Rosetta data reveals how a comet evaporates
Newly released Rosetta data has shown, for at least one area on the surface of Comet 67P/C-G, the process by which the surface ice is replaced by water ice from below as the comet rotates and sunlight causes the surface ice to evaporate away.
The data suggest that water ice on and a few centimetres below the surface ‘sublimates’ when illuminated by sunlight, turning it into gas that then flows away from the comet. Then, as the comet rotates and the same region falls into darkness, the surface rapidly cools again. However, the underlying layers remain warm owing to the sunlight they received in the previous hours, and, as a result, subsurface water ice keeps sublimating and finding its way to the surface through the comet’s porous interior.
But as soon as this ‘underground’ water vapour reaches the cold surface, it freezes again, blanketing that patch of comet surface with a thin layer of fresh ice. Eventually, as the Sun rises again over this part of the surface on the next comet day, the molecules in the newly formed ice layer are the first to sublimate and flow away from the comet, restarting the cycle.
They discovered this process when they noticed surface ice evaporating in this region during the comet’s 6-hour day and then getting resurfaced with ice during the comet’s 6-hour night.
Meanwhile, Rosetta is about to move as much as 1500 kilometers away from the comet for several weeks so that its scientists can study its coma more broadly.
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Newly released Rosetta data has shown, for at least one area on the surface of Comet 67P/C-G, the process by which the surface ice is replaced by water ice from below as the comet rotates and sunlight causes the surface ice to evaporate away.
The data suggest that water ice on and a few centimetres below the surface ‘sublimates’ when illuminated by sunlight, turning it into gas that then flows away from the comet. Then, as the comet rotates and the same region falls into darkness, the surface rapidly cools again. However, the underlying layers remain warm owing to the sunlight they received in the previous hours, and, as a result, subsurface water ice keeps sublimating and finding its way to the surface through the comet’s porous interior.
But as soon as this ‘underground’ water vapour reaches the cold surface, it freezes again, blanketing that patch of comet surface with a thin layer of fresh ice. Eventually, as the Sun rises again over this part of the surface on the next comet day, the molecules in the newly formed ice layer are the first to sublimate and flow away from the comet, restarting the cycle.
They discovered this process when they noticed surface ice evaporating in this region during the comet’s 6-hour day and then getting resurfaced with ice during the comet’s 6-hour night.
Meanwhile, Rosetta is about to move as much as 1500 kilometers away from the comet for several weeks so that its scientists can study its coma more broadly.
Readers!
Please consider supporting my work here at Behind the Black. Your support allows me the freedom and ability to analyze objectively the ongoing renaissance in space, as well as the cultural changes -- for good or ill -- that are happening across America. Fourteen years ago I wrote that SLS and Orion were a bad ideas, a waste of money, would be years behind schedule, and better replaced by commercial private enterprise. Only now does it appear that Washington might finally recognize this reality.
In 2020 when the world panicked over COVID I wrote that the panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Only in the past year have some of our so-called experts in the health field have begun to recognize these facts.
Your help allows me to do this kind of intelligent analysis. I take no advertising or sponsors, so my reporting isn't influenced by donations by established space or drug companies. Instead, I rely entirely on donations and subscriptions from my readers, which gives me the freedom to write what I think, unencumbered by outside influences.
You can support me either by giving a one-time contribution or a regular subscription. There are four ways of doing so:
1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.
2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
3. A Paypal Donation or subscription:
4. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652
You can also support me by buying one of my books, as noted in the boxes interspersed throughout the webpage or shown in the menu above.
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