New Horizons at Pluto

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.
 
Beelzebuddy said:
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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Wouldn't you then expect to see partially sublimated craters?
 
Ziggurat said:
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.
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So? You can do some rather clever multiple planetary slingshot maneuvers, à la Messenger, with multiple flybys and gradual deceleration. That probe left Earth orbit at ~11km/s and achieved Mercury orbit.
 
catsmate said:
So? You can do some rather clever multiple planetary slingshot maneuvers, à la Messenger, with multiple flybys and gradual deceleration. That probe left Earth orbit at ~11km/s and achieved Mercury orbit.
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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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catsmate said:
So? You can do some rather clever multiple planetary slingshot maneuvers
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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.

à la Messenger, with multiple flybys and gradual deceleration. That probe left Earth orbit at ~11km/s and achieved Mercury orbit.
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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?
 
rwguinn said:
I wasn't aware that sublimation of most ices was possible at the temperatures of Pluto.

Sent from my SM-G920V using Tapatalk
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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.
 
Ziggurat said:
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?
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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?
 
RussDill said:
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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[ Pluto's minimum separation from Uranus is 11 AU. ]
 
alexi_drago said:
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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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?.
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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alexi_drago said:
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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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:

hs-2010-06-a-web_print.jpg


ETA: looks like from grmcdorman's post that the atmosphere wouldn't be sufficient.
 
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BenBurch said:
Would need all possible heat for metabolism.
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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. :)
 
Ziggurat said:
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.
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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.
 
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.
 

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.
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No sound and it is in black and white. And the stars are visible.
 
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