Meteorite hunters may have found the largest known chunk of the Bronze Age Kaali Meteorite.

Two Polish meteorite hunters, Filip Nikodem and Andrzej Owczarzak, have recovered what they believe to be a fragment of the Kaali Meteorite, a large body which impacted the Estonian island of Saaremaa about 3500 years ago. The piece is reported to weigh about 40 kg, with a second fragment weighing 15 kg also found. The largest potential fragment of the meteorite discovered to date weighed 5.7 kg, and was found by Filip Nikodem in the spring of 2024.

A 40 kg potential fragment of the Kaali Meteorite found in Estonia by two Polish Meteorite Hunters. Z głową w gwiazdach/Facebook.

The Kaali Impact Structures are a series of nine circular crater lakes on the island of Saaremaa, the largest of which has a diameter of 110 m and a depth of 22 m. These are thought to have been caused by an object with a mass of between 20 and 80 tonnes entering the atmosphere at a velocity of somewhere between 10 and 20 km per second, and exploding in a fireball between 10 and 5 km above the ground. This explosion is thought to have largely vaporised the bolide, as well as removing about 81 000 m³ of rock on the ground, and incinerating vegetation up to 6 km from the impact site.  

The lake in the main Kaali Meteorite Crater on Saaremaa Island. The crater is about 110 m across, but the lake only occupies the central part of it. Wikimedia Commons.

This is thought to have happened about 3500 years ago, when the island was occupied by a Bronze Age population, although attempts to date the site and meteorite fragments from it have produced dates of between 5600 and 400 BC. A Bronze Age arrowhead made from meteoric iron which was found in Switzerland in the 1870s has been linked to the Kaali meteorites on the basis of its metallurgy, making a date of around 1500 BC more plausible.

(a) Overview of the Mörigen arrowhead (A/7396). Note adhering bright sediment material. Remnants of an older label on the left of the sample number. Total length is 39.3 mm. ( b) Side view of the Mörigen arrowhead. Layered texture is well visible. Point is to the right. Thomas Schüpbach in Hofmann et al. (2023).

Prior to 2023, the largest fragment of meteorite found at the Kaali sites weighed 6.21 g. However, in the autumn of that year Filip Nikodem obtained a search permit for the area, and, using a metal detector, found a series of pieces of iron which he believed to be meteoric in origin. These were handed to the Estonian National Heritage Board, who sent them to the University of Tartu, where a rapid X-ray fluorescence analysis found that the iron pieces contained between 0.6% and 4.8% nickel, as well as traces of titanium and vanadium, which is typical of meteoric iron.

The four pieces of meteoric iron handed to the Estonian National Heritage Board  by Filip Nikodem in 2023. Kristo Oks/University of Tartu.

In the spring of 2024, Filip Kikodem returned to the Kaali Lakes, collecting several more fragments with a total mass of 10.5 kg, the largest of which weighed 5.7 kg, making it (at that time) potentially the largest chunk of the Kaali bolide ever discovered. However, despite requests from the Estonian National Heritage Board, these pieces have never been surrendered to them. Instead, the Estonian authorities believe that the pieces were taken to Poland, where they are being analysed at a Polish university. Furthermore, the National Heritage Board received a letter from a lawyer in Poland, asserting Nikodem's ownership rights over the meteorite fragments.

A 5.7 kg possible meteorite fragment found by Filip Nikodem at Kaali Lakes in the spring of 2024. Filip Nikodem.

In the autumn of 2024 Filip Nikodem returned to Kaali Lakes, this time accompanied by meteorite hunter Andrzej Owczarzak, who did not posses a permit to search in Estonia, and was therefore in breach of Estonian heritage laws. At this time concerns were raised by the Estonian newspaper Saarte Hääl, which observed that the original search permit had been given to Filip Nikodem in relation to a two week project run by the University of Tartu in 2017, in which metal detectorists were given a short training course by the university then allowed to collect fragments for a display at a visitor centre, with the collectors being allowed to keep some fragments as a reward.

Saarte Hääl also noted that suspiciously large chunks of 'Kaali Meteorite' had begun to be offered for sale in Poland, and that some Polish enthusiasts had raised concerns that these might be fragments of the more common Morasko Meteorite, which fell near Potsdam about 5000 years ago. The newspaper also noted that Estonian law provides no specific protection for meteorites found in the country, although there are some restrictions upon where a metal detector can be used. 

Following the announcement of these discoveries, Jüri Plado of the University of Tartu applied for funding for a study on the feasibility of changing the law to protect meteorites found in Estonia, reasoning that such large objects would be a significant piece of national heritage and ought to be studied at an institute within the country, but this application was rejected. 

Local farmers talked to by Saarte Hääl stated that the Poles had shown them permits and promised to take any material found to the University of Tartu. However, several expressed doubts that the iron found was in fact meteoric, as it came from shallow depths on farmland, likely to have been disturbed since the Bronze Age, and resembled bog iron (impure iron deposits which precipitate out of solution in boggy soils). The newspaper contacted Kristo Oks of the Estonian National Heritage Board, who confirmed that it would be impossible to tell the difference between bog iron and meteorites without laboratory analysis. 

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World Tsunami Awareness Day.

November 5 2025 will mark the tenth annual World Tsunami Awareness Day. The event this year is dedicated to the theme 'Be Tsunami Ready: Invest in Tsunami Preparedness'. This intended to raise awareness of the risks presented by tsunamis, and promote investment in in tsunami early warning, evacuation mapping, risk education, and regular drills reduce mortality, limit disruption, and protect development gains along coasts. 

Social media art for World Tsunami Awareness Day 2025. United Nations Office for Disaster Risk Reduction.

