The Week in Space and Physics

On the Nobel Prizes, lakes on Mars, the history of the Moon's volcanoes and a long harsh winter on Pluto

Zoom in on a sheet of glass, close enough to pick out the atoms and the chemical bonds, and you will find a bit of a mess. Each individual atom – glass contains both silicon and oxygen – is placed well enough; each oxygen atom bonded to three of silicon, each silicon atom bonded to two of oxygen. As a whole, however, the structure loses all sense of pattern. Atoms scatter randomly across the sheet, and form clusters of irregular shapes.

Silica, by contrast, is quite different. The same elements – silicon and oxygen – are present, in the same ratio – two oxygen atoms for every silicon atom. But this time the atoms line up perfectly. They arrange themselves into hexagons, or cubes, or some other regular pattern. Throughout the crystal this arrangement holds, producing a structure that is much more like sand than glass.

This contrast, between order and disorder, holds for magnetic materials too. In strongly magnetic materials, like iron, the atoms are well ordered, their magnetic poles all pointing in the same direction. But in other materials, known as spin glasses, these magnetic poles point randomly. Like glass, spin glasses are examples of random and chaotic patterns in nature.

The study of these complex and chaotic patterns lay at the heart of this year’s Nobel Prize in physics. Three physicists were jointly awarded the prize: Syukuro Manabe, from Japan; Klaus Hasselmann, from Germany; and Giorgio Parisi, from Italy.

For Giorgio Parisi, the award focused on his work on modelling spin glasses; particularly on his efforts to understand the patterns formed by subatomic particles within spin glasses. But, as the Nobel Committee notes, his discoveries have broader applications. The techniques he found to describe subatomic chaos can be used for a wide range of complex systems, from atomic to planetary scales.

It is on that planetary scale that both Manabe and Hasselmann worked. The climate, like spin glasses, is a chaotic system. Small disturbances can spiral unpredictably, creating random outcomes, even on the largest of scales. Forecasting the climate, then, is a challenge – but not, as Manabe, Hasselmann and even Parisi showed, impossible.

Manabe, working in the 1960s, developed some of the first climate models to show the impact of rising levels of carbon dioxide. Though his models were simple, especially by modern standards, they were good enough to show that carbon dioxide would indeed cause global temperatures to rise – and to give a first estimate of how big that rise could be.

Hasselmann, working a decade later, helped to show why climate models could work at all, given the seeming randomness and chaos of the weather. The snow, rain and sun that make up the day-to-day variations, he found, could be contrasted with longer and slower changes in the climate – over the seasons or over the years. That, he found, allowed for a statistical approach to climate; a way of finding the signal buried in the noise.

By focusing on the physics of climate science, the Nobel Committee, and the three scientists awarded the prize, are joining the chorus of voices calling for urgent political action. We must, as Parisi noted at a press conference, “act now in a very fast way”.


An Ancient Martian Lake

Mars has been dead for a long time. Its surface is now bone dry, its atmosphere thin and fading. Once, however, the planet was rather different. Rivers and lakes flowed across its surface, and a vast ocean may have covered its northern hemisphere. Mars, back then, may not have appeared as the red planet it is now, but rather as a world of blues, whites, and, perhaps, even greens.

When NASA was looking for a landing site for the Perseverance rover, then, they wanted to find a place that could reveal traces of that long buried past. They chose Jezero Crater, a place that looked, at least from satellite photos, rather like an old lakebed. Rock features around the north and west of the crater suggest that rivers once flowed into the lake – making this a promising place to hunt for signs of ancient water.

Perseverance has now spent more than eight months on Mars, travelled over a mile across its surface and returned thousands of photographs to Earth. Jezero Crater, all that evidence shows, was indeed a lake; one that was more than a hundred metres deep and forty-five kilometres wide. And, billions of years ago, there was at least one substantial river flowing into it.

Mars was not, however, a gentle idyll. Instead the evidence points to episodes of catastrophic floods, when vast amounts of water poured across the surface. Giant boulders were found close to the river, worn smooth by the water but too massive to have been moved by a steady current. Scientists think these rocks must instead have been dumped there by torrents of floodwater.

What caused such immense floods is unknown. Perhaps, the authors speculate, Mars suffered from intense rainfall, or rapid temperature changes that sent cascades of melting snow into river valleys. Volcanoes or asteroid impacts could be another explanation, or even periodic melting of vast glacial lakes, a phenomenon that also occured on Earth at the end of the last ice age.


Volcanoes on the Moon

When Galileo pointed his telescope to the Moon, he discovered that it was not the smooth, perfect body taught by the church. Instead its surface was pockmarked, scattered with craters and canyons. He saw, too, large dark areas; regions he named maria, Latin for seas, thinking he might be seeing signs of water on the Moon.

Later, of course, it turned out that the Moon was a dry and dead world, that the maria were not, in fact seas, but were instead vast plains of solidified lava. When astronauts visited the Moon in the 1970s, they brought back samples of rocks. From these, scientists calculated that the maria formed three billion years ago, during a period of intense volcanism on the Moon.

Last year, however, a Chinese probe visited the Moon; landing in an area unvisited by the Apollo astronauts. It retrieved a sample of rocks and later brought them back to Earth – the first new samples from the Moon in more than forty years. Analysis of the rocks shows these are the youngest rocks ever found on the Moon; just two billion years old.

That, scientists say, proves that the Moon was volcanically active more recently than thought. The maria, therefore, are at least a billion years younger than believed. Quite how so much volcanism happened so late is, however, mysterious. The obvious candidate – radioactive heat from the Moon’s interior – seems unlikely, as scientists found no traces of radioactive materials in the rocks.


Winter Finally Dawns on Pluto

For the past few decades, Pluto’s atmosphere has been puzzling astronomers. The dwarf planet is slowly moving away from the Sun. Over the next century the planet will travel three billion kilometers outwards. As it does, and the tenuous heat of the Sun gradually fades, the planet, logically, should cool.

That, astronomers thought, would mean its atmosphere freezes, falling as snow onto Pluto’s surface. Instead, previous measurements have shown the opposite. Pluto’s atmosphere seems to be growing bigger – a result, some think, of heat lingering from its closest approach to the Sun in 1989.

Now, however, the atmosphere finally seems to be behaving as expected. Reporting on measurements taken in 2018, a team of American astronomers found that Pluto’s atmosphere has, finally, started to shrink. A long cold winter awaits Pluto – it will take at least another century and a half before spring comes to the dwarf planet.


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