Magnitude 7.3 Earthquake to the west of Efate Island, Vanuatu.

The United States Geological Survey recorded a Magnitude 7.3 Earthquake at a depth of 57.1 km, roughly 30 km to the west of of Efate Island, Vanuatu, slightly after 12.45 pm local time (slightly after 1.45 am) on Tuesday 17 December 2024. The initial event has been followed by a number of large aftershocks. At least fourteen people are known to have died as a result of the Earthquake, with more than 200 more injured. Many buildings, including hospitals on the island have been damaged, as have several important bridges, and seeveral major roads are reported to have been blocked by landslides.

The approximate location of the 17 December 2024 Vanuatu Earthquake. USGS.

Vanuatu is located on the southwestern fringe of the Pacific Plate, close to its boundary with the Australian Plate, which is being subducted along the New Hebrides Trench, to the west of the islands. The subducting Australian Plate passes under the islands of Vanuatu as it sinks into the Earth, causing Earthquakes as the plates stick together then break apart as the pressure builds up. As the plate sinks further it is partially melted by the heat of the friction combined with that of the Earth's interior. Some of the melted material then rises through the overlying Pacific Plate, fuelling the volcanoes of Vanuatu.

Damage to a building in Port Vila, Vanuatu. Tim Cutler/AP.

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The December Solstice.

The December (or Southern) Solstice this year falls on Saturday 21 December this year, with the Sun reaching its southernmost point in the sky at 9.20 am GMT. This is the shortest day of the year in the Northern Hemisphere, where it is known as the Winter Solstice and the longest day in the Southern Hemisphere, where it is known as the Summer Solstice. At very high latitudes the sun may not rise (Northern Hemisphere) or set (Southern Hemisphere) for several weeks on either side of the Southern Solstice.

The solstices are entirely a product of variation in the Earth's rotation on its axis, which is at an angle of 23.5° to the plain of the Earth's orbit about the Sun. This means that in December the Earth's Southern Pole is tilted towards the Sun, while the Northern Pole is tilted away from it. This means that around the Southern Solstice the Southern Hemisphere is receiving radiation from the Sun over a longer part of the than the Northern, and at a steeper angle (so that it to pass through less atmosphere to reach the planet), creating the southern summer and northern winter.

The tilt of the Earth during the December Solstice. Wikimedia Commons.

The solstices are fairly noticeable astronomical events, and tied to the seasons which govern the life cycles of life on Earth, and they have been celebrated under different names by cultures across the globe, but most notably by those at higher latitudes, who are more profoundly affected by the changes of the seasons.

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Florissantia sp.: A fossil flower from the Early Eocene of Rajasthan.

The Malvaceae first appeared in the Cretaceous in North America, and have achieved a global distribution today, most notably as a significant component of almost all tropical forests. The genus Florissantia shows a number of features associated with different extant subfamilies of the Malvaceae, and is known from the Middle Eocene till the Miocene of western North America, with specimens known from British Colombia, Colorado, Montana, Oregon, and Washington, as well as a single specimen being known from the Sikhote Alin mountains of the Russian Far East.

In a paper published in the journal Botany Letters on 21 October 2024, Ashif Ali and Mahasin Ali Khan of the Palaeobotany, Palynology, and Plant Evolution Laboratory at Sidho-Kanho-Birsha University, and Raman Patel and Rajendra Singh Rana of the Department of Geology at Rauthan Hemvati Nandan Bahuguna Garhwal University, describe a specimen of Florissantia from the Early Eocene Palana Formation of Rajasthan, India.

The specimen comes from the Laminate Maroon Shale Bed of the Palana Formation, which is exposed at the Gurha Open-cast Lignite Mine at Bikaner in northwest Rajasthan. It is preserved as part and counterpart on a piece of a piece of split- laminated shale, which has been further exposed by micro excavation of successive layers of the rock with fine needles under a dissection microscope. 

(a) Map of Rajasthan showing the location of the Gurha opencast lignite mine (red star) Bikaner Rajasthan, India; (b) view of the fossil locality. Ali et al. (2024).

The preserved fossil is a star-shaped flower about 13 mm in diameter (sgnificantly smaller than any other member of the genus), with a calyx made up of five fused and rounded sepals of roughly equal length; the petals are missing. Importantly, the sepals each show numerous prominent veins, the pattern of which is used by Ali et al. as a diagnostic tool to place the specimen in the genus Florissantia.

