Moscow: A Russian satellite that could weigh as much as three tonnes is expected to re-enter the Earth's atmosphere on Sunday, reportedly representing a "very real danger" to densely populated areas. The final movements of Kosmos-1220, a decommissioned Soviet military device, are being monitored by Russian space officials, and Colonel Alexei Zolotukhin told the news agency RIA Novosti that it would begin an uncontrolled descent on Sunday. Though the satellite will largely burn up as it passes through the atmosphere, experts said it was highly likely some fragments will survive to impact the planet's surface.

Colonel Zolotukhin said the debris was expected to come down somewhere in the Pacific Ocean, but added that the "impact time and location of the fragments from Kosmos-1220 may change due to external factors". According to RIA Novosti, the exact size of the naval surveillance satellite has never been disclosed - but the Tsiklon-2 rocket which put it into orbit in 1980 was capable of carrying around three tonnes.The uncertainty surrounding its re-entry time means debris from Kosmos-1220 could impact almost anywhere on earth, and Astronomy magazine editor David Eicher told Fox News this could represent a genuine threat to populated areas.

"Much of it will burn up in Earth's atmosphere, but no doubt fragments of Kosmos-1220 will reach Earth," Mr Eicher said.

"What we have going for us is that most of the planet is covered with water, and highly populated areas are in the minority of our planet's surface area. So it is unlikely that satellite debris will cause injuries or major damage. Still, with such a re-entry, we are playing the odds."

"This is a very real danger, given that a decaying orbit will carry this satellite down onto the planet," He added.The last high-profile satellite re-entry was when the European Space Agency's GOCE unit - dubbed the "space Ferrari" because of its sleek and compact design - came down without damage to property in November last year.