Theis a small world, only 310 miles in diameter, and until recently was considered one of the least interesting moons in the solar system. But Enceladus, one of the 146 moons that orbit Saturn, has become a hot astronomical attraction – scientists have found that it offers one of the best prospects for finding life on another world in our solar system.
The European Space Agency (ESA) has announced that it has begun planning a mission to take a robotic probe into a billion miles of space to investigate.
It will be an extremely taxing project. In addition to the colossal distance the probe will have to travel, it will need large reserves of fuel to maneuver itself into orbit around Enceladus and then land on the icy surface.
Still, the prospect of studying the tiny moon is enticing for astronomers who have discovered that Enceladus – first observed by William Herschel in 1789 – possesses geysers that regularly erupt from its surface and spray water into space. Even more surprising, these plumes contain complex organic compounds, including propane and ethane.
“Enceladus has three key components that are thought to be essential for the appearance of life,” said astronomer Prof Michele Dougherty of Imperial College London. “It has liquid water, organic material and a heat source. This combination makes it my favorite moon in the entire solar system.”
That view is shared by Esa, which recently designated a mission to travel to a moon of Jupiter or Saturn as its next target for a major science effort. Such a project is expected to bring “a transformative scientific return,” according to a panel of expert scientists who studied three main targets: Europa, Jupiter’s ice-covered moon; Titan, Saturn’s hydrocarbon-rich moon; and Enceladus. All possess subsurface oceans that hold the promise of harboring alien life forms and would make prime targets for scientific scrutiny.
After months of consideration, the panel reported a few weeks ago that it was the last on this interplanetary list, Enceladus, that should be prioritized over other targets. A mission should launch by 2040 with the goal of either landing on the Moon or flying through geysers spraying water and carbon chemicals from its surface into space. It is preferable that both goals are attempted, the panel added.
“The mission would provide a tremendous scientific return and would be essential for the successful discovery of biospheres on icy moons,” said Dr Zita Martins, an astrobiologist at the Instituto Superior Técnico, who chaired the panel.
However, such goals will not be easy to achieve, as Dougherty pointed out last week. “It’s one thing to put a probe into orbit around a moon or a large planet that has a strong gravitational field that can slow down an incoming spacecraft. But Enceladus is small with weak gravity, which means you’ll need a lot of fuel to slow it down so it doesn’t pass its target in deep space. This will be a complicated issue for those designing the mission.”
Dougherty’s particular interest in Enceladus stems from her role as principal investigator for the magnetometer flown on the Cassini mission that studied Saturn and its moons between 2004 and 2017.
“At one point, Cassini passed close to Enceladus, and our instrument showed that Saturn’s magnetic field was being pulled around the moon in a way that suggested the small moon had an atmosphere,” Dougherty said.
Cassini’s managers agreed to direct the probe to take a closer look and, in July 2005, the spacecraft skimmed the moon’s surface at an altitude of 173 km – and detected significant amounts of water vapor. “It was great,” Dougherty recalls.
Subsequent purges brought even greater miracles. Huge geysers of water were photographed erupting from geological fault lines at the South Pole. The only other body in the solar system, besides Earth, was discovered to have liquid water on its surface. Finally came the discovery of organic matter in those plumes, and Enceladus was transformed from a small, insignificant moon into a world that is now set to trigger the expenditure of billions of euros and decades of effort by European astronomers and space engineers.
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The red planet was a warm, watery world 4 billion years ago and possessed ideal conditions for the emergence of life. However, Mars later lost its magnetic field, as well as its water and atmosphere, and was hit by strong ultraviolet radiation. Life would have had a hard time surviving on the surface, but may have continued, as microbes, underground.
europe
One of Jupiter’s main moons, Europa is completely covered in ice and has the smoothest surface of any known solid object in the Solar System. Beneath its surface, it has an ocean of water that scientists believe could harbor extraterrestrial life that most likely consists of primitive bacteria-like entities.