On the first morning of June, the waning half-moon will shine below the bright, morning planet Jupiter. Through a pair of 10x binoculars, look for a small "star" nearly touching the planet's left side.
This pinpoint of light is Jupiter's fourth largest moon Europa. It measures 1,940 miles (3,122 km) across, about 200 miles smaller than our own moon. Despite its lesser size, it would far outshine Earth's moon if we could swap the two. Europa's covered in water-ice, which makes it a far better reflector of sunlight than the rocky lunar surface.
Sandwiched between that icy crust and a rocky interior, scientists have discovered strong evidence for a salty ocean with an estimated depth of 40 to 100 miles (60-150 km). The Hubble Space Telescope detected water vapor plumes erupting from surface in 2014 and 2016 which may be associated with this hidden body of water. Now, new research and computer modeling show that volcanic activity may have occurred on the seafloor of Europe in the recent past and could still be happening today.
How does a small object nearly a half-billion miles from the sun get hot enough to melt ice locked in its interior? Simple. It gets picked on on all sides.
Europa experiences a gravitational attraction from both Jupiter and its neighboring large moons Io, Ganymede and Callisto. These competing stresses change the shape of its orbit and cause Europa's distance from Jupiter to vary during its 3.5-day loop. When closer, Jupiter pulls on Europa harder then when it's farther away. The repeated tightening and relaxing of the planet's grip flexes and deforms the moon, heating its interior similar to how repeatedly bending a paperclip generates heat.
The new research shows that Jupiter-moon gravitational whiplash can produce enough heat to melt the rocky mantle at the bottom of Europa's ocean and potentially produce seafloor volcanoes. It wouldn't be surprising. We've known for decades that the planet's moon Io is the most volcanically active place in the solar system with hundreds of volcanoes that erupt lava fountains and plumes of gas and dust up to 250 miles (400 km) high. Its source of heat is identical to Europa's.
The authors of the paper, led by Marie Běhounková of the Czech Republic, predict that the volcanic activity will likely be found near Europa's poles, where the most heat is generated. Volcanoes or hydrothermal vents — fissures in the seafloor that release geothermically heated water — could potentially support a life-friendly environment. Seawater percolating through magma-heated rock in Earth's oceans becomes enriched in chemicals from which life can extract energy. In the sunless depths of Europa's ocean, perhaps a similar process might offer life a haven.
“Our findings provide additional evidence that Europa’s subsurface ocean may be an environment suitable for the emergence of life,” Běhounková said. If Europa has remained volcanically active for billions of years it may be one of the best places to search for signs of life.
NASA’s upcoming Europa Clipper mission, targeted to launch in 2024, will swoop close to the icy moon and collect measurements that may shed light on the recent findings. It will reach Jupiter in 2030 and perform dozens of close flybys of the moon to determine its composition and sample its thin atmosphere.
Scientists will be looking for traces of seawater on the surface and hoping to find ejected particles in the plumes that contain materials from the seafloor. The probe will measure the moon's gravity and magnetic field, looking for any anomalies in the polar regions that might provide further confirmation of volcanoes there.
Additional bodies that may harbor past or present life include Mars, Venus and Saturn's moons Enceladus and Titan. And those are just a few of the possibilities in our solar system. We know of nearly 3,515 other planetary systems with a total of 4,753 planets.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.