Tyler O'Neal, Staff Editor SYSTEMS

NCCR PlanetS simulations show how the habitability of exoplanets is influenced by their rocks

The weathering of silicate rocks plays an important role to keep the clement climate on Earth. Scientists led by the University of Bern and the Swiss national center of competence in research (NCCR) PlanetS, investigated the general principles of this process. Their results could influence how we interpret the signals from distant worlds including such that may hint towards life.

The conditions on Earth are ideal for life. Most places on our planet are neither too hot nor too cold and offer liquid water. These and other requirements for life, however, delicately depend on the right composition of the atmosphere. Too little or too much of certain gases – like carbon dioxide and Earth could become a ball of ice or turn into a pressure cooker. When scientists look for potentially habitable planets, a key component is therefore their atmosphere. Weathering of silicate rocks is part of the so-called carbon cycle that balances the temperate climate of Earth over long periods of time. Illustration by Jenny Leibundgut

Sometimes, that atmosphere is primitive and largely consists of the gases that were around when the planet formed – as is the case for Jupiter and Saturn. On terrestrial planets like Mars, Venus, or Earth, however, such primitive atmospheres are lost. Instead, their remaining atmospheres are strongly influenced by surface geochemistry. Processes like the weathering of rocks alter the composition of the atmosphere and thereby influence the habitability of the planet.

How exactly this works, especially under conditions very different from those on Earth, is what a team of scientists, led by Kaustubh Hakim of the Centre for Space and Habitability (CSH) at the University of Bern and the NCCR PlanetS, investigated. Their results were published today in The Planetary Science Journal.

Conditions are decisive Kaustubh Hakim is a post-doctoral researcher at the Centre for Space and Habitability at the University of Bern and the NCCR PlanetS. Credit: Vandana S. Kushwaha

“We want to understand how the chemical reactions between the atmosphere and the surface of planets change the composition of the atmosphere. On Earth, this process – the weathering of silicate rocks assisted by water – helps to maintain a temperate climate over long periods of time”, Hakim explains. “When the concentration of CO2 increases, temperatures also rise because of its greenhouse effect. Higher temperatures lead to more intense rainfall. Silicate weathering rates increase, which in turn reduce the CO2 concentration and subsequently lower the temperature”, says the researcher.

However, it need not necessarily work the same way on other planets. Using supercomputer simulations, the team tested how different conditions affect the weathering process. For example, they found that even in very arid climates, weathering can be more intense than on Earth if the chemical reactions occur sufficiently quickly. Rock types, too, influence the process and can lead to very different weathering rates according to Hakim. The team also found that at temperatures of around 70°C, contrary to popular theory, silicate weathering rates can decrease with rising temperatures. “This shows that for planets with very different conditions than on Earth, weathering could play very different roles”, Hakim says.

Implications for habitability and life detection

If astronomers ever find a habitable world, it will likely be in what they call the habitable zone. This zone is the area around a star, where the dose of radiation would allow water to be liquid. In the solar system, this zone roughly lies between Mars and Venus.

“Geochemistry has a profound impact on the habitability of planets in the habitable zone”, study co-author and professor of astronomy and planetary sciences at the University of Bern and member of the NCCR PlanetS, Kevin Heng, points out. As the team’s results indicate, increasing temperatures could reduce weathering and its balancing effect on other planets. What would potentially be a habitable world could turn out to be a hellish greenhouse instead.

As Heng further explains, understanding geochemical processes under different conditions are not only important to estimate the potential for life, but also for its detection. “Unless we have some idea of the results of geochemical processes under varying conditions, we will not be able to tell whether bio-signatures – possible hints of life like the Phosphine that was found on Venus last year – indeed come from biological activity”, the researcher concludes. Kevin Heng is a professor of astronomy and planetary sciences at the University of Bern and member of the NCCR PlanetS. Credit: Alessandro Della Bella

Publication details:
Kastubh Hakim et al.: Lithologic Controls on Silicate Weathering Regimes of Temperate Planets, The Planetary Science Journal, April 2021 DOI: https://doi.org/10.3847/PSJ/abe1b8

Australian researchers use machine learning to design quieter drone propellers

Tyler O'Neal, Staff Editor SYSTEMS

Researchers have published a study revealing their successful approach to designing much quieter propellers.

The Australian research team used machine learning to design their propellers, then 3D printed several of the most promising prototypes for experimental acoustic testing at the Commonwealth Scientific and Industrial Research Organisation's specialized 'echo-free chamber.

Results now published in Aerospace Research Central show the prototypes made around 15dB less noise than commercially available propellers, validating the team's design methodology.

RMIT University aerospace engineer and lead researcher Dr. Abdulghani Mohamed said the impressive results were enabled by two key innovations - the numerical algorithms developed to design the propellers and their consideration of how noise is perceived in the human ear - as part of the testing. Various propeller prototypes designed by the algorithm

"By using our algorithms to iterate through a variety of propeller designs, we were able to optimize for different metrics such as thrust, torque, sound directivity, and much more. We also formulated a new metric, which involves how the human ear perceives sound, and propose to use that in future designs," he said.