(a) Transversely impressed, radially symmetric, pentamerous fossil flower of Florissantia sp. (SKBU/PPL/R/F/01A, part); (b) magnified image of the specimen showing thick filaments (marked by red arrows) surrounding the compressed, carbonaceous central area; (c) enlarged view of a single calyx lobe showing prominent parallel (marked by blue arrows) and radiating reticulate (marked by white arrows) venation; (d) counterpart of fossil flower of Florissantia sp. (SKBU/PPL/R/F/01B); (e) central area of figured in higher magnification; (f) line drawing of (c) showing parallel (marked by blue arrows) and reticulate (marked by red arrows) venation, Scale bars are 2.5 mm for (a), (b), (d), and (e) and 500 μm for (c) and (f). Ali et al. (2024).

The Palana Formation of Rajasthan has been dated to between about 55 and 52 million years before the present on the basis of palynological data (fossil pollen). This Early Eocene date makes the Bikanar specimen the oldest representative of the genus Florissantia, which together with its unexpected location, potentially makes the specimen highly significant. 

Line drawings of the Bikanar specimen and earlier reported extinct fossil flower species: (a) Bikanar fossil flower of Florissantia sp.; (b )fossil flower of Florissantia ashwillii from the Oligocene of Oregon; (c) fossil flower of Chaneya membranosa from the Miocene of Poland; this appears similar to Florissantia spp, but has unequal sepals. Scale bars are 5 mm. Ali et al. (2024).

The Palana Formation was laid down on the shores of an ancient lake, which is consistent with other locations where members of the genus Florissantia have been found. Other members of the genus are known from lake-associated Floras in tropical, subtropical, and temperate environments, often with some volcanic input; although the presence of volcanic ashes helps to preserve fine structures such as flowers, so it is possible that this connection with volcanic input reflects preservation bias rather than an environmental preference of the living plants.

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Unknown disease kills 31 people in the Democratic Republic of Congo.

Between 24 October and as of 5 December 2024, 406 cases of an unknown disease were reported in the Panzi Health Zone of Kwango Province in the Democratic Republic of Congo, with 31 known fatalities, a case fatality ratio of 7.6%. Symptoms of the disease include fever, headache, cough, runny nose, and body ache, according to a press release issued by the World Health Organization on 8 December 2024. The number of both cases and deaths is likely to be higher than the official figure, with the Ministry of Health of the Democratic Republic reporting that they are aware of deaths within the local community of people who have not visited health facilities.

The approximate location of the Panzi Health Zone. Google Maps.

Cases of the unknown disease have been reported in nine of the thirty health areas which make up Panzi Health Zone, Kahumbulu, Kambandambi, Kanzangi, Kasanji, Kiama, Mbanza Kipungu, Makitapanzi, Mwini ngulu, and Tsakala Panzi, with the majority of the cases in Tsakala Panzi (169 cases), Makitapanzi (142 cases) and Kanzangi (78 cases).

Children under five years old account for 53% of cases and 54.8% of the deaths, with 64.3% of the cases and 71% of deaths occurring in children under 15. One hundred and forty five cases, including nine fatalities, have been  reported in adults.  Women and girls make up 59.9% of the cases, and the majority of deaths have occured in villages. 

Panzi Health Zone has a low vaccine uptake rate, poor food security, transport networks are poor (it takes about two days to reach Kinshasa by road in the rainy season). There are few trained health workers in the region, with very little care management and almost no access to diagnostic services.

Malaria is endemic to the region, with few control measures in place, as are a number of other potentially fatal diseases, including measles, influenza, respiratory tract infections, E. coli, and Covid-19. The high rate of food insecurity in the region means that malnutrition may be a contributing factor towards fatalities.

The lack of systematic medical recording in Panzi Health Zone means that although an increase in cases of fever, coughs, headaches, and body aches have been noted since October, it is unclear what the baseline rates for these symptoms are. Nor are there accurate records of vaccination schemes in the area, making it unclear to what extent the outbreak relates to vaccine deprivation. Many cases of the illness have been reported in family clusters, potentially suggesting transmission within households.

