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Tags astronomy , New Horizons , pluto

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Old 17th July 2015, 06:59 AM   #281
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Re: smooth surface, my money's on some kind of slow erosion caused by Pluto's atmosphere alternately sublimating when it's close(r) to the sun, and freezing out when it moves farther away. Sublimation should favor sunnier peaks and crater rims, deposition should favor shadowy valleys and crater floors, so the one should (very, very gently) shift mass into the other.
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Old 17th July 2015, 07:21 AM   #282
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Originally Posted by Beelzebuddy View Post
Re: smooth surface, my money's on some kind of slow erosion caused by Pluto's atmosphere alternately sublimating when it's close(r) to the sun, and freezing out when it moves farther away. Sublimation should favor sunnier peaks and crater rims, deposition should favor shadowy valleys and crater floors, so the one should (very, very gently) shift mass into the other.
Wouldn't you then expect to see partially sublimated craters?
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Old 17th July 2015, 07:37 AM   #283
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Originally Posted by Skeptic Ginger View Post
Wouldn't you then expect to see partially sublimated craters?
Yes. And, if NH's spectrometer can detect it, there should be crater-shaped patches of different material in the more exposed regions.
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Old 17th July 2015, 07:37 AM   #284
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Originally Posted by Skeptic Ginger View Post
Wouldn't you then expect to see partially sublimated craters?
Yes--plus, it wouldn't be evenly sublimated. It would be significantly rougher.
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Old 17th July 2015, 07:44 AM   #285
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Originally Posted by Dinwar View Post
Yes--plus, it wouldn't be evenly sublimated. It would be significantly rougher.
Rough enough to explain the youthful appearance of the mountain ranges?
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Old 17th July 2015, 08:05 AM   #286
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Originally Posted by Beelzebuddy View Post
Rough enough to explain the youthful appearance of the mountain ranges?
No, just rougher than we see in these images.
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Old 17th July 2015, 08:10 AM   #287
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Originally Posted by Ziggurat View Post
You don't need to crunch any numbers, just look two up and compare. Pluto's escape velocity is 1.2 km/s, and that's at the surface. New Horizon was flying by at a relative velocity of 13.8 km/s. There was never any possibility of gravitational capture.
So? You can do some rather clever multiple planetary slingshot maneuvers, la Messenger, with multiple flybys and gradual deceleration. That probe left Earth orbit at ~11km/s and achieved Mercury orbit.
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Old 17th July 2015, 08:14 AM   #288
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I wasn't aware that sublimation of most ices was possible at the temperatures of Pluto.

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Old 17th July 2015, 09:14 AM   #289
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Originally Posted by rwguinn View Post
I wasn't aware that sublimation of most ices was possible at the temperatures of Pluto.

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I think that the ices that can't sublimate at those temperatures won't be sublimating.

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Old 17th July 2015, 09:16 AM   #290
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Originally Posted by catsmate View Post
So? You can do some rather clever multiple planetary slingshot maneuvers, la Messenger, with multiple flybys and gradual deceleration. That probe left Earth orbit at ~11km/s and achieved Mercury orbit.
The comparison isn't even close. Mercury's escape velocity is 4.3km/s. If we send a probe at 4.3km/s towards Mercury, it will take about a year to get there. So there are all sorts of opportunities.

ETA: I see your 11km/s number, and it is greater than the 4.3km/s. But in Messenger's case, it was orbiting the sun several times during this time. I'm not sure if you want to wait for a probe to orbit the sun several times out near Pluto

Pluto's escape velocity is 1.2km/s. The closest any planet ever gets to Pluto is 12 AU (Neptune). It would take 71 years to get from Neptune to Pluto at 1.2km/s.

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Old 17th July 2015, 10:25 AM   #291
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Originally Posted by catsmate View Post
So? You can do some rather clever multiple planetary slingshot maneuvers
No. New Horizons was going more than 11 times the escape velocity of Pluto, relative to Pluto. The closes possible pass to Pluto would have produced a deflection, yes, but then what? Try to sling shot it again with Charon? Even less of a deflection, and almost no loss in energy (since Charon's velocity relative to Pluto is much smaller than New Horizon's relative velocity). So it would still be going at at least 10 times escape velocity. There's no second pass there, no multiple flybys. It's gone.

