Starship Asterisk*

TheGuybrarian wrote:I was a little disappointed to see the same photo of Europa re-used on the APOD blog. It was previously featured on January 30, 2011.

Q4: Have some APOD pictures been run more than once?
A4: Yes. Many of our readers have been with us less than a year and are unaware of some really spectacular or important astronomy pictures. New information about old pictures is becoming available over the WWW. The text and links for rerun pictures will make use of this newly available information. So although the picture might be old, some of the text and links of each APOD will be new. Also, more web surfers have larger bandwidth connections, which allows us to post higher-resolution image files that can be transferred conveniently. Software to handle more sophisticated image file formats has also become more common, so the picture's size and/or format might be new. Lastly, rerunning APODs saves us time and helps us update our archive. In general, our rerun policy currently is to only rerun APODs more than one year old to keep the pictures relatively "new" to new APOD viewers. We will almost never rerun more than two pictures in any given week. So when you load the current APOD,it is still, most probably, a new picture.

eltodesukane wrote:

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

During the tour, gravity assists with Callisto and Ganymede will shape the trajectory. Two targeted Europa flybys are included focusing on composition of the non water-ice material, and the first subsurface sounding of an icy moon. Additional, Callisto gravity assists will be also used to raise the orbit inclination to almost 30° and to enable observations of the Jupiter polar regions. The frequent Callisto flybys will enable unique remote observations of the moon and in situ measurements in its vicinity. The mission will culminate in a dedicated eight months orbital tour around Ganymede during which the spacecraft will perform detailed investigation of the moon and its environment and will eventually impact on Ganymede.

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

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

Ann

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.

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

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.

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.

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

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.

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

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.

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?

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?

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.

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.

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

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

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

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 ?

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