The first of the gas-giant orbiter's back-to-back flybys will provide a
close encounter with the massive moon after over 20 years.
On Monday, June 7, at 1:35 p.m. EDT (10:35 a.m. PDT), NASA's Juno spacecraft
will come within 645 miles (1,038 kilometers) of the surface of Jupiter's
largest moon, Ganymede. The flyby will be the closest a spacecraft has come
to the solar system's largest natural satellite since NASA's Galileo
spacecraft made its penultimate close approach back on May 20, 2000. Along
with striking imagery, the solar-powered spacecraft's flyby will yield
insights into the moon's composition, ionosphere, magnetosphere, and ice
shell. Juno's measurements of the radiation environment near the moon will
also benefit future missions to the Jovian system.
Ganymede is bigger than the planet Mercury and is the only moon in the solar
system with its own magnetosphere—a bubble-shaped region of charged
particles surrounding the celestial body.
"Juno carries a suite of sensitive instruments capable of seeing Ganymede in
ways never before possible," said Juno Principal Investigator Scott Bolton
of the Southwest Research Institute in San Antonio. "By flying so close, we
will bring the exploration of Ganymede into the 21st century, both
complementing future missions with our unique sensors and helping prepare
for the next generation of missions to the Jovian system—NASA's Europa
Clipper and ESA's [European Space Agency's] JUpiter ICy moons Explorer
[JUICE] mission."
Juno's science instruments will begin collecting data about three hours
before the spacecraft's closest approach. Along with the Ultraviolet
Spectrograph (UVS) and Jovian Infrared Auroral Mapper (JIRAM) instruments,
Juno's Microwave Radiometer's (MWR) will peer into Ganymede's water-ice
crust, obtaining data on its composition and temperature.
"Ganymede's ice shell has some light and dark regions, suggesting that some
areas may be pure ice while other areas contain dirty ice," said Bolton.
"MWR will provide the first in-depth investigation of how the composition
and structure of the ice varies with depth, leading to a better
understanding of how the ice shell forms and the ongoing processes that
resurface the ice over time." The results will complement those from ESA's
forthcoming JUICE mission, which will look at the ice using radar at
different wavelengths when it becomes the first spacecraft to orbit a moon
other than Earth's Moon in 2032.
Signals from Juno's X-band and Ka-band radio wavelengths will be used to
perform a radio occultation experiment to probe the moon's tenuous
ionosphere (the outer layer of an atmosphere where gases are excited by
solar radiation to form ions, which have an electrical charge).
"As Juno passes behind Ganymede, radio signals will pass through Ganymede's
ionosphere, causing small changes in the frequency that should be picked up
by two antennas at the Deep Space Network's Canberra complex in Australia,"
said Dustin Buccino, a signal analysis engineer for the Juno mission at JPL.
"If we can measure this change, we might be able to understand the
connection between Ganymede's ionosphere, its intrinsic magnetic field, and
Jupiter's magnetosphere."
Three Cameras, Two Jobs
Normally, Juno's Stellar Reference Unit (SRU) navigation camera is tasked
with helping keep the Jupiter orbiter on course, but during the flyby it
will do double duty. Along with its navigation duties, the camera—which is
well shielded against radiation that could otherwise adversely affect
it—will gather information on the high-energy radiation environment in the
region near Ganymede by collecting a special set of images.
"The signatures from penetrating high-energy particles in Jupiter's extreme
radiation environment appear as dots, squiggles, and streaks in the
images—like static on a television screen. We extract these
radiation-induced noise signatures from SRU images to obtain diagnostic
snapshots of the radiation levels encountered by Juno," said Heidi Becker,
Juno's radiation monitoring lead at JPL.
Meanwhile, the Advanced Stellar Compass camera, built at the Technical
University of Denmark, will count very energetic electrons that penetrate
its shielding with a measurement every quarter of a second.
Also being enlisted is the JunoCam imager. Conceived to bring the excitement
and beauty of Jupiter exploration to the public, the camera has provided an
abundance of useful science as well during the mission's almost five-year
tenure at Jupiter. For the Ganymede flyby, JunoCam will collect images at a
resolution equivalent to the best from Voyager and Galileo. The Juno science
team will scour the images, comparing them to those from previous missions,
looking for changes in surface features that might have occurred over
four-plus decades. Any changes to crater distribution on the surface could
help astronomers better understand the current population of objects that
impact moons in the outer solar system.
Due to the speed of the flyby, the icy moon will—from JunoCam's viewpoint—go
from being a point of light to a viewable disk then back to a point of light
in about 25 minutes. So that's just enough time for five images.
"Things usually happen pretty quick in the world of flybys, and we have two
back-to-back next week. So literally every second counts," said Juno Mission
Manager Matt Johnson of JPL. "On Monday, we are going to race past Ganymede
at almost 12 miles per second (19 kilometers per second). Less than 24 hours
later we're performing our 33rd science pass of Jupiter—screaming low over
the cloud tops, at about 36 miles per second (58 kilometers per second). It
is going to be a wild ride."
Reference:
NASA
Tags:
Space & Astrophysics