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la Messenger, with multiple flybys and gradual deceleration. That probe left Earth orbit at ~11km/s and achieved Mercury orbit.
Yes, and it took an Earth flyby, two Venus flybies, and three Mercury flybies to do it. And each flyby required basically another orbit around the sun, both for the probe and the flyby target.

Tell me: how long do you think it would take for New Horizon to pull a similar maneuver with Pluto?
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Old 17th July 2015, 10:36 AM   #292
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Originally Posted by rwguinn View Post
I wasn't aware that sublimation of most ices was possible at the temperatures of Pluto.

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Ice will sublimate at almost any temperature. The question is at what pressure and at what rate. Ice will sublimate until the atmospheric pressure halts that sublimation, but when things are very cold, the rate of sublimation will be very low, and the pressure needed to halt it will also be very low, so it may not matter much. But it can still happen.
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Old 17th July 2015, 01:00 PM   #293
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Originally Posted by Ziggurat View Post
No. New Horizons was going more than 11 times the escape velocity of Pluto, relative to Pluto. The closes possible pass to Pluto would have produced a deflection, yes, but then what? Try to sling shot it again with Charon? Even less of a deflection, and almost no loss in energy (since Charon's velocity relative to Pluto is much smaller than New Horizon's relative velocity). So it would still be going at at least 10 times escape velocity. There's no second pass there, no multiple flybys. It's gone.



Yes, and it took an Earth flyby, two Venus flybies, and three Mercury flybies to do it. And each flyby required basically another orbit around the sun, both for the probe and the flyby target.

Tell me: how long do you think it would take for New Horizon to pull a similar maneuver with Pluto?
What about entering the atmosphere, using that to slow down to orbital velocity and fly back out the atmosphere? It'd need a heatshield and control surfaces and other stuff i've not thought of but could that be done?
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Old 17th July 2015, 01:06 PM   #294
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Originally Posted by RussDill View Post
The comparison isn't even close. Mercury's escape velocity is 4.3km/s. If we send a probe at 4.3km/s towards Mercury, it will take about a year to get there. So there are all sorts of opportunities.

ETA: I see your 11km/s number, and it is greater than the 4.3km/s. But in Messenger's case, it was orbiting the sun several times during this time. I'm not sure if you want to wait for a probe to orbit the sun several times out near Pluto

Pluto's escape velocity is 1.2km/s. The closest any planet ever gets to Pluto is 12 AU (Neptune). It would take 71 years to get from Neptune to Pluto at 1.2km/s.

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Old 17th July 2015, 01:34 PM   #295
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Originally Posted by alexi_drago View Post
What about entering the atmosphere, using that to slow down to orbital velocity and fly back out the atmosphere? It'd need a heatshield and control surfaces and other stuff i've not thought of but could that be done?
Not enough atmosphere; what there is probably would have no measurable effect on the spacecraft's speed, and definitely not enough to slow it to orbital speeds.

See http://pluto.jhuapl.edu/Mission/FAQs.php - question Does Pluto have an atmosphere?.
Quote:
The pressure at the surface of Pluto is about 3 to 100 microbars or 3 to 100 millionths of the surface pressure of the Earth's atmosphere.
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Old 17th July 2015, 02:11 PM   #296
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Originally Posted by alexi_drago View Post
What about entering the atmosphere, using that to slow down to orbital velocity and fly back out the atmosphere? It'd need a heatshield and control surfaces and other stuff i've not thought of but could that be done?
I don't know if Pluto's atmosphere is thick enough to do that. But I do know that we certainly didn't have enough data about the atmosphere (hell, we didn't even have its diameter nailed down) to be able to plan such an attempt, even if the atmosphere were thick enough. Remember, this is the best picture we had of Pluto prior to New Horizon's arrival:



ETA: looks like from grmcdorman's post that the atmosphere wouldn't be sufficient.
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Old 17th July 2015, 02:47 PM   #297
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Originally Posted by BenBurch View Post
Would need all possible heat for metabolism.
That assumes that it's not some kind of extremophile that actually likes the cold.