The area where the outbreak is occurring is very remote, with poor roads, limited mobile phone and internet coverage, and frequent shortages of even basic medication. There is no functional diagnostic laboratory in Kwango Province, requiring samples to be shipped to Kinshasa for analysis, a journey of two days by road in the rainy season. This process is further hampered by a lack of a formal sampling procedure in the region, and a poor security situation, with a number of armed groups operating in the area.

The remote  locality of the outbreak may make it harder for the disease to spread to other areas, but with no effective monitoring or diagnostic program in place there is little way to be sure. In addition, the area of the outbreak is close to the border with Angola, creating a potential for the disease to spread across the border.

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Direct imaging of a possible planet orbiting the fast moving star HIP 36277.

In the past three decades almost six thousand exoplanets (planets orbititing stars other than our Sun) have been detected, using a variety of methods. Direct imaging has proven to be a useful technique for detecting planets with masses greater-than-or-equal-to that of Jupiter at distances of more than 10 AU from their host stars (i.e. more than ten times as far from their host stars as the Earth is from the Sun). Notable planets discovered in this way include 51 Eridani b, which has a mass 2.6 times that of Jupiter and orbits a star 96 light years from Earth in the constellation of Eridanus at a distance of 11.1 AU, HIP 65426 b (formally named Najsakopajk), which has a mass 7.1 times that of Jupiter, and orbits a star 385 light years from Earth in the constellation of Centaurus at a distance of 87 AU, and PDS 70 b and PDS 70 c, which have masses of 3.2 and 7.5 times that of Jupiter, and orbit a star 370 light years from Earth in the constellation of Centaurus at distances of 20.8 and 34.3 AU, respectively.

However, large planets at large separations from their host stars are relatively rare, which means that a large number of stellar systems have to be surveyed in this way in order to detect a few planets. Most giant planets known orbit their host stars at distances of 1-3 AU, which would make direct imaging them with current technology impossible if they are more than about 50 parsecs (163.1 light years) away from us. 

The radial velocity method uses the movement of stars to detect to infer the presence of companions. This has proven very effective as a  way to detect very large planets close to stars, such as Beta Pictoris c, which has a mass about nine times that of Jupiter, and orbits a star 63 light years from Earth in the constellation of Pictor at a distance of about 2.7 AU, or HD206893 c, which has a mass about 12.7 times that of Jupiter, and orbits a star 125 light years from  Earth in the constellation of Capricornus,  at a distance of 3.53 AU.

The proper motion anomaly method can identify potential companions to stars by measuring their parallax (the amount they move in a year because we are observing them from different points on the Earth's orbit) over several years; if the star moves more than predicted (i.e. anomalously), then this is likely to be because of an unseen companion moving the star. This method has been used to identify several potential planets which have subsequently been directly imaged. These include HIP 99770 b, which has a mass of about 16 times that of Jupiter, and which orbits a star 133 light years from Earth in the constellation of Cygnus at a distance of 17 AU, AF Leporis b, which is 2-5 times the mass of Jupiter and orbits a star 87.5 light years from Earth in the constellationof Lepus, as well as the brown dwarf HD21152 B, which has a mass 22-36 times that of Jupiter, and which orbits a star 150 light years from Earth in the constellation of Taurus at a distance of about 18 AU.

In a paper published in the Monthly Notices of the Royal Astronomical Society on 9 December 2024, a team of astronomers led by Dino Mesa of the Osservatorio Astronomico di Padova present the results of a study which targeted three stars in the Hipparcos-Gaia PMa catalogue identified as having proper motion anomalies with the SHARK-NIR coronagraphic camera and LMIRCam camera and coronagraph of the Large Binocular Telescope in Arizona. 

Because they were interested in planetary-sized companion bodies, rather than secondary stars, Mesa et al. looked for stars which showed small proper motion anomalies, and because they wished to be able to image bodies within 10 AU of their host star, they restricted themselves to objects within 50 parsecs (163 light years) of the Earth.

The first star selected, HIP 11696 A (also known as HD 15407 A) is an F-type (yellow-white dwarf) star with a mass about 1.40 times that of our Sun, 49.3 parsecs (160.8 light years) from Earth in the constellation of Persius. HIP 11696 is a young star, which has been estimated to be about 80 million years old, although it is also thought likely to be a member of the AAB Doradus Moving Group, which would make it between 125 and 149 million years old. Mesa et al. use an intermediate age of 137 million years for their calculations in their study.

