Level 1 - Absolute Beginner

Scientists have found something very special buried deep under the Pacific Ocean. They discovered tiny amounts of a material called plutonium-244 on the ocean floor. This type of plutonium does not come from Earth. It came from space.

The plutonium was made in a huge explosion in space called a kilonova. A kilonova happens when two very dense dead stars crash into each other. This explosion creates heavy materials like gold, silver, and plutonium.

The plutonium then fell to Earth and settled on the bottom of the ocean. Scientists can study these tiny amounts of material to learn more about stars and space events that happened a very long time ago.

plutonium

a radioactive material that can be found in nature or made in nuclear reactors

ocean floor

the ground at the very bottom of the sea

explosion

when something suddenly and violently bursts apart with a large release of energy

dense

having a lot of material packed very tightly into a small space

gold

a shiny yellow metal that is very valuable

sediment

material such as sand, rock, or dust that settles to the bottom of a liquid

stellar

relating to or coming from stars

kilonova

a very powerful explosion that happens when two neutron stars collide in space

Level 2 - Elementary

Scientists have discovered plutonium-244, a radioactive element produced in space, in samples of rock taken from the Pacific Ocean floor. The discovery was published in the journal Nature Astronomy. The plutonium was found inside ferromanganese crusts, which are layers of metal-rich rock that grow very slowly on the deep ocean floor over millions of years.

Plutonium-244 has a half-life of 81 million years, which means it takes 81 million years for half of it to disappear naturally. Scientists say this type of plutonium cannot be made inside normal stars. It is created in an event called a kilonova, which happens when two extremely dense dead stars called neutron stars collide and explode.

The kilonova that produced this plutonium happened somewhere in our galaxy within the last billion years. When the explosion occurred, it scattered heavy elements including gold, platinum, and plutonium through space. Some of this material eventually reached Earth and settled on the ocean floor, where it has been preserved in the rock layers.

radioactive

describing a material that releases energy as its atoms naturally break apart

ferromanganese crust

a layer of iron- and manganese-rich rock that slowly builds up on the deep ocean floor

half-life

the time it takes for half of a radioactive material to decay naturally

neutron star

the extremely dense core left behind after a massive star explodes; a teaspoon of its material would weigh billions of tonnes

platinum

a rare and valuable silvery-white metal used in jewellery and industry

galaxy

a large system of billions of stars, gas, and dust held together by gravity

preserve

to keep something in its original condition over a long period of time

scatter

to throw or spread things in many different directions

Level 3 - Intermediate

Researchers from a European-Australian collaboration published a study in Nature Astronomy confirming the detection of extraterrestrial plutonium-244 (Pu-244) in ferromanganese crusts recovered from the Pacific Ocean floor. Ferromanganese crusts grow at a rate of just 1 to 10 millimetres per million years, making them extraordinarily precise archives of the materials that settled from the water column over geological time. By sampling different depth layers within the crust, the team was able to assign approximate dates to the plutonium signal, narrowing the kilonova event to within the last billion years but more than 100 million years ago.

The key evidence distinguishing a kilonova origin from a supernova origin was the absence of curium-247 (Cm-247). Both kilonova and supernova events produce Pu-244, but only supernovae produce Cm-247 in comparable quantities. The absence of Cm-247 alongside the presence of Pu-244 therefore indicates that the source event was a kilonova, a merger of two neutron stars. This r-process nucleosynthesis, in which neutron-rich atomic nuclei rapidly capture free neutrons to build heavy elements, is the primary pathway for creating elements heavier than iron that cannot be made inside ordinary stars.

The significance of the discovery lies in its confirmation that kilonovae are a realistic source of r-process heavy elements reaching the inner solar system. Previous evidence for kilonova-produced material in the geological record was largely theoretical or based on isotopic anomalies in meteorites. Finding Pu-244 in a slowly accumulated terrestrial archive provides a new and sensitive tool for dating and localising past nucleosynthetic events in the Milky Way's history.

extraterrestrial

originating or existing outside the Earth or its atmosphere

geological time

the vast timescales over which the physical history of the Earth is measured, spanning billions of years

r-process nucleosynthesis

the rapid neutron capture process by which heavy elements are built up in extreme astrophysical environments

curium

a radioactive element heavier than plutonium that is produced in supernovae but not in significant quantities by kilonovae

isotopic anomaly

an unusual ratio of isotopes of an element compared to standard solar system values, indicating an exotic source

nucleosynthetic

relating to nucleosynthesis, the process by which atomic nuclei are created in stars and stellar explosions

water column

the continuous body of water from the ocean surface to the sea floor

merger

the joining together of two objects; here, the collision and combining of two neutron stars

Level 4 - Advanced

A research consortium spanning European and Australian institutions has reported in Nature Astronomy the detection of live extraterrestrial Pu-244 in ferromanganese crust samples dredged from the Pacific Ocean floor. With a half-life of 80.8 million years, Pu-244 is the longest-lived superheavy nuclide short of primordial uranium and thorium. Its detection as a live radioisotope (meaning measurable activity remains rather than purely stable daughter products) constrains the production event to within approximately one to three half-lives prior to deposition, placing the kilonova within the last billion years but no more recently than roughly 100 million years ago, a window inferred from the co-absence of shorter-lived r-process nuclides such as Cm-247 (t1/2 = 15.6 Myr).

The forensic discrimination between kilonova and core-collapse supernova origin rests on the differential r-process yield ratios of the actinide series. Core-collapse supernovae, particularly those with very neutron-rich ejecta from the neutrino-driven wind mechanism, produce both Pu-244 and Cm-247, whereas neutron star mergers favour the third r-process peak through a higher neutron-to-seed ratio, producing large quantities of Pu-244 while yielding Cm-247 below detection thresholds. The observed ratio (Pu-244 present, Cm-247 undetected) is thus a robust kilonova fingerprint. The absolute abundance of Pu-244 in the crust layers further constrains the event distance to within approximately 300 parsecs of the pre-solar nebula, consistent with ejecta reaching the inner solar system at the dilution levels observed.

Beyond the immediate result, the study demonstrates that ferromanganese crusts function as a novel class of cosmic ray and interstellar medium detector, complementing established archives such as deep-sea nodules and Antarctic micrometeorite collections. The growth rate of 1-10 mm per million years and the capacity for continuous accretion over hundreds of millions of years allow sub-million-year temporal resolution for late Phanerozoic events and Myr-scale resolution deeper in the stratigraphic column. Future surveys coupling Pu-244 measurements with I-129, Fe-60, and Mn-53 profiles from the same crust layers could disentangle multiple nucleosynthetic episodes, offering a window into the stochastic history of massive star and compact object mergers in the Galactic thin disk over the last few billion years.

superheavy nuclide

an atomic nucleus with an exceptionally high number of protons and neutrons, here referring to elements in the actinide series

actinide series

the group of 15 metallic elements from actinium (atomic number 89) to lawrencium (103), all of which are radioactive

neutrino-driven wind

the outflow of material from a newly formed neutron star powered by the enormous flux of neutrinos released during a core-collapse supernova

third r-process peak

the group of heavy elements around mass number 195 (including platinum and gold) most efficiently produced in neutron star mergers