I would imagine that any life we may find on other worlds would be very different from life on Earth simply because it would have had a different set of conditions to adapt to. We may find stuff that doesn't need external heat or light to survive. Or not.
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Old 17th July 2015, 04:26 PM   #298
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Originally Posted by Ziggurat View Post
I don't know if Pluto's atmosphere is thick enough to do that. But I do know that we certainly didn't have enough data about the atmosphere (hell, we didn't even have its diameter nailed down) to be able to plan such an attempt, even if the atmosphere were thick enough.

....

ETA: looks like from grmcdorman's post that the atmosphere wouldn't be sufficient.
Yeah, I forgot about that uncertainty. There's also the issue that, as Pluto is very small, you're going to exit the atmosphere very quickly on any open (non-orbital) path. Basically, using aerobraking at Pluto is pretty much a non-starter.
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Old 17th July 2015, 10:28 PM   #299
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Odd that the diameter and atmosphere is not known. There are plenty of stars in the sky. So wait for one of them to go behind Pluto and time how long the star cannot be seen. Then repeat a few times and the diameter and atmosphere composition and strength would be known.
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Old 17th July 2015, 11:16 PM   #300
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NASA's New Horizons spacecraft is sending back reams of data after its close Pluto flyby on Tuesday, including new details on what comprises its surface and atmosphere.

Scientists on Friday released a simulated flyover of Pluto's 11,000-foot-tall mountain range called the "Norgay Montes," which are named after Tenzing Norgay, one of the first two humans to reach the summit of Mount Everest. Norgay was Sir Edmund Hillary's Nepalese Sherpa when he made his record-breaking ascent of the mountain in 1953.
No sound and it is in black and white. And the stars are visible.
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Old 18th July 2015, 12:47 AM   #301
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Originally Posted by grmcdorman View Post
Yeah, I forgot about that uncertainty. There's also the issue that, as Pluto is very small, you're going to exit the atmosphere very quickly on any open (non-orbital) path. Basically, using aerobraking at Pluto is pretty much a non-starter.
Thanks, and for others replies too. I guess we won't be putting a man on Pluto any time soon then.
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Old 18th July 2015, 04:17 AM   #302
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Originally Posted by CelticRose View Post
That assumes that it's not some kind of extremophile that actually likes the cold.

I would imagine that any life we may find on other worlds would be very different from life on Earth simply because it would have had a different set of conditions to adapt to. We may find stuff that doesn't need external heat or light to survive. Or not.
Could be a lithophile. However, as close to absolute zero as Pluto gets I can't imagine life at the surface. It is one of the few physical constraints that is actually necessary.
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Old 18th July 2015, 04:34 AM   #303
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Originally Posted by rjh01 View Post
Odd that the diameter and atmosphere is not known. There are plenty of stars in the sky. So wait for one of them to go behind Pluto and time how long the star cannot be seen. Then repeat a few times and the diameter and atmosphere composition and strength would be known.
Occultations of usable stars are very rare.
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Old 18th July 2015, 05:10 AM   #304
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From the first photograph to the most recent data:http://www.nasa.gov/sites/default/fi...?itok=A_WsMQ7f
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Old 18th July 2015, 06:56 AM   #305
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Originally Posted by Monketi Ghost View Post
From the first photograph to the most recent data:http://www.nasa.gov/sites/default/fi...?itok=A_WsMQ7f
Thanks!