World Tsunami Awareness Day was adopted as an annual event in December 2015, as part of the Sendai Framework for Disaster Risk Reduction, a program intended to run from 2015 to 2030, which aims to increase the world's resilience to natural disasters, by providing United Nations member states with actions intended to protect development gains from natural disasters. The Sendai Framework is intended to run in concert with the Paris Agreement on climate change. The Sendai Framework was intended as the successor to the Hyogo Framework for Action, which was founded in 2005, in response to the Boxing Day Tsunami of 2004, which killed over 227 000 people in coastal communities around the Indian Ocean.

The word tsunami derives from the Japanese 津波 (tsu-nami), meaning 'harbour wave'. The term refers to the large waves which occur when large water movements enter an enclosed coastal area, such as harbours. The initial water movements are typically caused by geological events such as Earthquakes, volcanoes, landslides, or even meteor impacts, and can be almost invisible when crossing deep water, but become deadly when entering shallow and confined spaces. A tsunami typically takes the form of a sudden drop in sea level, often exposing areas of the seabed not normally exposed, followed by an inrush of water which sweeps over low-lying areas, often sweeping away coastal communities.

The Boxing Day Tsunami of 2004 was caused by a Magnitude 9.2 Earthquake off the west coast of northern Sumatra, and caused waves up to 30 m high to sweep over coastal communities in Indonesia, Thailand, Sri Lanka, the Maldives, and parts of India, with fatalities recorded as far away as South Africa.

Animation showing the movements of the 2004 Boxing Day Tsunami. NOAA/Center for Tsunami Research/Wikimedia Commons.

The 2011 Tōhoku Tsunami was caused by a Magnitude 9.0 Earthquake off the coast of the Oshika Peninsula, Japan, and caused waves over 40 m high travelling at speeds of over 700 km per hour to overwhelm communities as far as 10 km from the coast. This led to over 19 750 deaths, and the destruction of the Fukushima Nuclear Power Plant.

The 1883 Krakatoa eruption (in which the Krakatoa volcano essentially exploded) caused a tsunami within the Sunda Straight (which separates Sumatra from Java) with a maximum recorded height of 46 m, washing away coastal communities on both islands, and many smaller ones, and killing over 36 000 people, with fatalities recorded as far away as Sri Lanka.

The Minoan eruption, which occurred around 1600 BC, is destroyed much of the island of Santorini, and triggered a tsunami which swept over the island of Crete, destroying the Minoan civilisation which was based there. It has been suggested that the waves also reached other civilisations around the Eastern Mediterranean, including Egypt, although this has been hard to prove.

The Storegga Submarine Landslide, which occurred some time between 6225 and 6170 BC, displaced about 3500 km³ of material along a 290 km stretch of the continental shelf off the coast of Norway. This triggered a tsunami which scoured about 600 km of Scottish coastline, with waves reaching about 29 km inland, wiping out the Mesolithic civilisation which dwelt there. It has also been suggested that tsunamis caused by this event may have swamped Doggerland, the former landbridge which connected Great Britain to the European continent, although it is now generally accepted that this was drowned by rising waters associated with melting glaciers at the end of the Pleistocene.

No known example of a meteorite causing a tsunami has been recorded in Human history. However, the Chicxulub Impact at the End of the Cretaceous is thought to have caused waves up to 600 m high to hit the coast of what is now Louisiana, causing major sediment redistributions from Texas to Florida.

Tsunamis, therefore, present a series threat to coastal, and in extreme cases non-coastal communities and infrastructure. Human survival in the face of such events is often dependent on good early warning systems; part of the reason that the 2004 Boxing Day Tsunami was so deadly was that the Indian Ocean did not have a tsunami warning system similar to that which had been in place in the Pacific since 1965. One of the achievements of the Hyogo Framework being the establishment of the Indian Ocean Tsunami Warning and Mitigation System in 2006.

Social media art for World Tsunami Awareness Day 2025. United Nations Office for Disaster Risk Reduction.

The concept of World Tsunami Awareness Day 2025 is to promote five courses of action to protect coastal communities from the dangers of tsunamis. 

The first of these calls on national and local governments, finance ministries, development banks, insurers, and private investors to commit multi-year financing for tsunami preparedness and multi-hazard early warning systems. 

The second calls upon coastal municipalities, community groups, school systems, tourism operators, and media partners to elevate tsunami readiness, enrol in recognized community frameworks, and showcase real-world success stories. 

The third calls for disaster management authorities, educators, non-governmental organisations, and local media to co-develop and distribute tsunami risk-communication toolkits, and to institutionalise regular public education and community drills aligned with readiness indicators.

The fourth calls upon mayors, civil protection leads, school principals, health and port authorities, and faith/youth leaders to serve as visible champions for tsunami preparedness in their communities.

Finally, the fifth course of action calls upon research institutions, technology providers, and public agencies to promote international awareness and knowledge-sharing of disaster-risk-reduction technologies adapting and piloting them in high-risk coastal areas.

Social media art for World Tsunami Awareness Day 2025. United Nations Office for Disaster Risk Reduction.

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The Nqweba Bolide and Meteorite Fall Event.

It is thought that more than a hundred tons of cosmic debris enters the Earth's atmosphere every day, mostly in the form of micrometeorites, dust-to-gravel sized particles. Most particles entering the upper atmosphere are derived from the tails of comets, but others are remnants of the original protoplanetary disc from which the Solar System formed, or fragments from the surface of other planets or moons, knocked free by earlier impacts. When these objects enter the atmosphere, they generally do so at very high velocities, causing them to heat rapidly as they pass through the atmosphere, and causing their surfaces to melt and the surrounding gasses to ionise. This can result in a bright streak across the sky called a meteor.

