APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

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APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by APOD Robot » Sun May 05, 2019 4:08 am

Image Saturn, Titan, Rings, and Haze

Explanation: This is not a solar eclipse. Pictured here is a busy vista of moons and rings taken at Saturn. The large circular object in the center of the image is Titan, the largest moon of Saturn and one of the most intriguing objects in the entire Solar System. The dark spot in the center is the main solid part of the moon. The bright surrounding ring is atmospheric haze above Titan, gas that is scattering sunlight to a camera operating onboard the robotic Cassini spacecraft. Cutting horizontally across the image are the rings of Saturn, seen nearly edge on. At the lower right of Titan is Enceladus, a small moon of Saturn. Since the image was taken pointing nearly at the Sun, the surfaces of Titan and Enceladus appear in silhouette, and the rings of Saturn appear similar to a photographic negative. Now if you look really really closely at Enceladus, you can see a hint of icy jets shooting out toward the bottom of the image. It is these jets that inspired future proposals to land on Enceladus, burrow into the ice, and search for signs of extraterrestrial life.

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by Boomer12k » Sun May 05, 2019 8:51 am

And... Annular Eclipse???

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by orin stepanek » Sun May 05, 2019 10:59 am

I believe a third moon in between the the edges of the inner ring! :shock:
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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by Jim Leff » Sun May 05, 2019 11:37 am

Any quick/sloppy guesstimates on the odds that an appreciable quantity of sub-surface water on Enceladus has NOT been through a life-killing cycle of eruption and expulsion?

That strikes me as the key question. I.e. to what degree does Enceladus‘ cryovolcanic activity function as an efficient water sterilization technique?

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by HAL » Sun May 05, 2019 12:06 pm

David Bowman took this!

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by Chris Peterson » Sun May 05, 2019 1:00 pm

Jim Leff wrote:
Sun May 05, 2019 11:37 am
Any quick/sloppy guesstimates on the odds that an appreciable quantity of sub-surface water on Enceladus has NOT been through a life-killing cycle of eruption and expulsion?

That strikes me as the key question. I.e. to what degree does Enceladus‘ cryovolcanic activity function as an efficient water sterilization technique?
Given that the overwhelming majority of the water never gets much above freezing, I'd think there's no mechanism for mass sterilization.
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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by FLPhotoCatcher » Sun May 05, 2019 1:56 pm

Chris Peterson wrote:
Sun May 05, 2019 1:00 pm
Jim Leff wrote:
Sun May 05, 2019 11:37 am
Any quick/sloppy guesstimates on the odds that an appreciable quantity of sub-surface water on Enceladus has NOT been through a life-killing cycle of eruption and expulsion?

That strikes me as the key question. I.e. to what degree does Enceladus‘ cryovolcanic activity function as an efficient water sterilization technique?
Given that the overwhelming majority of the water never gets much above freezing, I'd think there's no mechanism for mass sterilization.
Given that there was no life to begin with (there's a slight possibly there are microbes from Earth), then there was no life to sterilize.

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by Chris Peterson » Sun May 05, 2019 2:00 pm

FLPhotoCatcher wrote:
Sun May 05, 2019 1:56 pm
Chris Peterson wrote:
Sun May 05, 2019 1:00 pm
Jim Leff wrote:
Sun May 05, 2019 11:37 am
Any quick/sloppy guesstimates on the odds that an appreciable quantity of sub-surface water on Enceladus has NOT been through a life-killing cycle of eruption and expulsion?

That strikes me as the key question. I.e. to what degree does Enceladus‘ cryovolcanic activity function as an efficient water sterilization technique?
Given that the overwhelming majority of the water never gets much above freezing, I'd think there's no mechanism for mass sterilization.
Given that there was no life to begin with (there's a slight possibly there are microbes from Earth), then there was no life to sterilize.
While I'd agree that it's unlikely, it's certainly a possibility. And I'd say naturally occurring life is far more likely than any contamination from Earth. It appears that everything necessary to sustain simple life is present; we don't yet know exactly what's required to allow life to develop.
Chris

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by Jim Leff » Sun May 05, 2019 6:46 pm

Alert the media: “FLPhotoCatcher” has definitive answers to scientific mysteries.

FLPhotoCatcher wrote:
Sun May 05, 2019 1:56 pm


Given that there was no life to begin with (there's a slight possibly there are microbes from Earth), then there was no life to sterilize.

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by alter-ego » Mon May 06, 2019 2:46 am

orin stepanek wrote:
Sun May 05, 2019 10:59 am
I believe a third moon in between the the edges of the inner ring! :shock:
Of course, this caught my attention so I looked into it. I don't know what you're looking at but I don't think you're seeing a moon.
Within a few minutes, the timing for this image was 15:40UT, Jun 10,2006. The JPL Solar System Simulator does show Tethys and Mimas well outside the field of view.
 
Other Moons Outside FoV.JPG
 
I then used HORIZONS to look for other moons which the simulator does not include. Sure enough, Pandora is within the FoV but I couldn't find it. It is located, like Titan, on the other side of Saturn's rings. Visibility is impeded for three reasons: It's immersed in the rings' scattered light, and, as viewed from Cassini, Pandora is estimated to be ~4.7mag fainter (~70 times) than Enceladus, and there's no atmosphere to scatter sunlight as Titan does. It's not surprising, looking at Enceladus' brightness, that Pandora is not visible.
 
