Dark Matter Detector Observes Rarest Event Ever Recorded

How do you observe a process that takes more than one trillion times longer than the age of the universe? The XENON Collaboration research team did it with an instrument built to find the most elusive particle in the universe—dark matter. In a paper to be published tomorrow in the journal Nature, researchers announce that they have observed the radioactive decay of xenon-124, which has a half-life of 1.8 X 1022 years.

“We actually saw this decay happen. It’s the longest, slowest process that has ever been directly observed, and our dark matter detector was sensitive enough to measure it,” said Ethan Brown, an assistant professor of physics at Rensselaer, and co-author of the study. “It’s an amazing to have witnessed this process, and it says that our detector can measure the rarest thing ever recorded.”

The XENON Collaboration runs XENON1T, a 1,300-kilogram vat of super-pure liquid xenon shielded from cosmic rays in a cryostat submerged in water deep 1,500 meters beneath the Gran Sasso mountains of Italy. The researchers search for dark matter (which is five times more abundant than ordinary matter, but seldom interacts with ordinary matter) by recording tiny flashes of light created when particles interact with xenon inside the detector. And while XENON1T was built to capture the interaction between a dark matter particle and the nucleus of a xenon atom, the detector actually picks up signals from any interactions with the xenon.

The evidence for xenon decay was produced as a proton inside the nucleus of a xenon atom converted into a neutron. In most elements subject to decay, that happens when one electron is pulled into the nucleus. But a proton in a xenon atom must absorb two electrons to convert into a neutron, an event called “double-electron capture.”

Double-electron capture only happens when two of the electrons are right next to the nucleus at just the right time, Brown said, which is “a rare thing multiplied by another rare thing, making it ultra-rare.”

When the ultra-rare happened, and a double-electron capture occurred inside the detector, instruments picked up the signal of electrons in the atom re-arranging to fill in for the two that were absorbed into the nucleus.

“Electrons in double-capture are removed from the innermost shell around the nucleus, and that creates room in that shell,” said Brown. “The remaining electrons collapse to the ground state, and we saw this collapse process in our detector.”

The achievement is the first time scientists have measured the half-life of this xenon isotope based on a direct observation of its radioactive decay.

“This is a fascinating finding that advances the frontiers of knowledge about the most fundamental characteristics of matter,” said Curt Breneman, dean of the School of Science. “Dr. Brown’s work in calibrating the detector and ensuring that the xenon is scrubbed to the highest possible standard of purity was critical to making this important observation.”

The XENON Collaboration includes more than 160 scientists from Europe, the United States, and the Middle East, and, since 2002, has operated three successively more sensitive liquid xenon detectors in the Gran Sasso National Laboratory in Italy. XENON1T, the largest detector of its type ever built, acquired data from 2016 until December 2018, when it was switched off. Scientists are currently upgrading the experiment for the new XENONnT phase, which will feature an active detector mass three times larger than XENON1T. Together with a reduced background level, this will boost the detector’s sensitivity by an order of magnitude.

Data Mining Digs Up Hidden Clues To Major California Earthquake Triggers

A powerful computational study of southern California seismic records has revealed detailed information about a plethora of previously undetected small earthquakes, giving a more precise picture about stress in the earth’s crust. A new publicly available catalog of these findings will help seismologists better understand the stresses triggering the larger earthquakes that occasionally rock the region.

“It’s very difficult to unpack what triggers larger earthquakes because they are infrequent, but with this new information about a huge number of small earthquakes, we can see how stress evolves in fault systems,” said Daniel Trugman, a post-doctoral fellow at Los Alamos National Laboratory and coauthor of a paper published in the journal Science today. “This new information about triggering mechanisms and hidden foreshocks gives us a much better platform for explaining how big quakes get started,” Trugman said.

Crunching the Numbers

Trugman and coauthors from the California Institute of Technology and Scripps Institution of Oceanography performed a massive data mining operation of the Southern California Seismic Network for real quakes buried in the noise. The team was able to detect, understand, and locate quakes more precisely, and they created the most comprehensive earthquake catalog to date. The work identified 1.81 million quakes — 10 times more earthquakes occurring 10 times more frequently than quakes previously identified using traditional seismology methods.

The team developed a comprehensive, detailed earthquake library for the entire southern California region, called the Quake Template Matching (QTM) catalog. They are using it to create a more complete map of California earthquake faults and behavior. This catalog may help researchers detect and locate quakes more precisely.

The team analyzed nearly two decades of data collected by the Southern California Seismic Network. The network, considered one of the world’s best seismic systems, amasses a catalog of quakes from 550 seismic monitoring stations in the region. The SCSN catalog is based entirely on the traditional approach: manual observation and visual analysis. But Trugman says this traditional approach misses many weak signals that are indicators of small earthquakes.

