Mohawk Valley Astronomical Society

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Storm Chaser

by Perry Pezzolanella

There will be more to celebrate this Fourth of July when a sophisticated spacecraft named Juno arrives at Jupiter to explore the turbulent atmosphere in a way that has not been done before. Much attention has been given to the moons, especially Europa, and yet how Jupiter’s weather works is still not fully understood.

Juno is a $1.1 billion solar powered spacecraft launched on August 5, 2011 that will go into polar orbit around Jupiter. It will orbit Jupiter at least 37 times in such a way as to avoid most of the hazardous radiation and will orbit Jupiter once every 14 days, coming as close as 2700 miles from Jupiter’s cloud tops to as far out as just beyond Callisto’s orbit. The mission is expected to last until February 2018 when it will be de-orbited and burn up in Jupiter’s atmosphere to avoid crashing into any of the moons, especially Europa, preventing contamination from potential microbes. Juno is the first spacecraft beyond the asteroid belt that will use solar power instead of nuclear power. Even though Jupiter receives only about 4% of the sunlight as Earth, the advances made in solar-cell technology have made it economical for use as far away as Jupiter. The “Juno Radiation Vault”, with titanium walls nearly ½-inch thick, will aid in protecting and shielding Juno’s electronics. Juno’s infrared and microwave instruments will measure the heat coming from deep within Jupiter’s atmosphere. It will study the abundance and distribution of water, convection, and thunderstorm evolution. By studying the convection and storms Juno will be able to better determine how they power the circulation patterns within Jupiter’s atmosphere. Juno will also study the gravitational field and polar magnetosphere.

The science objectives will be achieved with a payload of nine instruments which will:

* Determine the ratio of oxygen to hydrogen, which effectively measures the abundance of water in Jupiter.

* Obtain a more accurate measurement of the mass of its core.

* Precisely map Jupiter’s gravity field to assess the distribution of mass in Jupiter’s interior, including the properties of its structure and dynamics.

* Map the variation in atmospheric composition, temperature, structure, cloud thickness and dynamics to atmospheric pressures far greater than 100 times Earth’s at all latitudes.

* Characterize and explore the three-dimensional structure of Jupiter’s polar magnetosphere and its auroras.

The nine instruments that will carry out these investigations are:

* Microwave radiometer (MWR) – The primary goal is to probe the deep atmosphere of Jupiter at radio wavelengths to measure thermal emissions.

* Jovian Infrared Auroral Mapper (JIRAM) – The primary goal is to probe the upper layers of Jupiter’s atmosphere down to pressures 5-7 times Earth’s using an imager and a spectrometer.

* Magnetometer (MAG) – MAG has three goals: mapping of the magnetic field, determining the dynamics of Jupiter’s interior, and determination of the three-dimensional structure of the polar magnetosphere.

* Gravity Science (GS) – The Gravity Science Investigation will probe the mass properties of Jupiter by using the communication subsystem to perform Doppler tracking. It will utilize the 34-meter Deep Space Network antenna at Goldstone, California.

* Jovian Auroral Distribution Experiment (JADE) – JADE will resolve the plasma structure of Jupiter’s aurora by measuring the angular, energy and compositional distribution of particles in the polar magnetosphere.

* Jovian Energetic Particle Detector Instrument (JEDI) – JEDI will measure the energy and angular distribution of hydrogen, helium, oxygen, sulfur and other ions in Jupiter’s polar magnetosphere.

* Radio and Plasma Wave Sensor (Waves) – This instrument will identify the regions of auroral currents that define Jupiter’s radio emissions and acceleration of the auroral particles.

* Ultraviolet Imaging Spectrograph (UVS) – UVS will record the wavelength, position, and arrival time of detected ultraviolet photons during the time when the spectrograph slit views Jupiter during each turn of the spacecraft.

* JunoCam – A visible light camera/telescope, included in the payload to facilitate education and public outreach. It is expected to operate for only seven orbits around Jupiter before the powerful radiation and magnetic field destroy it.

JunoCam will support the Juno Mission’s Education and Public Outreach program. The camera, derived from the Mars Science Laboratory Orbiter, is designed to acquire red, green, and blue wavelength images of Jupiter’s polar regions and lower-latitude cloud tops during Juno’s first seven orbits around the planet. These images, of approximately 9.3 miles per pixel resolution, will be used by students to create the first color images of Jupiter’s poles, as well as high resolution views of lower-latitude cloud belts. After the required, seven orbit design life, JunoCam will continue to operate as long as possible in the harsh radiation environment.

Jupiter is a world ten times larger than Earth and can easily hold 1300 Earths by volume, by far the largest of the planets. Juno will come very close to the storms where winds howl over 400 miles per hour with hurricanes raging for centuries. Lightning is so powerful that it could vaporize a city and Juno will be dramatically close to these super bolts, which will flash brilliantly in the night. The Great Red Spot and all the storms will be raging in 2016-18 when Juno will be chasing them closely trying to unlock how Jupiter works, how it evolved, and hopefully provide vital information about Earth’s weather, like a true storm chaser!