If there is a place in the Solar System that may potentially harbor life, Enceladus may be the best bet. Astrobiologists are excited about this small moon of Saturn, hardly 311 miles across, and in spite of a mind-numbing -300ºF, it has all the key ingredients for life. Better yet, sampling Enceladus for life is easier than sampling Mars, Europa, or Titan. Plans are already underway to return to Enceladus as soon as feasibly possible.

Enceladus is an unusually smooth and bright moon that reflects up to 95% of the incident sunlight. It was suspected that something was resurfacing it when the two Voyager spacecraft flew by it in 1980 and 1981, but proof would have to wait until Cassini arrived at Saturn in 2004 with highly sophisticated instruments. In 2005, the big discovery was made when Cassini imaged geysers erupting from fissures running along the south polar region. Huge jets of water freeze instantly into ice crystals as they are shot over 100 miles above the surface so powerfully that they escape Enceladus’ gravity and form a tenuous icy ring around Saturn known as the E-ring. Cassini flew through the plumes several times without harm and coming within 30 miles of the vents confirmed that the plumes are made of water ice and that the fissures are a few hundred degrees warmer than the surrounding terrain, about -100ºF. Cassini also discovered a large underground ocean under the southern hemisphere that is liquid due to tidal flexing from Saturn, much like Jupiter flexes Io, heating its interior, which causes huge volcanic eruptions. The tidal flexing keeps the interior of Enceladus warm enough to maintain an ocean and to generate powerful geysers. There was even a bigger discovery: Enceladus has all the ingredients for life! Analysis of the plumes shows an abundance of organic carbon, nitrogen, chemical energy, and inorganic salts, all the necessary components for life as we know it. This means that the ocean interacts with the rocky surface deep down beneath it dredging up organics that get spewed out through the fissures. Life cannot exist in the plumes themselves as they would freeze to death in the intense cold and vacuum of space since Enceladus has no atmosphere. However, deep down in the warmer ocean beneath the icy crust it may be possible for life to exist. Cassini was not capable of determining if life exists as it did not have the necessary equipment to do so, but a future spacecraft can be designed to detect it.

What makes Enceladus so exciting to explore is that the water is easy to reach. It is not in a frozen state and deep underground like on Mars and Titan, or hidden deep underneath a thick crust of ice like Europa where intense drilling would be necessary. A spacecraft only has to fly through a plume to sample the water and Cassini already proved it is safe to do so. The Enceladus Life Finder (ELF) is a spacecraft that would orbit Saturn and repeatedly fly through the plumes of Enceladus. This highly sophisticated, but Enceladus-specific spacecraft, could fly as a Discovery-class mission capped at no more than $500 million and would have instruments that would specifically search for and identify complex organic molecules. There could be something living in the ocean beneath the icy crust, and even though it would freeze and die once ejected through the fissures, ELF would be capable of detecting it. Such a mission launched as soon as 2021 and arriving by 2028, would pave the way for a more-complex but inspiring mission called Life Investigation For Enceladus (LIFE), which would be a sample return mission. LIFE would orbit Saturn for several years, fly through the plumes to collect particles, and then return them to Earth for analysis. At a price of at least $1 billion, it would probably not fly until 2030 at the earliest, and take over a decade to accomplish its mission.

The question of whether life exists elsewhere in the Solar System has been a nagging question. The answer may come from a bright, icy moon a billion miles away instead of the dusty, red planet next door. Enceladus beckons, and someday, hopefully sooner than otherwise thought, we will return. ELF may finally answer that nagging question once and for all.