Larger bodies penetrate further into the atmosphere, burning longer and brighter, with those a few tens of centimetres in diameter producing meteors brighter in the sky than the planet Venus, which are termed 'fireballs'. Particularly large fireballs can sometimes be seen to visibly disinitegrate, and are known as bolides. The break up of such bolides is often audible from the ground, although, since they are typically tens of kilometres high, the sound typically reaches observers some time after the visible meteor, which can be confusing.

In a paper published in the South African Journal of Science on 29 May 2025, Roger Gibson of the School of Geosciences at the University of the Witwatersrand, Timothy Cooper of the Comet Asteroid and Meteor Section of the Astronomical Society of Southern Africa, Leonidas Vonopartis, also of the School of Geosciences at the University of the Witwatersrand, Carla Dodd of the Department of Geosciences and Institute for Coastal and Marine Research at Nelson Mandela University, Peter Hers of the Garden Route Centre of the Astronomical Society of Southern Africa, and Lewis Ashwal and Robyn Symons, once again of the School of Geosciences at the University of the Witwatersrand, describe a bolide event which took place over the coastal belt between Mossel Bay and Gqeberha, and as far north as the southern Karoo, on 25 August 2024.

Slightly before 9.00 am on Sunday 25 August 2024, residents of the area between Mossel Bay and Gqeberha and the southern Karoo heard a noise described as like rolling thunder which persisted for more than 30 seconds, despite the sky being clear of thunderclouds. Some residents of this area also reported ground tremors.

This provoked a great deal of speculation on social media, with people hypothesizing an earthquake, landslide, vehicle collision, aircraft crash, gas or electrical infrastructure explosion, or other events. At 9.02 am, Zoë van der Merwe of Cape St Francis posted a a cluster of rapidly moving, bright, silver-white fireballs in the sky that extinguished within seconds in the general vicinity of Gqeberha.

Selected frame-by-frame analysis of Zoë van der Merwe’s video (reproduced with permission) showing the bolide post-disruption phase with multiple secondary fragments flaring individually over about two seconds before entering dark flight. Gibson et al. (2025).

There is currently a global effort to better understand atmospheric fireball events, involving organisations in many different parts of the world. In Southern Africa, the Astronomical Society of Southern Africa maintains a database of fireball events, with a dedicated webpage where members of the public can report events. They also actively seek out reports of fireballs on social media, and quickly became aware of Zoë van der Merwe's post, and other reports of the Nqweba event, leading them to share reporting guidelines on social media groups. They also received reports of a bulletin on Luister FM, a radio station based in Port Elizabeth, which stated that a meteorite had been observed falling into the sea off the Eastern Cape at around 8.55 am.

Armed with these sources of data, they set out to determine whether the observed objects were in fact derived from a Solar System body, rather than being Human-made space junk re-entering the atmosphere. This is less complex than it sounds, as space junk will typically enter the atmosphere at a low angle and with a slow velocity, most often as a series of such events as debris from the same object falls to Earth. The Nqweba object did not fit this profile, and its occurrence did not coincide with any known satellite debris re-entering the atmosphere, making unlikely that it was space junk.

Initial reports all suggested that the bolide was moving out to sea, possibly splashing down in Jeffreys Bay, to the west of Gqeberha. As more reports came in it became it had been seen over a much wider area, north as far as Petrusburg, and west as far as Ceres. A further three videos of the object emerged, although the one taken by Zoë van der Merwe appears to cover the final part of the meteor's journey.

Shortly before 9.00 am, residents of Nqweba (formerly Kirkwood), about 100 km to the north of Cape St Francis, heard what they described as a loud thunderclap, followed by a long rumbling noise. Slightly after this, 9-year-old Eli-zé du Toit observed something falling through a large Wild Fig tree in her parents garden. When investigated, this turned out to be a rock smaller than her fist, with a shiny black crust, broken in places to reveal a light grey, concrete-like interior. When touched, the exterior layer of this rock was hot, while the interior was cold. Eli-zé's mother, Jesica Botha, posted several images of this and other fragments found in the garden to social media groups, leading to her being contacted by Carla Dodd of Nelson Mandela University.

(a) Photo of main meteorite mass retrieved by Eli-zé du Toit, displaying black fusion crust (top) and the grey interior containing multiple angular rock and mineral fragments. (b) Post submitted by Jesica Botha on the Snow Report Southern Africa Facebook page. Gibson et al. (2025).

Carla Dodd was able to arrange for the meteorite fragments to be transported to Nelson Mandela University for safekeeping; meteorites, along with fossils and archaeological artefacts are protected in South Africa by the National Heritage Resources Act (1999). Here the fragments were weighed, examined and placed into desiccators for storage. This preliminary inspction suggested that the fragments belonged to a type of stoney meteorite called a HED (howardite–eucrite–diogenite) achondrite breccia. These meteorites resemble terrestrial igneous rocks, and are therefore presumed to have come from bodies large enough for magma differentiation and igneous processing to have occurred.

Initial witness reports, and the two sites where meteors were reported to have fallen to Earth, Nqweba and the sea off Cape St Francis, are about 100 km apart, suggesting that the bolide had followed a north-south trajectory, shedding fragments as it went, towards the sea. However, bolides are notoriously confusing for observers, due to the long gap between the visual fireball and the sound reaching witnesses. Careful examination of witness reports and data from remote observation stations eventually led Gibson et al. to conclude that the bolide moved southwest-to-northeast, first appearing off Mossel Bay and moving inland towards Nqweba.

The Nqweba Bolide was the 20th bolide recorded globally in 2024, and one of the smallest. It is thought to have been about 1 m in diameter when it entered the atmosphere, and to have released energy equivalent to that released by the detonation of 92 tons of TNT.

