Re: APOD: Juno Approaching Jupiter (2016 Jul 01)
Posted: Wed Jul 06, 2016 3:15 am
Perhaps we'll be fortunate enough for Juno to have a ringside seat for the next Jovian Impactor
APOD and General Astronomy Discussion Forum
https://asterisk.apod.com/
Given its mission length, it will not be the next impactor (unless something goes terribly wrong!) And given its mass, it will never be a significant impactor.Nitpicker wrote:Juno itself, might be the next significant Jovian impactor.
Chris Peterson wrote:Given its mission length, it will not be the next impactor (unless something goes terribly wrong!) And given its mass, it will never be a significant impactor.Nitpicker wrote:
Juno itself, might be the next significant Jovian impactor.
https://en.wikipedia.org/wiki/If_a_tree_falls_in_a_forest wrote: <<"If a tree falls in a forest and no one is around to hear it, does it make a sound?"
Philosopher George Berkeley, in his work, A Treatise Concerning the Principles of Human Knowledge (1710), proposes, "But, say you, surely there is nothing easier than for me to imagine trees, for instance, in a park [...] and nobody by to perceive them. [...] The objects of sense exist only when they are perceived; the trees therefore are in the garden [...] no longer than while there is somebody by to perceive them."
Some years later, a similar question is posed. It is unknown whether the source of this question is Berkeley or not. In June 1883 in the magazine The Chautauquan, the question was put, "If a tree were to fall on an island where there were no human beings would there be any sound?" They then went on to answer the query with, "No. Sound is the sensation excited in the ear when the air or other medium is set in motion." This seems to imply that the question is posed not from a philosophical viewpoint, but from a purely scientific one. The magazine Scientific American corroborated the technical aspect of this question, while leaving out the philosophic side, a year later when they asked the question slightly reworded, "If a tree were to fall on an uninhabited island, would there be any sound?" And gave a more technical answer, "Sound is vibration, transmitted to our senses through the mechanism of the ear, and recognized as sound only at our nerve centers. The falling of the tree or any other disturbance will produce vibration of the air. If there be no ears to hear, there will be no sound."
Albert Einstein is reported to have asked his fellow physicist and friend Niels Bohr, one of the founding fathers of quantum mechanics, whether he realistically believed that 'the moon does not exist if nobody is looking at it.' To this Bohr replied that however hard he (Einstein) may try, he would not be able to prove that it does, thus giving the entire riddle the status of a kind of an infallible conjecture—one that cannot be either proved or disproved.>>
Okay. I'll take "significant" as at least energetic enough to be seen from Earth by sub-meter class telescopes. That means asteroidal bodies on the order of 10 meters or larger. Probably, there are several dozen such impact each year on Jupiter.neufer wrote:Chris Peterson wrote:Given its mission length, it will not be the next impactor (unless something goes terribly wrong!) And given its mass, it will never be a significant impactor.
- That sort of depends upon one's definition of "significant."
Wow. You managed to simultaneously insult Jupiter and compliment Trump!Ann wrote:What!! Who'da thunk that Donald Trump looked so much like Jupiter, or is it the other way round?
Well, Trump doesn't look like Jupiter in real life, but in that cartoon, with his one Great Not-Exactly-Red Eye, he was a semi-dead ringer for it.Chris Peterson wrote:Wow. You managed to simultaneously insult Jupiter and compliment Trump!Ann wrote:What!! Who'da thunk that Donald Trump looked so much like Jupiter, or is it the other way round?
I would class Juno as a significant impactor, on the basis that it is made and controlled by humans. For other, natural impactors, I was thinking they'd need to be much larger, and hence rarer, for me to deem them significant (i.e. the kind that I might be able to observe with my 6 inch telescope in the backyard, or that I might read about in the daily news). So yes, my statement depends entirely on the definition of "significant". But given it was my statement, I should also be allowed to define the terms of reference.Chris Peterson wrote:Okay. I'll take "significant" as at least energetic enough to be seen from Earth by sub-meter class telescopes. That means asteroidal bodies on the order of 10 meters or larger. Probably, there are several dozen such impact each year on Jupiter.neufer wrote:Chris Peterson wrote:Given its mission length, it will not be the next impactor (unless something goes terribly wrong!) And given its mass, it will never be a significant impactor.