HIP 11696 A has a companion star, HIP 1696 B, which is a K-type (orange dwarf) star with about 80% of the mass of our Sun, separated by about 1000 AU - far enough to be excluded from the field of view of the SHARK-NIR instrument. HIP 11696 A appears to be producing an unusual amount of light in the mid-infrared range, which may be indicative of a recent collision between rocky planets of planetary embryos in the inner part of the system. A debris disk has been detected at a distance of 0.6-1.0 AU from the star, which makes it unlikely that there are any massive planets orbiting close to the star. Nevertheless, an anomaly in the motion of HIP 11696 A which could not be explained by the presence of HIP 11969 B was detected. It has been suggested that this might be caused by a planet with a mass about 6.39 times that of Jupiter orbiting at 3 AU from HIP 11696 A, or a planet with a mass about 16.6 times that of Jupiter orbiting at about 30 AU from the star.

HIP 11696 A was observed with the SHARK-NIR and LMIRCam instrument on the night of 28 October 2023. Mesa et al. detected a bright object to the southeast of the star at a distance of 1.5" (1.5 arc seconds; the sky can be imagined as a sphere surrounding the Earth, divided into 360 degrees (°), with each degree divided into 60 arc minutes (') and each arc minute divided into 60 arc seconds (")). However, this object was also imaged previously by the Keck II telescope in November 2009, and the Gemini North Telescope in August 2013, with no movement relative to HIP 11696 A between these images, leading Mesa et al. to conclude that this is in fact a background object rather than a planetary companion to the star. Based upon this inability to image a planet close to the star, Mesa et al. calculate that if a planet is responsible for the observed wobble in HIP 11696 A's orbit, then this is likely to be between 2.5 and 28 AU from the star, and have a mass 4-16 times that of Jupiter.

(Top) Final image obtained for HIP 11696 using SHARK-NIR data. This image was obtained by applying a PCA method subtracting 5 principal components. (Bottom) Final image obtained for HIP 11696 using LMIRCam data. In this case, a PCA method subtracting 10 principal components was applied. In both cases, a bright candidate companion is visible South-East from the star. Because the image is looking up, the positions of east and west are reversed. Mesa et al. (2024).

The second star identified, HIP 47110 A (also known as HD 82939 A) is a G-type (yellow dwarf) star with about 98% of the mass of our Sun, 38.7 parsecs (126.2 light years) from Earth in the constellation of Leo Minor. HIP 47110 A has been identified as a possible member of the Pleiades Moving group, with an age of approximately 112 million years.

HIP 47110 A has a companion star, HIP 47110 B, which is a M-type (red dwarf) star with a separation of larger than 162" (interpreted to be more than 6280 AU), enabling it to be excluded from the field of vision. Again, there is an anomaly in the motion of HIP 47110 A which cannot be explained by the presence of HIP 447110 B, and which has been hypothesized to be caused by a planet. It has been suggested that this might be caused by a planet with a mass about 2.5 times that of Jupiter orbiting at between 5 and 10 AU from HIP 47110 A, or a planet with a mass about 11.35 times that of Jupiter orbiting at about 30 AU from the star.

HIP 47110 A was observed on the night of 20 February 2024, but no potential companion was observed. Based upon this, Mesa et al. exclude the possibility of a planet close to star, calculating that the observed orbitary wobble must be caused by a planet between 3 and 30 AU from the star with a mass of between 2 and 10 times that of Jupiter.

The third star in the study, HIP 36277, is a K-type (orange dwarf) star with a mass 0.67 times that of our Sun, located 46.3 parsecs (151 light years) from the Earth in the constellation of Dorado. HIP 36277 was identified as a young runaway star (star which has been ejected from the star cluster which birthed it, and which is therefore travelling at a high speed in a distance at odds with galactic rotation) with an age of about 41.2 million years. However, spectrographic analysis of the star has suggested a much older age, most probably more than a billion years old and possibly more than 10 billion years. 

An anomaly on the motion of HIP 36277, which has been interpreted as potentially due to a planet with a mass 2.3 times that of Jupiter at a distance of 5 AU from the star, 2.64 times that of Jupiter at 10 AU from the star, or 15.18 times the mass of Jupiter at 30 AU from the star.

