The Visitation of Jupiter’s Trojan Asteroids

NASA has launched an impressive and ambitious 12-year mission to study the Jovian Trojans, two groupings of asteroids that share Jupiter’s orbit. The spacecraft making the trip, built by Lockheed Martin and launched with United Launch Alliance’s Atlas V rocket for NASA on October 16th is called ‘Lucy’ and will travel 4 Billion miles through space to fly by and study eight asteroids in detail. Jupiter’s Trojans orbit the sun at two of the gas giant’s Lagrange points about sixty degrees ahead of it and sixty degrees behind. Because of Jupiter’s massive gravity, distance from the sun, and proximity to the asteroid belt, where for example earth only possesses two trojan asteroids that share its orbit that we know of, Jupiter has thousands. And some of these asteroids are huge, hundreds of kilometers in size. If their orbits were to be disturbed by a passing comet, for example, most of them could definitely ruin our day.

The largest Jupiter Trojan: 624 Hector is so huge, that it qualifies as a minor planet and even has its own moon: Skamandrios discovered in 2006. Unfortunately, Lucy won’t be visiting Hector and Samandrios, but it will be studying the second-largest Jupiter Trojan, in fact, a binary pair of asteroids Patroclus & Menoetius in March of 2033. Binaries like this are typical in the outer edge of the solar system past Neptune but are extremely rare further in.

According to the Southwest Research Institute’s mission tour of Lucy,

“On its way out to the Trojan asteroids, Lucy will travel through the main asteroid belt and fly by its first asteroid on April 2025. It will fly by (52246) Donaldjohanson, an asteroid that the Lucy team named after one of the co-discoverers of the Lucy fossil.

The Lucy spacecraft will continue outwards in to the leading swarm of Trojan asteroids, the L4 Trojan swarm. This is also known as the “Greek camp” of Trojan asteroids as most of the asteroids in this swarm (other than the Trojan “spy” Hektor) are named after Greek heroes around the time of the Trojan war. Lucy will fly by four of these “Greek” Trojans: (3548) Eurybates and its satellite Queta in August 2027, (15094) Polymele in September 2027, (11351) Leucus in April 2028, and (21900) Orus in November 2028.

The spacecraft’s orbit will then take Lucy back towards the orbit of Earth. When its orbit takes the spacecraft outwards again, Jupiter and the Trojan swarms will have rotated so that the spacecraft will pass through the trailing L5 swarm of Trojans Asteroids, otherwise known as the “Trojan camp.” Here, on March of 2033, Lucy will fly past the Greek “spies” in the Trojan camp, (617) Patroclus and its binary companion Menoetius. The flyby of this binary asteroid pair will be the grand finale of the mission. However, Lucy will be on a stable orbit and can continue flying through the Trojan swarms for many years to come.”

Spreadsheets In Jupiter’s Space

You’re never going to look at your Microsoft Office suite the same way again. What multi-billion dollar, high-powered NASA supercomputer, and software suite did they use to make the complex calculations necessary to plot the probe’s trajectory? Something from IBM? Or pioneered by the JPL? Nope, it was Microsoft Excel running a Macro… nope, not kidding. Granted… it was a very good Macro, but still Excel!

CNBC reported,

“Years before Lucy took off, Lockheed Martin mission architect Brian Sutter used Excel to chart the mission’s path and choose which of the about 5,000 Trojan asteroids the spacecraft should visit.

“Part of the science of this mission was to try to look at as many of these Trojans as we can in a single mission,” Sutter told CNBC.

While Lockheed Martin has a “high fidelity” tool to run individual trajectories, Sutter said that would have taken “forever.” He instead turned to an Excel macro, which is “perfectly suited for sorting through large quantities of data.”

“I had already found a trajectory that connected two of the asteroids to a trajectory that also connected to Earth,” Sutter said.

Orbit propagation – or modeling the future location of objects in space – “is what I do,” Sutter explained. While his macro consists of “different equations than you’d normally put into Excel,” he emphasized that “at the end of the day it’s all math.”

Lucy’s launch went largely to plan with the $981 million mission moving forward. Even though the launch was successful and Lucy is on course, it just wouldn’t be 2021 without a slight glitch, and NASA told the press on Oct. 17th that one of the two circular solar arrays “may not be fully latched.” But NASA doesn’t expect it to pose a problem,

“Lucy can continue to operate with no threat to its health and safety,” NASA said. “The team is analyzing spacecraft data to understand the situation and determine next steps to achieve full deployment of the solar array.”

The Lucy mission hearkens back to the excitement of the scientific excitement that surrounded the Voyager, Galileo, and New Horizons missions, and could provide us with spectacular images of our outer solar system unlike any we’ve ever seen before.