Since 1992, 493 fireball events have been recorded over South Africa, only about 3% of which have been visible during the day. The largest recorded bolide in Southern Africa was the 21 November 2009 event over northern South Africa and southern Botswana, which was probably about 200 times as large as the Nqweba Bolide, although no fragments of this were ever found.

Recovered meteorites in South Africa are strongly linked to observed meteorites, and particularly daytime events, with 21 of 51 known meteorites collected in South Africa connected to observed falls, 75% of these in the daytime. However, prior to the Nqweba Bolide,  the most recent of these fell on Lichtenburg, North West Province, in 1973, long before modern technology such as remote observation stations and mobile phones was available to help track these events.

South Africa is currently increasing its remote observation capacity, and therefore its ability to track fireballs.  It is currently home to 16 cameras running under the auspices of the NASA SETI Institute Cameras for Allsky Meteor Surveillance network, and a further ten operated by the Global Meteor Network (4 of which have been installed in Western Cape schools to promote STEM activities). These are already improving fireball-detection rates, but do not work well in daylight. The collection of meteorite fragments is largely dependent on direct observation of the objects falling, as was the case with the Nqweba Meteorite Fall, but networks of cameras can help triangulate the area in which meteorites might have fallen, improving the chances of finding meteorites which were not directly observed.

See also...

The Nadir Crater: A possible second End Cretaceous Impact Structure off the coast of West Africa.

High velocity impacts by large asteroids and comets are a known, but poorly understood, threat to life on Earth. Impactors with diameters of about 50 m (the estimated size of the object which caused the Tunguska explosion) are thought to hit the Earth roughly once every 900 years, and objects with diameters of 1 km or greater, likely to cause devastation on a regional or global scale, to impact the Earth roughly every million years. The largest impacts cause devastation on a global scale, with the best known of these being the Chicxulub impact 66 million years ago, an event thought to have caused the End Cretaceous Extinction Event. Despite the importance of such events, very little evidence of their having occurred is known, with only about 200 large impact craters known on Earth, of which only 15-20 are interpreted as having happened in a marine environment, despite 71% of the Earth's surface being covered by water. This lack of impact craters, and in particular well preserved impact craters, severely hampers our ability to understand the effects of the events which cause them.

In addition to this general lack of impact craters in the rock record, there is a proportional lack of double impact craters. About 15% of the asteroids in near-Earth orbits are thought to be binaries (i.e. pairs of gravitationally locked asteroids, whereas only 2-4% of known impact craters on Earth have ever been suggested as potentially being parts of pairs. Furthermore, most of these suggestions have either been disproven or are disputed. On Venus, where meteor impacts are generally recorded as 'dark splotches' rather than true craters, due to the much more destructive nature of the Venusian atmosphere, about 14% of impacts appear to be binary. Even allowing for a considerable degree of inaccuracy in these numbers, binary impacts seem to be significantly under-represented on Earth.

Another phenomenon seen elsewhere in the Solar System but largely absent on Earth is impact clustering, i.e. the formation of a series of impact craters over a relatively short period of time. This is typically caused by the breakup of a large object due to a gravitational encounter with a planet, followed by the debris from this breakup remaining on an orbit which intersects that of the planet, resulting in a series of impacts over a drawn out period of time. The only observed instance of such an event was the breakup of Comet Shoemaker-Levy 9 in 1992, which was followed by a series of impacts in 1994 as the debris from this breakup collided with Jupiter, but it is thought that the breakup of larger bodies can result in strings of impacts which could continue for several million years. Only a single such event has been recorded on Earth; a series of linked craters in the Ordovician, which is combined in a shift in the ratio of argon isotopes in the Earth's atmosphere at that time, and evidence for an increase in the amount of extraterrestrial dust raining down on the Earth at that time. Other proposals have been made for clusters of impacts in the Cretaceous and Eocene, but the evidence in support of such events is sparse. This is despite the Moon showing clear evidence of a number of periods of impact clustering, events which must surely also have affected the Earth.

In a paper published in the journal Science Advances on 17 August 2022, Uisdean Nicholson of the School of Energy, Geoscience, Infrastructure and Society at Heriot-Watt University, Veronica Bray of the Lunar and Planetary Laboratory at the University of Arizona, Sean Gulick of the Institute for Geophysics, Department of Geological Sciences and Center for Planetary Systems Habitability at the University of Texas at Austin, and Benedict Aduomahor, also of the School of Energy, Geoscience, Infrastructure and Society at Heriot-Watt University, announce the possible discovery of a second End-Cretaceous impact structure on the Guinea Plateau of the coast of West Africa, based upon evidence from two-dimensional seismic surveys.

The Guinea Plateau is an area of submerged continental crust extending southwest from the coasts of Guinea and Guinea Bissau for about 400 km, where it meets with the Guinea Fracture Zone, beyond which lies the deep ocean. The plateau can be divided roughly into two parts, an inner zone which is about 400 m deep across most of its extent, and an outer zone, known as the Guinea Terrace, which deepens gradually from about 400 m to about 1200 m. The Guinea Fracture Zone is home to a series of seamounts (inactive submarine volcanoes), including the Nadir Seamount.

Map and regional seismic sections showing location of Nadir Crater. (A) Regional bathymetry map of the Guinea Plateau and Guinea Terrace showing location of 2D seismic reflection and well data used in the study. JS, Jane Seamount; NS, Nadir Seamount; PS, Porter Seamount. The white dashed line shows the NE extent of high-amplitude discontinuous seismic facies at the top Maastrichtian interpreted as ejecta deposits and associated tsunami deposits. The north-east limit of this facies closely corresponds with the Maastrichtian shelf-slope break at the landward margin of the Guinea Terrace. Inset map shows a palaeogeographic reconstruction of the Atlantic near the end of the Cretaceous, about 66 Ma ago. Ch, Chicxulub Crater; Nd, Nadir Crater; Bo, Boltysh Crater. (B). Regional composite 2D seismic reflection profile extending from the GU-2B-1 well in the east to the deep Atlantic basin in the west, showing the structural and stratigraphic character of the Guinea Plateau and Guinea Terrace. (C) North-South seismic profile from the salt basin in the north to the Nadir Seamount, south of the Guinea Fracture Zone. Nicholson et al. (2022).

