(Sen) - NASA's Cassini spacecraft completed a close flyby of Saturn's moon Enceladus on May 2 to learn more about its internal structure.
Cassini flew to within about 74 kilometres (46 miles).
The flyby was the third part of a trilogy of flybys using Cassini's radio science experiment. The other flybys took place on April 28, 2010 and November 30, 2010.
Of particular interest to scientists is the structure around the southern polar region which is marked by four "tiger stripes" and which blasts jets of water ice, vapour and organic compounds into space.
A concentration of mass in that region could indicate the presence of a subsurface ocean of liquid water that might explain the unusual plume activity.
Cassini's scientists learn about the moon's internal structure by measuring variations in the gravitational pull of Enceladus against Cassini's radio link to NASA's Deep Space Network on Earth.
Cassini also took more images of Enceladus' icy jets during the flyby.
Cassini's imaging team is run by Carolyn Porco who believes Enceladus is the most promising place in the solar system for a 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."
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.
Cassini also flew by Dione at a distance of about 5,000 miles (8,000 kilometres) and captured further images of the icy moon. The spectrometer was also used to monitor heat emission from the moon.
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.