.Missions have discovered hints that a subsurface ocean exists beneath the icy crust of the Moon. Where there is warm, liquid, water, and the right chemistry, there may be life.
It won’t be easy to find out if this is true. Landing on the Moon, drilling through the ice, and sampling the water underneath would be a complicated and expensive option. Now, research has revealed a more viable option. The exciting results, which were published in Nature Astronomy, suggest that there could be plumes coming from Europa’s Ocean – meaning that a spacecraft can fly through them to test out the water. These findings will be important for future Europa Clipper and Juice missions.
The Moon has been spotted with geyser-like features before. Hubble’s Space Telescope observed transient plumes coming from Europa’s ocean subsurface in 2012 and 2016. The data were captured far away from the Earth (Hubble orbits). The new evidence comes instead from a flyby of Europa in 1997 by the Galileo Mission – confirming that there are indeed plumes on the Moon.
Europa’s subsurface ocean and ice sheet are not known to be the same thickness. In a 2011 study, it was found that water could be close to the surface near icy “chaos areas” similar to Antarctic structures.
Enceladus: Lessons to be Learned
The Cassini spacecraft to Saturn found huge plumes coming from Enceladus, the Moon. Magnetic field deflections and a large number of charged particles were the first signs. We know the dense gas of newly formed molecules and atoms within a watery plume is set (ionized) as electrons are knocked away. It becomes electrically conductive, which causes magnetic fields to change.
Enceladus south polar plumes as seen by Cassini on November 30, 2010. NASA/JPL-Caltech/Space Science Institute
The plumes can be seen in stunning images that appear to emanate from what seems to be tiger stripes at the south pole. Gravity measurements indicate that the source of this plume is a subsurface sea.
Cassini flew by Enceladus 22 different times to explore the plumes that were ejected from the ocean directly below. Cassini also found sodium in the plumes – an indication that the oceans are salty. Cassini also found silicates, which are indicative of a sandy ocean bottom and the possible existence of hydrothermal outlets.
It is important to note that chemical reactions between water and sand can produce enough energy to fuel microbial activity in water (and this usually occurs near hydrothermal vents). Cassini discovered hydrogen in plumes in 2107. This should be the by-product of the water-sand reaction. It is the closest you can come to proof of being a suitable candidate for life.
After these exciting discoveries, the search for plumes on Europa began. Hubble measurements in 2012 led to estimates that indicated the water released by the Europa plumes was 30 times greater than that on Enceladus. The plumes reached a height of about 200km. The ocean floor of Europa is likely to be in contact with rock and sand, just like Enceladus. The ocean floor of some moons, such as Ganymede or Callisto, is made up of ice.
The new study compared the magnetometer data collected from a Galileo flyby that occurred less than 400km over Europa’s icy surface with a computer model of what charged gas should look like. Based on an observed deflection of the magnetic field and a decrease over a distance of 1,000km, these results suggest that there is a dense area of charged particles. This is the strongest evidence yet that a plume caused this.
Coming missions
The Europa plumes, like Enceladus’s plumes, offer tantalizing prospects of sampling subsurface ocean material directly. This will be explored by two future missions. I am working on the JUICE Mission of the European Space Agency, which is due to launch in 2020. It will reach Jupiter’s system in 2030. As part of the sequence, two close flybys are planned of Europa before moving into orbit around Ganymede’s Moon in 2032.
The Europa Clipper of NASA will fly by Europa 45 times. These missions will be able to explore the plumes the same way that the Cassini orbiter explored Enceladus. In the future, landers or penetrators for Europa are being proposed (but funding has not yet been secured). While we wait, sampling plumes may provide some exciting new insights about what is happening in the ocean. We may be able, if we’re lucky, to detect biological activity. Cassini, unfortunately, was not equipped with the tools to search for these signatures on Enceladus.
NASA/JPL-Caltech/SETI Institute
There are four places in our solar system where life is likely to exist. The first place to look is Mars. Conditions on Mars were ideal for the formation of life 3.8 billion years ago. This will be explored further by the ExoMars2020 rover in which I am involved. The NASA Mars 2020 rover and its helicopter will also be able to drill down to two meters to look for biomarkers.
Therefe on Europa and Enceladus. Sampling them will reveal if this is true. We have found complex prebiotic chemistry on Titan, Saturn’s largest Moon. This chemistry was once responsible for the origin of life on Earth. It could be a place for current or future life.
It is important to return to Saturn’s system in order to find out if there are other forms of life. NASA’s Dragonfly Quadcopter for Titan is a possibility.
It is exciting to imagine that we could discover microbial life from another planet in a matter of years.
