Nature, Published online: 01 January 2025; doi:10.1038/d41586-024-04140-4During pregnancy, several organs are rewired to support the health of the mother and the offspring. A molecular signalling pathway called RANKRANKL drives the expansion of the layer that lines the inside of the intestine during pregnancy and lactation. This tissue remodelling process has a key role in mammalian life history.

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As Lockheed Martin prepares for the first flight of the X-59, its silent supersonic jet, NASA scientists are finalizing tests to measure the real impact of the aircrafts aerodynamic shape on its sonic shockwaves. NASA will measure the air vibrations caused by the jets sonic boom by surveying residents in areas where the X-59 passes overhead, but it will also need to measure it through scientific means.These shockwaves will be so small that the American aerospace agency had to reinvent the shockwave-sensitive probes that it previously used to measure sonic booms. Mike Frederick, the lead researcher on the project at NASAs Armstrong Flight Research Center, tells me in an email interview that these shock-sensing probes were adapted from existing designs to meet the unique requirements of capturing the X-59s quieter sonic boom.The probes will be mounted on booms placed on the nose tips of F-15B chase planes, measuring the pressure variations in the atmosphere caused by the X-59 in flight as the aircraft generates its sonic booms. Shaped like a long tube with a cone at its end, they contain five ports that measure pressure changes. One port is located at the cones tip, and the other four are distributed around its circumference. These sensors detect pressure changes, recording thousands of samples per second to calculate the intensity, duration, and propagation of the shockwaves generated by a supersonic aircraft.For the X-59, the probe will also compare the data collected during actual flight tests with predictions from mathematical simulations. Before starting these tests, NASA will conduct measurements to establish fundamental truththe empirical baseline data that will validate future measurements with the X-59. These measurements will be conducted using an F-15 flying supersonic followed by the F-15B equipped with the new probe to measure the shockwave of the X-59.A probe designed to measure the almost imperceptibleAccording to Frederick, the legacy design relied on long lengths of pneumatic tubing. That tubing tends to attenuate the shock features to a certain extent. The new ones use high sample rate transducersa device that transforms one form of energy into another, like a microphone turns your voice into an electric signaland very short lengths of tubing that do not suffer from the same amount of attenuation as the shockwave travels through them to reach the sensors. NASAs F-15B Aeronautics Research Test Bed performs a calibration flight of the shock-sensing probe over Edwards, California on Aug. 6, 2024. The probe will measure shock waves from NASAs X-59, providing data that may change limits for overland supersonic flight from being speed-based to sound-based. This work is part of NASAs Quesst mission, with the X-59 as its flagship aircraft. [Photo: Steve Freeman/NASA]This design is able to resolve very weak shocks more effectively, he says. The small amount of tubing in the probe still has a slight effect on the measured shocks, but its thought to be negligible. In a perfect world, Frederick says, they would mount the pressure transducer flush with the cone surface to completely eliminate any attenuation, but the probe isnt large enough in diameter to accommodate that design.The current probes also include a heating system to maintain a constant temperature during flight. Frederick tells me that this temperature stabilization is crucial to get an accurate reading. The probes pressure transducers have a piezoresistive sensing element, which is a type of sensor that changes its electrical resistance in response to applied pressure or mechanical stress. The output of this sensing element changes with temperature for a given pressure, he says, so, to ensure consistent output for a given pressure, we need to keep the pressure sensors at a constant temperature.This is complex because the probe temperature is affected by the temperature of the atmosphere and the aerodynamic heating of the probe, which occurs when flying supersonic because of extreme air friction. Without a thermally controlled environment of the sensors, Frederick points out, wed have an unacceptable amount of variation in the pressure measurements due solely to temperature changes. According to him, this thermally stable environment has been their biggest advancement. We had to implement some calibration tricks to ensure the very small pressure range met the pressure resolution requirements for X-59.The probe design has also been optimized into two versions for different uses. The first version measures shockwaves near their source, at an altitude of approximately 55,000 feet, flying directly behind the X-59. The near-field probe provides the primary measurement, he says. This measurement will be compared with the results from NASAs computational fluid dynamics simulations of the near-field shock signature. The mid-field probe will fly very close to the ground and will capture a secondary measurement that will be compared to the simulations of how the shockwave travels through the atmosphere down to the ground. This two-pronged approach will give a complete picture of how the X-59s boom generates and propagates but also will improve future simulations with its empirical data.A new era of commercial supersonic flightThe X-59 is designed and built by Lockheed Martin Skunk Works to demonstrate that supersonic flights over land are feasible without causing discomfort to humans. This experimental aircraft will test a groundbreaking aerodynamic design, reducing costs by using components reused from other aircraft. According to Dave Richardson, director of the X-59 program at Lockheed Martin, [Reducing the sonic boom] is not based on exotic materials or revolutionary technologies but simply on the shape of the aircraft. This shape was developed from work NASA conducted in the 1960s with wind tunnel tests.The X-59s engine, a General Electric F414-GE-100, generates 22,000 pounds of thrust and is the same used in the U.S. Navys F/A-18 Super Hornet, although modified for this aircraft. With this engine, the X-59 can cruise at a speed of Mach 1.42 (approximately 940 mph) at an altitude of 55,000 feet. Additionally, its cockpit lacks a windshield, allowing for a cleaner aerodynamic profile. Instead, pilots use an external vision system, with cameras projecting the surroundings onto screens inside the cockpita design that has already received approval from the Federal Aviation Administration (FAA).The X-59 also stands out for significantly reducing development times and costs thanks to supercomputing and digital modeling, optimizing the design process by avoiding numerous wind tunnel tests. Richardson explains that [Digital models allow predicting the propagation of shockwaves] from the aircraft to the ground, something that in the past would have required countless wind tunnel tests at prohibitive costs.After successfully completing engine tests in early November, the team is now preparing for the final steps before the X-59s first flight, scheduled for early 2025. Paul Dees, deputy propulsion lead for the X-59 at NASA, notes, The exact date of the first flight will depend on the success of each test, but we are confident it will be soon.Once airborne, the X-59 will fly over U.S. communities, where surveys of residents and sound samples collected with ground microphones will be used to measure both the subjective reactions of humans and the objective variations in sound levels. In addition to the scientific measurements from this instrument, these data will serve as a basis for regulatory decisions by national and international agencies, aiming to lift the current ban on commercial supersonic flights over land.If successful, this weird airplane design will be the basic blueprint for the airlines of the future. Private companies will be able to use this public research to build their own designs, following the path open by the thunderous Concorde, but this time tiptoeing at supersonic speed.

