Challenge Questions

What system of physics would allow a spiral orbit?

what system of physics would allow an eliptical orbit. could we put a sattellite in an eliptical orbit around the earth?

Yes - most of the closer satellite orbits are approximately elliptical - although the gravitational effect of the moon does of course distort their orbits.

On the physics side of things, Newtonian mechanics predicts orbits that are elliptical - at least for simple systems that consist of just two rigid objects orbiting each-other; that applies both to planets around suns and (slightly approximately) moons around planets (relative to the position of the heavier object in both cases). So-called circular orbits would just be ellipses that have major and minor axes that are approximately equal.

Orbits are not exactly elliptical for at least three reasons:
a) Fundamental: Newtonian mechanics is only an approximation. Einstein's general theory of relativity accurately predicts how the axes of the ellipse does not remain at the same angles from one orbit to the next - see here.
b) Gravitational fields from other objects (for planets that would principally be the fields of other planets or of their moons) will modify the shapes of the orbits.
c) Tidal action will very gradually alter the orbit.
. The example that you doubtless know is that interaction with our tides are forcing the moon into a very slow outward spiral, which will eventually cause it to escape the Earth's gravitational field. But this is only happening very slowly - the expected increase in the radius of the orbit is 38-mm per year (or 0.00001% per millennium).
. The rate of change of orbit will depend on size of the the tide that the moon (planet) has on the planet (star) that it is orbiting. That means that the tidal effect on the orbit of a planet is directly proportional to the planet's mass. (It also falls off rapidly with distance). That has the (initially curious) result that the cumulative tidal effect that the sun's rotation has on Jupiter will be more than five orders of magnitude larger than its effect on Pluto.
. So we can readily say that the long-term tidal effect of the sun on Pluto's orbit will be small. So, apart from possible near-collisions with objects as yet unobserved, Pluto-Charon's orbit* is best described as an ellipse with relatively minor disturbances by interactions with the larger outer planets - and by the closer approaches to other Kuiper objects. Eventually, assuming that Pluto survives until the sun grows into a red giant, it will be subject to an increase in the solar wind; Pluto's orbit would then become the spiral you ask about, and it would be driven out of the solar system. That, however, is way outside the time-scale in which "you" might conceptually arrive there (with or without a thermometer to measure the temperature).
*The daily but small-scale orbit around Charon is not significant from the aspect of affecting the seasons

Confused? I've barely started...

If Pluto is beyond the orbit of Neptune, you know what part of its orbit is currently happening and that determines the "season" and temperature. You don't need the thermometer.

Maybe - but I like to do it with a thermometer!

Rotznase!

For most of the year, the temperature will vary across the mini-planet by a great deal more than does the average temperature of the planet. This is because the axis of rotation is at a large angle to the orbital axis, so parts of the planet will will either be continuously dark or continuously illuminated/heated for over a hundred earth-years at a time.
(Of course the dark regions are not visible from the Earth - but space telescopes should in due course be able to observe the differences between the continuously-illuminated pole and the equatorial regions).
1-degree accuracy over 20-40 Kelvin should be more than adequate for the purpose.

Assuming that Pluto has an axis of rotation (it does) and that this axis is inclined relative to the axis of its orbit (it is) then Pluto will have seasons, just like the earth does. What season is it on Earth right now? If you say spring you are WRONG. What you really mean is that you either live in or for some reason 'identify' with the northern (upright) hemisphere, and have adopted their season-naming conventions. If you say fall you are also WRONG, but you have given yourself away as being an inhabitant in the southern (subversive) hemisphere. The only correct answer would be that on Earth right now it is Spring-Fall. The same would be true on Pluto - it will be experiencing two seasons at any given time.

I read the wording of the challenge as lazy writing meaning "the season at the location where you landed". If you are looking for global Plutonic seasons (as SpringFall or SummerWinter) you would need all sorts of information in addition to the temperature. You would for example have the problem that one SpringFall will be substantially cooler than the other - and the temperature at the equator in both SummerWinters could be cooler than it is at the cooler of the SpringFalls (that would depend to an extent on how the atmosphere behaves). If you had a clock you could use it and the thermometer to measure day length - but that might only be usable if you had other means to assess your latitude.

(I'm basing this on the fact that the poles of Pluto will actually get appreciably hotter in their respective summers than the equator ever does, and that the equator temperature varies sufficiently for it to have a winter. These changes are sufficiently large and should all be well-enough centred around the same temperature that you could to define season in terms of specific temperatures - regardless of location. (The relationship of the seasons to the year would be rather un-Earthlike near the equator, but that's the penalty for stretching Earthomorphisms too far.)

