NASA's Lucy mission to visit Jupiter's Trojan asteroids in 2021

The mission will provide new details about planetesimals - the ancient building blocks of planets

NASA is working to launch a mission in 2021 to explore Jupiter's Trojan asteroids. This mission, called Lucy, will be the first-ever space mission to study Jupiter's Trojans, and is expected to provide new details about the objects that comprised the original planetesimal disk of the solar system.

Jupiter's Trojan asteroids are the last remnants of 'planetesimals' - the ancient building blocks of planets in the solar system. These asteroids circle the Sun in synchrony with Jupiter and follow almost the same path.

They have been categorised into two loose groups - one group (named the Greek camp) always moves ahead of Jupiter in the path, while the second group (named the Trojan camp) is always behind Jupiter.

According to NASA, most of the early planetesimals were lost in the Milky Way as the orbits of the giant planets shifted in our solar system. However, some were trapped in two different regions, close to the Lagrange points (L4 and L5), where the gravitational pulls of the Sun and Jupiter balance each other. These asteroids have been orbiting the Sun for the past billions of years, and have remained mostly untouched.

NASA's Lucy mission will fly by six of these Trojan asteroids, providing us an opportunity to get the first glimpse of these trapped objects.

The mission is named after the fossil of a primitive ancestor of modern humans, which roamed on Earth nearly four million years ago. The fossilised skeleton of this primitive human was discovered by Donald Johanson - an anthropologist - in Ethiopia about 34 years ago, and was named Lucy, after the Beatles' popular song 'Lucy in the Sky with Diamonds'.

In its journey towards Trojan asteroids, Lucy spacecraft will also visit another asteroid named 'Donaldjohanson' after Donald Johanson who discovered the fossil.

Lucy mission will carry with it four main instruments:

1. L'Ralph - consisting of a multi-color imager, a Multi-spectral Visible Imaging Camera, and Linear Etalon Imaging Spectral Array (LEISA) - to investigate the presence of organics, silicates, and ices on these asteroids;
2. Long Range Reconnaissance Imager ('LORRI) to capture high-definition images of the Trojans;
3. Thermal Emission Spectrometer (L'TES) to probe the physical state of the Trojans' surfaces; and
4. Communications (radio) and target acquisition system (TTCam) to determine the mass and density of the Trojans.

According to NASA, all these Trojans are dark and reflect just four to five per cent of the light hitting them. Scientists believe these Trojans may have organic compounds on their surfaces.

"If many of the Trojans we survey show evidence of organics, it will imply that the building blocks for life were common throughout the early solar system." said Amy Simon, a deputy principal investigator at NASA Goddard.