Cassini will make another close flyby of Saturn's moon Enceladus today.
The space probe in orbit around Saturn will fly to within 74 kilometres (46 miles) of the south polar region.
The main objective of the flyby is for Cassini's ion and neutral mass spectrometer to "taste" the particles bursting out of the southern region of the moon.
The flyby follows a similar enounter in March, as scientists try and learn more about the composition of the icy jets. Combined with the March 27 flyby and a similar flyby in October 2011, this close encounter will provide a sense of the jets’ three-dimensional structure and help determine how much they change over time.
"More than 90 jets of all sizes near Enceladus's south pole are spraying water vapor, icy particles, and organic compounds all over the place. Cassini has flown several times now through this spray and has tasted it. And we have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth's oceans," said Carolyn Porco, leader of the Imaging Science team for Cassini, talking about the recent flyby.
Porco believes Enceladus is the most promising place in the solar system for a "flagship-scale" astrobiology mission to search for microbial life. In an interview with NASA Science she reasoned:
"The kind of ecologies Enceladus might harbor could be like those deep within our own planet. Abundant heat and liquid water are found in Earth's subterranean volcanic rocks. Organisms in those rocks thrive on hydrogen (produced by reactions between liquid water and hot rocks) and available carbon dioxide and make methane, which gets recycled back into hydrogen. And it's all done entirely in the absence of sunlight or anything produced by sunlight."
A flyby planned for October 2015 will bring Cassini even closer to the south pole region, to a distance of about 25 kilometres (16 miles).
Enceladus has a diameter of 504 kilometres (313 miles) and its icy surface is highly reflective of sunlight. The icy jets burst out of the southern region where the moon is scarred by its "tiger stripes" - four parallel claw marks scratched into the smooth icy surface. The tiger stripes are about 120 kilometres in length.
The ice and dust that form's Saturn's E ring have been found to originate from Enceladus itself so that the moon forges the ring in which it sits.
Enceladus is one of over 60 moons orbiting the ringed planet.
After flying by Enceladus, Cassini will pass Tethys at a distance of about 6,000 miles (9,000 kilometers). The composite infrared spectrometer will look for patterns in Tethys’ thermal signature. Other instruments will study the moon’s composition and geology.
Cassini was launched in 1997 and entered Saturn's orbit in 2004. Cassini continues to provide much information and stunning images of Saturn, its rings and its moons.
The Cassini imaging operations center (CICLOPS) and team leader (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.