Level 1 - Absolute Beginner

A NASA spacecraft called Lucy flew very close to a big rock in space. The rock is called an asteroid. Its name is Donaldjohanson.

Scientists found that Donaldjohanson looks like a peanut. It is about 8 kilometres long. It is made of two pieces that stuck together a very long time ago.

Lucy took pictures and collected information about the asteroid. Scientists study this information to learn how the solar system was made.

The results surprised many scientists. The asteroid looks different from what they expected. They will keep studying the data to learn more.

spacecraft

a vehicle that travels in outer space

asteroid

a large rock that travels around the Sun in space

scientist

a person who studies nature and the world using experiments and evidence

solar system

the Sun and all the planets and other objects that orbit it

data

information collected by scientists or computers

surface

the outside layer of something

kilometre

a unit of length equal to 1,000 metres

discover

to find something for the first time

Level 2 - Elementary

Scientists have published exciting new results from NASA's Lucy spacecraft, which flew close to an asteroid named Donaldjohanson in April 2025. The findings appeared this week in the journal Nature.

The study revealed that Donaldjohanson is a contact binary, meaning it is formed from two separate bodies that collided and merged billions of years ago. Together they form a peanut shape about 8 kilometres long.

Lucy's instruments mapped the asteroid's surface in detail. Scientists found a smooth ridge around the middle, very few minerals that contain water, and long cracks called fault scarps on the surface. These cracks suggest the asteroid was geologically active more recently than expected.

The Lucy mission was launched in 2021 to study a group of asteroids called Trojans that share Jupiter's orbit. Donaldjohanson was an extra target on the way. Scientists say the new data will help them understand how the solar system formed billions of years ago.

contact binary

an object made of two bodies that have touched and merged while both still keeping their original shapes

journal

a scientific publication where researchers share new findings

instrument

a scientific tool used to measure or detect something

ridge

a long narrow raised area of land or on a surface

fault scarp

a steep cliff or step formed when the ground breaks along a crack and one side drops lower

geologically active

describing a body that has experienced geological changes such as quakes, eruptions, or surface movement

Trojans

asteroids that share an orbit with a large planet, staying near two gravitationally stable points

composition

the materials that something is made of

Level 3 - Intermediate

Newly published results from NASA's Lucy spacecraft flyby of asteroid Donaldjohanson, appearing this week in Nature, have reshaped scientists' understanding of small body geology in the inner solar system. Lucy passed within 960 kilometres of Donaldjohanson in April 2025, collecting high-resolution imagery and spectral data that have now been fully analysed.

The most striking finding is that Donaldjohanson is a contact binary roughly 8 kilometres in length, formed when two originally separate bodies collided at low velocity billions of years ago and merged without fully mixing. The resulting peanut-shaped object shows a pronounced equatorial ridge at the neck connecting the two lobes, a feature geologists believe was created by slow mass transfer from one lobe to the other during an early period of spin-down.

Surface spectroscopy revealed a composition depleted in hydrated silicates, indicating that Donaldjohanson lost most of its volatile material early in the solar system's history, probably through heating by the young Sun or through collisional gardening. More surprisingly, a network of fault scarps indicates relatively recent tectonic activity, suggesting the asteroid has continued to deform under its own internal stresses long after scientists assumed such small bodies had become geologically inert.

The findings complicate existing formation models and raise questions about the thermal and mechanical history of inner solar system bodies. The Lucy team plans two flyby encounters with Trojan asteroids near Jupiter's L4 and L5 Lagrange points between 2027 and 2033, encounters expected to provide comparison data that will test whether Donaldjohanson's unusual characteristics are typical or anomalous.

contact binary

an object composed of two lobes that formed separately and merged at low velocity, retaining their individual shapes

spectral data

information about the wavelengths of light reflected or emitted by an object, used to identify its chemical composition

equatorial ridge

a raised band of material running around the middle of a planetary body, often formed by mass redistribution

hydrated silicate

a mineral that contains water molecules chemically bound into its structure, indicating past exposure to liquid water

volatile

easily evaporated; in planetary science, referring to materials such as water ice or carbon compounds that are lost at relatively low temperatures

tectonic activity

movement and deformation of a body's outer layer due to internal stresses

Lagrange point

one of five gravitationally stable positions where a small object can maintain a fixed position relative to two larger bodies

geologically inert

no longer undergoing any internal geological processes or surface deformation

Level 4 - Advanced

The Nature publication of Lucy flyby data from asteroid Donaldjohanson introduces empirical constraints that significantly challenge the canonical rubble-pile accretion model for kilometre-scale inner solar system bodies. High-resolution imaging at a closest approach of 960 kilometres enabled the Lucy team to resolve surface features at sub-metre scale, revealing a morphological complexity inconsistent with a simple undifferentiated aggregate.

Donaldjohanson's contact-binary morphology, defined by two lobes of contrasting albedo and crater density connected by an equatorial neck bearing a pronounced compressional ridge, indicates a low-velocity merger event rather than a disruptive collision. Rotational modelling constrained by light-curve data suggests the pre-merger components spun down gradually through YORP (Yarkovsky-O'Keefe-Radzievskii-Paddack) thermal torque before mass transfer across the neck stabilised the combined system at its current 8.5-hour rotation period.

The volatile depletion inferred from near-infrared spectra, specifically the absence of the 0.7-micron phyllosilicate absorption feature, places Donaldjohanson in the S-complex taxonomic class and implies early thermal processing within approximately 3 AU of the protosun. More unexpected is the system of extensional fault scarps concentrated in the southern lobe, whose freshness index, derived from crater superposition statistics, suggests resurfacing within the last few hundred million years, an order of magnitude more recently than models predict for a body of this size and heliocentric distance.

These findings carry implications beyond Donaldjohanson itself. If fault scarps of comparable youth are identified on the Trojan targets during Lucy's 2027-2033 encounters, it would suggest that tidal and orbital evolution mechanisms capable of inducing late-stage geological activity are more widespread among small bodies than current dynamical models accommodate. The data also inform ongoing debate about the primordial compositional gradient between the inner and outer solar system and the degree to which radial mixing during the Grand Tack instability homogenised the planetesimal population.

rubble-pile accretion model

the hypothesis that small bodies such as asteroids formed by gradual gravitational accumulation of loosely bound debris rather than monolithic rock

YORP effect

a slow change in the rotation rate and axial tilt of a small body caused by asymmetric re-radiation of solar heat

phyllosilicate absorption feature

a spectral signature at 0.7 micrometres indicative of hydrated clay minerals, signalling past aqueous alteration

S-complex taxonomy

a classification of silicaceous asteroids characterised by moderate albedo and spectral features dominated by olivine and pyroxene

extensional fault scarp

a cliff formed when a body's crust is pulled apart under tensional stress, causing one block to drop relative to another