NASA tracks about 23,000 pieces of space debris bigger than a grapefruit orbiting Earth. This space junk is of human origin and includes defunct satellites, bits discarded by space missions, and pieces created by the fragmentation of the previous two categories. Furthermore, NASA estimates that there are millions of pieces in orbit that are too small for the space agency to keep track of.

Some of this junk is travelling as fast as 28,000 km/h and even a small piece can do serious damage if it collides with a satellite. As a result, the people who design spacecraft are keen to protect their missions from space junk.

Now,  Gary Simpson, KT Ramesh, and colleagues at Johns Hopkins University in the US have done a spectacular study that provides further insights into how tiny bits of high-speed space junk impact objects. The study is quite literally spectacular because of the videos that they have taken of the impacts.

Ultrafast jet

The team fired stainless steel spheres at an aluminium plate at a speed of 10,000 km/h. The resulting impact flashes were captured by a high-speed camera (see video) and the team studied the intensity and spectral nature of the light. The images show the emergence of an ultrafast jet of material that blasts out from the point of impact.

The team found that the composition of the target and the size of the jetted particles could be inferred from the flash – which could prove useful for studying the impact of space junk on satellites. The research is described in PNAS Nexus.

We do like a good story about ultrasound here at Physics World, and we have written about research covering everything from medical applications to ultrasound-based tractor beams. Today, I was pleased to discover two uses of ultrasound related to food and drink.

Frozen chops

If you eat meat, you might be tempted to defrost a frozen chop in the microwave if you don’t have the patience for defrosting it at room temperature. Now, researchers in China and Australia have investigated whether it’s a good idea to use ultrasound to defrost pork.

Zhongyuan Chen and colleagues found that ultrasonic assisted thawing decreased the thawing time by as much as 65% when compared to conventional water-immersion thawing. The pork also exhibited better water retention and tenderness. You can read more in Food Physics.

Meanwhile in Spain, researchers at the University of Castilla-La Mancha and the University of Murcia have developed a way to use ultrasound in a key step in the making of rosé wine called maceration. Maceration involves the leaching of tannins and other compounds from the skins of grapes. Some of these compounds give red and rosé wine its colour and flavour.

Colouring wine

High-powered ultrasound has already been used in the maceration of red wine, but it had not been clear if it could be used for making the much paler rosé. This involves shorter maceration times to avoid creating wines with an undesirable dark colour and flavours.

Now, Encarna Gomez Plaza and colleagues have shown that ultrasound-driven maceration (called sonication) created wines with “superior aroma”. Indeed, the researchers say, “Sonication gave rise to wines with intense red berry and flowery odours, with scores higher than those of wine from macerated grapes”.

They describe their work in the Journal of the Science of Food and Agriculture.