- That sort of depends upon one's definition of "significant."
No argument. With natural Jupiter impactors having been in the news the last couple of years (and, of course, SL9 a couple of decades back), that's where my mind went.Nitpicker wrote:I would class Juno as a significant impactor, on the basis that it is made and controlled by humans. For other, natural impactors, I was thinking they'd need to be much larger, and hence rarer, for me to deem them significant (i.e. the kind that I might be able to observe with my 6 inch telescope in the backyard, or that I might read about in the daily news). So yes, my statement depends entirely on the definition of "significant". But given it was my statement, I should also be allowed to define the terms of reference. :PChris Peterson wrote:Okay. I'll take "significant" as at least energetic enough to be seen from Earth by sub-meter class telescopes. That means asteroidal bodies on the order of 10 meters or larger. Probably, there are several dozen such impact each year on Jupiter.neufer wrote:
- That sort of depends upon one's definition of "significant."
Like the proverbial tree, a "significant" event is simply one of which humans are aware.Chris Peterson wrote:
That said, unless you restrict your definition of "significant" to man-made objects, however, Juno is very unlikely to be the next significant impactor. Or so we hope!
Thanks for the interesting data on these two moons. It appears that these little guys are not tidally locked. For the scenario I imagined to arise, one would have to have a large enough moon that people lived on one side of it and had never travelled to the planet-facing side until their society's mobility increased.neufer wrote:However, for a good view of Saturn's rings one really needs to be on a high inclination satellite like Siarnaq or Albiorix.
geckzilla wrote:Heh, yeah, that would probably be rather advantageous.neufer wrote:
Of course, Titanians would probably have evolved near-infrared eyes.
http://www.universetoday.com/129759/life-titan-possible-without-water/ wrote:
<<According to the Cornell research team – which is led by Dr. Martin Rahm – Titan presents an opportunity to see how life could emerge... which are much colder than Earth and don’t involve water. Previous experiments have shown that hydrogen cyanide (HCN) molecules can link together to form polyimine, a polymer that can serve as a precursor to amino acids and nucleic acids. Previous surveys have also shown that hydrogen cyanide is the most abundant hydrogen-containing molecule in Titan’s atmosphere.
Using quantum mechanical calculations, the Cornell team showed that polyimine has electronic and structural properties that could facilitate prebiotic chemistry under very cold conditions. These involve the ability to absorb a wide spectrum of light, which is predicted to occur in a window of relative transparency in Titan’s atmosphere.
“Polyimine can form sheets,” said Lunine, “which like clays might serve as a catalytic surface for prebiotic reactions. We also find the polyimine absorbs sunlight where Titan’s atmosphere is quite transparent, which might help to energize reactions.”>>
I doubt that a Titanian "Galileo" would have any more to say about the rings than, perhaps:MarkBour wrote:
You bring up an interesting point that if they grew up on either Titan or Dione, then when they finally walked around, they'd not get a good view of the rings. But as you immediately pointed out as well, they would have the ring shadows for additional contemplation. I am finding this an equally fascinating question, actually, of how it would impact such a people to first view Saturn from a position that was precisely in the ring plane! They'd see a strange, thin, perfectly straight line bisecting the grand orb and extending beyond it. What religious debates would it induce? How much time would go by before some genius like Galileo explained that the shadows were shadows of the line? I think even people as sophisticated as our modern-day scientists would have had a hard time sorting that out and believing it, let alone humans from the year 1500.
