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NASA's Juno Enters Orbit Around Jupiter

Marcia S. Smith
Posted: 04-Jul-2016
Updated: 05-Jul-2016 02:10 AM

NASA's Juno spacecraft successfully entered orbit around Jupiter tonight Eastern Daylight Time (EDT) after a 5-year journey.  Juno is the first solar-powered spacecraft to visit the outer planets, where the Sun's strength is comparatively low.  Coupled with the harsh radiation environment the spacecraft will endure as it dips closer to the planet's cloud-tops than any previous spacecraft, it has a limited lifetime, but is expected to produce groundbreaking data about aspects of the planet never observed before.

Several spacecraft have flown past Jupiter (Pioneer 10 and 11, Voyager 1 and 2, Ulysses, Cassini, and New Horizons) and one orbited it for many years (Galileo), but Juno is the first designed to look beneath the cloud-tops and study the interior.   It also is the first to study Jupiter's poles.   

Artist's illustration of Juno spacecraft orbiting Jupiter.  Image credit:  NASA/JPL-Caltech

Juno was placed into an elliptical (oval) orbit where it will dip as close as 3,100 miles (5,000 kilometers) to Jupiter's cloud-tops and then swing back out again, away from the most intense radiation.  The burn that took place tonight (July 4 EDT) placed it into an initial 53.5-day orbit.  After two of those orbits, the engine will fire again to lower it to a 14-day orbit optimized for the science investigations.

Artist's illustration of Juno spacecraft and its science instruments.  Image credit: NASA/JPL

In addition to the science instruments, the spacecraft is carrying the JunoCam camera, a public outreach effort.  The principal investigator (PI) of the Juno mission, Scott Bolton from the Southwest Research Institute (SwRI), calls it "the public's camera."  It has already taken many images of Jupiter, but few have made it into the public domain.  All of them will, he said, once technical issues are resolved.  JunoCam has its own website where images from JunoCam will be posted, amateur astronomers may upload their own images and data about the planet, and the public may vote on points of interest to observe.  Bolton's team created a movie (with music by Vangelis) of Jupiter as the spacecraft approached the planet using JunoCam images that was just posted on YouTube, rather than the JunoCam website.  It clearly shows the four Galilean moons (Io, Europa, Ganymede and Callisto), discovered by Galileo in 1610, orbiting the planet.  (Actually Callisto, the furthest out, is a bit harder to see than the others.) Bolton said it took 17 days for JunoCam to get all the images; they were condensed into 3 minutes for the video.

Juno is named after the Roman goddess, sister and wife of Jupiter, who could see through clouds.  It was launched on an Atlas V rocket on August 5, 2011.

Jupiter receives 1/25th of the amount of sunlight as Earth. To capture as much of it as possible, each of the three solar panels is 29.5 by 8.7 feet (9 by 2.65 meters) with more than 650 square feet (60 square meters) of surface area.   The total energy output is 500 watts (as in five 100-watt light bulbs).  All other spacecraft that have visited the outer planets (beyond Mars) have nuclear power sources.

The spacecraft will study Jupiter over the course of 20 months, making 37 orbits (33 optimized for science), after which it will be commanded to enter Jupiter's atmosphere where it will be destroyed.  That is currently expected on February 20, 2018.  Scientists do not want to risk the spacecraft impacting Jupiter's moons, some of which -- like Europa -- may have environments conducive for life.  NASA plans to send a spacecraft to Europa in the early 2020s to look for life and, if any is found, wants to be sure it is indigenous, not Earth life deposited by Juno.

Juno is one of NASA's "New Frontiers" missions, a series of medium-sized space missions for which scientific teams led by a PI like Bolton compete.  The New Horizons mission that reached Pluto last year was the first.  Juno is the second.  The third is the asteroid sample return mission OSIRIS-REx scheduled for launch in September. NASA is getting ready for the next round of competitions.  The program was created in 2003 with the intent to ensure a stable cadence of new missions every three years, although budget constraints necessarily affect how often the competitions can occur.  The missions are cost-capped.  The current cap is $850 million, excluding launch and operations.

Note:  This article was updated following a 1:00 am EDT NASA/JPL press briefing on July 5.

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