"Our method for optimizing design can be applied to small propellers used on drones to much larger ones used for future urban air mobility vehicles - or air taxis - designed to carry human passengers."

The team, which also included Melbourne-based aerospace company XROTOR, explored how various manipulations of propeller blade noise affected how it was perceived by the human ear.

Mohamed said this modulation had the potential to be used as an important design metric for future propellers.

"The modulation of high-frequency noise is a major factor in the human perception of rotor noise. Human ears are more sensitive to certain frequencies than others and our perception of sound also changes as we age," he explained.

"By designing to such metrics, which take into account human perception, we can design less annoying propellers, which one day may actually be pleasant to hear."

XROTOR Managing Director, Geoff Durham, said it was exciting to see prototype testing show the new designs could significantly reduce the sound impact of drones.

"Not only were the designs appreciably quieter to the human ear, but the propellers had a higher thrust profile against standard market propellers at the same throttle signal input," he said. Echo-free test chamber

The RMIT research team also included Dr. Woutijn Baars, Dr. Robert Carrese, Professor Simon Watkins, and Professor Pier Marzocca. The prototypes were 3D printed at RMIT's Advanced Manufacturing Precinct.

RMIT Aerospace Engineering student Liam Bullard was also involved in the project and said having that opportunity while still, an undergraduate was one of the main reasons he chose to study at RMIT.

"As a student, it's great to get to get to work on projects where I can apply knowledge to a real-world industry problem," he said.

The paper, 'Quantifying modulation in the acoustic field of a small-scale rotor using bispectral analysis' is published in Aerospace Research Central (DOI:10.2514/6.2021-0713).

Bitcoin price boom locked-in vast energy consumption

Tyler O'Neal, Staff Editor SYSTEMS

The cryptocurrency market has been abuzz as Bitcoin gains popularity with investors, reaching an all-time high of over $58,000 apiece in February. In a commentary published March 10 in the journal Joule, financial economist Alex de Vries quantifies how the surging Bitcoin price is driving increasing energy consumption, exacerbating the global shortage of chips, and even threatening international safety.

Theoretically, any computer with access to the internet and electricity can "mine" Bitcoin, a process to receive cryptocurrency by solving sophisticated mathematical equations. It is estimated that all miners combined makeover 150 quintillion--that is 18 zeros following 150--attempts every second to solve the equation, according to numbers from January 11, 2021. Computational power and electricity cost become crucial to profiting from Bitcoins.

"If you're a Bitcoin user making transactions, you're not the one directly paying for electricity. It's a bit of a hidden cost from a user perspective," says author Alex de Vries, the founder of Digiconomist (@DigiEconomist), a blog that highlights new digital trends such as cryptocurrency.

The hidden cost goes beyond energy consumption. Based on the Bitcoin price in January, de Vries estimated that the entire Bitcoin network could consume up to 184 TWh per year, close to the amount of energy all data centers consumed globally. The consumed energy also results in 90.2 million metric tons of CO2, compared to the carbon footprint of metropolitan London.

"That's a pretty mind-blowing number," says de Vries. "Those data centers serve the most of global civilization, and then there's Bitcoin, which serves almost no one but still manages to consume about an equal amount of electricity."

The market price of Bitcoin is an incentive for miners to invest in hardware and electricity. As the price rises, more people put in orders to purchase and run the hardware, causing an increase in energy consumption, and vice versa when the price drops. Due to the overwhelming demand, hardware manufacturers have reported that their devices are sold out, and some customers may not receive their orders until later. This suggests that the amount of energy consumption is "locked-in" at the time of purchase.

"The price of Bitcoin can crash by 25%, 30%, and you may still end up at the same energy consumption point because of the lock-in effect," says de Vries. "The whole idea of my article is to translate what the skyrocketing Bitcoin price is going to mean, not just for the environment, but also externalities that go beyond that."

Bitcoin mining rigs' short shelf-life can mean a substantial amount of electronic waste in the coming years. Mining devices also exacerbate the current global chip shortage by competing for the same chips as personal electronics and electric vehicles, which play an essential role in combatting climate change. Countries with inexpensive electricity, such as Iran, can introduce new revenue streams through Bitcoin mining.

"You can do a lot about these problems. Mining facilities are usually centralized. They're pretty easy to target," says de Vries. Policymakers can intervene by raising electricity rates or confiscating mining equipment. Taxing Bitcoin mining device manufacturers or limiting their access to chips are also strategies to consider. Although Bitcoin is a decentralized currency, government agencies can regulate exchange platforms and prevent its trading to influence the value.

De Vries notes that "we are limited to the information that we have today," and he cautions predictions for future trends regarding Bitcoin. "Who knows what will happen in 2024? Maybe everyone is using bitcoin, maybe nobody, maybe everyone forgot about it could also be the case," he says.

Joule, de Vries: "Bitcoin boom: what rising prices mean for the network's energy consumption"
https://www.cell.com/joule/fulltext/S2542-4351(21)00083-0