https://en.wikipedia.org/wiki/Rings_of_Saturn wrote:<<Galileo Galilei was the first to observe the rings of Saturn in 1610 using his telescope, but was unable to identify them as such. He wrote to the Duke of Tuscany that "[t]he planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the zodiac, and the middle one (Saturn itself) is about three times the size of the lateral ones [the edges of the rings]." He also described Saturn as having "ears". In 1612, the plane of the rings was oriented directly at the Earth and the rings appeared to vanish. Mystified, Galileo wondered, "has Saturn swallowed his children?", referencing the myth of Saturn's consumption of his children to prevent them from overthrowing him. They then reappeared in 1613, further confusing Galileo. Early astronomers used anagrams as a form of commitment scheme to lay claim to new discoveries before their results were ready for publication. Galileo used smaismrmilmepoetaleumibunenugttauiras for Altissimum planetam tergeminum observavi ("I have observed the most distant planet to have a triple form") for discovering the rings of Saturn.
In 1655, Christiaan Huygens became the first person to suggest that Saturn was surrounded by a ring. Using a 50 power refracting telescope that he designed himself, far superior to those available to Galileo, Huygens observed Saturn and wrote that "It [Saturn] is surrounded by a thin, flat, ring, nowhere touching, inclined to the ecliptic". Robert Hooke was another early observer of the rings of Saturn, and noted the casting of shadows on the rings.>>
I certainly hope it is not.Chris Peterson wrote:Given its mission length, it will not be the next impactor (unless something goes terribly wrong!) And given its mass, it will never be a significant impactor.Nitpicker wrote:Juno itself, might be the next significant Jovian impactor.
This raises the concern of the contamination of Jupiter itself. I hope the entry does indeed sterilize everything, but just hearing of the plan leaves me with doubts about that.From Wikipedia https://en.wikipedia.org/wiki/Juno_(spacecraft) the probe will be de-orbited to burn up in Jupiter's outer atmosphere, so as to avoid any possibility of impact and biological contamination of one of its moons.
neufer wrote:Universe Today wrote:
Life On Titan Possible Without Water
Part of the problem with any civilization developing on a moon is the probability of tidal locking and the effect of 100-200+ hour long days and nightsMarkBour wrote:Thanks for the interesting data on these two moons. It appears that these little guys are not tidally locked. For the scenario I imagined to arise, one would have to have a large enough moon that people lived on one side of it and had never travelled to the planet-facing side until their society's mobility increased.neufer wrote:However, for a good view of Saturn's rings one really needs to be on a high inclination satellite like Siarnaq or Albiorix.
You bring up an interesting point that if they grew up on either Titan or Dione, then when they finally walked around, they'd not get a good view of the rings. But as you immediately pointed out as well, they would have the ring shadows for additional contemplation. I am finding this an equally fascinating question, actually, of how it would impact such a people to first view Saturn from a position that was precisely in the ring plane! They'd see a strange, thin, perfectly straight line bisecting the grand orb and extending beyond it. What religious debates would it induce? How much time would go by before some genius like Galileo explained that the shadows were shadows of the line? I think even people as sophisticated as our modern-day scientists would have had a hard time sorting that out and believing it, let alone humans from the year 1500.
I see a recent Cassini APOD that makes your point perfectly: http://apod.nasa.gov/apod/ap150824.html.
I guess I'm leaving out the other evidence that could have come their way by this point, if such a civilization developed similarly to ours. In the case of a moon of Jupiter or Saturn, if they had astronomers by that point, they would have been able to observe motions of many sister moons, and to wonder about them. Possibly they would even have put a fair number of their more intelligent folk to death by this point.
I think you're anthropomorphizing. Do not discount the power of evolution to mold life into its environment, even if that environment seems extreme to us.BMAONE23 wrote:Part of the problem with any civilization developing on a moon is the probability of tidal locking and the effect of 100-200+ hour long days and nights
Ganymede's night lasts 86 hours.
Callisto's night lasts 204 hours
Europa's night lasts 42 hours
and Titan's night lasts 192 hours.
Too long in dark and too cold at their respective mean solar distances for surface dewllwers