HIP 36277 was observed on the night of 21 February 2024, with a bright object observed to the southeast of the star in both SHARK-NIR and LMIRCam images. This body could also be identified in images from the Gaia space telescope, with similar parallax and proper motion values, which demonstrates physical association with the star. The object is separated from the star by 1.9". The precise size of this object is difficult to calculate, given the uncertainty of the age of the star, but Mesa et al. calculate that if the star is 41 million years old, then it would have a mass of between 16.2 and 73.9 times that of Jupiter (with a median value of 37.8 Jupiter masses), making it most likely a brown dwarf companion to the star (brown dwarfs are objects intermediate to stars and planets in size; they are not large enough to fuse ordinary hydrogen in their cores, but are large enough to fuse the heavier isotope deuterium). However, if the star is about five billion years old, then the body is likely to have a mass about 0.1 times that of our Sun, making it a small M-type (red dwarf) star. 

A second object was also visible in the SHARK-NIR data, but not observed by LMIRCam. This object is to the south of the star, and separated by about 0.0625", which Mesa et al. calculate to be equivalent to about 28.9 AU. Again, the mass of such an object would be dependent on its age, with a 41-million-year-old object having a mass about 7.6 times that of Jupiter, making it a large planet, while at 5 billion years old it would have a mass between 65.9 and 72.1 times that of Jupiter, again indicative of a brown dwarf.

(Top) Final image obtained for HIP 36277 using SHARK-NIR data. This image was obtained by applying a PCA method subtracting 5 principal components. (Bottom) Final image obtained for HIP 36277 using LMIRCam data. In this case, a PCA method subtracting 10 principal components was applied. In both cases, a bright candidate companion is visible southeast from the star. Furthermore, in the SHARK-NIR image, a possible fainter object is visible just south of the star. Mesa et al. (2024).

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Magnitude 7.0 Earthquake off the coast of Northern California.

The United States Geological Survey recorded a Magnitude 7.0 Earthquake at a depth of about 10.0 km a little  over 50 km off Cape Mendocino in Humboldt County, California, slightly before 10.45 am local time (slightly before 6.45 pm GMT) on Thursday 5 December 2024. There are no reports of any casualties associated with this event, but the size and location of the Earthquake led to a tsunami being issued, advising about half a million people in California to seek high ground (in the event no tsunami was recorded), and minor damage to highways and buildings were recorded in several places, as well as disruption to power networks which left about 10 000 people in Humbolt County without power. The initial Earthquake has been followed by a large number of aftershocks, with the USGS estimating there is a 5% chance of another quake with a Magnitude of 6.0 or greater occurring in the same area within a week, and a 34% chance of a quake with a Magnitude of 5.0 or greater occurring.

The approximate location of the 5 December 2024 California Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

Goods knocked from shelves in Hoby's Market & Deli in Scotia, California, following a Magnitude 7.0 Earthquake on 5 December 2024. Dylan McNeil/The Times Standard/AP.

However, the 5 December 2024 Earthquake happened close to the southern part of the Mendocino Fracture Zone, a westward extension of the San Andreas Fault, where the Gorda Plate to the north is moving westward relative to the Pacific Plate to the south. Along this boundary the rocks of the two plates continuously stick together, then become stressed as the motion of the two plates draws them apart. This stress builds up until the rocks are forcibly snapped apart, which we experience as Earthquakes.

A crack is seen on Blue Slide Road in Rio Dell, California, following a Magnitude 7.0 Earthquake on 5 December 2024. City of Rio Dell/ABC News.

The Gorda Plate, along with the Explorer and Juan de Fuca Plates are remnants of an ancient oceanic plate, the Fallaron Plate which has almost completely disappeared beneath North America. The Fallaron Plate formerly diverged from the Pacific Plate along the Fallaron Ridge, but as the plate has been subducted both it and the ridge have broken up. The remnants of the plate are now the Explorer Plate in the north, then the Juan de Fuca Plate, then the Gorda Plate in the south. This borders onto the Pacific Plate along the Mendocino Fracture Zone, which extends on land as the San Andreas Fault.

North of California the San Andreas Fault becomes the Mendocino Fracture Zone. USGS.

Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here. 

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