Sudden outburst activity on Comet 67P/C-G

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jet on Comet 67P/C-G

Cool image time! As Comet 67P/C-G approaches perihelion, Rosetta is detecting and imaging more and more activity coming from the nucleus, including a power outburst lasting less than a half hour.

In the approach to perihelion over the past few weeks, Rosetta has been witnessing growing activity from Comet 67P/Churyumov–Gerasimenko, with one dramatic outburst event proving so powerful that it even pushed away the incoming solar wind.

The comet reaches perihelion on Thursday, the moment in its 6.5-year orbit when it is closest to the Sun. In recent months, the increasing solar energy has been warming the comet’s frozen ices, turning them to gas, which pours out into space, dragging dust along with it.

The three pictures above were taken 18 minutes apart. The first shows nothing, and in the last the jet has almost completed dissipated. In the middle image, however, the jet is well defined, and data from the spacecraft indicated that it was so strong that it “had pushed away the solar wind magnetic field from around the nucleus.”


  • Tom Billings

    One wonders about jets and pits, and causation versus result.

    That they are not linked is almost impossible, IMHO.

    Which precedes the majority of the other, however? It seems that such pits as are large in relation to the size of the comet would be the results of long-term continual jet material expulsion. However, that they often seem filled with dust and relatively nonvolatile material prevents us from seeing just how deep inside the comet they go. I wonder if that fill material could be the result of ejected material during perihelion staying close enough to the nucleus that, as the comet rises towards aphelion, it is attracted back to the nucleus. That would happen with the less volatile material’s larger pieces, projected by the jets at lower velocities, if at all.

    The pictures tell us little bout the depth of the pits underneath the loose fill material, and nothing of their structure at deeper depths. Yet, I have seen speculation about great depth, resulting from heat near the core of the nucleus. It seems the only heat source is the Sun’s radiation. However, at perihelion, one wonders about the gravity gradient along the long axis of the nucleus. As the nucleus tumbles, that gravity gradient would shift, creating strains all the way to the core of the nucleus. Even if it did not cause all that much internal heat those strains could create cracks, through which gas can move.

    We know that jets change the orbit of the comet through reaction on the nucleus as a whole. But what about localized effects? Are gasses in the pits that are not projected outwards being projected inwards? Gas expansion pressure *should* be isotropic, after all. Could gas, heated near the surface by solar radiation, actually move *into* the core, through those cracks, providing heat that drives out the lowest volatility gasses, enlarging the cracks to passages?

    If this were the case, then what of CC Asteroids? It is often speculated that these are “burnt out comets”. If that were true, as well as shifting gravity gradients causing deep cracking being common among comet nuclei, then we might see these “burnt out comets” retain the passages opened up and expanded before they were “burnt out”. That would allow several things to be done. First, exploration of CC Asteroids could tell us much about whether this is one method of pit and crack formation in cometary nuclei. Second, these passages could be exploited as habitat shelters by asteroid miners accompanying the robots that would do most of the work of asteroid mining, doing things robots cannot quite do yet.

    That would provide ready made shelter from radiation, just as lava tube caves would on larger bodies. There are far more CC Asteroids than the lava tube cave candidates so far seen on the Moon and Mars. They might yet provide shelter for larger human populations than any planets ever will, even before being turned into O’Niel type Space Colonies. Of course, Ceres, given its size and composition may also provide more such living space than all the CC Asteroids from outgassing of its ices during its own perihelion. Still, those asteroids that many disdain as targets for examination could yet be bite-sized settlement locations for any number of different settlement groups.

  • Rosetta and New Horizons are adding to human knowledge of the universe by the minute. Two very cool and (so far) successful missions. I sincerely hope that these aren’t the high-water mark of human exploration, but given the increasing drag of unsustainable societal priorities, I’m not especially sanguine.

  • Edward

    Don’t forget about Dawn, exploring two asteroids/dwarf planets in one economical mission.

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