Unlike the landers, which sample only one point at a time, Nereus, run by the Woods Hole Oceanographic Institution, can rove around while transmitting video to its mother ship through a 40km-long fibre-optic cable. For the first time, scientists will really be able to survey the deeps. No one is certain what to expect but past trawling expeditions suggest encounters with giant numbers of sea cucumbers, an animal which looks as its name suggests and slowly eats its way through sea-floor sludge.
A big question will be what supports so much life so deep down. A possibility is that trenches act like giant funnels so that debris falling from large areas of the fertile sea far above is concentrated into the narrow trench axis below. Earthquakes may help by shaking a bonanza of detritus from the shelf slopes. Even volcanic springs may power this dark world’s productivity, as there are creatures that can draw energy from the chemicals flowing from them, rather than from the light of the sun.
As Hadal researchers are busy puzzling out how this hellish ecosystem works and where its inhabitants came from, other scientists will be looking skywards, waiting for their big day in December when the European Space Agency (ESA) sendsGaia into space.
On a clear night, you can see the Milky Way as a luminous band stretching across the sky. That is the plane of the disc-shaped galaxy, which the sun, along with a hundred billion other stars, is part of. Over five years, Gaia’s telescopes will record the location, movement and characteristics of 1 billion of those stars, a staggering achievement enabling astronomers to tackle many profound questions.
One is how our galaxy was created. It may all have come from a colossal cloud of gas collapsing inwards, or, more likely, be a cannibal that started small and grew ever bigger as it gobbled up other passing groups of stars. Gaia’s map will make it possible to separate out stars which still move together and give away their histories as once-independent groups. “Gaia will even trace how many proto-entities have been eaten at which time; you will really be able to unfold back the history of the formation of our galaxy,” explains Fabio Favata, head of ESA’s Science Co-ordination Office.
Then there is the deep mystery of “dark matter”. Astronomers know that the way stars move shows that they are being pulled by gravity from something we cannot see. Adding up the gravitational forces from all the stars that we can detect still leaves a “missing mass” which, astonishingly, is many times larger than the mass of everything we know about. Ideas of what that missing mass might be range from a sea of invisible particles to massive non-luminous bodies. By charting the movements of so many stars, Gaia will help pinpoint the whereabouts of at least some of it.
There is much more. From small wobbles in the positions of stars, Gaia will detect around 10,000 unknown planets circling distant suns. It will help test theories of relativity and provide a census of near-Earth asteroids. And by mapping objects as odd as anything found in the sea’s depths—the brown dwarfs which were too small to burst into life as stars and the white dwarfs that are the burnt-out remains of stars—it will help astronomers understand the way stars are born and die.
Alun Anderson: science journalist and author