APOD: Gibbous Europa (2013 Dec 15)

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APOD: Gibbous Europa (2013 Dec 15)

Postby APOD Robot » Sun Dec 15, 2013 5:10 am

Image Gibbous Europa

Explanation: Although the phase of this moon might appear familiar, the moon itself might not. In fact, this gibbous phase shows part of Jupiter's moon Europa. The robot spacecraft Galileo captured this image mosaic during its mission orbiting Jupiter from 1995 - 2003. Visible are plains of bright ice, cracks that run to the horizon, and dark patches that likely contain both ice and dirt. Raised terrain is particularly apparent near the terminator, where it casts shadows. Europa is nearly the same size as Earth's Moon, but much smoother, showing few highlands or large impact craters. Evidence and images from the Galileo spacecraft, indicated that liquid oceans might exist below the icy surface. To test speculation that these seas hold life, ESA has started preliminary development of the Jupiter Icy Moons Explorer (JUICE), a spacecraft proposed for launch around 2022 that would further explore Jupiter and in particular Europa. Recent observations by the Hubble Space Telescope have uncovered new evidence that Europa, like Saturn's moon Enceladus, has ice venting from its surface.

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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Ann » Sun Dec 15, 2013 5:43 am

Europa just becomes more and more interesting. I hope we can find a way to explore it.

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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby A_Z » Sun Dec 15, 2013 6:37 am

Today's APOD reminded me of one thing I have been wondering, posting it here thinking I'll get an answer by someone -

I've noticed, many images of some objects are from when some spacecraft flew by that object years (sometimes 2,5,10,15) back. Why we don't see latest and greatest images of those same objects using Hubble ? e.g., today's Europa's image is from years back, why we don't have better (in resolution, clarity, details) image of it by Hubble taken most recently (in last 1 year or so) ? We just heard yesterday that Hubble found water geysers on Europa, so, it's not as if Hubble is busy looking at something else ..

In some cases, if we are comparing the images (back then v/s now) or for some specific reason Hubble won't be able to get the image from specific angle etc, then it's fine, we can understand. But in other cases, it should be doable. No ? Am I missing something ?

Thanks in advance for educating me.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Baci » Sun Dec 15, 2013 7:10 am

Are there any thoughts in relation to the square structure below centre in the middle of the picture?
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Ann » Sun Dec 15, 2013 9:28 am

A_Z wrote:Today's APOD reminded me of one thing I have been wondering, posting it here thinking I'll get an answer by someone -

I've noticed, many images of some objects are from when some spacecraft flew by that object years (sometimes 2,5,10,15) back. Why we don't see latest and greatest images of those same objects using Hubble ? e.g., today's Europa's image is from years back, why we don't have better (in resolution, clarity, details) image of it by Hubble taken most recently (in last 1 year or so) ? We just heard yesterday that Hubble found water geysers on Europa, so, it's not as if Hubble is busy looking at something else ..

In some cases, if we are comparing the images (back then v/s now) or for some specific reason Hubble won't be able to get the image from specific angle etc, then it's fine, we can understand. But in other cases, it should be doable. No ? Am I missing something ?

Thanks in advance for educating me.


I'm not necessarily the person who should answer you here, but there are two things, at least, that I can tell you. First, Sundays are repeat days on APOD, so you should not be surprised if you see an old picture on a Sunday.

But second, I'm not too sure that there are any better pictures of Europa than this one. Hubble isn't able to take better pictures of Europa than an orbiting probe like Galileo. Indeed, Hubble isn't able to take better pictures of a target than a spacecraft that is orbiting this particular target, or at least that is what I think.

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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Nitpicker » Sun Dec 15, 2013 10:17 am

A_Z wrote:Today's APOD reminded me of one thing I have been wondering, posting it here thinking I'll get an answer by someone -

I've noticed, many images of some objects are from when some spacecraft flew by that object years (sometimes 2,5,10,15) back. Why we don't see latest and greatest images of those same objects using Hubble ? e.g., today's Europa's image is from years back, why we don't have better (in resolution, clarity, details) image of it by Hubble taken most recently (in last 1 year or so) ? We just heard yesterday that Hubble found water geysers on Europa, so, it's not as if Hubble is busy looking at something else ..

