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An international research team of American and German astronomers and engineers has
succeeded in the delicate task of observing the occultation of a distant star caused
by the transit of the dwarf planet Pluto.
The event, the results from which are still being analysed, occurred on 23rd June
over the Pacific ocean, and in order to observe it NASA's flying SOFIA (Stratospheric
Observatory for Infrared Astronomy) observatory was used. This is a modified Boeing
747SP that carries a 2.5 metre diameter telescope for infrared observations. To
follow the occultation the High-Speed Imaging Photometer for Occultation (HIPO)
instrument was used, which is essentially a very accurate, very fast light meter.
SOFIA met with Pluto's shadow almost 3000 km from its base. The most difficult aspect
was the calculation of the precise location of the narrow occultation path, and given
that the shadow would travel at 24 km/s, even a small error in this calculation would
have compromised the mission.
To reduce possible errors to a minimum, the same evening of 23rd June, astronomers at
the Lowell Observatory took last minute images of Pluto and the star and sent them to
the Massachusetts Institute of Technology (MIT), where the occultation trajectory was
recalculated.
Just two hours before the start of the event, MIT communicated the
coordinates of the centre of the path to the SOFIA team; it actually ended up being
200 km further north than initially thought.
Another 20 minutes passed before air traffic control clearance was received to change
the flight plan, but in the end the plane was located and the telescope pointed in
time to observe the whole event.
The light curve data should enable the density and
temperature profile of Pluto's atmosphere to be studied even to very low altitudes. |
