Plutos New Moons Part 2, News ... |
Plutos New Moons Part 2, News ... |
![]()
Post
#1
|
|
![]() Member ![]() ![]() ![]() Group: Members Posts: 531 Joined: 24-August 05 Member No.: 471 ![]() |
Orbits and photometry of Pluto's satellites: Charon, S/2005 P1 and S/2005 P2
http://arxiv.org/abs/astro-ph/0512491 Orbital periods: Charon - 6.3872304 +/- 0.0000011 days S/2005 P2 - 24.8562 +/- 0.0013 days S/2005 P1 - 38.2065 +/- 0.0014 days Note: The old thread - http://www.unmannedspaceflight.com/index.p...wtopic=1622&hl= -------------------- - blue_scape / Nico -
|
|
|
![]() |
![]()
Post
#2
|
|
![]() Administrator ![]() ![]() ![]() ![]() Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 ![]() |
I'm a geologist, not an astronomer, so I only know what I have to know about spectroscopy...but...does it seem premature to anyone else to call things "the same color" when you only have views through two filters? That's a two-point spectrum. I understand that the filters on Hubble have probably been carefully chosen to make the most of differences at particular points on the electromagnetic spectrum, but still, two points isn't much of a spectrum, is it? Am I missing something?
--Emily -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
|
|
|
![]()
Post
#3
|
|
![]() Senior Member ![]() ![]() ![]() ![]() Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 ![]() |
I'm a geologist, not an astronomer, so I only know what I have to know about spectroscopy...but...does it seem premature to anyone else to call things "the same color" when you only have views through two filters? That's a two-point spectrum. I understand that the filters on Hubble have probably been carefully chosen to make the most of differences at particular points on the electromagnetic spectrum, but still, two points isn't much of a spectrum, is it? Am I missing something? --Emily Well, with three we can tell the difference between roses, emeralds, and the blue sky of a summer day. Not to trivialize the difference between two and three: there's a reason why tripods sell better than bipods. I think the answer lies in looking at known spectra. Typically, you see either a flat line, a sloped line, or a "hump", with definite exceptions for absorption lines that send the spectrum potentially near to zero, before returning the the general trend. It's easy to avoid the likely absorption lines, since we know that these worlds might have CO2, CO, N2, CH4, and H2O ices on their surfaces and aren't likely to be beryllium-strontium-cobalt. Then the question is, how many samples do you need to distinguish a flat line from a slope or a hump? Two seems to do it if you can avoid the case where you sample two values on opposite sides of the hump. Check out the visible spectrum of Pluto (left end of the top figure here) http://ifp.uni-muenster.de/~sohl/images/pl...to_spectrum.jpg It rises quite steeply through the visible. Two points could distinguish something like that from a flat line. Of course, it's theoretically possible that something psychopathic happens to a spectrum between two samples, but when we can constrain the possible materials, we can virtually eliminate that possibility. |
|
|
![]()
Post
#4
|
|
![]() Senior Member ![]() ![]() ![]() ![]() Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 ![]() |
Astrophysics, abstract
astro-ph/0603214 From: Man Hoi Lee [view email] Date: Wed, 8 Mar 2006 23:51:27 GMT (85kb) On the Orbits and Masses of the Satellites of the Pluto-Charon System Authors: Man Hoi Lee, S. J. Peale (UCSB) Comments: 24 pages, including 11 figures; uses AASTeX; submitted to Icarus (Abridged) The orbits of the recently discovered satellites of Pluto, S/2005 P2 and S/2005 P1, are significantly non-Keplerian, even if P2 and P1 have negligible masses, because the mass ratio of Charon-Pluto is ~0.1. We present an analytic theory with P2 and P1 treated as test particles. This analytic theory shows that the azimuthal periods of P2 and P1 are shorter than the Keplerian orbital periods and that the periapse and ascending node precess at nearly equal rates in opposite directions for P2 and P1. The deviation from Kepler's third law is already detected in the unperturbed Keplerian fit of Buie and coworkers. We also present direct numerical orbit integrations with different assumed masses for P2 and P1 within the ranges allowed by the albedo uncertainties. If the albedos are as high as that of Charon, the masses of P2 and P1 are sufficiently low that their orbits are well described by the analytic theory. There is at present no evidence that P2 has any significant epicyclic eccentricity. However, the orbit of P1 has a significant epicyclic eccentricity, and its prograde periapse precession with a period of 5300 days should be easily detectable. If the albedos are as low as that of comets, the large inferred masses induce significant variations in the epicyclic eccentricities and/or periapse longitudes on the 400-500-day timescales, due to the proximity of P2 and P1 to the 3:2 mean-motion commensurability. In fact, for the maximum inferred masses, P2 and P1 may be in the 3:2 mean-motion resonance, with the resonance variable involving the periapse longitude of P1 librating. Observations that sample the orbits of P2 and P1 well on the 400- 500-day timescales should provide strong constraints on the masses of P2 and P1 in the near future. http://arxiv.org/abs/astro-ph/0603214 -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
|
|
![]() ![]() |
![]() |
Lo-Fi Version | Time is now: 28th June 2024 - 09:00 AM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |
![]() |