How ice-penetrating rockets and robotic submarines could help find life beyond Earth
When it comes to exploring other worlds, we typically think of observation satellites taking pictures and scientific measurements from orbit or robotic rovers trekking along the red desert of Mars.
But what about harpooning the icy shell of a moon, like Europa, with a rocket-propelled spear and searching for life beneath the surface with an autonomous robotic submarine?
This is one of many alluring concepts that could be employed in man’s undying quest to find life beyond our planet. Beyond Mars, Europa seems like our next closest hope for finding the past or present signature of biological life forms somewhere in our solar system.
Europa’s Ingredients for Life
Scientists believe that Europa, one of Jupiter’s many moons, possesses the ingredients for life: water, chemistry and energy.
Long-held predictions that Europa has an ocean of liquid water beneath its icy crust were confirmed in 2019 by scientific observation through the world’s largest telescope, the Keck Observatory, in Hawaii. An international group of researchers spotted water vapor emitting from a geyser on the moon’s surface, a phenomenon that explains Europa’s unique surface “chaos” geology.
This observation has heightened interest in the Galilean world, with NASA and the European Space Agency (ESA) both planning missions to Europa in the 2020s. NASA’s Europa Clipper mission would be ready for launch in the 2023-25 timeframe, whereas ESA’s JUpiter ICy moons Explorer (JUICE) spacecraft is already taking shape with a planned launch in 2022.
These two missions primarily focus on scientific observation but depending on the data they return, mankind might want to take a closer and more exploratory look. One option is to land a mobile probe on the surface like the Mars rovers. But another – perhaps more fruitful – endeavor is to go beneath the crust and swim around looking for life such as floating bacteria or more complex organisms, like the fish and crustaceans we find living deep within our own oceans.
Breaking the Crust
The first challenge is to find an opening in the crust through which to send a robot carrying various sensors, such as acoustics for detection, gas chromatography and mass spectroscopy for chemistry, cameras for observation and sonar for mapping.
For this kind of mission in a far off world, there would be a lot of cross-pollination between the technologies developed by the civil space sector for interplanetary observation (i.e. launch vehicles, deep space communications, re-entry and landing, etc.) and the national security sector ( i.e. rocket motors, penetrators, communications, navigation, sensors, etc.). Over the past few decades, the U.S. military has ramped up the development of so-called hard-target munitions – or bunker busters – to destroy structures buried deep underground. Additionally, billions of dollars have been invested in exquisite sensors for land, air, sea and space platforms to get a better view of the battle space and detect hazards like roadside bombs.
Together, these two technology sets could form the basis for an eventual Europa mission. To punch an opening in the surface, a large, high-kinetic energy penetrator could be propelled like a pile driver into an area of Europa where the ice is the thinnest to create a straight opening through which an autonomous robot could enter.
In the military, aircraft drop guided earth penetrators from high altitudes to take out underground bunkers using the sheer kinetic force produced by gravity, often combined with depleted uranium, a high density element which generates large kinetic energy. However, because Europa is smaller and has far less gravitational pull than Earth, the spear would need to be very dense, and accelerated by a rocket booster.
Using kinetic energy to punch a hole in a distant world might seem like an extraordinary measure, but this isn’t a novel concept. In April 2019, Japan’s Hayabusa-2 asteroid sample-return mission made history by firing a copper lug into the rocky surface of the asteroid Ryugu. The spacecraft essentially shot the asteroid using an instrument called the Small Carry-on Impactor (SCI) to blast a crater and free up debris for collection.
Not to be outdone, NASA plans to slam a spacecraft into the Didymos binary asteroid in an attempt to nudge it off course. This Double Asteroid Redirection Test (DART) will prove whether it is possible to stop Armageddon by changing the trajectory of an asteroid before it potentially collides with Earth.
Deep Dive into Europa’s Waters
Once the ice shell of Europa is breached, an autonomous unmanned underwater vehicle could be lowered through the opening to start exploring the newly unlocked ocean. There are many similarities between this type of vehicle and the towed or free-swimming mine-hunters used by the U.S. maritime force to protect ships from undersea mines. Aerospace and defense companies such as Northrop Grumman are leaders in this field, with expertise in undersea minehunting and torpedo guidance, navigation, communications, sonar, infrared and other areas.
There needs to be some way to beam data back to Earth for analysis. That information would be passed from the robotic explorer to a relay on the surface of Europa and then to an orbiter for deep-space communications back to Earth.
Passing information from the explorer to the surface relay would be the greatest challenge, since the jagged ice would rip, crush or sever any trailing copper or optical fiber cables. This problem would be familiar to military forces operating in the Canadian North, Arctic or Antarctic.
The autonomous undersea robot would instead need to communicate using low-bandwidth radio frequency, free-space optical or acoustic transmission. Each type of transmitter has its limitations, but some data is better than no data. The bit rate of the transmissions would range from low to very low depending on the thickness and opacity of the moon’s icy crust.
Onboard the explorer would be a navigation and guidance system as well as eyes in the form of electro-optical/infrared cameras for a near field of view. A sensitive microphone should also be onboard to detect the acoustic signals of geological movement and biological life in the deep ocean. A gas chromatograph and spectrometer is desirable for chemical analysis. In order to detect weak magnetic fields, a superconducting quantum interference device, or SQUID, which is a very sensitive magnetometer could be used to observe the magnetic environment.
The primary instrument for mapping the hereto uncharted world is a miniature synthetic aperture sonar. The military uses sonar, a system for detecting objects under water and measuring depth by emitting sound pulses measuring their return, for submarine and torpedo navigation, mapping, and detecting undersea threats like anti-vessel mines. Ocean explorers have been using sonar since the 1980s to discover, map and photograph shipwrecks like the Titanic.
Unlocking the mysteries of Europa would be a monumental scientific and technological achievement for mankind and many of the elements needed for success already exist. How you combine them and structure the mission makes the difference.
Thanks to ambitious Clipper and JUICE projects being pursued by NASA and ESA, respectively, we Earthlings should soon know if the potential for life on Europa is great enough to merit such an ambitious undertaking.
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