The Guinea Plateau formed by extensional rifting in the Triassic-Jurassic, as the opening of the Atlantic Ocean pulled the North American landmass away from the west coast of Africa. The plateau remained part of the passive (i.e. seismically inactive) margin of the Central Atlantic until about 100 million years ago, when the its southern margin underwent further rifting, as South America separated from Africa.

The crater which Nicholson et al. propose is located on the southwestern part of the Guinea Terrace, roughly 60 km to the north of the Guinea Fracture Zone and 100 km northwest of the Nadir Seamount. The crater is covered by about 400 m of sediment, and a water column about 900 m deep.

The stratigraphy of the area has been determined from boreholes and seismic surveys. Cretaceous deposits here can be divided into a Lower Cretaceous sequence, roughly 145-100 million years old, and an Upper Cretaceous sequence, 100-66 million years old, separated by an unconformity known as the Top Albian. The deposits making up the Upper Cretaceous sequence are largely undeformed, and extend laterally across the Guinea Terrace. These deposits can be further subdivided by a series of (seismically) reflective surfaces, numbered KU1-KU4, which are interpreted as representing major flooding events. The Upper Cretaceous sequence can be divided into a Lower Unit, which is about 300 m thick and contains a series of high amplitude reflective surfaces, and an Upper Unit, which is about 500 m thick and contains moderate-to-low amplitude reflective surfaces.

Seismic characteristics of the Nadir Crater. (A) Seabed depth map of crater showing seismic line locations and the mapped extent of the crater rim and damage zone.  (B)  West-east  seismic  section  (pre-stack  depth  migration  –  depth  domain)  across  the  crater,  highlighting  the  crater  morphology  and  damage  zone,  and  the  extent  of  subsurface deformation. (C) Detailed seismic stratigraphic and structural elements of the crater. KP, Cretaceous-Paleogene sequence (KP1 equivalent to Top Maastrichtian); KU, Upper Cretaceous seismic horizons. KU1 and KP1 'regionals' are schematic reconstructions of these seismic horizons before formation of the crater at the end of the Cretaceous and have been used to reconstruct a conceptual model of crater formation. (D) Southwest-northeast seismic section (pre-stack time migration – time domain) across the crater, showing crater morphology and seismic facies outside the crater, including high-amplitude seismic facies sitting above a roughly 100-ms-thick unit of chaotic reflections, interpreted to have formed as a result of seismic shaking following the impact event. Nicholson et al. (2022).

The end of the Cretaceous sequence here, identified as the Top Maastrichtian, is clearly identifiable, and well defined, but the age of other reflective surfaces in the sequence is less certain. The KU-1 reflective surface may mark the Top Turonian, making it about 90 million years old, and the high amplitude surfaces between this and the underlying Top Albian surface may represent black shale deposits, with elevated levels of organic carbon. The lower amplitude reflective surfaces above KU-1 probably represent marine shales and marls.

The Top Maastrichtian Surface lies at the top of another set of distinctive, high amplitude reflective surfaces, and is marked by an erosional unconformity on the southwest part on the Guinea Terrace, which is not present to the north and east. The reflective surfaces at this level extend laterally across the Guinea Plateau, although they are eroded away on both the continental slope and the inshore shallows. On the Guinea Terrace these surfaces overlie a chaotic seismic surface about 100 m deep.

Overlying the Top Maastrichtian, the Cainozoic deposits begin with a thick sequence of carbonates and clastic sediments, although these are considerably thinner on the Guinea Terrace than elsewhere on main Guinea Plateau. Precise dating of these sediments is again difficult, though sediments younger than about 23 million years old are apparently absent on the Guinea Terrace; strat here comprise a Palaeocene-Eocene sequence about 300 m thick, overlain by a series of Oligocene mass transport deposits (debris from submarine landslides).

The feature which Nicholson et al. identify as the Nadir Crater is a depression at least 8.5 km wide in the Top Maastrichtian. This can be seen where two separate seismic profiles cross one-another, suggesting a rounded or elliptical shape. Since there is no particular reason to believe that the intersection of the two seismic profiles lies at the centre of the depression, 8.5 km wide must be taken as a minimum measurement. The crater bed is 200 m below the 'seafloor' represented by the Top Maastrichtian, while the crater rim is raised 20-40 m above this level. There appears to be a slight uplift in the centre of the crater at the Top Maastrichtian level; this is more pronounced at the Top Albian level, where it rises 350 m above the surrounding terrain. On either side of this central uplift the strata below the crater floor and rime are intensely deformed, with a column of extensively folded and fractured material extending downwards 700 m from the Maastrichtian surface. A wider area of faulting extends 10-12 km from the crater in all directions, with all faults dipping towards the crater.

All of these phenomena are consistent with large impact craters elsewhere on Earth and other Solar System bodies. The rim is raised  above the surrounding terrain approximately one tenth as much as the crater floor is depressed beneath it. The crater is approximately one twentieth as deep as it is wide. The damage zone around the crater is approximately twice as wide as the crater itself. The crater has a terraces structure and a raised central peak.

The deformation beneath the crater is also consistent with the predictions for large craters of this sort. The central uplift seen in such craters is caused by the elastic rebound of shock waves passing through the rock, causing material beneath the crater to flow upwards, initially flowing freely the brecciating as the rock regains its brittleness. The deformations seen in the zone 10-12 km from the crater are consistent with these areas being subjected to a significant shockwave, then flowing back towards the crater to fill a partial void.