Climate change keeps getting harder to ignore. Phoenix lived through 113 consecutive days above 100 degrees last summer. A record number of fires burned in rainforests in South America in 2024. Climate havens like Asheville, North Carolina, were devastated by floods. Emissions keep growing. But its also true that climate solutions are rolling out faster than ever before. It took decades, for example, for the world to install 760 gigawatts of solar power by 2020; in 2024 alone, the world installed another 593 gigawatts, breaking a record set the year before. Here are five ways that the world is moving in the right direction.New climate solutions are becoming realitySome industries are especially hard to decarbonizefor example, shipping, since cargo ships cant easily run on batteries. But new solutions are successfully proving themselves and scaling up. The worlds largest wind-powered cargo ship made its first trip across the Atlantic in 2024. Infinium, a company that makes fuel from CO2 and green hydrogen that can be used in planes, ships, and trucks, started commercial-scale production in 2024. Twelve, another company pioneering CO2-based fuel, expects to begin commercial-scale production in 2025, and will partner with Alaska Airlines to power a commercial flight.Clean energy projects are booming in the U.S.Since the Inflation Reduction Act passed two years ago, driving new investment in climate tech, more than 140 new clean energy projectsfrom massive battery factories to plants assembling EVshave been built in the U.S, according to the Clean Economy Tracker. Another 93 are under construction, and 293 are in planning. Recently launched plants are scaling up production, such as a factory that now makes batteries inside a formerly abandoned Rust Belt building near Pittsburgh. In West Virginia, on the site of a former steel factory, another startup is making cutting-edge, sustainable iron-air batteries.Now, the Trump administration wants Congress to repeal the IRA, though the jobs that new clean energy factories are bringing to red districts may help keep it in place. And even if IRA incentives are taken away, state support and other investment could potentially keep the sector growing; some solutions are already more economical for customers even without incentives.EVs are getting more affordableIn China, where more than half of new car sales are reportedly now electric or hybrid vehicles, most electric cars are cheaper than their gas equivalents, according to the International Energy Agency. Thats without subsidies. And though tariffs in the EU and U.S. will limit the sale of cheap Chinese cars abroad, Chinese manufacturers are also exporting large numbers of affordable EVs to places like Thailand and Brazil. Battery prices dropped by 20% in 2024, which will also help bring down the cost of EVs. Even in the U.S., where the upfront cost of EVs is still higher, the lifetime cost of owning an electric car is often already less expensive than a gas car. And new options for affordable EVs will be hitting the market in 2025.Solar power broke new recordsThe U.S. installed a record 32 gigawatts of solar power in 2024, enough to power as many as 32 million homes. China installed as much as 260 gigawatts of solar, including an enormous 33,000-acre solar farm that produces, on its own, as much energy as the entire country of Luxembourg uses in a year. Solar is also growing in less expected places like Pakistan, where farms, factories, and homeowners installed 17 gigawatts of solar over the year to help fight the rising cost of fossil fuelpowered energy.Global solar installations could hit 593 gigawatts this year29% more than 2023, which was already a record year. While growth is likely to slow in the U.S. in 2025 because of tariffs and potential Trump administration policies, the exponential global growth is much faster than expected.Communities are becoming more resilientThis year was the hottest year on recordand incredibly destructive, from wildfires in the Amazon to hurricanes in the U.S. Cities are nowhere near prepared. Still, some communities are beginning to make changes that can help. Cities from Asheville to Seattle are using public libraries as disaster hubs. A recently built neighborhood in Florida was designed to survive hurricanes and keep the power on. In Paris, to help deal both with extreme heat and extreme rainfall, the city is de-paving some areas to add more green space.