Star behind Uranus’s rings Eclipse Transit Occultation

Stellar Occultation Observation by Airborne Platform

SOFIA’s predecessor, the Kuiper Airborne Observatory (KAO)

Star behind Uranus and rings The rings of Uranus – discovered via occultation observations by the KAO. Star behind Uranus and rings Data record shows ‘dropouts’ in brightness of the star as it was occulted by each ring.

An atmosphere gives an object a “soft edge” observable via occultation.

Image of <= Pluto merged with image of background star.

2015 occultation light curve

2011 Pluto occultation light curve observed by SOFIA. *** SEEMS TO SHOW LESS ATMOSPHERE THAN IN 2015.

Large regions of Pluto are craterless, with folded mountain belts at their edges … signs of tectonic activity! Internal activity could be what sustains Pluto’s atmosphere.

■ Figure 24-13 Because Neptune’s equator is inclined almost 29° in its orbit, it experiences seasons. Because of the planet’s orbital period, each season lasts about 40 years. Since Voyager 2 visited in 1989, spring has come to the southern hemisphere, and the weather has clearly changed, which is surprising because sunlight on Neptune is 900 times dimmer than on Earth. Figure 24-13a p550

■ Figure 24-15 Nereid has a large, elliptical orbit around Neptune, but Triton follows a small, circular, retrograde orbit. At a distance of 30 AU from Earth, Triton is never seen farther than 16 arc seconds from the center of Neptune. Figure 24-15 p551

Voyage 2 images of Triton showing signs of geologic activity. Black smoke plumes from cyro-volcanoes Voyage 2 images of Triton showing signs of geologic activity. ■ Figure 24-16 (a) Triton’s south pole (bottom) had been in sunlight for 30 years when Voyager 2 flew past in 1989. The frozen nitrogen in the polar cap appears to be vaporizing, perhaps to refreeze in the darkness at the planet’s north pole. The dark smudges are produced when liquid nitrogen in the crust vaporizes and drives nitrogen geysers. (b) Roughly round basins on Triton may be old impact basins flooded repeatedly by liquids from the interior. Notice the small number of craters on Triton, a clue that it is a partially active world. Smooth surfaces covered by flows of water “lava”.

Triton shadow path 5 Oct 2017