Science & Technology

Lucy in the sky: Things to know about NASA mission to Jupiter’s Trojans

NASA’s Lucy mission is going where no one else has before. It aims to look back into the origins of the solar system through Trojans 

By Anshika Ravi
Published: Monday 18 October 2021

A United Launch Alliance Atlas V rocket with the Lucy spacecraft aboard is seen in this 2 minute and 30 second exposure photograph as it launches from Space Launch Complex 41, Saturday, Oct. 16, 2021, at Cape Canaveral Space Force Station in Florida. Lucy will be the first spacecraft to study Jupiter's Trojan Asteroids. Like the mission's namesake – the fossilized human ancestor,

Lucy is in the outer space and will go where no one else has before — to the Jupiter Trojan asteroids. Astronomers hope it will look back into the origins and evolution of the solar system formed over 4 billion years ago through these celestial bodies.

What are Jupiter Trojan asteroids?

Simply known as Trojans, they are a large group of asteroids that share the Jupiter’s orbit around the Sun. Thousands of such asteroids exist in a gravitationally stable space.

The United States National Aeronautics and Space Administration (NASA) launched Lucy, the spacecraft, October 16, 2021, on a 12-year cruise to the swarms of these Trojans.

The swarms lead and follow the planet Jupiter along its orbit around the Sun.

Lucy will fly by eight asteroids—seven Trojans and one main-belt asteroid — over the next 12 years. It is the agency’s first single spacecraft mission in history to explore so many different asteroids.

What exactly are Trojans?

Lucy’s Trojan destinations are trapped near Jupiter’s Lagrange (L) points, which are gravitationally stable locations — it is where the gravity from the Sun and from Jupiter cancel each other out. This means their orbits are stable and the Trojans are trapped in the space between.

This also means that asteroids are as far away from Jupiter as they are from the Sun.

Jupiter’s leading and trailing Lagrangian points (L4 and L5) have been stable over the age of the solar system. This means that that their orbits have accumulated many, many asteroids. It makes sense to call a Trojan a co-orbital object, which moves around one of the two stable Lagrangian points.

More than 7,000 Jupiter Trojan asteroids have been discovered as of 2020, two-thirds of which are located near L4 and the remaining near L5.

When — and how — were they discovered?

It took many a scientist to understand Trojans, and subsequently name them so.

On February 22, 1906, German astrophotographer Max Wolf made an important discovery: An asteroid with a particularly unusual orbit. As Jupiter moved, this asteroid remained ahead of Jupiter.

According to NASA:

German astronomer Adolf Berberich observed that the asteroid was nearly 60 degrees in front of Jupiter. This specific position reminded Swedish astronomer Carl Charlier of a peculiar behaviour predicted by the Italian-French mathematician Joseph-Louis Lagrange over 100 years earlier.

Lagrange had argued that if a small celestial body is placed at one of two stable points in a planet’s orbit around the Sun (the L4 and L5), the asteroid would remain stationary from the planet’s perspective due to the combined gravitational forces of the planet and the Sun.

It wasn’t until Wolf discovered the asteroid that Lagrange’s prediction acquired credibility. More such asteroids were discovered over subsequent months in Jupiter’s Lagrange point L5.

Why ‘Trojan’?

Until Wolf’s discovery, most asteroids were given the names of women from Roman or Greek mythology.

Names such as Achilles, Patroclus and Hektor were recommended from the Illiad, an ancient Greek poem.

As more and more asteroids were discovered in Jupiter’s Lagrange points, astronomers also started naming them from the Trojan War and began referring to them as ‘Trojan asteroids’.

They finally settled at both Greek and Trojan characters: Jupiter’s L4 asteroids were named after Greek characters and Jupiter’s L5 asteroids after Trojan characters.

Who is Lucy?

It is the fossil of a hominin that lived 3.2 million years ago. She is known to be one of the most famous pre-human fossil in history. Nearly 40 per cent of the fossilised skeleton of this hominin was discovered in 1974 by a team of paleoanthropologists led by Donald Johanson.  

The name was inspired from the famous Beatles song “Lucy in the Sky With Diamonds,” which Johanson’s team listened to at camp the night of their discovery.

Lucy will run on solar power out to 850 million kilometers away from the Sun. This makes it the farthest-flung solar powered spacecraft ever, according to NASA.

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