NASA embarks on 12 year mission to study 'Trojan' asteroids

The Lucy probe began a 12 mission to study Trojan asteroids, left overs from the formation of the solar system. But why are they called "Trojans"?

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Lucy spacecraft near a Trojan asteroid
Tony Rice
, NASA Ambassador

NASA's Lucy mission lifted off before dawn this morning from Cape Canaveral, Florida on a twelve year mission to study Trojan asteroids.

German astronomer Max Wolf, a pioneer in the field of astrophotography, discovered his first comet at 21, and would go on to discover over 300 asteroids.

Wolf discovered the first Trojan asteroid, which would be named 588 Achilles, on Feb. 22, 1906. Looking at a pair of photographs taken of the same part of the sky, at different times, he noticed something moving. The stereoscopic comparator he helped develop would later be used by Clyde Tombaugh in 1930 to discover Pluto.

Wolf also noticed the newly discovered asteroid shared Jupiter's orbit, about 60º ahead. A few months later, one of Wolf's graduate students discovered 624 Hektor and 617 Patroclus in a similar position trailing Jupiter.

This orbit had been predicted 100 years earlier, but not yet observed, by Italian mathematician Joseph-Louis Lagrange.

Why Trojan?

Trojan asteroids in orbit with Jupiter: Credit NASA/SwRi
Astronomers continued finding Trojans hiding in swarms around those Lagrange points, naming each for heroes of the Trojan War. Asteroids in orbit ahead of Jupiter were named for heroes of Troy. Asteroids trailing Jupiter were named for heroes of Greece.

Lagrange points.

As of a few weeks ago, there were 6,506 known asteroids in the Greek camp and 4,006 in the Trojan camp. Astronomers estimate there are about 1 million Jupiter Trojans bigger than 1 km total roughly equivalent to the number in the main astroid belt between Mars and Jupiter.

When astronomers ran out of heroes, the International Astronomical Union adjusted the naming convention for Jupiter Trojans to include modern Olympic athletes.

Last year, the Lucy mission team discovered a small Trojan asteroid orbiting one of Lucy’s flyby targets, Eurybates. The tiny satellite was named for track and field athlete Enriqueta (Queta) Basilio. Queta was the first woman to light the Olympic cauldron, when she was the final torch-bearer of the Summer Olympics in Mexico City in 1968.

Lucy will visit Eurybates (and Queta) and Polymele in 2027, Leucus, and Orus in 2028 in the "Greek camp" and Patroculs and Menoetius in the "Troy camp" in 2033. Main belt asteroid Donald Johanson, named for the paleoanthropologist who discovered Lucy's fossil namesake in Ethiopia, will help test Lucy's (the spacecraft) instruments along the way in 2025.

Named for mathemetician Joseph-Louis Lagrange who theorized small-bodies like asteroids would gather at these points of gravitational balance between larger planets and the massive Sun.

Lagrange points

Lagrange points are gravitational hilltops between the planets and the Sun. Nature has been storing solar system left overs there for billions of years and NASA has been parking spacecraft there for decades.

Lagrange points are very stable, allowing spacecraft to operate there with very little fuel required to maintain their orbits.

We will be hearing more about those Lagrange Points when the James Webb Space Telescope, named for a NASA Administrator during the Apollo era and North Carolina Native, launches in December. The next generation telescope will be positioned at L2 facing away from Earth and the Sun, into deep space.

Space is only cold in the movies, or in the shadows. The computers, solar panels, and communications equipment on JWST's "hot side" facing Earth, will be a toasty 185º F.

After launch, a tennis-court-sized sunshield will be unfurled, blocking heat and glare from the Sun as well as radio noise from Earth. This also allows the telescopes suite of instruments to operate at the 50º Kelvin (-370º F) needed to provide the best images.


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