Imaging Hell at High-Resolution

Avi Loeb
4 min readDec 15, 2022


NASA’s Juno mission captured this infrared view of Jupiter’s volcanic moon Io on July 5, 2022, when the spacecraft was about 80,000 kilometers away. (Credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM)

Imagine a moon painted in yellow, red, white, black, and green, largely due to toxic compounds of sulfur, with over 400 active volcanos and hot lava flowing into magma oceans boiling at 1,200 degrees Celsius. Sounds like “the fiery lake of burning sulfur” of hell in the Christian Book of Revelation 21:8 or the fires of Gehinnom in Jewish tradition, both referring to a place of spiritual punishment for unethical behavior, the opposite of heaven.

This might seem like a fantasy from a horror science-fiction story but it actually represents science-fact.

Jupiter’s moon Io is the most volcanically active body in the solar system, featuring the above qualities. NASA’s Juno mission is scheduled to obtain close-up images of Io starting today, December 15, 2022, with nine subsequent flybys — two of them from a distance of just 1,500 kilometers, comparable to Io’s radius of 1822 kilometers. Scientists will use those flybys to perform the first high-resolution monitoring campaign of Io’s volcanoes and their interaction with Jupiter’s powerful magnetosphere and aurora.

These names have historic origins. In ancient Greek mythology, Io is a mortal woman trapped in a dispute between the god Zeus — identical to Jupiter in Roman mythology — and his wife, Juno.

Discovered by Galileo Galilei on 7 January 1610, the moon Io is the innermost and second-smallest of the four moons of Jupiter, slightly larger than Earth’s moon. Its extreme geological activity is powered by the gravitational tide generated within Io’s interior as it is pulled between Jupiter and the other Galilean moons — Europa, Ganymede and Callisto. This gravitational heating results in the surface of Io being constantly renewed, filling in any impact craters with molten lava lakes. Io’s thin atmosphere is composed primarily of sulfur dioxide.

The interaction of Io with Jupiter’s magnetic field, generates an electric potential drop of 400,000 Volts across its surface, thereby inducing an electric current of 3 million amperes. The total electric power emanating from this giant battery is 1.2 Terra-watts, comparable to the total electric power consumption in city lights on Earth. Io’s electric current follows Jupiter’s magnetic field lines, creating lightning in Jupiter’s upper atmosphere.

In a paper that I wrote with Princeton’s Ed Turner a decade ago, we suggested searching for city light on planets, moons, asteroids or spacecraft at the outskirts of the Solar system. Based on our calculation, NASA’s Webb telescope could detect the light of a single city — like Tokyo, beyond the distance of Pluto. The Io-Jupiter system illustrates that natural light bulbs could also be lit out there for moons around planets. We should keep this in mind as we study the deepest images from the Webb telescope!

Remarkably, every second Io deposits a ton of its volcanic gases through its magnetic bridge to Jupiter. This adds up to transferring a tenth of a percent of the entire mass of Io to Jupiter over the age of the Solar system.

Finally, let us ponder the most interesting question. Could sufficiently-resilient life forms survive through the harsh physical reality on Io?

So far, no organic molecules have been detected on Io’s surface, and it has only an extremely thin atmosphere devoid of detectable water vapor. However, Io’s rocky surface might hide liquid water underneath. Geothermal activity and sulfur compounds could provide microbes with sufficient energy to survive. Lava tubes could protect living organisms from damaging radiation. But until we find life on Io, future astronaut communities who maintain traditional faiths, may find Io as the real-world incarnation of hell within the Solar system.

As of now, the high-resolution photos of Io coming from the Juno spacecraft would be a reminder to all humans of how heavenly Earth is right now and why we should keep it habitable for as long as we can. We must moderate our damaging impact on the Earth’s climate and limit the pollution of our atmosphere with space trash. After all, there is no place like home.


Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He chairs the advisory board for the Breakthrough Starshot project, and is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, is scheduled for publication in August 2023.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".