In some cases, if we are comparing the images (back then v/s now) or for some specific reason Hubble won't be able to get the image from specific angle etc, then it's fine, we can understand. But in other cases, it should be doable. No ? Am I missing something ?

Thanks in advance for educating me.


I understand that the theoretical resolution of a 2.5m telescope -- similar to the HST -- is about 0.05 arcsec. The maximum apparent diameter of Europa from Earth is about 1.0 arcsec, meaning that the best image possible of Europa from the HST would likely be no finer than maybe 200 pixels across, probably less. The pixel scale of today's APOD is much finer than anything the HST could capture of Europa, not so much because of the quality of the camera on Galileo, but because of Europa's much larger apparent diameter to Galileo at the time the image was taken.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby rstevenson » Sun Dec 15, 2013 12:43 pm

Baci wrote:Are there any thoughts in relation to the square structure below centre in the middle of the picture?

Pareidolia. Either that or it's a parking lot. Given the scale of the picture, I can't quite tell.

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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby dasher251 » Sun Dec 15, 2013 1:02 pm

Europa is a gorgeous planet. I noticed a faint line like a gorge that extended right across planets surface (right to left ,It's easy to notice if you imagine drawing a line around the top half of an egg Was wondering if any one else noticed it ?
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Europagazer » Sun Dec 15, 2013 1:08 pm

dasher251 wrote:Europa is a gorgeous planet. I noticed a faint line like a gorge that extended right across planets surface (right to left ,It's easy to notice if you imagine drawing a line around the top half of an egg Was wondering if any one else noticed it ?


Thank you, thank you, very much indeed. Europa looks just like the back of my head when I step out of the shower, so I appreciate the compliment. 8-)
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Chris Peterson » Sun Dec 15, 2013 2:21 pm

Ann wrote:Europa just becomes more and more interesting. I hope we can find a way to explore it.

That's a proposal with interesting scientific and ethical considerations. Europa is such a strong candidate for life- possibly the strongest in the Solar System- that we need to be extra careful not to contaminate it with our probes. But it's unclear how to avoid that. Despite our best efforts, evidence suggests every probe we've launched has carried Earth microbes (including Martian probes that we actually tried to sterilize). Apparently, ensuring an entire lander is germ-free is a very difficult task- something that would need to be figured out, I think, before we land on Europa.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby BDanielMayfield » Sun Dec 15, 2013 2:44 pm

APOD Robot wrote:[/ Explanation: Evidence and images from the Galileo spacecraft, indicated that liquid oceans might exist below the icy surface.


Is there still uncertainty about the current presence of a liquid ocean under the icy crust of Europa? Wouldn’t at least some of its interior have to be liquid due to continuous heating from tidal forces?

Sky and Telescope’s site reported on Friday a finding of geyser or plume activity on Europa. If liquids at times find there way to the surface then there must be liquids inside this moon, at least locally if not globally.

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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby geckzilla » Sun Dec 15, 2013 2:51 pm

A_Z wrote:Why we don't see latest and greatest images of those same objects using Hubble ?


Latest and greatest images of Europa's plumes are available in this thread: viewtopic.php?f=8&t=32580
Also check out the paper which was linked to because there are more images in there.

Those are pretty low resolution images but even if Hubble switches over to its highest resolution camera, the images are not even close to being as detailed as images taken from a nearby probe's camera. Here is an example of the best Hubble can do. It's a picture of Ganymede (Europa is comparable but slightly smaller) about to disappear behind the limb of Jupiter. I grabbed this data straight from the archive. It was taken using Hubble's ACS/HRC (Advanced Camera for Surveys / High Resolution Channel) which displays Ganymede at just under 60 pixels wide. That's great, but it's not necessarily very impressive to a lay person who is used to giant close-ups, either. Oh, and the black bar on the left is the occulting finger.