Regards

Fyz

Since Pluto's orbit is elliptical to the point that at perihelion it is inside the orbit of Neptune, the position in its orbit would be the primary factor in assessing the season. In this case summer would be summer over the whole planetlet. Tilted axes of revolution and such would have little effect. That thermometer would be of little use, even if made to measure the temperature of liquid helium, without data on the mean temperature over the average Pluto year. What would be the best indicator would be observation of where it is on it's orbit. Which means that if you were any kind of astronaut you would already know before you got there.

Boils Law

Try telling that to a hypothetical Plutonian who is situated on one of Pluto's poles throughout the 100-year dark season. By the middle of that period atmosphere in the surrounding area would have frozen completely, so the temperature would continue to fall almost until light returned. Just as on Earth, one of these polar regions will have summer at the same time as the other experiences winter.

Pluto rotates on it's side like Uranus so it does not experience seasons for the same reason the Earth does. However, Plutos highly eccentric orbit brings it inside the orbit of Neptune at its' perihelion which is WAY warmer than at the point of aphelion. However aphelion is 49 AU from the sun (Plutos' winter) so I think I missed by 90,000,000 miles or so. Oh, well Eris is bigger and anyway I want to find Voyager. I have this thing for bald female Borg.

"On this we forge a fragile truth

From skeptical consensus

That leads us from the reign of tooth

To daydreams that connect us."

From "The Multiverse" by me ;>)

"Pluto rotates on it's side like Uranus so it does not experience seasons for the same reason the Earth does"
Your reasoning is topsy-turvy. The Earth's seasons are precisely because the polar axis is not exactly parallel to the orbital axis. If the axis were on its side, each pole would see no light at all for half the year - and be continuously illuminated for the other half. That means that Pluto would have seasons for the same reason as we have them on Earth, but in spades. In fact the angle is not quite 90^O, but the principle remains the same - Pluto will have seasons for the same reason as Earth.

Pluto's axis of rotation is actually only about 11 degrees to the Sun's axis, or quite similar to the other planets. Pluto's orbital plane is uniquely inclined with respect to the Sun's equatorial plane, inhabited by the other planets and the belt. Pluto's 'rise and fall' means its 'south' pole is 'hot' when Pluto is 'above', and its 'north' pole is 'hot' when it is 'below', and 'mid temperature' approximates passing through the plane of the belt and other planets. So if the seasonal concept of Earth is transferable, and I am travelling "through the Kuiper belt", so on or about the planetary plane, logically it is autumn or spring on Pluto, relative to one pole or the other.

Good insight that "travelling through the Kuiper belt" is likely (though not certain) to mean that you are arriving at around the time Pluto is in the plain of the belt. Unfortunately, I cannot award you a GA because (so far as I can judge) everything else in your posting appears to be incorrect.
Pluto's equinoxes are at aphelion and at perihelion, which are the times that its position is furthest outside the plane of the Kuiper belt. So you will be arriving nearer the solstices - but quite noticeably before or after because of the elliptical orbit. Taking the seasons as changing at the solstice (as we do on Earht), that would mean that you could be arriving during any one of the four seasons - albeit fairly close to midsummer or midwinter's day.
Next, the angle of Pluto's polar axis. The important relationship is to the orbital axis, and that angle is about 120^O (i.e. the polar axis is at about 60^O to the orbital axis, plus the directions of rotation are inverse). So summers and winters should be long and extreme (both impossibly cold by our standards, of course). As I read it, you believe you are giving the angle between Pluto's polar axis and the Sun's polar axis; I don't know what that is, but it cannot be less than 39^O plus a reversal (= 60-14-7, the 14 and 7 being the angles between Pluto's orbit and the Earth's and the 7 being the angle between the Sun's polar axis and the Earth's)

Maybe this will help with the visualization I was trying to convey. It's from http://cseligman.com/text/planets/pluto.htm

Sorry, forgot to log in, but that's me above.

Where the diagram is clear*, it accords closely with what I wrote** Naturally some of the angles are a couple of degrees different, as these values are still being refined (I wouldn't care to hazard which of us is more out-of-date).

So where ... did your 11^O value come from (to say nothing of it being spring or autumn when Pluto passes through the Kuiper belt)?