Matching Templates Is Key

The team improved on this catalog with data mining. Using parallel computing, they crunched nearly 100 terabytes of data across 200 graphics processing units. Zooming in at high resolution for a 10-year period, they performed template matching using seismograms (waveforms or signals) of previously identified quakes. To create templates, they cut out pieces of waveforms from previously recorded earthquakes and matched those waveforms to patterns of signals recorded simultaneously from multiple seismic stations. Template matching has been done before, but never at this scale.

“Now we can automate it and search exhaustively through the full waveform archive to find signals of very small earthquakes previously hidden in the noise,” Trugman explained.

Applying the templates found events quake precursors, foreshocks and small quakes that had been missed with manual methods. Those events often provide key physical and geographic details to help predict big quakes. The team also identified initiation sequences that reveal how quakes are triggered.

New details also revealed three-dimensional geometry and fault structures, which will support development of more realistic models.

Recently, Trugman and Los Alamos colleagues have applied machine learning to study earthquakes created in laboratory quake machines. That works has uncovered important details about earthquake behavior that may be used to predict quakes.

“In the laboratory, we see small events as precursors to big slip events, but we don’t see this consistently in the real world. This big data template-matching analysis bridges the gap,” he said. “And now we’ve discovered quakes previously discounted as noise and learned more about their behavior. If we can identify these sequences as foreshocks in real time, we can predict the big one.”

NASA’s InSight Detects First Likely ‘Quake’ On Mars

NASA’s Mars InSight lander has measured and recorded for the first time ever a likely “marsquake.”

The faint seismic signal, detected by the lander’s Seismic Experiment for Interior Structure (SEIS) instrument, was recorded on April 6, the lander’s 128th Martian day, or sol. This is the first recorded trembling that appears to have come from inside the planet, as opposed to being caused by forces above the surface, such as wind. Scientists still are examining the data to determine the exact cause of the signal.

“InSight’s first readings carry on the science that began with NASA’s Apollo missions,” said InSight Principal Investigator Bruce Banerdt of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “We’ve been collecting background noise up until now, but this first event officially kicks off a new field: Martian seismology!”

The new seismic event was too small to provide solid data on the Martian interior, which is one of InSight’s main objectives. The Martian surface is extremely quiet, allowing SEIS, InSight’s specially designed seismometer, to pick up faint rumbles. In contrast, Earth’s surface is quivering constantly from seismic noise created by oceans and weather. An event of this size in Southern California would be lost among dozens of tiny crackles that occur every day.

“The Martian Sol 128 event is exciting because its size and longer duration fit the profile of moonquakes detected on the lunar surface during the Apollo missions,” said Lori Glaze, Planetary Science Division director at NASA Headquarters.

NASA’s Apollo astronauts installed five seismometers that measured thousands of quakes while operating on the Moon between 1969 and 1977, revealing seismic activity on the Moon. Different materials can change the speed of seismic waves or reflect them, allowing scientists to use these waves to learn about the interior of the Moon and model its formation. NASA currently is planning to return astronauts to the Moon by 2024, laying the foundation that will eventually enable human exploration of Mars.

InSight’s seismometer, which the lander placed on the planet’s surface on Dec. 19, 2018, will enable scientists to gather similar data about Mars. By studying the deep interior of Mars, they hope to learn how other rocky worlds, including Earth and the Moon, formed.

Three other seismic signals occurred on March 14 (Sol 105), April 10 (Sol 132) and April 11 (Sol 133). Detected by SEIS’ more sensitive Very Broad Band sensors, these signals were even smaller than the Sol 128 event and more ambiguous in origin. The team will continue to study these events to try to determine their cause.

Regardless of its cause, the Sol 128 signal is an exciting milestone for the team.

“We’ve been waiting months for a signal like this,” said Philippe Lognonné, SEIS team lead at the Institut de Physique du Globe de Paris (IPGP) in France. “It’s so exciting to finally have proof that Mars is still seismically active. We’re looking forward to sharing detailed results once we’ve had a chance to analyze them.”

Most people are familiar with quakes on Earth, which occur on faults created by the motion of tectonic plates. Mars and the Moon do not have tectonic plates, but they still experience quakes — in their cases, caused by a continual process of cooling and contraction that creates stress. This stress builds over time, until it is strong enough to break the crust, causing a quake.

Detecting these tiny quakes required a huge feat of engineering. On Earth, high-quality seismometers often are sealed in underground vaults to isolate them from changes in temperature and weather. InSight’s instrument has several ingenious insulating barriers, including a cover built by JPL called the Wind and Thermal Shield, to protect it from the planet’s extreme temperature changes and high winds.

SEIS has surpassed the team’s expectations in terms of its sensitivity. The instrument was provided for InSight by the French space agency, Centre National d’Études Spatiales (CNES), while these first seismic events were identified by InSight’s Marsquake Service team, led by the Swiss Federal Institute of Technology.

