Rosetta's 10-billion-tonne comet
The comet being followed by Europe's Rosetta spacecraft has a mass of roughly 10 billion tonnes.
The number has been calculated by monitoring the gravitational tug the 4km-wide "ice mountain" exerts on the probe.
Ten billion tonnes sounds a lot, but it means Comet 67P/Churyumov-Gerasimenko has quite a low bulk density, something in the region of 300kg per cubic metre.
If you could put the object in an ocean, it would float.
The calculation would seem to confirm suspicions that the comet is highly porous, and may even hide voids inside its body - but this is all to be determined.
DigitalGlobe launches super-sharp WorldView-3 Earth imager
Rosetta heads for space 'rubber duck'
Europe's mission to land on a comet was always going to be difficult, but the pictures released this week of the giant ice ball illustrate just how daunting the task will be.
Comet 67P/Churyumov-Gerasimenko is far more irregular in shape than anyone imagined.
Spaceport Britain: 'No challenge is insurmountable'
It's more than 40 years since Britain abandoned its own launch capability, cancelling the Black Arrow programme just as it successfully lofted the Prospero satellite.
The subsequent withdrawal from the European Ariane programme confirmed Britain's deep aversion to rockets. Until now. The climate is changing. Ministers are putting public funds (albeit a small sum) into an air-breathing rocket-engine technology, and they've declared their desire to see a home spaceport.
Rosetta: 'Spuds in space'
With the Rosetta probe closing in on Comet 67P/Churyumov-Gerasimenko, we're beginning to get a sense of the ice mountain's shape.
The latest picture release from the European Space Agency (Esa) may only cover an area of about 30 pixels, but it's clear that 67P is no sphere. In some views, the object appears quite elongated.
Ariane 6: Customers call the shots
Europe's rocket industry is currently going through something of an epiphany - the realisation that it must adapt, and fast, or simply become irrelevant.
More than half of the big commercial satellites that are working up there - the ones that relay our TV, phone calls, and internet traffic - were lofted by Ariane vehicles. But that dominance is now under threat from new launchers that promise to undercut Europe's best on price.
Rosetta edges towards Comet 67P
Europe's Rosetta spacecraft is edging ever closer to its quarry - the 4km-wide Comet 67P/Churyumov-Gerasimenko.
Thursday's separation is just 43,000km, and the narrowing gap is evident in the probe's latest photo release.
Malaysian jet MH370: Refined analysis drives new search area
As expected, and reported by the BBC last week, the search for MH370 is going to shift hundreds of kilometres to the south of where an Australian defence vessel thought, mistakenly, it had detected signals from the jet’s submerged flight recorders.
The new region is a consequence of further, refined analysis of the brief, automated satellite communications with the plane in its last hours.
Rosetta: Icy quarry coming into view
Take your seats because the show is about to begin.
The European Space Agency's Rosetta probe is edging ever closer to the Comet 67P/Churyumov-Gerasimenko for what is expected to be one of the most daring space encounters in history.
Skylon ‘spaceplane economics stack up’
It appears a feasible proposition, economically. That is the conclusion of a study that considered a European launch service based on a Skylon re-usable spaceplane.
The report, commissioned by the European Space Agency (Esa), was led by Reaction Engines Limited (REL) of Oxfordshire with help from a range of other contractors such as London Economics, QinetiQ and Thales Alenia Space (TAS).