Mars may have a network of liquid water flowing through the frozen ground. All buried permafrost, on Earth and beyond, is expected to host narrow veins of liquid, and new calculations show on Mars, they could be big enough to support living organisms. "For Mars we always live on the edge of maybe habitable, maybe not, so I set out to do this research thinking maybe I can close this loop and say that it's very unlikely to have enough water and have it be arranged so that it's habitable for microbes," says Hanna Sizemore at the Planetary Science Institute in Arizona. She and her colleagues used measurements of the soil composition on Mars to calculate how much of the icy soil could actually be liquid water and the size of the channels that water would run through. It is tricky to keep water liquid on Mars, because temperatures can get as low as -150 C (-240 F) on the planet.

It's one of the most profound questions in science – did life ever exist on Mars? Now, experts have unearthed evidence that the Red Planet was once habitable. Scientists have found carbon residue in Martian rocks, indicating that an ancient carbon cycle existed. And it means the Red Planet was likely once warm enough to sustain life. Researchers have long believed that, billions of years ago, Mars had a thick, carbon dioxide-rich atmosphere with liquid water on its surface.

The accuracy of the training data limits the accuracy of bulk properties from machine-learned potentials. For example, hybrid functionals or wave-function-based quantum chemical methods are readily available for cluster data but effectively out-of-scope for periodic structures. We show that local, atom-centred descriptors for machine-learned potentials enable the prediction of bulk properties from cluster model training data, agreeing reasonably well with predictions from bulk training data. We demonstrate such transferability by studying structural and dynamical properties of bulk liquid water with density functional theory and have found an excellent agreement with experimental as well as theoretical counterparts.

We present two machine learning methodologies that are capable of predicting diffusion Monte Carlo (DMC) energies with small datasets (~60 DMC calculations in total). The first uses voxel deep neural networks (VDNNs) to predict DMC energy densities using Kohn-Sham density functional theory (DFT) electron densities as input. The second uses kernel ridge regression (KRR) to predict atomic contributions to the DMC total energy using atomic environment vectors as input (we used atom centred symmetry functions, atomic environment vectors from the ANI models, and smooth overlap of atomic positions). We first compare the methodologies on pristine graphene lattices, where we find the KRR methodology performs best in comparison to gradient boosted decision trees, random forest, gaussian process regression, and multilayer perceptrons. In addition, KRR outperforms VDNNs by an order of magnitude. Afterwards, we study the generalizability of KRR to predict the energy barrier associated with a Stone-Wales defect. Lastly, we move from 2D to 3D materials and use KRR to predict total energies of liquid water. In all cases, we find that the KRR models are more accurate than Kohn-Sham DFT and all mean absolute errors are less than chemical accuracy.

Recently, the development of machine learning (ML) potentials has made it possible to perform large-scale and long-time molecular simulations with the accuracy of quantum mechanical (QM) models. However, for high-level QM methods, such as density functional theory (DFT) at the meta-GGA level and/or with exact exchange, quantum Monte Carlo, etc., generating a sufficient amount of data for training a ML potential has remained computationally challenging due to their high cost. In this work, we demonstrate that this issue can be largely alleviated with Deep Kohn-Sham (DeePKS), a ML-based DFT model. DeePKS employs a computationally efficient neural network-based functional model to construct a correction term added upon a cheap DFT model. Upon training, DeePKS offers closely-matched energies and forces compared with high-level QM method, but the number of training data required is orders of magnitude less than that required for training a reliable ML potential. As such, DeePKS can serve as a bridge between expensive QM models and ML potentials: one can generate a decent amount of high-accuracy QM data to train a DeePKS model, and then use the DeePKS model to label a much larger amount of configurations to train a ML potential. This scheme for periodic systems is implemented in a DFT package ABACUS, which is open-source and ready for use in various applications.

The field of extrasolar planet studies is undergoing a seismic shift. To date, 4,940 exoplanets have been confirmed in 3,711 planetary systems, with another 8,709 candidates awaiting confirmation. With so many planets available for study and improvements in telescope sensitivity and data analysis, the focus is transitioning from discovery to characterization. Instead of simply looking for more planets, astrobiologists will examine "potentially-habitable" worlds for potential "biosignatures." This refers to the chemical signatures associated with life and biological processes, one of the most important of which is water.

The field of extrasolar planet studies is undergoing a seismic shift. To date, 4,940 exoplanets have been confirmed in 3,711 planetary systems, with another 8,709 candidates awaiting confirmation. With so many planets available for study and improvements in telescope sensitivity and data analysis, the focus is transitioning from discovery to characterization. Instead of simply looking for more planets, astrobiologists will examine "potentially-habitable" worlds for potential "biosignatures." This refers to the chemical signatures associated with life and biological processes, one of the most important of which is water. As the only known solvent that life (as we know it) cannot exist, water is considered the divining rod for finding life.

NASA has marked the Curiosity rover's ninth anniversary on Mars by unveiling a new panoramic image of the Martian landscape, a locale that may explain why the Red Planet became dry. The panoramic image, which was put together on July 3 by stitching 129 individual images together, shows Curiosity's current home, Mount Sharp, a 5-mile-tall mountain inside Mars' Gale Crater. NASA marked the Curiosity rover's ninth anniversary on Mars by unveiling a new panoramic image. The image was created by the rover's Mast Camera, or Mastcam. Upon arrival at Mount Sharp in 2014, Curiosity has been traveling up the rock formation for the past several years.

At first glance at this image, you'd be forgiven for mistaking it as a still from the latest science fiction blockbuster. But the photo is very much real, and was snapped by NASA's Curiosity Mars rover this week. The selfie shows the rover alongside a rock formation dubbed'Mont Mercou', a nickname taken from a mountain in France. And while the photo is impressive on its own, it was actually taken to celebrate Curiosity's 30th sample to date, after the rover drilled a hole at a nearby rock sample nicknamed'Nontron.' The selfie shows the rover alongside a rock formation dubbed'Mont Mercou', a nickname taken from a mountain in France So far 2021 has been the'year of Mars' with three spaceships from Earth arriving at the Red Planet.

It is well known in the field of machine learning that committee models improve accuracy, provide generalization error estimates, and enable active learning strategies. In this work, we adapt these concepts to interatomic potentials based on artificial neural networks. Instead of a single model, multiple models that share the same atomic environment descriptors yield an average that outperforms its individual members as well as a measure of the generalization error in the form of the committee disagreement. We not only use this disagreement to identify the most relevant configurations to build up the model's training set in an active learning procedure, but also monitor and bias it during simulations to control the generalization error. This facilitates the adaptive development of committee neural network potentials and their training sets, while keeping the number of ab initio calculations to a minimum. To illustrate the benefits of this methodology, we apply it to the development of a committee model for water in the condensed phase. Starting from a single reference ab initio simulation, we use active learning to expand into new state points and to describe the quantum nature of the nuclei. The final model, trained on 814 reference calculations, yields excellent results under a range of conditions, from liquid water at ambient and elevated temperatures and pressures to different phases of ice, and the air-water interface - all including nuclear quantum effects. This approach to committee models will enable the systematic development of robust machine learning models for a broad range of systems.