A digest of popular science news for the week that we haven't written about

Evidence of lunar caves is emerging as humans seek hospitable refuge beneath the lunar surface

Scientists discovered evidence of the existence of underground caves on the Moon that people could use as shelter during a flight to the Earth's natural satellite.

The idea that there may be underground channels on the Moon, with entrances found in depressions on the surface, has been discussed for over 50 years. The depressions are thought to have been formed by the collapse of underlying lava tubes. Whether there are any unexplored lava tubes that suggest underground caves is unknown, although over 200 pits have been identified so far.

A new study led by Leonardo Carrera, an associate professor at Italy's University of Trento, has put forward evidence that underground cave channels originate from an open pit on the Moon, based on an analysis of radar data obtained by the Lunar Reconnaissance Orbiter (LRO) from the Mare Tranquillitatis pit, the deepest known pit on the Moon, with a radius of about 100 meters.

In 2022, data from LRO led scientists to conclude that there are about 200 “pits” on the Moon that maintain a stable, human-friendly temperature. According to NASA, the temperature in the pits “is always at a comfortable 63F/17°C, while surface temperatures can fluctuate between 127C/260F and -173C/-280F during the lunar day.”

Noticing an increase in radar brightness on the western side of the pit in the LRO data, the team used modeling based on the radar images to suggest that the results could be explained by a cavernous void or channel widening out from the western side of the pit floor. The authors of the study, published today in the journal Nature Astronomy, estimate that the caves could be located between 130 and 170 meters below ground and up to 80 meters long and 45 meters wide.

The researchers suggest that their work could be expanded if orbital radar sensors with a resolution capable of covering the interior of all the lunar pits detected by LRO were deployed in lunar orbit.

“A complete survey of all known lunar pits would allow us to identify the most promising access points for exploring the lunar subsurface and provide information on the potential for establishing a human lunar base in an environment protected from cosmic radiation and with stable temperatures,” the paper says. The authors of the study believe that a similar technique could be used on Mars, where 1,000 cave entrances have already been discovered.

Evidence of water found in atmosphere of mysterious exoplanet Smertrios

Astronomers may have discovered presence of water in the atmosphere of a white-hot planet that is also one of the most metallic worlds ever observed. The planet's formation remains a mystery that this discovery may help solve.

The exoplanet in question is HD 149026 b, also known as Smertriosmeaning “Nurse” or “Seer”, worshipped in Gaelic tradition as a god of war. Smertrios orbits the yellow subgiant star HD 149026, located approximately 247 light years from Earth.

The planet is about 4 million miles from its parent star and completes an orbit in less than three Earth days. Smertrios, which is about three-quarters the width of Jupiter, is a “hot Saturn” planet, named after the solar system's smaller gas giant.

Smertrios's proximity to its star means it is tidally locked, with its dayside always facing its host star, where temperatures reach 1,420°C. The relatively cooler nightside always faces space. But it is the density and composition of Smertrios, discovered in 2005 as it crossed, or “transited,” its star's disk, that makes it truly odd.

Hot gas giants are exoplanets similar in size to Jupiter or Saturn, but orbiting their host stars at very close distances. Typically, their orbital period is less than ten days, meaning that one year on such planets could be less than a week!” says Syed Ali Rafi, a member of the team that made the discovery and an astronomy researcher at the University of Tokyo, told Space.com“This planet is of particular interest because it is one of the most metal-rich and dense gas giants we know of to date.”

When astronomers like Ali Rafi talk about “metals,” they mean elements heavier than hydrogen and helium. When the James Webb Space Telescope (JWST) looked at Smertrios in 2023, the powerful space telescope found that the planet’s metallicity — the proportion of metals to hydrogen — is much higher than most hot Saturns and larger hot Jupiters. The ratio for Smertrios is also much higher than for the solar system’s giants, Jupiter and Saturn.

Liquid lakes on Saturn's moon have waves and currents

Earth isn't the only place in the solar system with rivers, lakes, and seas. Titan, Saturn's largest moon, has a surface covered in liquid, but it's not water, it's liquid hydrocarbons like ethane and methane. Titan has hundreds of times more liquid hydrocarbons than all of Earth's known oil and natural gas reserves combined.