Based upon examination of other impact craters on Earth, the zone of uplift beneath a crater 8.5 km wide would be expected to extend downwards to between 630 and 780 m beneath the impact surface. That of the Nadir Crater extends down about 800 m, with some deformation extending downwards into underlying Jurassic Sediments. However, this does not necessarily imply a much larger crater; rather it may be a consequence of a bolide impacting soft, unconsoidated marine sediments. The Mjølnir Crater, in the Barents Sea off the coast of Norway, shows a similar pattern of deformation beneath the crater, although here there is less deformation outside the crater rim, as is the case at Chicxulub. This deeper pattern of damage at sites where large, high velocity objects impact shallow marine sediments may be caused by the sudden decrease in the porosity of the strata impacted, resulting greater brecciation, and the formation of hydrothermal systems which could potentially last for millions of years.

The Top Maastrichtian layer within the crater is overlain by a series of high amplitude reflective layers identified as KP-1 to KP-3, with KP-1 marking the boundary between the Maastrichtian and the Palaeocene. Between the Top Maastrichtian and KP-1 is a layer about 100 m thick and relatively transparent to seismic waves, which Nicholson et al. interpret as a possible suevite layer (i.e melt materia), similar to that seen as the Chicxulub Crater. Above this, between KP-1 and KP-2 is a unit made up of a series of low-amplitude reflective surfaces onlapping onto the inner crater walls, which Nicholson et al. interpret as reworked ejecta material. 

The crater is surrounded by a blanket of material made up of a series of high amplitude reflective surfaces, which Nicholson et al. also interpret as reworked ejecta, combined with material deposited by tsunamis triggered by the impact. Beneath this is a layer of chaotic material, which may represent older strata re-organised by the shock wave from the impact.

The Nadir Crater a deep inner crater with in inner peak and a flat outer zone, surrounded by a raised rim, features also seen in confirmed marine craters such as the Chesapeake Crater (off the east coast of North America), Lockne Crater (in northern Sweden), and Flynn Creek Crater (in Tennessee), strongly supporting the idea that this is an impact crater, although this hypothesis will only be confirmed by drilling into the structure.

There are other processes which can form structures resembling impact craters, such as the dissolution of salt deposits, escape of gas or fluids, volcanic activity, deformation due to tectonic stresses, or any combination of these. However, none of these possible alternatives appears consistent with the geology of the Guinea Terrace,

Salt diapers (domes formed when salt intrudes into overlying rocks) can collapse as the salt within them dissolves into the water column, leaving a circular depression surrounded by radial faults. However, such structures do not have uplifted central zones, nor would they be surrounded by a ring of high amplitude material of the type Nicholson et al. interpret as ejecta at the Nadir Crater. Furthermore, while there are salt diapers on the Guinea Terrace, these are in a zone far to the northwest of the Nadir Crater, with the closest diaper being over 250 km from the crater. 

Craters left by fluids escaping from mud layers as they are buried and then subjected to pressure, are common features on the seafloor, being particularly common on the continental margins, where large amounts of methane are generated. Most of these are a few metres to a few hundred metres across, but the largest can exceed 10 km, making ruling our such an origin for the Nadir Crater impossible on the basis of size alone. However, such structures are almost always found in clusters, and no structures similar to the Nadir Crater can be seen anywhere else on the Guinea Plateau, nor are there any other signs of gas or fluid escape in this region. Furthermore, craters formed by fluid escape do not typically produce crater rings, central uplift, or ejecta, all of which can be seen at the Nadir Crater. 

A variety of depressions, typically bounded by fault zones, can be formed when slip-strike deformation leads to areas of seafloor being pulled apart. However, such depressions are rarely circular, typically being more than twice as long as they are wide. Nor do such structures have rims or centrally uplifted zones. More importantly, the Nadir Crater is located on an area of the African continental margin where slip strike activity is thought to have ceased about 44 million years before it formed, making such an origin highly unlikely.

The most plausible alternative hypothesis for the origin of the Nadir Crater is volcanism. Phreatic explosions, which occur when hot magma comes into contact with water, can form maars (broad, low relief volcanic craters) similar in form to the Nadir Crater. Furthermore, there clearly was volcanic activity nearly contemporary to the formation of the crater in the area; the Nadir Seamont is only 100 km away from the Nadir Crater, and 7.4 million years younger, i.e. close enough to be part of the same volcanic complex, along with the nearby Grimaldi Seamounts. However, maar structures seldom exceed 2-3 km in diameter, and their three dimensional structure has a distinctive funnel-shape unlike anything revealed by the seismic surveys at the Nadir Crater. Furthermore, maars do not have a central uplift structure, making it highly unlikely that the Nadir Crater is a volcanic maar.

Next Nicholson et al. used a hydrocode model to simulate the impact of a 400 m wide object (the estimated size of the Nadir impactor) into soft sediments covered by a range of water depths. All of the models produced a crater between seven and nine kilometres in diameter, with elevated rims and significant central uplift. The amount of subsequent rim collapse varied with water depth, with impacts into deeper water showing more collapse. This lead to more infill into the crater, resulting in a flatter profile and a less prominent central uplift zone. At depths of greater than 1 km, the rim completely collapsed into the crater, creating a very flat profile. In all cases, regardless of depth, the impact resulted in a crater surrounded by a network of faults.

Numerical model results of iSALE hydrocode simulations of final crater architecture for different water depths (200, 500, 800, 1100, and 1500 m, as indicated on the figure) Models assume a 400 m diameter impactor with an impact angle of 90°. The water layer has been removed from each image to better highlight the final crater morphology. Model outcomes show total plastic strain on the left and deformed lithologies on the right - the gray unit represents the assumed Cenomanian-Turonian black shale deposits as a marker horizon. Nicholson et al. (2022).

