Q&A: Bringing Jupiter’s mysteries to light
Photo courtesy of Sally Dodson-Robinson July 01, 2016
UD expert comments on NASA mission to jumbo planet
As NASA’s Juno spacecraft arrives at Jupiter on July 4, UDaily checks in with Sally Dodson-Robinson, an expert on planet formation in the University of Delaware's Department of Physics and Astronomy, for a deeper look at the mysterious world it will explore.
Of all the planets, why visit Jupiter?
The planets in the solar system are leftovers from the sun's formation. Stars collapse from cold clouds of gas and dust, and because these clouds rotate as they collapse, they form a disk around the young star to conserve angular momentum. Planets form in the disk, but planet formation is inefficient: perhaps one part in 100 of the original mass of the disk eventually got converted to planets. The rest was blown away by a combination of radiation and magnetically driven winds. All of the planets put together contain only about 1/1000 of the sun's mass.
Jupiter, however, is the biggest of the leftovers. Jupiter has more than three times the mass of the other planets combined, and it sculpted the rest of the solar system. We have an asteroid belt because the gravitational influence of Jupiter prevented planetesimals between Jupiter and Mars from growing into full-fledged planets.
There is also a theory (the "Nice model") that gravitational interactions between Jupiter and Saturn destabilized the outer solar system, pushing Uranus and Neptune outward to their current orbits. There is no object in the solar system that has not felt Jupiter's influence.
What do you and other scientists hope to learn about Jupiter?
One of the big mysteries is how much of Jupiter's mass comes from elements heavier than hydrogen and helium. Knowing Jupiter's interior composition will help us figure out where and how fast Jupiter formed. (It is possible for planets to move around during their formation.) Knowing the amount of oxygen in Jupiter would help us figure out whether the planet formed in a cold, icy region or a warm region of the disk around the young sun.
Another big mystery is where Earth got its water. It is likely that Earth formed in a region that was too hot for ice to exist, and there are no liquids in planet-forming disks. Most planetary scientists believe that icy planetesimals from the outer edge of the asteroid belt hit Earth, bringing the water for our oceans and mantle. The question, then, is how the icy planetesimals were kicked inward toward Earth. Jupiter was probably responsible for sending them inward. By understanding Jupiter's composition and formation, we hope to get a better idea of how Earth got its water.
What’s it like on Jupiter compared to here on Earth?
Jupiter has no solid surface, so it's not possible to stand "on" Jupiter. Instead, Jupiter's outer layers are made mostly of molecular hydrogen gas with helium mixed in. Jupiter rotates very quickly, so that its day is only about 10 hours long. Usually, it is surrounded by a plasma cloud (plasma is ionized gas) that comes from the moon Io's volcanoes. While Earth's moon orbits us every 28 days, Jupiter's gravity is so strong that it whips its innermost moon, Io, around a full orbit in only 1.8 days.
Is Juno equipped with instruments unlike any other NASA mission?
The most visually compelling results will come from JunoCam, which is Juno's visible light camera. It will return the most detailed images of Jupiter ever taken, with resolution of 15 kilometers per pixel. JunoCam has been specially designed to withstand Jupiter's intense magnetosphere. There is also JIRAM, the Jovian InfraRed Auroral Mapper, which records both images and spectra. JIRAM is designed to study Jupiter's aurorae and "hot spots," which give off lots of infrared light, and will return very detailed images that can be rendered in false color for public viewing. Juno has many more instruments, including a magnetometer and a microwave radiometer.