Farewell, Herschel space observatory

The European Space Agency’s Herschel space observatory — the largest,
most powerful infrared telescope ever flown in space — has run out of
liquid helium coolant, ending more than three years of pioneering
observations of the distant, “cool universe.”

Herschel was highly sensitive to a wide range of low temperatures,
from a few hundred to less than ten degrees above absolute zero —
operating at far-infrared and sub-millimeter wavelengths. To observe
cold regions with high sensitivity, liquid helium was used to cool the
instruments to nearly absolute zero (or -271 degrees Celsius).

We knew this day would come. The mission began with over 2,300 liters
of liquid helium — which weighed 335 kg, nearly 10 percent of
Herschel’s mass at launch on May 14, 2009. The helium has been
evaporating ever since the final top-up the day before.

Earlier this week, the temperature rose in all of Herschel’s
instruments. Later this month, the spacecraft will be propelled to a
stable parking orbit around the sun, where it will remain
indefinitely.

http://www.smartplanet.com/blog/bull...ervatory/18890

Why not send the thing to Pluto? Wouldn't it be cold enough there?