Sun warming causes comet’s eruption
Three years ago, in 2007, the comet named Hoimes (17P) exploded with a blast that can be compared to a small nuclear bomb. It wouldn’t be so weird and mysterious if that eruption didn’t come from an exotic form of ice. Comet 17P/Hoimes became a million times brighter when it erupted three years ago. A collision with an asteroid could have explained that blast, had it been a one-off. But the same comet also exploded in 1992 and that is suggesting something else might be triggering those eruptions.
Researchers from the California Institute of Technology in Pasadena think the culprit may be an exotic and unstable form of water ice at the comet’s heart. When water freezes naturally on Earth, it forms a highly regular crystal structure. It’s a different story at the much lower temperatures of the outer solar system, where comets condensed from primordial gas and dust. The water molecules would have stuck together much more haphazardly, forming so-called amorphous ice. When such ice is warmed to -133°C, it reverts to the familiar crystalline form. This would squeeze out any gases trapped within the amorphous ice during the comet’s formation. Heat would also be released, perhaps prompting a runaway conversion of any nearby amorphous ice. The sun’s heat may have triggered such a conversion in comet 17P/Holmes, with pressure from the released gases blasting a hole in its side. The size of the debris cloud created by the 2007 blast suggests that the explosion was as powerful as the detonation of 31 kilotonnes of TNT or a small nuclear bomb.
To release this much energy would require the transformation of a million tonnes of amorphous ice, just a fraction of the mass of the comet’s 3.4-kilometre nucleus. But David Jewitt of the University of California, Los Angeles, cautions that gas might simply leak out through cracks in amorphous ice, rather than build to the high pressures needed for a violent eruption. “There is evidence that the tensile strengths of comet nuclei are very low,” he says. This suggests that the nuclei of comets may not be able to contain the gases long enough for an explosion to occur.
Related posts:
- Can whiter clouds reduce global warming?
- How warming saves Greenland’s ice
- Volcanoes and global warming
- More facts you wanted to know about global warming
- Volcanic eruption boosts ocean life