All models show the development of a central uplift, although the extent of this varies with depth, with larger central uplift zones in impacts at greater depth, possibly representing the rocks rebounding more when the weight of the overlying water is removed by the flash-vaporization cause by the impact. These simulations showed material from as deep as 2 km below the surface being moves upwards, with material from up to 1 km deep reaching the subsurface within the central peak; based upon the available data Nicholson et al. estimate that material from as deep as 750 m beneath the Nadir Crater is present within its central peak.

Snapshots of numerical model results of an iSALE hydrocode simulation for 800 m target water depth. Considered this to be the most likely water depth for the impact, based on crater morphology. Model snapshots show transient crater formation and generation of a rim-wave tsunami after 3 seconds; rebound of central uplift and propagation of a rim-wave tsunami away from crater at 38 seconds; crater collapse, resurge, and central jet formation at 85 seconds; and further resurge at 245 seconds. Nicholson et al. (2022).

All of the simulated impacts produced zones of brecciation beneath the crater, with the depth to which this extended ranging from about 1 km up to about 2.5 km. Areas of damage were also present around all the simulated craters, with faults and fractures extending at least 5 km from the craters and reaching depths of at least 1 km.

The models are consistent with the observed features at the Nadir Crater, insofar as all of the craters forming at depths shallower than 1 km produced raised rims, uplifted central areas, terraces made up of debris, and areas of damage outside the crater. The models which produced craters most similar to the Nadir Crater had water depths of about 800 m.

Based upon the data gained by running these simulations, Nicholson et al. developed a conceptual model for the chain of events around the impact. It is assumed that the initial stratigraphy of the area comprised a series of flat, horizontal bedding plains, overlain by about 800 m of seawater. The initial impact would have formed a transient crater about 1 km deep, followed rapidly by the formation of the central uplifted zone, and the collapse of the initial crater rims. This would produce the current observed structure; a crater with a marked central uplift and observable rims surrounded by terraces of collapsed material, and a wider area of fallen ejecta, a hypothesis which they propose could by tested by drilling in the area, in order to confirm the actual nature of the deposits observed in the seismic profiles.

Conceptual model of the impact sequence at the Nadir impact site, based on seismic observations and analog models.  (A) At time zero, the impactor hits the water surface at a velocity of about 20 km per second, initiating a rim-wave tsunami in its wake. (B) Several seconds later, the transient crater forms, as the impactor and a substantial body of water are vaporised. Impactites (melt rock and breccias) line the transient cavity. Tsunami waves propagate away from the evacuated crater. Shock waves cause substantial damage below and around the impact site, and seismic waves propagate across the plateau; (C) major uplift (roughly 400 m relative to pre-impact regional) occurs in the 'rebound' crater modification phase, resulting in the formation of a raised crater peak; (D) radial collapse of the subsurface damage zone results in further modification of the crater, including the formation of terraces at the surface. Resurge of water transports substantial volume of ejecta and other sediment into the crater, deposited above the impactites. Nicholson et al. (2022).

Taking the data from the simulations, Nicholson et al. used the Earth Impacts Effect Program to assess the environmental damage caused by the event which formed the Nadir Crater. The initial impact would vaporise vast amounts of seawater and seafloor sediment and release an amount of energy roughly equivalent to 5000 megatons of TNT. This in turn would lead to the formation of a fireball over 5 km in diameter, an an air blast which would be travelling at about 470 km per hour at a distance of 50 km from the impact site. 

The event would release seismic waves equivalent to a Magnitude 7.0 Earthquake, fluidising seafloor sediments for hundreds of kilometres in all directions. Following fluidisation of the sediments they would likely be reworked extensively by the tsunami waves caused by the impact. The seismic waves would also be likely to trigger massive landslides along the Guinea Terrace.

The initial impact would cause an 'ejecta curtain', made up of water and sediment, over 2 km high, which would then collapse back onto the sea surface, triggering the formation of a tsunami wave over 500 m high, which would spread at about 400 m per second. As well as spreading out from the rim of the crater, this tsunami would spread inwards, forming a central water jet rising to over 2 km. This would then collapse back into the crater, forming a new tsunami, a process which might repeat itself several times. These repeated tsunamis would cause extensive reworking of sediments along the Guinea Terrace, at depths of up to 800 m. They would also cause extensive scouring of the West African coastline, and to a lesser extent that of South America, which, despite being about 1000 km away, would still be hit by waves about 5 m high. 

The impact would lead to large volumes of water entering the atmosphere, as well as black carbon dust derived from the black shale deposits laid down on the Guinea Plateau during the Cenomanian  and  Turonian.  The high temperatures and pressures unleashed by the impact would turn much of the organic material present in the area directly into methane, with global climatic implications, albeit short lived ones. The seismic shock wave could potentially release a lot more methane from gas hydrate deposits on the Guinea Plateau, and adjacent areas of the deep sea floor.

The impact which caused the Nadir Crater appears to have happened at, or very close to, the Cretaceous-Palaeocene boundary. This places the Nadir Impact very close to the Chicxulub Impact, chronologically speaking, raising the question as to whether the two events were connected. Potentially the Nadir and Chicxulub impactors might have been two parts of a binary object, two fragments of an object which broke up as it came within the Earth's gravitational field, two objects from a longer impact cluster, or two unrelated objects which happened to fall at about the same time. 

Impacts by binary asteroids have previously been suggested as the cause of other crater pairs, including the Lockne and Målingen craters in  Sweden, the East and West Clearwater craters in Quebec, and the Suvasvesi craters in Finland, although more refined dating has shown that neither the Clearwater and Suvasvesi craters are in fact binaries, and no there is no evidence in favour of the Lockne and Målingen craters being related, and therefore no evidence of a binary impact anywhere on Earth. 

