British astronaut Tim Peake began a marathon in space on Sunday, 400 kilometres above the London marathon taking place at the same time.
The former test pilot is using a specially adapted running machine on the International Space Station to take part in the 42-kilometre run.
Peake, who once completed the London marathon in under 3 hours and 20 minutes, is held by elastic straps attached to his shoulders to stop him floating away from the treadmill, the European Space Agency said.
Marco Frigatti, a judge from the Guinness Book of Records, said the 43-year-old astronaut was set to break a world record if he successfully completes the run in the space under 4 hours and 24 minutes, the time previously set by ISS astronaut Sunita Williams taking part in the Boston marathon in 2007.
Peake has been orbiting earth in the space station as part of a six-month stay since he and two other astronauts were launched on a Russian rocket from the Baikonur space centre in Kazakhstan in December.
The British astronaut made his country's first spacewalk earlier this year as part of a mission to undertake repairs to the outside of the orbital structure.