The swirling atmosphere over Jupiter’s south pole, captured by Juno on 2 February.

NASA/JPL-Caltech/SwRI/MSSS/John Landino

To avoid risk of misfire, NASA's Juno probe will keep its distance from Jupiter

NASA’s Juno spacecraft will remain in 53-day-long orbits around Jupiter, rather than attempting to shift closer to the planet and risk a misfire of its balky engine, the agency announced today. The longer orbits should not jeopardize the spacecraft’s scientific mission, which could now stretch until 2021, as long as its systems stay operational and funding remains.

Juno arrived at Jupiter this past July, and the original plan for the $1.1 billion spacecraft had it passing through two longer orbits before firing its engine once again to end up in 14-day orbits for the majority of its mission. However, when preparing for the maneuver in October 2016, two helium valves in Juno’s propulsion system did not pressurize properly, prompting NASA to delay the October burn. Ultimately, engineers at the Jet Propulsion Laboratory in Pasadena, California, could not find a fix that would not risk Juno’s scientific goals.

In its current, longer orbit, Juno approaches Jupiter as closely as it would have in the shorter, 14-day traverse, zipping 4100 kilometers above its clouds, allowing similar measurements. Indeed, “The science opportunities are truly better in the longer orbit,” says Scott Bolton, the project’s principal investigator and a planetary scientist at the Southwest Research Institute in Boulder, Colorado. In addition to its planned measures of Jupiter’s gravity, used to probe its cloud-shrouded interior structure, and gauging the planet’s water on its close approaches, Juno will take its extra time to measure the farther reaches of the planet’s magnetosphere—“bonus science,” the agency said.

“Juno is healthy, its science instruments are fully operational, and the data and images we’ve received are nothing short of amazing,” said Thomas Zurbuchen, NASA’s associate administrator for science in Washington, D.C., in a release. “The decision to forego the burn is the right thing to do—preserving a valuable asset so that Juno can continue its exciting journey of discovery.”

Under its previous plan, Juno was scheduled to finish its primary scientific mission of 37 orbits in early 2018 with a dive into the planet. Now, completing those same observations will require the spacecraft to operate until mid-2021. Unlike previous missions to Jupiter, Juno is powered by solar panels, not a decaying nuclear power source. Those panels, along with the limited time Juno will spend in the harshest stretches of Jupiter’s radiation belt, could help extend the spacecraft’s life.

At the least, the longer orbits will mean slower publications and delayed careers for the many scientists who are part of Juno’s team. The spacecraft’s measurements of Jupiter’s gravity, which are weighted toward the second half of its mission, will be at particular risk should Juno malfunction or NASA decide not to extend the mission. Currently, Juno is funded until July 2018, when it will have made 12 science orbits. The extended orbits could sap resources from other planetary missions, and make it less likely that the spacecraft will surpass its planned science goals and collect more data, which many planetary scientists hoped to see.

Still, the spacecraft has already taken spectacular photos of the planet, with its first scientific results expected in the next few months. Juno’s next flyby of Jupiter will occur on 27 March.