Neutrinos: messengers from the underworld

 作者:戴妙     |      日期:2019-03-14 08:18:00
By Anil Ananthaswamy WILLIAM MCDONOUGH doesn’t mince his words about our attempts to get to grips with the lump of rock we call home. “Think of it as many blind people grabbing an elephant,” he says. While we learn ever more of other worlds in our solar system and beyond, our picture of the Earth beneath our feet remains surprisingly sketchy. What exactly is it made of? How did it form? We are left groping for answers. McDonough, a geochemist at the University of Maryland, College Park, aims to change that. His goal is to shed light on the planet’s most mysterious region – the vast netherworld of Earth’s mantle that lies between its hot central core and thin outer crust. Light, though, is not McDonough’s thing: he and his colleagues are planning to get their answers using neutrinos. Implausible as it might sound, these reclusive particles could be just the thing to spill the beans about our planet’s past and present. There is just one proviso: we have to catch enough of them first. It is not that we know absolutely nothing about the elephant below. We know that about 4.6 billion years ago, in an outer spiral arm of the Milky Way, a dense cloud of hydrogen gas and dust began to collapse in on itself. Its centre ignited to make the sun, while farther out grains of dust slowly coalesced to form larger and larger solid bodies. A few million years later,