Reconstructions show that the Nadir Crater site would have been about 5500 km from the Chicxulub Crater site at the end of the Cretaceous; significantly less than the 8000 km that separates them today, but still to far apart to have been caused by the impacts of two parts of a single object which broke up within the Earth's Roche limit (the minimum distance to which a large satellite can approach a larger body without tidal forces overcoming the internal gravity holding the satellite together), or within the Earth's atmosphere. 

This does not, however, rule out two fragments of a single object which was broken into fragments by an earlier encounter with the Earth's tidal field, then impacted the Earth on a subsequent encounter, in the way that Comet Shoemaker-Levy 9 was torn apart by Jupiter's gravitational field, then impacted Jupiter in several fragments on a subsequent pass several years later. There is some evidence of other large impacts around the End of the Cretaceous, most notably at Boltysh in Ukraine (currently dated to 65.4 million years ago, or 650 000 years younger than the Chixulub impact), as well as preserved fossil meteorites from Poland and the North Pacific. This could imply that the Earth was not just hit by a single large impact, but a protracted asteroid shower, lasting from months to one or two million years, with each impact triggering earthquakes and tsunamis, and contributing to rising atmospheric levels of greenhouse gasses and aerosols.

Estimates as to how often objects the size of the Nadir impactor hit the Earth vary from about once every 100 000 years to about once every 700 000 years. Thus even if it can be demonstrated that the Nadir Impactor fell within a million years of the Chicxulub impactor, it would be impossible to demonstrate that the two events were part of a single asteroid shower (Near Earth Asteroid (101995) 1999 RQ36 is roughly equivalent in size to the Nadir impactor, and is estimated to have a 1 in 1750 chance of hitting the Earth within the next few hundred years). However, if it can be demonstrated that the Chicxulub, Nadir, and Boltysh events all happened within a relatively short period of time, then it would present a much stronger case for the events being related, with important implications for our understanding of events at the End of the Cretaceous.

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Large bolide impact detected on the surface of Jupiter.

Optical flashes caused by impact events on the surface of Jupiter have been within the detection capabilities of amateur astronomers for some time, with six such flashes reported between 2010 and 2020. These events have the potential to provide us with information about the abundance of small objects in the Outer Solar System, which are close to impossible to detect by direct observations, as well as the consequences of such impacts on planetary atmospheres, information which can be used to improve models of such impacts on Earth.

Models suggest that the majority of impacts on Jupiter are caused by Jupiter Family Comets (bodies with orbital periods of less than 20 years and relatively low orbital inclinations), while the majority of detections are of bodies with sizes calculated to be in the tens of metres range. However, these detections have all been essentially made by luck, when a professional or amateur telescope happened to be pointing in the right direction, rather than as a result of organised monitoring, which would provide statistically useful data on the frequency of such events.

In a paper published on the arXiv database at Cornell University and submitted to the Astrophysical Journal Letters, Ko Arimatsu of the Astronomical Observatory at Kyoto University, Kohji Tsumuru of the Department of Natural Science at Tokyo City University, Fumihiko Usui of the Department of Space Astronomy and Astrophysics at the Japan Aerospace Exploration Agency, and Jun-Ichi Watanabe of the Astronomy Data Center at the National Astronomical Observatory of Japan, report the first detection of an impact event on Jupiter by the Planetary ObservatioN Camera for Optical Transient Surveys observation system, which was set up to continuously monitor the surface of Jupiter for impact flashes, and commenced operating on 9 September 2021.

The event was detected at 1.24 pm GMT on 15 October 2021 (i.e. 36 days after the system began continuous observations of Jupiter), in both the visual and methane-absorbance bands of the spectrum, in the north tropical zone of Jupiter. The flash was also seen by two amateur astronomers in Japan, and one in Singapore; these observations provide a corroboration of the event which confirms it occurred on Jupiter, not in the Earth's atmosphere. No subsequent after-effects of the impact could be observed from Earth. An observation by the Juno Spacecraft made 28 hours after the impact showed some darkening at the site of the event, although it is impossible to determine if this was related.

Impact flash on Jupiter on 15 October 2021. Arimatsu et al. (2022).

The impact had a maximum apparent magnitude of 4.7 in the visual part of the spectrum (comparable to the Jovian moon Io at it's brightest), and lasted for about 5.5 seconds. This is brighter and longer lasting than any Jovian impact recorded since the Shoemaker Levy 9 impact observed by the Hubble Space Telescope in 1994.

The impact was significantly brighter at visible wavelengths than it was in the methane-absorbance part of the spectrum, which Arimatsu et al. attribute to reflection of light at these wavelengths by the Jovian clouds. Arimatsu et al. further calculate that the impact released an energy of about 740 000 000 megajoules, roughly equivalent to the detonation of 1.8 megatons of TNT. This is roughly equivalent to the amount of energy thought to have been released by the Tunguska explosion in 1908, and an order of magnitude greater than any Jovian impact previously recorded, with the exception of the Shoemaker Levy 9 impact.

Based upon this, Arimatsu et al. calculate that the impactor would have had a mass of about 4 100 000 kg, which would equate to a diameter of roughly 15-30 m, depending on the density and composition of the object.

By calculating the amount of time known to have been dedicated to the direct observation of Jupiter by telescopes capable of detecting large impacts since 2010, and the number of impacts observed in this time, Arimatsu et al. calculate that such impacts are 2-3 orders of magnitude more common on Jupiter than on Earth. This is an order of magnitude greater than previous estimates based upon observations of impact craters on the Jovian moons. 

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