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.

The waning third-quarter moon will shine about 5° south of Jupiter at dawn on Tuesday, June 1. Saturn appears about two outstretched fists to the right of the bright planet. (Stellarium)
The waning third-quarter moon will shine about 5° south of Jupiter at dawn on Tuesday, June 1. Saturn appears about two outstretched fists to the right of the bright planet. (Stellarium)

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.

You can spot Europa in a pair of 10x binoculars just to the left (east) of the planet around 4 a.m. local time in the Americas. It's even easier to see in the smallest telescope.  (Stellarium)
You can spot Europa in a pair of 10x binoculars just to the left (east) of the planet around 4 a.m. local time in the Americas. It's even easier to see in the smallest telescope. (Stellarium)

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.

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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.

This is a montage of Jupiter's four largest moons shown with their relative sizes.. They're also known as the Galilean moons because they were first seen by the Italian astronomer Galileo. The moons' gravitational interactions, in tandem with Jupiter's pull, have fully or partially melted the interiors of Io, Europa and Ganymede. (NASA / JPL / DLR)
This is a montage of Jupiter's four largest moons shown with their relative sizes.. They're also known as the Galilean moons because they were first seen by the Italian astronomer Galileo. The moons' gravitational interactions, in tandem with Jupiter's pull, have fully or partially melted the interiors of Io, Europa and Ganymede. (NASA / JPL / DLR)

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.

Europa, the smoothest known object in the solar system, possesses an icy crust 10-15 miles thick scored by crisscrossing cracks. Beneath the surface there's strong evidence for a salty ocean. (NASA / JPL-Caltech)
Europa, the smoothest known object in the solar system, possesses an icy crust 10-15 miles thick scored by crisscrossing cracks. Beneath the surface there's strong evidence for a salty ocean. (NASA / JPL-Caltech)

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.

Data from orbiting spacecraft and the Hubble Space Telescope suggest that the interior of Jupiter’s moon Europa may consist of an iron core, surrounded by a rocky mantle in direct contact with an ocean under the icy crust. Internal heat may fuel volcanoes on the seafloor. (NASA / JPL-Caltech / Michael Carroll)
Data from orbiting spacecraft and the Hubble Space Telescope suggest that the interior of Jupiter’s moon Europa may consist of an iron core, surrounded by a rocky mantle in direct contact with an ocean under the icy crust. Internal heat may fuel volcanoes on the seafloor. (NASA / JPL-Caltech / Michael Carroll)

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.

A close-up of Europa's surface shows interlocking sheets of fractured water ice. The brown color may be radiation-bombarded sea salt from an underground ocean. (NASA / JPL-Caltech)
A close-up of Europa's surface shows interlocking sheets of fractured water ice. The brown color may be radiation-bombarded sea salt from an underground ocean. (NASA / JPL-Caltech)

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.