The Week in Space and Physics: Io Up Close
On photographing Io, American Moon landings, Exomoons and a trio of Magellanic clouds

Few worlds in our solar system appear as perilous as Io. Violent eruptions constantly burst outwards from its surface; some so energetic that they throw rocks and lava hundreds of miles out into space. Intense radiation bathes its surface, strong enough to induce madness in computers and to kill a human, if one were so foolish as to visit, within hours.
All this is a consequence of the moon’s location. Io is the innermost of Jupiter’s four large moons, sitting close enough to the gas giant to swing around once every two of our days. Powerful tides sweep through the moon as it does, fuelling raging volcanoes across its surface. The material they expel gets swept up in Jupiter’s magnetic field; forming a harsh belt of radiation around the planet.
The first of our probes to visit, Pioneer 10, suffered badly from the radiation. As it flew past Io, in 1973, the surge of particles triggered a flurry of false commands in its computer system, making it impossible to photograph the moon. The probe later recovered, and Pioneer 11 - flying past a year later - managed to send back the first close-up view of the moon.
Later images came as Voyager and Cassini flew past Jupiter, but our most detailed view of Io so far has come from Galileo, a probe that spent eight years orbiting the gas giant. At first Galileo kept its distance from Io, fearing damage from the radiation. But in 1999, having already completed its key goals, the probe swung in close to Io and passed just a few hundred miles from its surface.
Once again radiation damaged cameras on the probe, affecting the quality of the images it sent back. Later efforts, in 2001 and 2002, suffered similar problems, and in 2003, as fuel ran short, Galileo was deliberately crashed into Jupiter to avoid the risk of accidentally contaminating any of the planet’s moons.
A decade later Juno arrived at Jupiter. As with Galileo, commanders at first kept it away from Io’s intense radiation. But in 2021, after the probe had completed its initial work, they cleared it for a closer look. A first flyby came in 2022, when Juno passed forty thousand miles from Io.
At the end of December last year, however, they went one better. Juno passed less than one thousand miles from Io’s surface, capturing the closest pictures taken since Galileo. The radiation, of course, has once again affected their quality - but they should still allow researchers to trace the flow of volcanoes erupting on its surface.
Juno is scheduled to make another flyby of Io in February. In 2025, however, operators will bring its mission to an end. Like Galileo, they plan to crash Juno into Jupiter - choosing to destroy the craft rather than risk contaminating any of the fascinating moons of the outer solar system.
An American Moon Landing in 2024?
In a more optimistic timeline, this year could have seen American astronauts once more set foot on the lunar surface. Under plans sketched out in 2019, NASA was told to target a moon landing in 2024 - a goal which, officially at least, has slipped only until next year. Realistically, however, NASA has no chance of making it. A Moon landing looks more likely to happen in 2028, or, if that proves impossible, perhaps by 2030.
Instead hope for this year may come from two private companies, Astrobotic Technology and Intuitive Machines. Both companies have built robotic landers of their own, and both hope to put them on the surface of the Moon in the first few months of the year.
First to try will be Astrobotic. Their “Peregrine” lander rode aboard the maiden launch of the Vulcan Centaur rocket, a new launcher that lifted off yesterday. On board are instruments and experiments provided by both NASA and private companies, as well as a collection of human ashes - a cargo that has sparked some controversy.
Though the launch went well, Astrobotic reported early issues with the lander. Most concerning is a problem with its propulsion system, which is preventing the spacecraft from correctly positioning its solar panels towards the Sun. That, if it can’t be fixed, would likely also prevent it from landing on the Moon.
The other company, Intuitive Machines, plans to launch in February. Their lander is targeting the southern regions of the Moon, a rarely visited area that may host water ice deep within its craters. As for Peregrine, Intuitive Machines are also carrying instruments for NASA and cargo provided by private companies.
These are not the first private companies to attempt a moon landing. Last year a lander belonging to a Japanese company, ispace, crashed as it approached the surface. Beresheet, built by a private Israeli group, also failed as it neared a landing in 2019.
Those efforts, then, reveal the challenges of landing on the Moon. Few nations or organisations have successfully managed it the first time around. So far at least, only space agencies backed by a superpower - from the United States to India - have got there at all.
Have We Found Exomoons?
In recent decades astronomers have found thousands of planets around other stars. They spotted worlds smaller than the Earth, far larger than Jupiter and even spied a handful in other galaxies. They have not, however, yet found any moons beyond our own solar system.
Moons are certainly out there. They probably - just as in our solar system - come in a huge variety of shapes, from volcanic hellholes to oceanic paradises. Some, indeed, may be habitable and, in certain places, may even represent the best bets for life to emerge.
Yet spotting them is hard. Moons are generally small and dark, and that makes them hard to pick up with telescopes. Despite that, occasional claims of having found one have been made. Most notable are two purported exomoons, each as large as Neptune, which may be orbiting distant gas giants.
According to a recent study of those claims, however, they may not really exist. Both discoveries used observations from Kepler, a space telescope dedicated to the hunt for exoplanets. Buried in the data of two of those exoplanets, the initial claim said, were signs of additional large moons.
Yet the new study says those signs are unreliable, and partly down to the way the data was processed. More likely, they said, is that the observations show a darkening effect common as a planet passes the edge of its star. This could have created a short lived illusion of a moon - which was then picked up in the original claims.
One Galaxy, or Two?
The skies of the southern hemisphere are home to two clouds of stars. These, known as the Magellanic Clouds, are a pair of nearby galaxies. Both seem to be in orbit around the Milky Way, and both are far smaller than our own galaxy.
In the 1980s, however, a group of astronomers proposed that the smaller cloud was actually two separate galaxies. Probably, they said, the two galaxies had once formed a single object. But about two hundred million years ago a close encounter with the larger Magellanic cloud had ripped them apart, setting them on separate paths through space.
In a new study, astronomers found more evidence for this idea. Data from the Gaia space telescope showed the cloud is made up of two separate groups of stars, one of which seems to be slightly closer than the other. From Earth, however, the two groups appear along the same line of sight - which is why they look like a single object to us.