Ancient Mars impacts created tornado-like winds that scoured surface

Brown University geologist Peter Schultz observed sets of strange bright streaks coming from a few large-impact craters on the planet’s surface. The streaks are strange because they extend much farther from the craters than normal ejecta patterns, and they are only visible in thermal infrared images taken during the Martian night. Using geological observation, laboratory impact experiments and computer modeling, Schultz and Brown graduate student Stephanie Quintana have offered a new explanation for how those streaks were formed. They show that tornado-like wind vortices created by crater-forming impacts and swirling at 500 miles per hour or more, scoured the surface and blasted away dust and small rocks to expose the blockier surfaces beneath.

Schultz states he first saw the streaks during one of his ‘exploration of Mars’. In his downtime between projects, he pulls up random images from NASA’s orbital spacecraft just to see if he might observe anything interesting. In this scenario, he was looking at infrared images which capture contrasts in heat retention on the surface. Brighter regions at night indicate surfaces that retain more heat from the previous day than surrounding surfaces, just as grassy fields cool off at night while buildings in the city remain warmer.

Schultz’s experiments showed that vapor plumes travel outward from an impact point, just above the impact surface, at incredible speeds. Scaling laboratory impacts to the size of those on Mars, a vapor plume’s speed would be supersonic. And it would interact with the Martian atmosphere to generate powerful winds. Schultz and Quintana showed that the streaks are nearly always seen in conjunction with raised surface features. As the plume raced outward from the larger impact, it encountered the small crater rim, leaving bright twin streaks on the downwind side.

The researchers’ experiments show that the presence of volatile compounds, a thick layer of water ice on the surface or subsurface, affect the vapor amount that rushes out from an impact. The streaks now can serve as indicators of whether ice may have been present at the time of an impact, which could lend insight into reconstructions of past climate on Mars. Equally possible, the streaks could be related to the composition of the impactor, such as rare collisions by high-volatile objects, such as comets.

Source: sciencedirect.com

China proves its first resupply spacecraft can reach orbit

China’s space program just hit a milestone: according to Reuters, its first cargo probe has successfully proven that it can ferry supplies to orbit. Tianzhou-1 took off from the Wenchang Satellite Launch Center in the mainland on April 20th. In the early hours of April 22nd, Eastern time, it performed an automated docking maneuver to attach itself to the country’s orbiting lab, the Tiangong-2. You can think of Tiangong 2 (or “Heavenly Space Lab”) as China’s experimental space station, which housed two astronauts for a month in October 2016. The country is using it to test new technologies for the larger manned space station that it hopes to establish in orbit by 2022.

Based on state media reports, China considers the event a huge accomplishment, since Chinese President Xi Jinping has decided to make its space program a priority to strengthen national security. It also provides an “important technological basis” for the construction of the country’s permanent orbiting lab. In its current form, it can reportedly fly autonomously for up to three months while carrying up to 6 tons of goods and 2 tons of cargo.

While Tianzhou-1’s success is a cause for celebration for China, some United States officials might see it as a cause for concern instead. In a 2015 annual report it prepared for Congress, the US Department of Defense claims China has been heavily investing in space capabilities “designed to limit or prevent the use of space-based assets by adversaries during a crisis or conflict, including the development of directed-energy weapons and satellite jammers.”

Most habitable planets may be completely covered in water

When you imagine what a rocky, habitable planet looks like, it’s easy to picture an alternate Earth where land and oceans exist in an ideal balance. Unfortunately, that’s not necessarily how it will pan out in real life… in fact, you might be surprised if there’s land at all. University of Barcelona researcher Fergus Simpson has published a study suggesting that most planets with any significant amount of water are likely to be completely (or almost completely) submerged in it. He ran computer simulations accounting for numerous factors in a planet (such as the deep water cycle and erosion), and most with substantial water levels had an above-water land mass of less than 10 percent — well below Earth’s 29 percent.

Those planets that had less water tended to have much less, to the point where deserts dominated the landscape. Also, size plays a role. Larger habitable planets (including Earth) are more likely to be water worlds thanks to deeper oceans and stronger gravity, according to the calculations, while smaller ones are drier.

If reasonably accurate, the data points to Earth hitting a rare sweet spot, possibly due to unusually deep water basins. And that makes sense at first glance. Despite what Earth looks like, water only occupies a tiny amount of volume compared to the rest of the planet. It wouldn’t take much more to inundate the land, or much less to make it barren. You can see for yourself in the video below.

There is reason to be skeptical. Astrophysicist Sean Raymond warnsGizmodo that there are still a number of unknowns that may play an important role in water levels, and recent models suggest that water delivery to planets is relatively “reliable” with fewer surges or shortfalls. However, Simpson is quick to add that his theory should be testable soon. Future instruments (likely including the James Webb Space Telescope) will have enough power to measure the atmospheric compositions of alien planets, giving a clue as to how much water there is on the surface. If nothing else, the study is a reminder that we shouldn’t assume a planet is human-friendly just because there’s plenty of H2O.

Simulated galaxies provide fresh evidence of dark matter

Further evidence of the existence of dark matter – the mysterious substance that is believed to hold the Universe together – has been produced by Cosmologists at Durham University

Using sophisticated computer modelling techniques, the research team simulated the formation of galaxies in the presence of dark matter and were able to demonstrate that their size and rotation speed were linked to their brightness in a similar way to observations made by astronomers.

One of the simulations is pictured, showing the main ingredients that make up a galaxy: the stars (blue), the gas from which the stars are born (red), and the dark matter halo that surrounds the galaxy (light grey).

Alternative theories

Until now, theories of dark matter have predicted a much more complex relationship between the size, mass and brightness (or luminosity) of galaxies than is actually observed, which has led to dark matter sceptics proposing alternative theories that are seemingly a better fit with what we see.

The research led by Dr Aaron Ludlow of the Institute for Computational Cosmology, is published in the academic journal, Physical Review Letters.

Most cosmologists believe that more than 80 per cent of the total mass of the Universe is made up of dark matter – a mysterious particle that has so far not been detected but explains many of the properties of the Universe such as the microwave background measured by the Planck satellite.

Convincing explanations

Alternative theories include Modified Newtonian Dynamics, or MOND. While this does not explain some observations of the Universe as convincingly as dark matter theory it has, until now, provided a simpler description of the coupling of the brightness and rotation velocity, observed in galaxies of all shapes and sizes.

The Durham team used powerful supercomputers to model the formation of galaxies of various sizes, compressing billions of years of evolution into a few weeks, in order to demonstrate that the existence of dark matter is consistent with the observed relationship between mass, size and luminosity of galaxies.

Long-standing problem resolved

Dr Ludlow said: “This solves a long-standing problem that has troubled the dark matter model for over a decade. The dark matter hypothesis remains the main explanation for the source of the gravity that binds galaxies. Although the particles are difficult to detect, physicists must persevere.”

Durham University collaborated on the project with Leiden University, Netherlands; Liverpool John Moores University, England and the University of Victoria, Canada. The research was funded by the European Research Council, the Science and Technology Facilities Council, Netherlands Organisation for Scientific Research, COFUND and The Royal Society.