On March 31, 1972, the Soviet Union as part of a series of unmanned missions to Venus known as the Venera program. But the spacecraft never made it to Venus. Instead, the capsule — dubbed Kosmos-482 — began spiraling back towards Earth. Researchers now say it's somewhere on the planet this weekend.
Jonathan McDowell, an astronomer with the Center for Astrophysics | Harvard & Smithsonian, says the reason Kosmos-482 has been stuck in Earth's orbit has to do with a malfunction of its final rocket stage.
"Halfway through the rocket firing, the engines sort of spluttered and died," McDowell said. "And so it wasn't getting fast enough to reach escape velocity. And so it ended up in a big elliptical orbit around the Earth."
McDowell says it's hard to predict where exactly on the planet the capsule will land, as it's flying around the planet at a speed of around 17,000 miles per hour.
"I imagine by late Friday, early Saturday, we might have the re-entry time narrowed down to maybe a few hours," McDowell said. "But a few hours is still twice around the earth. And so we probably won't know where until after the event.
"McDowell says it's not clear whether or not the capsule will disintegrate in the Earth's atmosphere. When it was launched, it was equipped with a heat shield that was designed to withstand the nearly 900 degree Fahrenheit temperatures of Venus.
"If you can survive Venus, you can absolutely survive Earth," McDowell said. "On the other hand, it's been in orbit for 50 years. I don't really know whether exposure to the outer atmosphere has kind of cracked the shield or degraded it in some way.
"Even if Kosmos-482 does survive reentry into Earth's atmosphere, McDowell says that given the fact that the planet's surface is 70% ocean, the half-ton capsule will most likely land in the water.
McDowell adds that there's a possibility it will pass close enough to civilization to allow people to get spectacular photos of the spacecraft blazing through the sky like a comet.
This story was edited for radio by Adam Bearne and produced by Lindsay Totty.
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