god Jupiter, is amusingly appropriate: the Roman goddess Juno has a long history of investigating Jupiter. In one story, Jupiter draws a veil of clouds to hide his infidelity with Io (whose name graces one of the planet’s moons) from his suspicious spouse. Juno sees through his trick, blowing away the clouds to reveal what Jupiter is up to.
Much like the god, the planet Jupiter hides behind dense layers of clouds, which give the planet its characteristic light and dark bands (Figure 1). These clouds pose a challenge for scientists investigating the planet’s composition. Juno will overcome this challenge with its many instruments capable of peeking through Jupiter’s thick clouds.
Scientists believe that understanding Jupiter’s composition can help them sort out competing theories about how the planet formed. One of Juno’s missions is to analyze Jupiter’s composition more precisely than previous missions to make Jupiter’s origin story more complete.
Jupiter may have been born from the same hydrogen-helium cloud that gave birth to the sun. If so, the sun and Jupiter should have similar compositions—mostly hydrogen and helium. On the other hand, it’s possible that Jupiter was formed far from the sun and later moved inward to its current orbit. In that case, the sun and Jupiter may not have similar compositions. If Juno finds a lot of water on Jupiter, then it is more likely that Jupiter was formed distant from the sun, in colder and icier regions.
In the 1990’s and 2000’s, the Galileo probe provided data suggesting that Jupiter has three times the amount of heavy elements, such as carbon and nitrogen, as the sun. But this discovery didn’t necessarily kill the “same origin” hypothesis: Jupiter may have picked up those heavy elements after its birth, as a result of asteroids and comets crashing into the planet.
But Galileo’s data puzzled the scientists. The collisions should also have brought water to Jupiter, and Galileo found no evidence of water. It is possible that Galileo landed in a particularly dry spot, since data from the 1979 Voyager mission indicated the presence of water.
One of Juno’s tasks is to resolve this discrepancy by detecting the amounts of heavy elements and water. When it does, the scientists will have two hypotheses for Jupiter’s origin that they will need to further investigate: 1. Jupiter and the sun formed from the same cloud, and Jupiter became enriched in heavy elements and water its birth due to asteroids and comets and 2. Jupiter was formed elsewhere distant from the sun, and it had heavy elements and water since its birth.
It would be nice to cut Jupiter in half to see what it is made of, but since we can’t (where would we find a knife that big?), scientists came have come up with an indirect way to analyze Jupiter’s composition. An object orbiting around a planet is pulled by the planet’s gravitational force, which is in turn influenced by what the planet is made of. Hence, measuring Juno’s orbital trajectory around Jupiter allows scientists to guess what Jupiter is made of (Bill Nye explains it further in this video).
What Jupiter can tell us about life on Earth
According to Scott Bolton, the Principal Investigator of the Juno mission, the composition of Jupiter may tell us not only about that Jupiter’s birth, but also about the origin of life on our own planet.
“We know this is important because the stuff that Jupiter has more of, the heavy elements, is what life itself is made of,” Bolton told Wired. “Understanding how Jupiter got that way, how it formed, how it started the enrichment process, is the smoking gun as to how we all got here.”
Heavy elements, like the ones found on Jupiter, are the building blocks of life on Earth. For instance, carbon is as a component of proteins, nucleic acids, carbohydrates, and lipids, which are required by all living organisms. In fact, three heavy elements—carbon, oxygen, and nitrogen—make up 86.7% of the human body. Water, of course, is also essential to life. Like Jupiter, Earth may have gotten its heavy elements and water from asteroids and comets, so learning more about Jupiter’s history may shed light on our own.
The mission is still in its infancy. The spacecraft is scheduled to make 37 orbits around Jupiter before ending its mission in February 2018. In the meantime, Earthlings can indirectly participate in the mission by discussing and voting on which features of the planet JunoCam, a camera on the spacecraft, should capture. We can also keep our eyes out for official Tweets and press releases when Juno finally unlocks the secrets beneath Jupiter’s clouds.
About the author
So Hae (Irene) Park is a fifth-year Human Genetics PhD student at the University of Michigan Medical School and the Science Column Editor (keep your eye out for more info about our upcoming weekly column in The Michigan Daily). Before attending UMich, she received her BA in Biological Sciences and Philosophy at Cornell University. Now under the joint supervision of Drs. Thomas Wilson and Thomas Glover, Irene is investigating what causes genome instability—an accumulation of mutations in the cells—and how it can be avoided. Genome instability is commonly seen in many human diseases, like cancer. When she is not working during the wee hours in her laboratory or writing about the latest cool topics in science and medicine in The Michigan Daily or HIPPO Reads, Irene likes to watch movies, watch The Food Network, collect anything cute, learn how to make different types of coffee drinks, listen to music, travel, and read. Follow her on Twitter (@S_Park89).
Read all posts by Irene here.
Image Source: NASA/JPL/University of Arizona, From http://photojournal.jpl.nasa.gov/catalog/PIA02863, https://commons.wikimedia.org/wiki/File:PIA02863_-_Jupiter_surface_motion_animation.gif