Two astronauts who are stranded on the International Space Station (ISS) until next year have reported hearing 'strange' noises during their time on board.
On 5 June, NASA test-pilots Barry 'Butch' Wilmore and Sunita Williams embarked on a short trip to the ISS. They were due to return to Earth later the same month.
However, they ran into trouble when the new Boeing Starliner capsule that was supposed to bring them home experienced a number of technical issues.
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As a result, Wilmore and Williams have been stranded on the ISS for almost three months.
And it doesn't look like they'll be heading home anytime soon, with NASA confirming in a press conference last month (24 August) that the astronauts will be picked up by the crew of SpaceX's Crew-9 mission, with an expected return date of February 2025.
Meanwhile, the Starliner is set undock from the ISS and return to Earth without anyone on board in just a few days on 6 September.
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While the pair remain 'confident' that NASA will get them home safely, they've reported hearing 'strange' noises while up in space.
On Saturday (31 August), Butch Wilmore reportedly contacted Houston's Johnson Space Center to share his concerns.
"I've got a question about Starliner. There's a strange noise coming through the speaker and I didn't know if you can connect into the Starliner... I don't know what's making it," he said.
Mission control confirmed that they could configure a way for the sound to be played, after which Wilmore held a phone up to the Starliner's speakers.
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They responded: "Butch, that one came through. It was kind of like a pulsating noise, almost like a sonar ping.
"Good recording, thanks Butch. We will pass it onto the team and let you know what we find."
They asked one more time if there was any other noise and confirmed that it was coming from the Starliner.
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Wilmore could then be heard telling mission control that he hopes they will 'scratch [their] heads and see if you can figure out what's going on.'
The cause of the noise is yet to be determined.
While the stranded astronauts have sufficient supplies and resources to last until they're finally rescued, experts have warned of the 'life-altering' effects they will face after being in space for so long.
This includes loss of bone density and muscle atrophy, changes to their heart function, vision problems and intense radiation exposure.
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And the longer they're stuck up there, the more severe the effects are likely to be.
Rachael Seidler, a professor of Applied Physiology and Kinesiology at the University of Florida, told DailyMail.com: "Generally, almost all of the changes that we see with human spaceflight in terms of physiology seem to be dose dependent.
"The longer you're there, the bigger the change."