The Week in Space and Physics: A World With Two Suns
On binary star solar systems, neutrinos and protons, a wobble in the Earth's core and icy interstellar clouds
The Three Body Problem, a novel by Cixin Liu, imagines a world with three suns. Its inhabitants have no time to marvel at the spectacular sunsets this surely implies. Instead they face constant peril: sometimes hurled into the frigid depths of space, at others scorching under a close approach to a star. In horror they watch as the other planets of their solar system are slowly destroyed, plunging one by one into the fierce hearts of their suns.
This is fiction, of course, but astronomers have long wondered if the chaos of multiple star systems allows planets to thrive. Many stars in our galaxy are found in such systems. Most are binary pairs, but some - like the nearby Alpha Centauri system - form larger groupings.
So far the evidence suggests that planets are rare in such systems. Only a handful of examples are known, out of several thousand exoplanets. But the characteristics of multiple star systems also make it hard for us to detect exoplanets; so it could be that they are common and we just can’t see them.
Recently a team of astronomers announced the discovery of a gas giant orbiting a pair of stars. This, they note, is interesting because we had already discovered a planet in that system. It is thus only the second known example of a solar system with multiple stars and multiple planets. But they also spotted it using a “radial velocity” approach, a technique that has never before found planets in a binary system.
Could these planets, or their moons, be stable enough for life? Past studies have suggested that the shifting positions of these world’s stars must play havoc with their climates. This could be made even worse by unstable orbital arrangements. Some planets, for example, might spend years orbiting one star, before bouncing towards the other. Others might orbit around both: an arrangement that, as long as the planet is far enough away from the pair of stars, could last for millions of years.
A recent study, reported in ScienceNews, modeled the orbits of planets in binary systems. They found that the orbits are indeed highly unstable, with a significant fraction of the planets flung off into deep space. Others swing in and out of habitable zones, leaving them at risk of boiling oceans or freezing temperatures.
Yet models found some planets are indeed stable for long periods of time. That could allow time for life to emerge, and perhaps even to evolve into more complex beings. If so, there may well be civilizations out there with two suns in the sky. They, if they exist, must look upon the calm security of our world, orbiting serenely around its single star, with jealous eyes.
Seeing Protons with Neutrinos
More than a century ago a pair of physicists, Ernest Marsden and Hans Geiger, fired a beam of alpha particles at a gold sheet. The idea was to carefully measure how those particles scattered off the gold sheet. That, they hoped, would reveal how electrons were spread through the gold sheet.
At the time physics had only the vaguest sense of how atoms were structured. We knew atoms contained separate positive charges and negative charges - represented, respectively, by the alpha particles and the electrons. But we did not know how those charges were distributed in the atoms. Many believed in the “plum pudding” model, where the electrons were dotted in a “dough” of positive charge.
Yet the results of the scattering experiment proved this radically wrong. Most of the alpha particles passed right through the sheet, unaffected by the positive charges. A few, however, bounced right back: an effect as unexpected, team-leader Rutherford said, as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you.
The results could only be explained if the nuclei of atoms - containing the positive charge - were highly concentrated. Atoms, Rutherford realised, are mostly empty space: made of a tiny core of positive charge surrounded by a cloud of electrons.
Today, of course, this is well known. But similar experiments are still used to probe smaller particles - especially the protons that sit in the atomic nucleus. Instead of alpha particles, researchers instead use electrons to determine their structure, measuring how electric charge shapes the particle.
Now, however, researchers have developed a way to use neutrinos instead. These elusive particles rarely interact with protons at all. They are impervious to the electric force, which scatters electrons and protons. Instead their interactions with protons are determined by the weak nuclear force - a detail that allows them to measure the role “weak charge” plays in a proton.
Experiments run at MINERvA, a neutrino experiment at Fermilab, measured the radius of the proton using this technique. The results it found match those already obtained with electrons - though they are, admittedly, less precise. Still, the experiment is an early sign of how physicists are learning to use neutrinos to probe nature at a fundamental scale.
The Earth’s Core Wobbles
Buried far below our feet is the Earth’s inner core: a solid ball of iron measuring more than a thousand kilometers across. Though the core itself is solid, it is surrounded by the outer core, a vast ocean of molten metal. That, geologists have known for decades, allows the core to spin at a different rate to the rest of the planet.
Figuring out exactly what the core is doing, of course, is challenging. It is hidden under thousands of miles of impenetrable rock and metal; so deep and hot that no drill could hope to reach it. Yet geologists can monitor the way seismic waves made by earthquakes travel through the planet. Subtle changes in these waves can reveal what is going on deep inside the planet.
A recent study from Peking University, in China, looked at patterns of seismic waves going back decades. According to them, there is evidence of a seventy year long cycle of the core slowing and speeding up its rotation. Over the last decade, they say, the core has been slowing down: so much so that it is now rotating slower than the rest of the planet.
Yet studying seismic waves is a tricky art, and not all researchers are convinced by their findings. Other studies have concluded differently, as ScienceNews reports, finding that the core follows a much faster three year cycle, or simply does not vary its rotation at all. Variations in seismic waves might instead, they argue, be caused by slight changes in the shape of the core.
The James Webb Spies Icy Clouds
After the James Webb Space Telescope finished commissioning, researchers launched a series of programs to get up to speed with using its instruments. One of those programs, named IceAge, recently published the results of its observations.
IceAge honed in on the Chameleon I molecular cloud, one of the closest places to Earth in which stars are being born. Such molecular clouds are mostly made of hydrogen - the main ingredient in star formation. Yet they are also, as the James Webb found, home to more complex molecules.
These molecules - which contain carbon, oxygen and nitrogen - appear in the form of ice frozen around grains of dust. Over time, as the clouds collapse into newly born stars, those icy grains of dust may find their way to young planets, filling their oceans and atmospheres with vital chemicals.
Long ago such a process must have helped life to form on Earth - without carbon or oxygen, life as we know it would be impossible. Now we know those same elements and molecules are widespread - and, therefore, so are the basic ingredients of life.