International Space Agencies – Missions and Discoveries

Lucy Mission to probe Jupiter’s Trojan Asteroids


From UPSC perspective, the following things are important :

Prelims level : Lagrange Points, Lucy Mission

Mains level : NA

NASA is set to send its first spacecraft to study Jupiter’s Trojan asteroids to glean new insights into the solar system’s formation 4.5 billion years ago.

Lucy Mission

  • Lucy will fly by eight Jupiter asteroids—seven Trojans and one main-belt asteroid — over the next 12 years.
  • It is NASA’s first single spacecraft mission in history to explore so many different asteroids.
  • Lucy will run on solar power out to 850 million km away from the Sun.
  • This makes it the farthest-flung solar-powered spacecraft ever, according to NASA.

What is Jupiter Trojan Asteroids?

  • Simply known as Trojans, they are a large group of asteroids that share Jupiter’s orbit around the Sun.
  • Thousands of such asteroids exist in a gravitationally stable space.
  • The swarms lead and follow the planet Jupiter along its orbit around the Sun.

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 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.

When and how were they discovered?

  • It took many a scientist to understand Trojans, and subsequently, name them so.
  • A German astrophotographer in 1906 made an important discovery: An asteroid with a particularly unusual orbit. As Jupiter moved, this asteroid remained ahead of Jupiter.
  • It was observed that the asteroid was nearly 60 degrees in front of Jupiter.

Students with engineering background would better understand who Lagrange was. Rest need not care.

Lagrange’s propositions

  • This specific position of a particular behavior was 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.
  • This is due to the combined gravitational forces of the planet and the Sun.
  • Thus, Lagrange’s prediction acquired credibility. More such asteroids were discovered over subsequent months in Jupiter’s Lagrange point L5.

Behind the name: 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 fossils in history.
  • Nearly 40 percent of the fossilized 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.

Back2Basics: Lagrange Points

  • Lagrange points are positions in space where objects sent there tend to stay put.
  • They are named after Italian-French mathematician Josephy-Louis Lagrange.
  • At Lagrange points, the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them.
  • These points in space can be used by spacecraft to reduce the fuel consumption needed to remain in position.
  • There are five special points where a small mass can orbit in a constant pattern with two larger masses.


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