Astronomy Picture of the Day -- Perihelion Approaches

NASA ^ | August 15, 2015 | (see photo credit)

[SunkenCiv]

Explanation: This dramatic outburst from the nucleus of Comet 67P/Churyumov-Gerasimenko occured on August 12, just hours before perihelion, its closest approach to the Sun. Completing an orbit of the Sun once every 6.45 years, perihelion distance for this periodic comet is about 1.3 astronomical units (AU), still outside the orbit of planet Earth (at 1 AU). The stark image of the 4 kilometer wide, double-lobed nucleus in bright sunlight and dark shadows was taken by the Rosetta spacecraft's science camera about 325 kilometers away. Too close to see the comet's growing tail, Rosetta maintains its ringside seat to watch the nucleus warm and become more active in coming weeks, as primordial ices sublimating from the surface produce jets of gas and dust. Of course, dust from the nucleus of periodic comet Swift-Tuttle, whose last perihelion passage was in 1992 at a distance of 0.96 AU, fell to Earth just this week.

[SunkenCiv]

[Credit: ESA / Rosetta / MPS for OSIRIS Team; MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA]

[SunkenCiv]

The Big One

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[left that other site]

That is an awesome picture.

Not as “cosmic” as some of the galactic ones, but, in some ways, more interesting! :-)

[BenLurkin]

This is very cool. Rosetta is a huge success!

[Swordmaker]

. . .become more active in coming weeks, as primordial ices sublimating from the surface produce jets of gas and dust.

What ice? Where's the water? They are still stuck on their "Dirty Snowball" canard even though after TEN visits and flybys of comets, all of which have turned out to be bone dry ROCKS, with little to no water, you'd think they might be starting to get a clue they are NOT "dirty snowballs".

Here is the list of the chemicals outgassing from 67P/Churyumov-Gerasimenko and water composes only 3.3% of the total materials, if that:

H₂O is only about 1 part in about 37.5 parts of the total outgassing from comet 67P/Churyumov-Gerasimenko

• —10.5% CH₄: Methane
• —10.1% NH₃: Ammonia
• — 3.3% H₂O: Water
• — 8.0% HH₂: Acetylene
• — 8.6% HCN: Hydrogen Cyanide
• — 6.6% CO: Carbon Monoxide
• — 6.8% C₂H₆: Ethane
• — 6.7% CH₃OH: Methanol
• —18.6% H₂S: Hydrogen Sulfide
• — 6.8% CO₂: Carbon Dioxide
• — 4.3% OCS: Carbonyl Sulfide
• — 3.3% SO₂: Sulfur Dioxide
• — 6.4% CS₂: Carbon Disulfide
  —100% Total Coma components

[Swordmaker]

In addition, if it were sublimating from the surface, it would not form "jets" which would require some kind of naturally forming nozzle to eject the gasses from the interior—which would require the entire mass of the comet to heat enough to first melt then convert the chemicals to their gassy states INSIDE the not inconsiderable mass of the comet, sometimes at a distance where the sunlight falling on the comet is insufficient to do such a thing, especially on a tumbling, rotating body, which will be rapidly turning, sometimes turning one side to the sun, other times turning the just warmed side to radiate the heat gained to space. Often the outgassing occurs on the DARK side of the comets.

If the theory of sublimation were true, the gasses would form on the surface and evanesce equally from everywhere on the surface exposed to the heating of the sun. . . shrinking the comet from the outside in, forming very obvious sublimation formations as seen in ice caves without air movement which have never risen above zero Fº. . .

And which we've never seen on any comet surface. . . instead we see surfaces indistinguishable from every asteroid we've seen. Rocky cratered surfaces.

Of course ice is a very good reflector and an excellent reflector of heat in particular.

[BenLurkin]

Sequence of OSIRIS narrow-angle camera images from 12 August 2015, just a few hours before the comet reached perihelion. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA