UARS official re-entry... and up next: ROSAT

Bad Astronomy
The entire universe in blog form
Sept. 27 2011 11:51 AM

UARS official re-entry... and up next: ROSAT

NASA has released the final update on the UARS bird that burned up in re-entry last week: it came down in the Pacific, west of the US.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

The Earth's atmosphere is not a lid over us, but gets thinner with height, so it's hard to define exactly what it means to say that the satellite burned up at such-and-such a spot. However, at 04:01 UTC on September 24th, the satellite's motion became dominated by the Earth's atmosphere, and for all intents and purposes that can be called the point where it came back in... or at least, where it started. The forward motion of the satellite took the pieces along a track 500 - 1300 km (300 to 800 miles) long, which is still safely out in the ocean.

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Thus ends the UARS tale.

... but we're not quite done yet. The venerable German astronomical satellite ROSAT is due to come back down in about a month or so. Smaller than UARS -- a little over 2 tons, as opposed to over 6 -- ROSAT will probably have more pieces survive the ride down because its mirrors had to be shielded from heat to operate. That means the odds of it hitting someone will be slightly higher than from UARS, about 1 in 2000. Bear in mind that's still really small odds! The chance of a specific individual getting hit are still something like only 1 in 14 trillion.

ROSAT is an X-ray satellite, designed to study high-energy radiation from astronomical sources. Years ago, I looked briefly at ROSAT data of a supernova remnant while putting together an educational activity about exploding stars. I don't feel the same connection to the satellite as I do to, say, Hubble, but still, it's a little sad to see it come down. However, it did provide years of outstanding service to the astronomical community, and gathered a vast amount of data about the high-energy Universe around us.

Image credits: NASA; German Aerospace Center (DLR)

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