HST_10192_02_ACS_HRC_F435W_02_sci.jpg


Edit: I should have also mentioned that the HRC is currently disabled.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby BDanielMayfield » Sun Dec 15, 2013 2:57 pm

Chris Peterson wrote:
Ann wrote:Europa just becomes more and more interesting. I hope we can find a way to explore it.

That's a proposal with interesting scientific and ethical considerations. Europa is such a strong candidate for life- possibly the strongest in the Solar System- that we need to be extra careful not to contaminate it with our probes. But it's unclear how to avoid that. Despite our best efforts, evidence suggests every probe we've launched has carried Earth microbes (including Martian probes that we actually tried to sterilize). Apparently, ensuring an entire lander is germ-free is a very difficult task- something that would need to be figured out, I think, before we land on Europa.


It could very well be possible to get material from beneath Europa's crust without even needing to land :!:

The plumes reportedly reached altitudes of 125 miles above the moon's surface, so an orbiter in a polar orbit could collect material ejected from the interior.

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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Chris Peterson » Sun Dec 15, 2013 2:58 pm

BDanielMayfield wrote:Is there still uncertainty about the current presence of a liquid ocean under the icy crust of Europa? Wouldn’t at least some of its interior have to be liquid due to continuous heating from tidal forces?

Europa isn't a water planet- it's made of rock with a differentiated iron core. The water is just a film on the surface- perhaps 100 km thick. How much of that is ice and how much is liquid (if any) isn't known. Yes, there's good reason to believe that tidal heating, radioactive decay, and other internal heat sources might be sufficient to create a liquid water ocean under the ice. But it's not certain, and much depends on assumptions about the internal structure of the Moon that haven't been well tested.

Sky and Telescope’s site reported on Friday a finding of geyser or plume activity on Europa. If liquids at times find there way to the surface then there must be liquids inside this moon, at least locally if not globally.

That distinction between local and global is critical, though, isn't it?
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby BDanielMayfield » Sun Dec 15, 2013 3:20 pm

Chris Peterson wrote:
BDanielMayfield wrote:Is there still uncertainty about the current presence of a liquid ocean under the icy crust of Europa? Wouldn’t at least some of its interior have to be liquid due to continuous heating from tidal forces?

Europa isn't a water planet- it's made of rock with a differentiated iron core. The water is just a film on the surface- perhaps 100 km thick. How much of that is ice and how much is liquid (if any) isn't known. Yes, there's good reason to believe that tidal heating, radioactive decay, and other internal heat sources might be sufficient to create a liquid water ocean under the ice. But it's not certain, and much depends on assumptions about the internal structure of the Moon that haven't been well tested.

Thanks. I didn't realize the water or ice layer was so thin. I have to repete what Ann said then, 'Europa keeps getting more and more interesting.'

If liquids at times find there way to the surface then there must be liquids inside this moon, at least locally if not globally.

That distinction between local and global is critical, though, isn't it?


Yes. But all the fractured terrane on the surface shows that at least in the past chunks of crust were rearranged enormously, like ice flows on the Artic Ocean. So to me it looks like a global ocean must have existed on Europa at some point.

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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby stephen63 » Sun Dec 15, 2013 3:58 pm

BDanielMayfield wrote:Thanks. I didn't realize the water or ice layer was so thin. I have to repete what Ann said then, 'Europa keeps getting more and more interesting.'

Yes. But all the fractured terrane on the surface shows that at least in the past chunks of crust were rearranged enormously, like ice flows on the Artic Ocean. So to me it looks like a global ocean must have existed on Europa at some point.

Bruce

From what I can tell, it's believed that the liquid ocean on Europa is 100km deep, which would probably make it global. If there were life there, then it would necessarily be expelled through a geyser, wouldn't it? It would be a lot easier to look there than going through all that ice.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby BDanielMayfield » Sun Dec 15, 2013 4:03 pm

Art has some interesting info on this here: http://asterisk.apod.com/viewtopic.php?f=8&t=32580
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Chris Peterson » Sun Dec 15, 2013 4:10 pm

stephen63 wrote:From what I can tell, it's believed that the liquid ocean on Europa is 100km deep, which would probably make it global. If there were life there, then it would necessarily be expelled through a geyser, wouldn't it? It would be a lot easier to look there than going through all that ice.

