If it did come down in the Bay of Bengal, the satellite would have been approaching heavily populated cities in China before it started to tumble through the Earth's atmosphere, a fall that would have taken up to 15 minutes.
Although the likelihood of the 2.4 ton X-ray satellite causing death and destruction was low (at 1-in-2,000), these odds were higher than last month's NASA Upper Atmosphere Research Satellite (UARS) crash. The likelihood of UARS hitting someone on Earth was set at 1-in-3,200, even though UARS was a larger piece of kit than ROSAT.
The reason for the increased ROSAT risk was down to the satellite's large 32-inch (81 cm) wide, 880-pound (400 kg) high-temperature mirror - most of which was expected to survive the reentry burn.
Like UARS, scientists had very little idea as to where ROSAT was going to reenter. Having depleted its fuel many years ago, ROSAT was flying around in low-Earth orbit uncontrolled, under the mercy of the dynamic upper atmosphere.
Due to the recent uptick in solar activity, the atmosphere has been heated, causing it to swell. As the atmosphere swells, upper atmospheric gasses reach to higher altitudes. As there have been a series of recent flares bathing our atmosphere in extreme-ultraviolet and X-ray radiation, ROSAT began flying through a thicker orbital medium, creating drag.
Although ROSAT was given a "stay of execution" during the extended solar minimum from the mid-2000′s to 2009, the recent flaring activity ensured ROSAT wouldn't have to wait long until the atmosphere dragged it back down to Earth.
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Image credit: German Aerospace Center