BBC:
The European Space Agency's (ESA's)
Herschel Space Observatory
was launched in 2009 to observe the formation and
evolution of stars and galaxies, the chemical composition of
bodies in our solar system, and molecular chemistry of objects
throughout the universe. The instruments onboard require
extremely low temperatures, but the 2000 L of helium
refrigerant
Herschel carried at launch will run out in the next
few weeks, almost exactly when originally predicted. The
telescope was placed at Earth's second
Lagrangian
pointâmdash;a point 1.5 million km from
Earth, where the gravitational forces of Earth and of the Sun
balance in the two bodies' rotating reference
frameâmdash;to keep the spacecraft in Earth's
shadow. Its 3.5-m single-piece mirror, the largest ever
launched, was able to observe light in the far-IR and
submillimeter wavelengths. When the helium supply runs out, the
instruments will quickly warm beyond the point of usability. At
that point, ESA will put the satellite into a slow-drifting
orbit around the Sun.