“We are delighted about this first achievement and are eager to make many similar measurements with SEIS in the years to come,” said Charles Yana, SEIS mission operations manager at CNES.

JPL manages InSight for NASA’s Science Mission Directorate. InSight is part of NASA’s Discovery Program, managed by the agency’s Marshall Space Flight Center in Huntsville, Alabama. Lockheed Martin Space in Denver built the InSight spacecraft, including its cruise stage and lander, and supports spacecraft operations for the mission.

A number of European partners, including CNES and the German Aerospace Center (DLR), support the InSight mission. CNES provided the SEIS instrument to NASA, with the principal investigator at IPGP. Significant contributions for SEIS came from IPGP; the Max Planck Institute for Solar System Research in Germany; the Swiss Federal Institute of Technology (ETH Zurich) in Switzerland; Imperial College London and Oxford University in the United Kingdom; and JPL. DLR provided the Heat Flow and Physical Properties Package (HP3) instrument, with significant contributions from the Space Research Center of the Polish Academy of Sciences and Astronika in Poland. Spain’s Centro de Astrobiología supplied the temperature and wind sensors.

Another Tropical Cyclone Is Taking Aim At Storm-Wrecked Mozambique

Another tropical storm is heading toward Mozambique, the southern African nation still reeling from the historic death and devastation wrought by Cyclone Idai.

The new storm, Tropical Cyclone Kenneth, strengthened rapidly Wednesday, with a wind speed of 140 kph (85 mph), and will continue to intensify as it moves over the Comoro Islands. It is expected to make landfall Thursday in the far north of Mozambique, about 1,000 km (620 miles) north of where Idai struck.

“Residents along the Mozambique/Tanzania border should make preparations for storm surge along the coasts, heavy rainfall, and hurricane-force winds,” NASA warned.

In Tanzania, Kenneth is expected to hit the coastal areas of Dar es Salaam, the port city of Tanga and Pemba Island, according to the Tanzania Meteorological Agency. Strong winds and rain may affect the Lake Victoria basin, its mountainous regions and the coast, forecasters said.
While the zone slammed by Idai will be spared, Kenneth still will strike Mozambique just one month after that storm killed more than 700 people and displaced tens of thousands. It caused an estimated $1 billion dollars in damage, or nearly 10% of the nation’s gross domestic product.

Kenneth could be stronger, less devastating than Idai
Kenneth formed this week in the southern Indian Ocean as a moderate tropical storm and moved north of Madagascar, with maximum winds on Tuesday of 65 kph (40 mph).

The storm could strengthen to the equivalent of a Category 3 hurricane, with winds up to 195 kph (120 mph). That would make it stronger than Idai was when it hit central Mozambique and could rank it among the strongest storms to ever hit the country.

However, Kenneth is not expected to have as devastating an impact on the country as Idai, which delivered heavy rains for days before and after making landfall on March 15, with winds near 175 kph (109 mph).

Idai’s sustained rainfall, combined with strong winds and storm surge, set the stage for catastrophic flooding that submerged towns and villages as the storm pushed inland toward Zimbabwe and Malawi.

Northern Mozambique also is not as populated as Beira, the population hub struck by Idai. Several rivers come together there and flow into the Mozambique Channel, a factor that made the region more vulnerable to flooding.

Moreover, the nation’s northern region has not seen intense rainfall in recent days, which hopefully will mitigate the impact of flooding compared with Idai.

Tropical Cyclone Leon-Eline remains the strongest cyclone to ever hit Mozambique. It ripped through the region in 2000, with winds stronger than 210 kph (130 mph) and killed about 800 people.

All Types of Large Earthquakes Produce Prompt Gravity Signals

When major earthquakes occur, they displace enormous amounts of mass. This motion creates tiny perturbations in Earth’s gravitational field that travel at the speed of light—more than 4 orders of magnitude faster than the elastic seismic waves emanating from the same tremor. Because these prompt elastogravity signals (PEGS) precede seismic waves, the perturbations have the potential to improve early-warning systems by reducing the time it takes to estimate the size of large-magnitude earthquakes.

The weakness of these elastogravity waves, however, has made them extremely difficult to detect; the first PEGS observations weren’t published until 2016. Now Vallée and Juhel report multiple new observations of these signals from five earthquakes ranging in magnitude from 7.9 to 8.8, significantly smaller events than the magnitude 9.1 Tohoku earthquake from which their existence was first discovered.

The researchers identified these faint signals using a multistep approach. First, to better understand the conditions under which elastogravity waves are easiest to detect, the team developed a series of numerical simulations to evaluate how the depth and type of earthquake affect the signals’ expected amplitude. The results, which indicate that shallow strike-slip and deep events have a greater chance of being recorded than megathrust subduction zone earthquakes, helped inform the authors’ ensuing analysis of the records from large earthquakes that have occurred within the past 25 years.