A new paper published today in the journal Nature Communications reveals Titan's bizarre bodies of water, including waves, currents, estuaries and straits.

The work uses archival data from NASA's Cassini mission, which orbited Saturn from 2004 to 2017 and whose Huygens probe transmitted the first-ever images of Titan's surface in 2005. They showed ancient dry shores reminiscent of Earth's and rivers of methane.

Titan is the most Earth-like planet known to us, with an atmosphere (albeit one made up of 98% nitrogen and 2% methane), as well as rain, ice, lakes, oceans, valleys, mountain ranges, and dunes. The landscape is dominated by large dune fields, flat plains, and polar regions with large seas and lakes of liquid hydrocarbons. The surface temperature is about -179°C, and Titan's gravity is 14% that of Earth's. It receives only 1% of the sunlight that Earth receives.

So Titan is hardly Earth-like, although aerial and radar images show streams of liquid methane, not water, rippling its surface.

NASA halts work on VIPER lunar rover, citing cost and schedule concerns

NASA has said it intends to halt development of the VIPER rover due to rising costs and schedule delays, but the agency is also pointing to other opportunities for robotic exploration of the moon's south polar region.

The Volatiles Investigating Polar Exploration Rover was originally scheduled to launch in late 2023 and target the western rim of Nobile Crater near the Moon's south pole.

The south polar region is a prime target for exploration because it is believed to contain water ice that could support future lunar settlements. NASA plans to send astronauts to the region as early as 2026 for the first crewed lunar landing since 1972.

Unfortunately, the VIPER project has faced a number of delays due to difficulties in testing and developing the rover, as well as the astronomical Griffin lander that would deliver the rover to the lunar surface. The completion date for VIPER and Griffin was recently pushed back to September 2025.

During an internal review, NASA officials determined that continuing VIPER development would increase costs, which could lead to the cancellation or disruption of other lunar missions under NASA's Commercial Lunar Payload Services (CLPS) program. NASA notified Congress of its intention to terminate development.

The budgeted cost to build VIPER was $433.5 million, and the estimated cost to build and launch the Griffin lander was $235.6 million, according to a 2022 report from NASA's Office of Inspector General.

'Chronometers of the Universe' Hint at Invisible Objects Floating in the Milky Way

Pulsars are some of the best clocks in the universe. They are the product of a supernova explosion, neutron stars that spin rapidly and emit pulses of radiation. This is how these cosmic clocks tick. And they can be used to search for invisible objects floating in the Milky Way.

The key idea behind the research comes from general relativity. Being in a gravitational field affects the passage of time. Professor John LoSecco reasoned that these changes could be measured if the behaviour of pulsars was studied well.

Luckily for his idea, many groups of scientists are already working on compiling just such catalogues. Using the pulses and knowing them with sufficient precision, one could use these stellar objects as a gravitational-wave observatory spanning thousands of light years. But achieving the necessary precision was a real feat.

“Pulsars don't exist in a vacuum. These pulses come from millisecond pulsars, many of which are in binary systems. That is, they are moving, orbiting another object. So you have to subtract all that motion. The Earth is moving around the Sun. You have to subtract that motion. You have to subtract all that motion to get the actual arrival time [сигнала]”,” Professor Losecco from the University of Notre Dame told IFLScience.

If you remove the motion, you get a precise pulse interval. And if a massive object passes in front of the pulsar, the pulse will suddenly become longer. An object the mass of the Sun will create a delay of 10 microseconds. This is negligible in terms of human time, but for the accuracy of the Pulsar Timing Array, it is a large number.

«[У нас] “There were 12 candidates, and they came from eight independent pulsars,” Losecco told IFLScience. The pulsar catalog used 65 millisecond pulsars that were tracked for up to 10,000 days. Some events are very statistically significant. The masses of the objects involved can be relatively small. One was about one-fifth the mass of the Sun.

If these discovered candidates are real, the question arises: what are they? They could be massive rogue planets — planetary objects that have been ejected from their planetary systems. They could be small stellar objects, such as a brown or white dwarf. They could be clumps of dark matter simply floating around the galaxy. The astronomer cautions that we can’t say for sure yet.