*I couldn't see it in the main thread, but it appeared when I started to answer!
**The significant lack of clarity in the diagram is in the times of equinox and solstice. You will find data that allows you to deduce these elsewhere in the article you reference. Equinox will occur close to the date of maximum eclipse - which was in 1988. That would place equinox easily within an Earth-decade of 1989***, which marks the closest approach (aphelion) of Pluto to the sun (and one of the times it is at a maximum distance from the plane of the Kuiper belt).
***So far as I could see, that date is not really indicated in the article - I obtained it from the Wikipedia article on Pluto which sates that "Pluto was last inside the orbit of Neptune between February 1979 and February 1999".
***There is one other potentially misleading aspect to this illustration - the pale speckles appear to indicate aphelion as not being the closest approach to the Sun (!!). Just one of the perils of attempting static, single-aspect 2D illustrations of dynamic 3D events, I fear.

Dear Physicist? It is easier to grasp if you apply the terms in the standard manner, as sources such as Professor of Astronomy, Courtney Seligman, tend to. E.g. Aphelion - the point on its orbit when the Earth is farthest from the sun. Perihelion - the point on its orbit when the Earth is closest to the sun. See http://en.wikipedia.org/wiki/Aphelion

However some of your confusion is possibly my doing, as failing to recognise your level, I did alter things in an attempt to break the Earth like focus on orbital plane and axis of rotation as 'seasonal determinates' in of a body in significantly elliptical orbit.

Perhaps a simpler analogy is; it wouldn't matter if this was Halley's Comet. The principals are the same for any number and any arrangement of axis tilt and/or orbit plane tilt. Presuming a radiant 'sun', an elliptically orbiting Body experiences 'hot' when 'near', 'cold' when 'away' and 'transition' at ± ~90 degrees.

So to reprise the question without naughtiness;

In Pluto, these thermal principals manifest in atmospheric evolution/devolution. Logically maximum atmosphere = perihelion = 'summer'. 90 degrees after = autumn, and so on. As the orbit planes intersect ~ the belt, ~ 90 degrees, it is one of these 'thermal transition' seasons on Pluto. It could be any year of synchronicity with Neptune – so either 'side' – as date/century/millennia are unspecified.

Or perhaps synchronicity is irrelevant due to the craft's speed capabilities.

Therefore the answer, and maximum precision is; autumn/spring – as said.

Resources for 'solving',

All you need is the 'plane intersection picture' (see Seligman's diagram I 'borrowed') and to grasp 'elliptic thermal principal'. An advantage is; experience of a "beautiful, but sub zero, day" on Earth.

The last raises;

Many have struggled with a 'bright' period in winter makes it "summer". This is as flawed on Earth as it is on Pluto. 'Bright sides' on illustrations are just pigment. Pluto's 'daylight' is more akin the darkest night in an Earth desert or 'endless night' on Earth's poles. So it may be perpetual 'daylight' on a surface of Pluto, (with a pole), at coincidence with the belt plane, but it is less hot than 'summer' on Pluto (and warmer than 'winter').

Where to Land?

This is a choice between presumably nearer zero K on the 'night' side, or a postulated 'autumnal' mean of 44 K on the 'daylight' bit. ('Day' is the only bit we can see/measure - as yet). Presuming the range is 40 C, you could face the similar temperature range choice, landing on Earth, by day or night.

What to wear?

Taking a good jacket is an excellent idea, even on Earth.

For Pluto; a fairly good space suit over it is worth thought and a good torch a useful accessory, as aside from cold or colder you're stepping into black or blacker and nothing breathable.

From this information you could not. Where on pluto would you land? The season would depend on the hemisphere you would be in (N or S) and the time of the landing... So from this information all I can determin is that it will be pretty darn chilly outside, bring a jacket.

We can use the infrared radiations that are reflected back from Pluto to check the temperature.

We know that at different temperatures the intensity of radiations reflected varies along with the temperature.

we can use this property to find the temperature on pluto.

This theory comes from the Planck's Law.

Fingers crossed, I hope its correct. :D

Hey - what people are talking there (science/Technicians or business people) about thins (ä things) of interest

Lots of interesting comments... But I will just stick to the question that was asked. How do you determine the season. Having come from the earth, I have to interpret season as the extremes of summer and winter. That is my reference. I read that when Pluto is closest to the sun, the atmosphere warms up and forms a hazy cloud. That would be summer. When it moves farther from the sun, the atmosphere freezes and falls like snow. That would be winter. Therfore, when Pluto is closest to the sun it is summer.