This analysis revealed the presence of PEGS preceding seismic waves during several major earthquakes. These include the 2012 magnitude 8.6 Wharton Basin event, the largest strike-slip earthquake ever recorded, and two large and very deep tremors: the 2018 magnitude 8.2 Fiji earthquake and the 1994 magnitude 8.2 Bolivia event. By combining observations from several instruments, the team was also able to improve the signal-to-noise ratios enough to detect elastogravity waves from two additional tremors, including the 2018 magnitude 7.9 strike-slip event off Alaska.

The results show that the successful detection of PEGS is not restricted to exceptional (greater than magnitude 9) megathrust earthquakes. These findings indicate that PEGS observations have the potential to significantly improve the speed and reliability of early-warning systems in a lot of settings where the faster detection of major earthquakes could enhance rapid emergency response and/or improve tsunami hazard assessments.

2 Earthquakes Shake The Philippines; At Least 16 Dead

A powerful 6.4 earthquake struck the Philippines on Tuesday, the day after a different temblor took lives and collapsed buildings.

Rescuers continued to search for survivors from Monday’s quake, centered just 50 miles northwest of Manila, the capital. That quake killed at least 16 people, according to The Associated Press. So far, it appears that Tuesday’s 6.4 magnitude quake in Eastern Samar province did not cause any casualties or major damage.

Monday’s magnitude 6.1 quake struck Pampanga province, north of Manila, shortly after 5 p.m. local time. A supermarket collapsed in the municipality of Porac, killing at least five people, the AP reports. Others remain missing.

One man was reportedly pulled out alive from the supermarket’s rubble on Tuesday morning, to cheers from onlookers.

“We’re all very happy, many clapped their hands in relief because we’re still finding survivors after several hours,” Porac Councilor Maynard Lapid told the AP.

Fifteen of the dead were in Pampanga province, the state news service reported. Philippine President Rodrigo Duterte arrived in the affected area Tuesday, where he inspected the damage and was briefed on the situation.

Aurelia Daeng, 65, told Reuters that she was in her family’s drugstore when Monday’s quake struck. “It was very strong. It was our first time experiencing something like that,” she told the news service. “This one, it’s terrifying.”

Monday’s quake also shook the nation’s capital, where panicked office workers fled buildings, some in hard hats, according to Reuters.

More than 400 aftershocks continued to unsettle residents after Monday’s quake, and the government closed more than 1,600 schools in the region. Central Luzon, the area struck, is in one of the country’s most seismically active regions, home to three major faults and an oceanic trench.

Philippine seismologists said the two earthquakes were not related, the AP reports. The country is part of the “Ring of Fire,” a belt of heavy seismic activity where some 90 percent of the world’s earthquakes occur, according to the U.S. Geological Survey.

Strong Earthquake Strikes Philippines, Killing 11 People

MANILA — A powerful earthquake shook the northern Philippines on Monday, leaving at least 11 people dead in collapsed buildings, municipal and disaster relief officials said.

The Philippine Institute of Volcanology and Seismology said the quake had registered a magnitude of 6.1 and had been centered near the town of Castillejos in Zambales Province, west of Manila. It struck shortly after 5 p.m., as government offices and private businesses were closing for the day.

In the town of Porac, northwest of Manila, five people were reported crushed to death after a wall in a four-story supermarket collapsed, RJ Mago, a spokesman for the National Disaster Risk Reduction and Management Council, told a local radio station.

[One day after the deadly tremor, a powerful earthquake struck Samar, an island in the central eastern Philippines.]

He said an older woman and her granddaughter who had been injured at the supermarket had been taken to a hospital and were in good condition.

Lilia Pineda, the governor of the northern province of Pampanga, said that she had received reports that the quake had killed eight people there and had knocked out power.

“Almost all concrete electric posts in the villages of Lubao town have fallen down,” she said.

The quake was felt in varying intensities in Manila, where news outlets reported panicked workers fleeing tall office buildings. It was also intense in Malolos and Obando, north of the capital; in Lipa, a city south of Manila; and in the town of Magalang in Pampanga Province. At least 25 urban centers and provinces recorded tremors.

Renato U. Solidum Jr., an official at the Department of Science and Technology, said that although the quake had not caused extensive damage, it could produce many aftershocks.

“This earthquake is not a major earthquake, but it’s a strong earthquake,” he said, adding, “This is already far from Metro Manila but a little bit shallow so we can feel it.” Seventeen aftershocks were recorded by the state seismology institute.

Because of its location on the so-called Pacific Ring of Fire, the Philippines is prone to earthquakes and volcanic eruptions caused by the movement of tectonic plates.

In October 2013, nearly 100 people were killed after a powerful earthquake struck the central island of Bohol.