Close scrape at Saturn's moon
Posted: Friday, March 07, 2008 4:21 PM by Alan Boyle
The Cassini orbiter is due to make its closest-ever approach to a celestial body next Wednesday, when it comes within 30 miles of the surface of Enceladus, one of Saturn’s myriad moons. Enceladus isn’t just any moon: It just happens to shoot up geysers of ice crystals, which may hint at the presence of liquid water (and perhaps even life) beneath the moon's frozen surface. Cassini will be “scraping” right through the heart of the plume, at an altitude high enough to escape damage - but low enough to take samples and find out whether life’s building blocks lurk in that alien sleet.
"We should come away from this flyby with a better idea of the composition of the plume, in particular, a better measure than we've had up until now of the abundances of ammonia and some simple organic compounds, both of which are important to ascertaining the astrobiological potential of the source environment of the jets," the Space Science Institute's Carolyn Porco, leader of Cassini's imaging team, said in an e-mail.
Cassini has had close brushes with Enceladus before, but those flybys were nowhere near this close. In fact, at the precise moment when Cassini is closest to Enceladus, the bus-sized spacecraft will be zooming so fast that it can't really take any useful pictures.
The good news is that Cassini will be taking in data like crazy when it goes through Enceladus' south polar plume just a half-minute later, at an altitude of 120 miles (200 kilometers). John Spencer, a Southwest Research Institute planetary scientist on the Cassini team, said the previous flybys had at best a glancing encounter with the ice plume. "This time, we're really plunging into the plume," he said in a NASA video explaining the flyby.
That's why this year's series of Enceladus encounters are called "scraping flybys." It may sound scary to subject a $3.4 billion space probe to a sleet storm, but Cassini's mission managers say this sleet shouldn't pose a threat: At a height of 120 miles, the particles of ice are expected to be no more than a micron wide (that's 0.00004 inch).
The entire time line for Wednesday's flyby is outlined on the Cassini imaging team's Web site, and to celebrate Cassini's first scrape, NASA's Jet Propulsion Laboratory has put together a goodie bag of Enceladus-flavored treats:
While you're at it, check out everything we have to offer on Enceladus, including this slide show highlighting the moon's plume and "tiger stripes." And stay tuned for updates: After Wednesday's scrape with Enceladus, Cassini is due to dig in again in August, and then at least twice more during the probe's extended mission.
If the results are interesting, that would bolster the case for making an even more ambitious trip to Enceladus. Later this month, European scientists are due to discuss a future space mission called TANDEM, which could send probes to the surface of Enceladus as well as Titan, another one of Saturn's most mysterious moons. NASA has a similar concept for a follow-up mission to Saturn's moons, called the Titan Explorer, which would be launched sometime after 2020.
There are lots of places to look for traces of life in our solar system - ranging from Enceladus to Mars to Jupiter's ice-covered moons. What do you think we'll find? Feel free to leave your comments below.