Excellent!
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Old 18th July 2015, 07:07 AM   #306
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Originally Posted by BenBurch
Originally Posted by rjh01 View Post
Odd that the diameter and atmosphere is not known. There are plenty of stars in the sky. So wait for one of them to go behind Pluto and time how long the star cannot be seen. Then repeat a few times and the diameter and atmosphere composition and strength would be known.
Occultations of usable stars are very rare.
Yes, occultations are rare; but they were able to do that. The issue is not that the size is completely unknown, but that the error in the measurement - i.e. the uncertainty - was sufficiently large to be a problem. New Horizons, in fact, found that Pluto is larger than estimated by a small amount, just over 3%: see https://www.nasa.gov/feature/how-big...es-long-debate and http://www.space.com/29924-pluto-lar...asa-flyby.html

Apparently Pluto's atmosphere is a problem; an atmosphere leads to a gradual dimming (and bending) of a star's light, unlike an airless body where it will just wink out and back in.

From the latter link:
Originally Posted by space.com
New Horizons' latest views of Pluto have shown the dwarf planet to be 1,473 miles (2,370 kilometers) across ...
Previous estimates for the size of Pluto had put its radius at 1,430 miles (2,301 km)
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Old 18th July 2015, 07:15 AM   #307
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Originally Posted by Rincewind View Post
Thanks!

Excellent!
Yes, it's exciting, and I never thought Pluto would be.
From blurry image to close ups of ice mountains. Stunning achievement: when Tombaugh found it we couldn't get off the planet and now we've just sent a probe by.
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Old 18th July 2015, 07:42 AM   #308
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Originally Posted by Beelzebuddy View Post
Re: smooth surface, my money's on some kind of slow erosion caused by Pluto's atmosphere alternately sublimating when it's close(r) to the sun, and freezing out when it moves farther away. Sublimation should favor sunnier peaks and crater rims, deposition should favor shadowy valleys and crater floors, so the one should (very, very gently) shift mass into the other.
Interesting. I hadn't thought of that. Does it happen seasonally on Earth on glaciers and the like, or do other effects, such as precipitation, overwhelm it?
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Old 18th July 2015, 08:43 AM   #309
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Originally Posted by Monketi Ghost View Post
Yes, it's exciting, and I never thought Pluto would be.
From blurry image to close ups of ice mountains. Stunning achievement: when Tombaugh found it we couldn't get off the planet and now we've just sent a probe by.
My thoughts exactly. What with this and Rosetta/Philae we're on a bit of a roll above the stratosphere. Below not so much, of course, but from the gutter we gaze at the stars.
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Old 18th July 2015, 09:12 AM   #310
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Originally Posted by alexi_drago View Post
What about entering the atmosphere, using that to slow down to orbital velocity and fly back out the atmosphere? It'd need a heatshield and control surfaces and other stuff i've not thought of but could that be done?
This seems relevant.
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Old 19th July 2015, 01:02 PM   #311
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Originally Posted by BenBurch View Post
The alternative (because this won't work) is you take 90 years to get there so you have a manageable velocity for capture.
As I already posted on this thread, with an ion engine a Pluto orbiter could be done with "only" 15 years travel time:

http://www.esa.int/gsp/ACT/doc/PRO/A...2004-Pluto.pdf
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Old 19th July 2015, 03:36 PM   #312
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Thing is, the ion engine wasn't on the table as an engineering option when New Horizons was designed, as far as I know. What's more, Dawn has been, in part, a proof-of-concept for the engine; for the NH mission, I don't think that planners would opt for it even now until it has been proven for long duration missions.
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Old 19th July 2015, 06:09 PM   #313
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Actually, proof-of-concept was Deep Space 1, launched in 1998. So yes, it was available when New Horizons was designed.

However, the design to which I linked calls for 4 RTG's -- NASA did not have that much plutonium-238.
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Old 19th July 2015, 06:31 PM   #314
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Ah. I stand (sit) corrected, then.

Mind you, it still would require ~15 years transit (going by the posts here), and be relying on cutting-edge techniques; from what I've read, the NH project was touch and go for a while; adding a new, cutting-edge feature to it might have been enough to push it off the table (even leaving aside the issue of enough RTG fuel).
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Old 19th July 2015, 09:18 PM   #315
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Originally Posted by grmcdorman View Post
Ah. I stand (sit) corrected, then.