Very likely. But the important point is that while there is good reason to believe there is a liquid ocean beneath the ice, it remains far from certain. The possibility that the ice extends to the underlying rock remains.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby BDanielMayfield » Sun Dec 15, 2013 4:25 pm

stephen63 wrote:If there were life there, then it would necessarily be expelled through a geyser, wouldn't it?

Microscopic, single celled “life as we know it” should be. But even if whole cells aren’t ejected then chemical byproducts of life would almost certainly be. And they’d be fresh, rapidly freeze dried samples too. :)
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby stephen63 » Sun Dec 15, 2013 4:31 pm

Chris Peterson wrote:
stephen63 wrote:From what I can tell, it's believed that the liquid ocean on Europa is 100km deep, which would probably make it global. If there were life there, then it would necessarily be expelled through a geyser, wouldn't it? It would be a lot easier to look there than going through all that ice.

Very likely. But the important point is that while there is good reason to believe there is a liquid ocean beneath the ice, it remains far from certain. The possibility that the ice extends to the underlying rock remains.

True, but the best explanation for the lineae being global would be water, or at least warm ice filling the cracks of surface ice that has shifted.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby geckzilla » Sun Dec 15, 2013 4:37 pm

Or, perhaps, the most wishful explanation...
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby Chris Peterson » Sun Dec 15, 2013 5:01 pm

stephen63 wrote:
Chris Peterson wrote:
stephen63 wrote:From what I can tell, it's believed that the liquid ocean on Europa is 100km deep, which would probably make it global. If there were life there, then it would necessarily be expelled through a geyser, wouldn't it? It would be a lot easier to look there than going through all that ice.

Very likely. But the important point is that while there is good reason to believe there is a liquid ocean beneath the ice, it remains far from certain. The possibility that the ice extends to the underlying rock remains.

True, but the best explanation for the lineae being global would be water, or at least warm ice filling the cracks of surface ice that has shifted.

I don't know if I'd go so far as to say that's the best explanation, just that it's a good one.

Don't think I'm arguing against a subsurface sea on Europa. In fact, I think the best evidence supports that conclusion. I'm simply pointing out that there remains a good deal of uncertainty in the matter, and as good skeptics we shouldn't get too enamored of our beliefs.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby BDanielMayfield » Sun Dec 15, 2013 5:11 pm

geckzilla wrote:Or, perhaps, the most wishful explanation...

Percivel Lowell would be proud.
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby stephen63 » Sun Dec 15, 2013 5:18 pm

Chris Peterson wrote:I don't know if I'd go so far as to say that's the best explanation, just that it's a good one.

Don't think I'm arguing against a subsurface sea on Europa. In fact, I think the best evidence supports that conclusion. I'm simply pointing out that there remains a good deal of uncertainty in the matter, and as good skeptics we shouldn't get too enamored of our beliefs.

I usually read a few abstracts before I become too enamored!
http://adsabs.harvard.edu/abs/2001AGUFM.U12B..06P
http://adsabs.harvard.edu/abs/2007AGUFM.P51E..03K
However, as is often the case, I usually come away with more questions than answers!
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Re: APOD: Gibbous Europa (2013 Dec 15)

Postby eltodesukane » Sun Dec 15, 2013 8:16 pm

Ann wrote:Europa just becomes more and more interesting. I hope we can find a way to explore it.

Ann


JUICE is planning to go there, but not before 2031, (JUICE = JUpiter ICy moons Explorer)

JUICE is the first large-class mission in ESA's Cosmic Vision 2015-2025 programme. Planned for launch in 2022 and arrival at Jupiter in 2030, it will spend at least three years making detailed observations of the giant gaseous planet Jupiter and three of its largest moons, Ganymede, Callisto and Europa.

http://sci.esa.int/juice/
http://www.lpi.usra.edu/opag/mar2012/pr ... ummary.pdf
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