Just my best guess

A local counter-example: Earth is closest to the Sun at the beginning of winter in the Northern hemisphere.

Because Pluto has equinox when it is at the furthest point, things will be different there. However, the difference between aphelion and perihelion (1.66:1) is not so great that the difference will not be that the varying distance between Pluto and the sun determines the season. Indeed, the Polar axis is so strongly inclined to the orbital axis that at the equator it will be colder at the two solstices than it is at aphelion (see calculation below). (However, the ellipticity will mean that both sostices are considerably closer in time to perihelion than they are to aphelion
On the other hand, the seasons in the arctic regions will depend on the angle between the polar axis and direction of insolation - just as they do on Earth - albeit there will be a substantial temperature difference between the spring and autumn (at the moment, Pluto's arctics should be experiencing a relatively warm spring-autumn.

As regards the equator, the daily mean temperature now is about 43K (brr). If for simplicity we were to assume that Pluto behaved like a grey body (and ignored the medium-delaying effect of specific heat and the delaying/distorting effect of latent heat):
During aphelion, the equatorial surface temperature would average about 43.√1.66) 33K (shudder). At solstices, based on the polar axis being at 119.6^O to the orbital axis, that temperature would be <≈43.(cos(60.4))^1/4.√0.801 ≈32K.
Note: the 0.801:1 term is the ratio of distance between Pluto and the Sun (perihelion:solstice).

On the same basis, we would expect polar solstice temperatures to be around:
summer: 43.∏^1/4.√0.801.sin(60.4)^1/4 ≈ 49.5K and
winter: 3K** (background radiation and backscatter only)

To be honest, the effects of temperature on Pluto's surface means that I don't believe any of these temperatures are remotely correct - but I do believe that they give a good indication of when the warmest and coolest periods are to be expected.

**Clearly the orbital period is nowhere near long enough to get remotely close to this temperature; this is because thermal radiation reduces so rapidly. I therefore suspect that even the hundred-years available at the poles is unlikely to allow cooling below about 15K). But it means that winter will be very easy to detect at the poles.

no

You will not be able to ascertain the season on Pluto by means of a thermometer.

The temperature on Pluto is influenced more by the distance of Pluto from the sun (between 30 and 50 AU) than it is by the considerable tilt of its axis toward the sun.

Pluto is currently near perihelion, so if you are going to encounter Pluto at 50 AU from the sun, it will be either over 100 years ago or 100 years in the future.

Can anybody on Pluto detect when it's June 2?

Or February 30th?

Baloney! The sublimation is occuring where it's warm. The condensation is occuring where it's cold.

Even on the assumptions given, a barometer would be useless. The pressure would be at most 30-Pa, so maybe a vacuum gauge would do the job. But the theory on which this answer is based appears riddled with inconsistencies (see below), and a sufficiently sensitive thermometer would work under all conditions.

"And the answer is..." is based on the idea that Pluto's temperature is due to equilibrium between solid nitrogen and its vapour. However, the mean temperature is thought to be 43K, which corresponds to an equilibrium vapour pressure of about 30-Pa, compared with the best-estimate of surface pressure (based on atmospheric refraction) of 0.3-Pa.
The other support for the theory behind the "the answer" is reportage that the surface temperature of Pluto is uniform. These reports were based on measurements using the changes in luminosity when the surface was obscured by Charon; however, the resolution of these measurements was quite limited, and the interpretation uncertain.
More recent work indicates that the present temperature almost certainly varies considerably across the surface - with a likely range of between 38K** and 60K. To my mind this means that we can now regard the causes of summer and winter as being driven by local radiation, rather than by the average across the planet (another apparent assumption of "the answer").

It is also worth noting that with a modest atmosphere summer and winter may be more properly associated with the temperature of an object above the surface rather than with surface or atmospheric temperature per se. In this case we could have effective summers and winters even if the temperature were nearly constant as postulated in "the answer" - and these would be measurable with a thermometer (but not with a pressure sensor).

**Note that 38K corresponds to a saturated vapour pressure of 0.2-Pa, so it is more than possible that the minimum (winter) temperature will be determined by condensation of atmosphere transported from the warmer regions rather than purely by radiative equilibrium. In this regard it is worth noting that the high-temperature effects will be considerably more rapid than low-temperature ones, and this could result in (interesting) complexities that are way outside our abilities to anticipate given our present lack of knowledge of Pluto's detailed structure.