NASA’s Neil Gehrels Swift Observatory is expected to fall back to Earth in the coming hours. Most of the spacecraft, which weighs about 1.5 tons, is forecast to burn up as it reenters the atmosphere, though some heavier fragments could survive and reach the surface.

On Tuesday afternoon, Aerospace Corporation forecast that Swift’s reentry would occur at 7:12 a.m. Wednesday, with an uncertainty of eight hours in either direction. NASA said possible debris could include titanium parts, such as an instrument mount, rings and fittings, as well as the telescope’s nickel mirror assembly.

NASA estimates that the chance of a fragment injuring someone is low. The observatory’s path passes over parts of Africa, Central and South America, Asia and Australia, where the risk is described as very small. The risk is zero in many regions, including Europe and the United States.

Launched on November 20, 2004, Swift was designed to study the afterglow of gamma-ray bursts. Its wide-field instrument could spot gamma-ray flashes, after which the spacecraft would quickly turn toward the source and make detailed observations as the high-energy light faded. The bursts can mark violent cosmic events, including stellar explosions and collisions between neutron stars.

The mission was initially planned to last two years, and NASA had no contingency plan to boost Swift’s orbit. Atmospheric drag gradually lowered the spacecraft’s altitude. Increased solar activity two years ago expanded Earth’s atmosphere and accelerated the descent of satellites including Swift.

NASA hired Arizona-based startup Katalyst Space Technologies to attempt to raise the observatory’s orbit. The rescue spacecraft launched successfully in July, but suffered a failure as it approached Swift. NASA and Katalyst abandoned the effort in August.

Swift resumed science operations for a final round of observations before NASA shut it down on the 20th of last month. John Nousek, who directed mission operations, said the spacecraft had no propulsion system and relied on solar power and batteries. He said it was not surprising that it had lasted as long as it did.

Astrophysicist Brad Cenko, Swift’s principal investigator at NASA’s Goddard Space Flight Center, said the observatory’s end was a sad moment for the team. Members planned to gather on Wednesday evening to remember the spacecraft and share stories.

Sources: Folha Ciência.