WE THOUGHT we knew the solar system. Apart from Earth, all the worlds out there were dead lumps freezing in the blackness of space. But when Voyager I started beaming back images as it flew by Jupiter's moon Io in 1979, something wasn't right.
For one thing, its surface was too young – nothing like the antique landscapes of our moon or Mars, whose craters date back billions of years to the early days of the solar system. There were strange pock marks interspersed among smooth plains and mountains that jutted higher than Everest, but they looked more like open sores on a world that could not heal.
There was no Photoshop back then, so scientists assembled the jigsaw of images by hand as they arrived from the distant probe (which recently left the solar system... honest!). Though primitive by the standards of the full-colour visuals brought to us by later probes, they allowed scientists to watch volcanic eruptions as they happened. It was smoking-gun evidence: after billions of years out in the cold, Io was more than still warm – it was seething with volcanic activity.
The reason for this is Io's unique position in the Jovian system. It sits closer to Jupiter than any of the other large moons. Here, tugged and flexed by the planet's huge gravitational pull, as well as that of the more distant moons Europa and Ganymede, friction keeps Io piping hot.
This article appeared in print under the headline "A world on fire"
- Subscribe to New Scientist and you'll get:
- New Scientist magazine delivered every week
- Unlimited access to all New Scientist online content -
a benefit only available to subscribers - Great savings from the normal price
- Subscribe now!
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
Have your say
Only subscribers may leave comments on this article. Please log in.
Only personal subscribers may leave comments on this article
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support.
