Ganymede, Dark Matter and the Future of Space Exploration
Space and physics updates from the previous week
The nature of dark matter - a mysterious substance that astronomers believe dominates the universe - has long been unknown. Every experiment designed to directly detect it has failed - every one, that is, bar one. For more than twenty years an experiment in Italy has recorded a signal regularly varying over the course of each year, exactly as one might expect if the Earth were moving through a cloud of dark matter.
Though intriguing, the result has long been considered controversial. The Italian experiment, buried deep under the Gran Sasso mountain, stands alone. No other study has managed to back the results up; resulting in speculation that something else is causing the annual variation.
To try clearing matters up, scientists built a copy of the experiment in Spain and started watching for signs of the signal. The results, reported at the end of May, are discouraging. The scientists behind the project failed to find signs of dark matter - which indicates that some kind of error must be causing the result in Italy.
Fast Radio Bursts, or FRBs, are another cosmic mystery. Back in 2007, researchers scanning through troves of collected data noticed energetic radio signals coming from deep space. These signals were powerful but short-lived - throwing out vast amounts of energy in a fraction of second.
Over the years since, astronomers have found another hundred or so of these signals. This has been enough to give some basic ideas about what they might be. We know they are extremely distant, originating far outside our galaxy. They seem to come from small objects - something made apparent by their rapid nature.
But beyond this, speculation runs wild. Aliens, of course, are invoked as one possible explanation. Others link them to highly magnetic stars - magnetars - or wonder if they are released when black holes or neutron stars collide. They could, some exotic theories say, be a sign of a fractured universe, evidence of ancient “cosmic strings” stretching for light years.
Researchers have long believed them to be common, with perhaps hundreds lighting up the sky every day. A recent study of data from the Canadian CHIME observatory has revealed more than five hundred FRBs from just a year of data, suggesting they really are frequent events. With hundreds more samples to work with, astronomers can now start studying them in depth. Perhaps one cosmic mystery will soon find a solution.
Four hundred years ago Galileo spotted four pinpricks of light moving around Jupiter. With the help of the newly invented telescope he soon established that these were moons - a discovery that helped dislodge the established idea that the Earth lay at the centre of the universe.
The largest of those four moons, and indeed, the largest moon in the Solar System, is Ganymede. Over the centuries dozens more moons have been found around Jupiter, but the four largest have maintained their aura of intrigue. Ganymede may, astronomers now believe, have a vast ocean lying under a layer of ice.
Last week the Juno spacecraft, in orbit around Jupiter since 2016, flew just six hundred miles from the surface of Ganymede. In doing so astronomers captured some of the best ever pictures of the planet’s surface, revealing a pockmarked and scarred terrain.
Space missions must be planned years in advance. Each flight to the planets can cost billions and involve thousands of engineers working over ten years or more. Even after launching, reaching distant worlds can take decades. So it should come as no surprise that space agencies are already planning missions for the 2040s and 2050s.
ESA’s Voyage 2050 program aims to do exactly that, sketching out ideas for useful scientific missions that should launch by 2050. Back in 2019 the European Space Agency reached out to researchers across the continent, receiving more than a hundred ideas for potential spacecraft. Now the agency has further defined the themes of those missions.
Three key priorities have been announced. Top of the list is the ongoing search for life across the Solar System. Jupiter and Saturn’s moons - especially Europa and Enceladus - are of especial interest. Scientists believe both moons hold vast oceans and potentially host alien microorganisms.
In second place is the need for new probes of the early universe. This might take the form of a gravitational wave observatory; expanding our view of the universe in so far little explored areas. ESA also want to look more deeply at our own galaxy, mapping stars and exoplanets in unprecedented detail.