The Sky is Falling

The sky is falling, but when?

All week we’ve heard about a NASA satellite returning home in pieces. When will it arrive? Where will it land?

This morning we received a little more news from NASA, though still a bit vague. From their website (Update #10):

Re-entry is expected late Friday, Sept. 23, or early Saturday, Sept. 24, Eastern Daylight Time. Solar activity is no longer the major factor in the satellite’s rate of descent. The satellite’s orientation or configuration apparently has changed, and that is now slowing its descent. There is a low probability any debris that survives re-entry will land in the United States, but the possibility cannot be discounted because of this changing rate of descent. It is still too early to predict the time and location of re-entry with any certainty, but predictions will become more refined in the next 12 to 18 hours.

The Upper Atmosphere Research Satellite (UARS) was sent into orbit in 1991 by the space shuttle Discovery. At the time of this writing, it is about 35 feet long (about the size of a small bus) and weighs over six tons. It focused on Earth’s upper atmosphere, measuring ozone and chemical compounds found in the ozone layer; wind and temperature in the stratosphere; and the energy output of the Sun.

The satellite was decommissioned in 2005, simply adding to the rest of the space junk. The satellite was expected to return to Earth soon, but not this soon.  Earlier this week National Geographic News hinted at the reason for the early return:

The satellite's speed is due to a recent spike in the amount of ultraviolet rays being emitted by the sun…

NASA scientists estimate that satellites this size return to Earth at least once per year, mostly disintegrating at re-entry, with the remaining pieces causing very little damage or injury.

The New York Times estimates the return size and gives us a comparison:

At least 26 pieces, the largest 330 pounds, are expected to survive the plunge and land along a path 500 miles long… When the space shuttle Columbia disintegrated during re-entry in 2003… no one on the ground was injured as 42.5 tons of debris showered down from West Texas to Southwest Louisiana.

So if the odds that any pieces will land in the US are low, where will it land? Want to take a guess or make a bet? There’s a bookie for that! According to ScienceNOW, the odds that the debris will land in Africa are 9-to-4. Not bad. The odds that YOU will be hit by debris? NASA says about 1 in 22 trillion…

Image: NASA