This story is one for both the astrophotographers and the planetary scientists, but not for Pamela because I’m going to discuss a mission that hasn’t launched, yet. That mission is Lucy, which is a NASA Discovery Program mission to explore Trojan asteroids and a main-belt asteroid. It’s a twelve-year mission, and the launch window opens up on October 16 of this year.

So what are the Trojan asteroids? How did we find them? Here is where astrophotography comes in.

In the late 1800s, German astrophotographer Max Wolf had already made a name for himself at the ripe old age of 21 by discovering his first comet. At 27, he decided to search for new asteroids using wide-field photography – the first person to attempt such a feat. Within two years, he had found eighteen new asteroids. After that, he became the first person to use a “stereo comparator”, which is like a View-Master, that helped make those asteroids more easily visible against the background of stars.

Then in 1906, Wolf found an asteroid with what appeared to be an unusual orbit – it remained ahead of Jupiter as Jupiter moved. Another German astronomer, Adolf Berberich, confirmed the discovery and noted that the asteroid’s orbit was about sixty degrees in front of Jupiter.

And here is where work by Joseph-Louis Lagrange comes in. I’m sure a lot of our regular viewers are familiar with Lagrange points, but let’s give a quick summation for those who are not. Lagrange was a mathematician who theorized that a small body, like an asteroid, could be caught in the same orbit as a planet if it ended up at one of two stable points in that orbit, what we now call the L4 and L5 Lagrange Points. Essentially, at sixty degrees ahead of or behind, the smaller body benefits from the combined gravitational forces of the planet and the Sun. If you could stand on Jupiter, these asteroids would look like they weren’t moving.

Up until Wolf’s discovery, Lagrange’s work was purely mathematical. Now, astronomers had photographic evidence.

Within a few months, two more of these Lagrange point asteroids had been discovered by other astronomers. And now that there were several, it was time to give them a name. Remember, astronomers like objects to fit into boxes, and then we name those boxes. Most of the asteroids in the main asteroid belt had been given the names of women from Roman and Greek mythology — think Ceres or Vesta — so Austrian astronomer Johann Palisa suggested these new Jupiter asteroids be called Achilles, Patroclus, and Hektor after characters in The Iliad. And so, a naming convention was born.

But not quite. Here’s where the story gets fun, and I’m going to quote a NASA article because it’s perfect.

As astronomers continued discovering asteroids hiding in Jupiter’s Lagrange points, they continued naming them after heroes of the Trojan War and began referring to them as “Trojan asteroids.” (“Trojan asteroids” would eventually refer to asteroids inhabiting any planet’s stable Lagrange points, though names from The Iliad are reserved for Jupiter’s Trojans.) It later became convention to name Jupiter’s L4 asteroids after Greek characters and Jupiter’s L5 asteroids after Trojan characters, so L4 and L5 became the “Greek camp” and the “Trojan camp” respectively. Palisa apparently did not foresee this tradition, for his naming of first three asteroids led to a Greek “spy” residing in the Trojan camp (Patroclus) and a confused Trojan (Hektor) who probably wandered into the Greek camp hoping to order some of their famous custom-built wooden horses.

These Trojan asteroids are thought to be the remnants of the material from which our outer planets formed. Some resemble icy bodies found in the Kuiper Belt, some resemble main-belt asteroids. All are thought to have an abundance of dark carbon compounds as well as an insulating blanket of dust that covers a wealth of water and other volatiles.

Now for the first time, we are sending a mission to study some of these Trojans, including Patroclus. The Lucy spacecraft is named for the skeleton of a human ancestor whose discovery led to breakthroughs in our understanding of human evolution. The spacecraft is expected to do the same for our understanding of planetary formation and evolution here in our solar system.

After Lucy’s launch, the craft will use boosts from Earth’s gravity to travel between the L4 and L5 Trojans, targeting seven asteroids in total, including one main-belt asteroid, Donalddjohnason [Ed. note: This asteroid is named for one of the co-discoverers of the Lucy fossils]. The initial mission will take twelve years to complete, and after that, Lucy will continue to cycle back and forth between the two points every six years. We’re excited about this launch, and we’ll keep you up-to-date on the timeline here on Daily Space.

More Information

NASA article

Lucy mission overview (NASA)