Comet Lovejoy Plunges Into the Sun and Survives

boldie writes with a link to NASA's account of comet Lovejoy's close encounter with the sun. Excerpting: "This morning, an armada of spacecraft witnessed something that many experts thought impossible. Comet Lovejoy flew through the hot atmosphere of the sun and emerged intact. ... The comet's close encounter was recorded by at least five spacecraft: NASA's Solar Dynamics Observatory and twin STEREO probes, Europe's Proba2 microsatellite, and the ESA/NASA Solar and Heliospheric Observatory. The most dramatic footage so far comes from SDO, which saw the comet go in (movie) and then come back out again (movie)." Here are larger QuickTime versions of the comet's entrance (22MB) and exit (26MB).

Comments

You can all thank Dr. Reyga...

[Anonymous Coward]

for a successful demonstration of Metaphasic Shields.

Misleading title

[aneroid]

Sounds a lot more sensational when you compare the title's "comet plunges into sun and survives" event vs the actual "comet flew through hot atmosphere of the sun".

/. worthy event nevertheless.

Re:Misleading title

[MaskedSlacker]

You realize that the sun doesn't actually have a surface, right? It's increasingly dense atmosphere all the way down.

Re:Misleading title

[reverseengineer]

The sun's corona is intensely hot- about 1 million kelvin, much hotter than the photosphere beneath, but the plasma is very diffuse. The photosphere, the layer that appears to us to generate the opaque disk of the sun (and is the closest thing it has to a surface) is a mere 6000K, but it's 10^12 times denser than the corona. In turn, the photosphere is about one ten-thousandth of the density of Earth's atmosphere at sea level. This really skews notions of "temperature" when we talk about a star. On Earth, we're used to objects placed in a medium fairly rapidly equilibrating to the temperature of that medium. We realize that some substances conduct faster or slower than others, but overall putting something in a hot environment makes it hot.

For all but the most finicky of physics experiments, if we had pressure conditions of the density of the sun's corona, it would be "high vacuum." Very little conduction of heat from the plasma to a comet is going to take place. The bombardment by solar photons and the gigantic magnetic and gravitational fields of the sun play a greater role here than the actual material of the sun, and thus NASA can be pleasantly surprised by Comet Lovejoy's survival of its close encounter. But it's the wrong idea to picture this comet plunging into some sort of molten inferno. Of course, the sun's core is another story. 15 times denser than lead and 16 million kelvin. I'll like to see the comet that survives that.

Re:Misleading title

[schroedingers_hat]

This is true to a small extent, but there's a feedback loop where the star gets bigger and cooler if the fusion rate increases. This results in (predominantly) only one element being fused at a time, so you have Hydrogen->Helium (with some slightly heavier elements, C,N, and O can be involved) until the star is almost out of hydrogen, then Helium->Things between LIthium and Oxygen, and after that the star goes boom pretty quickly (or lacks the mass to go any further).
By comparison the amount of fusion of elements heavier than the one it is burning at the time is extremely small.
The majority of all stars (such as our own) are burning Hydrogen.
The majority of all heavy elements come from supernovae (the stars that our sun was made of before it became a star again).
That being said, there is probably a large chunk of iron and other heavy elements (from past supernovae) in the middle of our sun, but we generally ignore it because it is such a small percentage.

Re:Misleading title

[PyroMosh]

The effect we're discussing is easily observable to anyone who's reasonably familiar with a kitchen.

Ever fry french fries in oil? This is typically what? 350F?

Baking a pizza will typically be around 450F.

Yet it's easy to reach into a 450 degree oven and remove the pizza. As long as you use a towel or a tool, your hand can be in the same environment that just cooked the pizza for a relatively long time..

But any fool knows that reaching into the oil with your bare hand *at all* will burn your skin in less than a second. Even though the oil is 100 degrees cooler than the oven.

It's just a dramatic, every-day example of the difference in heat transfer between mediums (in this case, oil vs air).

Re:Misleading title

[Anonymous Coward]

That's quite a bold statement!

Re:Misleading title

[JTW]

A thought experiment worthy.

If you took a ball of Iron the size of say planet Earth, and it were to plunge into the heart of the Sun. What would be the result.. a Nova, SuperNova.. fizzle.

And what if it were slightly off target and merely circled the center for a while.. would it retain its shape or spinout into a smeared ball of plasma.. undoing the star?
Something somewhat like this probably already happened.. the Lithium content of our star for example.. guess it just wasn't significant emough.

Better title:

[circletimessquare]

"The Sun somehow survives close call with badass comet Lovejoy. Meekly vows to be more respectful next time."

Energy Depleted

[Anonymous Coward]

The comet's fuel reserves were low; flew into a star to recharge.

Of course it is possible ....

[Anonymous Coward]

Just as you can plunge your hand in a dewar of liquid nitrogen and not have your hand immediately frozen, a comet will survive for the same reason. With your hand, the liquid nitrogen boils from the heat of your hand creating an insulating layer of air between your hand and the liquid nitrogen. With the comet, the comet evaporates creating an insulating layer of gasses that protect the entire from immediately evaporating.

I've kept my fist in liquid nitrogen for a total of 38 seconds. (Not the smartest thing I've done.) I had a touch of frost bite on the pads of my fingers where liquid nitrogen seeped into my fist and the gasses escape properly and couldn't insulate as needed. The rest of my hand was just fine and I could have probably left it in there longer had I chose with little ill effects -- other than on the pads of my fingers.

Re:we are all doomed!

[Colonel Korn]

It's going to come back and smash into the earth in 2012.

Quite possible as, quoting TFA:

"There is still a possibility that Comet Lovejoy will start to fragment,"

No telling which directions those pieces might fly off.

Absolutely. When a single object slowly fragments due to thermal gradients, it ignores conservation of momentum and sometimes even conservation of mass. It's possible this ~100-500 m radius comet will launch a 50000 m chunk at us with a velocity of over half the speed of light!

Velocity of Comet

[dispersionrelation]

I went ahead and calculated the velocity of the comet at its Perihelion (closest distance to the sun) to be or 618km/s which is the same as 383 mi/s which is the same as 0.2% the speed of light, very fast!

Re:That's not a comet.

[Anonymous Coward]

Uh, the tail WAS blowing away from the sun. Take a look at the coronograph footage for a view that isn't wildly foreshortened:

Re:we are all doomed!

[Anonymous Coward]

It may end the earth as we know it!

Man, everything ends the earth as we know it.

I could go out there and shit in the bushes and BAM, the earth as you knew it where that bush was shit free? GONE.

btw, don't go out to your bushes for another few minutes. Bring toilet paper.