Mind you, it still would require ~15 years transit (going by the posts here), and be relying on cutting-edge techniques; from what I've read, the NH project was touch and go for a while; adding a new, cutting-edge feature to it might have been enough to push it off the table (even leaving aside the issue of enough RTG fuel).
Perhaps the science findings will provide motivation for such a future mission.
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Old 20th July 2015, 04:01 AM   #316
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Originally Posted by Mark6 View Post
Actually, proof-of-concept was Deep Space 1, launched in 1998. So yes, it was available when New Horizons was designed.

However, the design to which I linked calls for 4 RTG's -- NASA did not have that much plutonium-238.
They still don't, the supply is (IIRR) about 16kg, much of which is earmarked for the Mars rover programme.
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Old 20th July 2015, 06:14 AM   #317
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Originally Posted by RussDill View Post
Perhaps the science findings will provide motivation for such a future mission.
[Farnsworth]A man can dream, though. A man can dream.[/Farnsworth]

I hope this does generate sufficient interest to get people looking up at space again, and have a certain personal stake in it (my company doesn't do rocket design/testing, but my work with NASA is affected by their budget). That said, I don't think anything short of confirmed alien life wil get folks interested. We haver two cases of potential life (I believe we have found fossil stromatolites on Mars, and we may have found evidence of life on a moon) and people STILL say mathematically illiterate nonsense like "Why don't we use that money to solve problems on Earth first?" New Horizons is a great thing, but I have little hope for it generating sufficient public interest to have an impact on the budget.
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Old 20th July 2015, 06:25 AM   #318
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Originally Posted by Dinwar View Post
[Farnsworth]A man can dream, though. A man can dream.[/Farnsworth]

I hope this does generate sufficient interest to get people looking up at space again, and have a certain personal stake in it (my company doesn't do rocket design/testing, but my work with NASA is affected by their budget). That said, I don't think anything short of confirmed alien life wil get folks interested. We haver two cases of potential life (I believe we have found fossil stromatolites on Mars, and we may have found evidence of life on a moon) and people STILL say mathematically illiterate nonsense like "Why don't we use that money to solve problems on Earth first?" New Horizons is a great thing, but I have little hope for it generating sufficient public interest to have an impact on the budget.
I can only second this.
The early pictures of Saturn/Neptune/Uranus are at least part of what got me into science in the first place, even though I chose a different field in the end.
Personally I hope to see a serious expedition to the potential water bearing moons to see if there is an ocean under that ice, and if there is something alive in there.

As for the 'we must solve problems now' crowd. I always counter that most real progress we made came from curiosity rather than problem oriented research. Those that first researched electricity or nuclear physics did not do so to create computers or nuclear power plants.
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Old 20th July 2015, 08:01 AM   #319
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Originally Posted by Dinwar View Post
[Farnsworth]A man can dream, though. A man can dream.[/Farnsworth]

I hope this does generate sufficient interest to get people looking up at space again, and have a certain personal stake in it (my company doesn't do rocket design/testing, but my work with NASA is affected by their budget). That said, I don't think anything short of confirmed alien life wil get folks interested. We haver two cases of potential life (I believe we have found fossil stromatolites on Mars, and we may have found evidence of life on a moon) and people STILL say mathematically illiterate nonsense like "Why don't we use that money to solve problems on Earth first?" New Horizons is a great thing, but I have little hope for it generating sufficient public interest to have an impact on the budget.
Yeah, don't hold your breath.
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Old 20th July 2015, 08:25 AM   #320
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Originally Posted by Dinwar View Post
New Horizons is a great thing, but I have little hope for it generating sufficient public interest to have an impact on the budget.
A wonderful thing indeed but there's an unfortunate air of completion about it. It doesn't open on to anything, unlike, say Hubble or the Mars Rovers, or Rosetta - manoeuvring about amongst bolides is surely going to be a thing of the future.

Pluto : tick. Won't go back. (If we do go out there again we'll surely visit a different body.)
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