Titan, Enceladus, Pandora.JPG
 
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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by Bugui » Mon May 06, 2019 7:36 am

Why do we see so big differences in Titan's atmosphere thickness? Is it an optical effect? Or is really like that? Thank you.

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by orin stepanek » Mon May 06, 2019 11:34 am

alter-ego wrote:
Mon May 06, 2019 2:46 am
orin stepanek wrote:
Sun May 05, 2019 10:59 am
I believe a third moon in between the the edges of the inner ring! :shock:
Of course, this caught my attention so I looked into it. I don't know what you're looking at but I don't think you're seeing a moon.
Within a few minutes, the timing for this image was 15:40UT, Jun 10,2006. The JPL Solar System Simulator does show Tethys and Mimas well outside the field of view.
 
Other Moons Outside FoV.JPG
 
I then used HORIZONS to look for other moons which the simulator does not include. Sure enough, Pandora is within the FoV but I couldn't find it. It is located, like Titan, on the other side of Saturn's rings. Visibility is impeded for three reasons: It's immersed in the rings' scattered light, and, as viewed from Cassini, Pandora is estimated to be ~4.7mag fainter (~70 times) than Enceladus, and there's no atmosphere to scatter sunlight as Titan does. It's not surprising, looking at Enceladus' brightness, that Pandora is not visible.
 
Titan, Enceladus, Pandora.JPG 
OK; maybe it's an artifact of the end of the inner ring; but there is a dot of white on Titan"s left on the end of a ring!
Orin

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Twilight of the (Titan) God

Post by neufer » Mon May 06, 2019 1:41 pm

Bugui wrote:
Mon May 06, 2019 7:36 am

Why do we see so big differences in Titan's atmosphere thickness?

Is it an optical effect? Or is really like that? Thank you.
Space stations on our own Moon observe a big difference in the solar illumination of the Earth's atmosphere during a penumbra lunar eclipse due to the asymmetric back-lighting from the Sun: https://apod.nasa.gov/apod/ap140407.html

Atmosphere free moons (such as Enceladus in todays APOD) produce a thin crescent.

A thick hazy moon like Titan can extend that crescent into a broad asymmetric ring.
Bugui wrote:
Mon May 06, 2019 7:36 am

Why do we see so big differences in Titan's atmosphere thickness?
Is it an optical effect? Or is really like that? Thank you.
https://solarsystem.nasa.gov/resources/13189/amazing-hazes/ wrote:

Saturn's atmosphere
Photojournal: PIA08214
Published: July 5, 2006

<<Sunlight streams through the high-altitude haze layer that extends completely around the giant moon, Titan, in this view of the moon taken by the Cassini spacecraft. Some fine structure can be spotted in the ever-shifting hazes in Titan's northern polar reaches to the top.

The distant sky beyond Titan (5,150 kilometers across) is not empty, but instead is filled in the lower half by the barely visible, immense bulk of Saturn 1.3 million kilometers (800,000 miles) beyond. The view is toward the night side of both worlds.

Titan's image is saturated, or over exposed, near the five o'clock position, obscuring the details in the atmosphere.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 2, 2006 at a distance of approximately 2.3 million kilometers (1.4 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 163 degrees. Image scale is 14 kilometers per pixel on Titan.
https://www.nature.com/articles/s41550-017-0114 wrote: Titan brighter at twilight than in daylight
by A. García Muñoz, P. Lavvas & R. A. West

Nature Astronomy volume 1, Article number: 0114 (2017)
Letter | Published: 24 April 2017

Abstract: Investigating the overall brightness of planets (and moons) provides insights into their envelopes and energy budgets 1,​2,​3,​4 . Phase curves (a representation of the overall brightness versus the Sun–object–observer phase angle) for Titan have been published over a limited range of phase angles and spectral passbands. Such information has been key to the study of the stratification, microphysics and aggregate nature of Titan’s atmospheric haze and has complemented the spatially resolved observations showing that the haze scatters efficiently in the forward direction. Here, we present Cassini Imaging Science Subsystem whole-disk brightness measurements of Titan from ultraviolet to near-infrared wavelengths. The observations show that Titan’s twilight (loosely defined as the view at phase angles ≳150°) outshines its daylight at various wavelengths. From the match between measurements and models, we show that at even larger phase angles, the back-illuminated moon will appear much brighter than when fully illuminated. This behaviour is unique in our Solar System to Titan and is caused by its extended atmosphere and the efficient forward scattering of sunlight by its atmospheric haze. We infer a solar energy deposition rate (for a solar constant of 14.9 W m−2) of (2.84 ± 0.11) × 1014 W, consistent to within one to two standard deviations with Titan’s time-varying thermal emission from 2007 to 2013. We propose that a forward scattering signature may also occur at large phase angles in the brightness of exoplanets with extended hazy atmospheres and that this signature has a valuable diagnostic potential for atmospheric characterization.
Art Neuendorffer

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Re: APOD: Saturn, Titan, Rings, and Haze (2019 May 05)

Post by MarkBour » Mon May 06, 2019 10:15 pm

The Cassini team gave us some of the most beautiful and amazing photographs.
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