A NASA spacecraft is set to make the closest flyby yet of
an icy moon of Saturn on Thursday.
The Cassini probe is poised for a return plunge through the
cold
shower plume of the Saturnian moon Enceladus on Oct. 9, and can expect
another icy reception for a following flyby on Oct. 31 in an attempt to uncover
possible changes inside the frigid satellite.
"The October doubleheader gives Cassini two more
opportunities to hit the ball out of the park," said Bob Pappalardo,
Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena,
Calif. "With high scores in geology, surface heat, watery plumes and
magnetospheric effects, Enceladus could win the 'world championship' title this
year!"
Scientists expect Cassini to pass just 16 miles (25 km)
above the moon's surface during the closest approach at 4:30 p.m. EDT (2030
GMT). The probe's cruising speed should hit 39,594 mph (63,720 kph).
Cassini is currently on a $160-million, two-year
extended tour of Saturn and its moons following the completion of its main
four-year mission on June 30. Scientists took the opportunity to schedule seven
flybys of Enceladus, where they have debated the existence
of an ocean of water beneath the moon's frozen shell.
Previous visits to Enceladus detected comet-like organic
molecules within the moon's icy, geyser-like jets. A more recent Aug. 11
flyby pinpointed the locations of surface
fractures, nicknamed "tiger stripes," where those jets erupt out
into space.
The upcoming October flybys may support findings from the
most recent Enceladus flyby that suggest changes within the moon. Temperatures
over a surface fracture dubbed "Damascus Sulcus" checked out at a chilly minus 171
to minus 159 degrees Fahrenheit (160 to 167 Kelvin), well below the minus 136
degrees Fahrenheit reported during a March flyby this year (180 Kelvin).
"We don't know yet if this is due to a real cooling
of this tiger stripe, or to the fact that we were looking much closer, at a
relatively small area, and might have missed the warmest spot," said John
Spencer, a Cassini scientist at the Southwest Research Institute in Boulder,
Colo.
Scientists should have another shot beyond this year with
a second Enceladus doubleheader on Nov. 2 and Nov. 21 in 2009.
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