* Astronomy

Members Login
Post Info
TOPIC: Neptune


L

Posts: 131433
Date:
Neptune Migration
Permalink  
 


Title: The Evidence for Slow Migration of Neptune from the Inclination Distribution of Kuiper Belt Objects
Author: David Nesvorny

Much of the dynamical structure of the Kuiper belt can be explained if Neptune migrated over several AU, and/or if Neptune was scattered to an eccentric orbit during planetary instability. An outstanding problem with the existing formation models is that the distribution of orbital inclinations they predicted is narrower than the one inferred from observations. Here we perform numerical simulations of Kuiper belt formation starting from an initial state with Neptune at 20 < a_{N,0} < 30 AU and a dynamically cold outer disk extending from beyond a_{N,0} to 30 AU. Neptune's orbit is migrated into the disk on an e-folding timescale 1 <= tau <= 100 Myr. A small fraction (~10^{-3}) of the disk planetesimals become implanted into the Kuiper belt in the simulations. By analyzing the orbital distribution of the implanted bodies in different cases we find that the inclination constraint implies that tau >= 10 Myr and a_{N,0} <= 25 AU. The models with tau < 10 Myr do not satisfy the inclination constraint, because there is not enough time for various dynamical processes to raise inclinations. The slow migration of Neptune is consistent with other Kuiper belt constraints, and with recently developed models of planetary instability/migration. Neptune's eccentricity and inclination are never large in these models (e_N<0.1, i_N<2 deg), as required to avoid excessive orbital excitation in the >40 AU region, where the Cold Classicals presumably formed.

Read more (1064kb, PDF)



__________________


L

Posts: 131433
Date:
RE: Neptune
Permalink  
 


Title: Spatially-Resolved Millimetre-Wavelength Maps of Neptune
Authors: S. H. Luszcz-Cook, I. de Pater, M. Wright

We present maps of Neptune in and near the CO (2-1) rotation line at 230.538 GHz. These data, taken with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) represent the first published spatially-resolved maps in the millimetre. At large (~5 GHz) offsets from the CO line center, the majority of the emission originates from depths of 1.1-4.7 bar. We observe a latitudinal gradient in the brightness temperature at these frequencies, increasing by 2-3 K from 40 degrees N to the south pole. This corresponds to a decrease in the gas opacity of about 30% near the south pole at altitudes below 1 bar, or a decrease of order a factor of 50 in the gas opacity at pressures greater than 4 bar. We look at three potential causes of the observed gradient: variations in the tropospheric methane abundance, variations in the H2S abundance, and deviations from equilibrium in the ortho/para ratio of hydrogen. At smaller offsets (0-213 MHz) from the center of the CO line, lower atmospheric pressures are probed, with contributions from mbar levels down to several bars. We find evidence of latitudinal variations at the 2-3% level in the CO line, which are consistent with the variations in zonal-mean temperature near the tropopause found by Conrath et al. (1998) and Orton et al. (2007).

Read more (2714kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Galileo Galilei's drawings show that he first observed Neptune on December 28, 1612, and again on January 27, 1613. On both occasions, Galileo mistook Neptune for a fixed star when it appeared very close - in conjunction - to Jupiter in the night sky; hence, he is not credited with Neptune's discovery. 
Read more



__________________


L

Posts: 131433
Date:
Permalink  
 

On this day, in  1846, French astronomer Urbain Jean Joseph Le Verrier and British astronomer John Couch Adams discovered the planet Neptune. The discovery was verified by German astronomer Johann Gottfried Galle. 

Neptune was mathematically predicted before it was directly observed. With a prediction by Urbain Le Verrier, telescopic observations confirming the existence of a major planet were made on the night of September 23, 1846, and into the early morning of the 24th, at the Berlin Observatory, by astronomer Johann Gottfried Galle (assisted by Heinrich Louis d'Arrest), working from Le Verrier's calculations.
Read more



__________________


L

Posts: 131433
Date:
Permalink  
 

Neptune-004b.gif
Expand (203kb, 800 x 600)


__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Neptune's wild days: constraints from the eccentricity distribution of the classical Kuiper Belt
Authors: Rebekah I. Dawson, Ruth Murray-Clay

Neptune's dynamical history shaped the current orbits of Kuiper belt objects (KBOs), leaving clues to the planet's orbital evolution. In the "classical" region, a population of dynamically "hot" high-inclination KBOs overlies a flat "cold" population with distinct physical properties. Simulations of qualitatively different histories for Neptune -including smooth migration on a circular orbit or scattering by other planets to a high eccentricity - have not simultaneously produced both populations. We explore a general Kuiper belt assembly model that forms hot classical KBOs interior to Neptune and delivers them to the classical region, where the cold population forms in situ. First, we present evidence that the cold population is confined to eccentricities well below the limit dictated by long-term survival. Therefore Neptune must deliver hot KBOs into the long-term survival region without excessively exciting the eccentricities of the cold population. Imposing this constraint, we explore the parameter space of Neptune's eccentricity and eccentricity damping, migration, and apsidal precession. We rule out much of parameter space, except where Neptune is scattered to a moderately eccentric orbit (e > 0.15) and subsequently migrates a distance Delta aN=1-6 AU. Neptune's moderate eccentricity must either damp quickly or be accompanied by fast apsidal precession. We find that Neptune's high eccentricity alone dos not generate a chaotic sea in the classical region. Chaos can result from Neptune's interactions with Uranus, exciting the cold KBOs and placing additional constraints. Finally, we discuss how to interpret our constraints in the context of the full, complex dynamical history of the solar system.

Read more (1360kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

A Day on Neptune Is Less Than 16 Hours Long

Not long after Neptune completed its first orbit around the sun since its discovery in 1846, scientists have managed to calculate the exact length of one day on the distant gas giant planet.
Unlike their rocky counterparts, gas giants have long challenged astronomers when it comes to calculating their rotation.

Read more 



__________________


L

Posts: 131433
Date:
Permalink  
 

Neptune Day Length Determined


Astronomers used over 500 images from the Hubble Space Telescope and the Voyager probe to determine that 15hr:57min:59sec calls it a day on the "blue planet". This animation of images shows Neptune in its full rotational glory (time-lapsed).
Credit: E. Karkoschka/The University of Arizona/NASA



__________________


L

Posts: 131433
Date:
Permalink  
 

Discovery of Neptune by Johann Galle's in 1846

Neptune was mathematically predicted before it was directly observed. With a prediction by Urbain Le Verrier, telescopic observations confirming the existence of a major planet were made on the night of September 23, 1846, and into the early morning of the 24th, at the Berlin Observatory, by astronomer Johann Gottfried Galle (assisted by Heinrich Louis d'Arrest), working from Le Verrier's calculations.
Read more



__________________


L

Posts: 131433
Date:
Permalink  
 

Let's face it -- we just don't get to see enough of Neptune these days. For good reason, I suppose, as it's pretty far away -- say, 2.7 billion miles away, or 30 times the distance from here to the sun -- and it hasn't been visited by a spacecraft since Voyager 2 passed by back in the summer of '89.
It's not visible with the naked eye from Earth, and even with a telescope it can be tricky to observe for the average backyard astronomer. But Neptune is very much a full-fledged and fascinating member of our solar system's family and was recently targeted by California Institute of Technology astronomer Mike Brown, who took some great shots of the distant world with the 10-meter (33-foot) telescope at Hawaii's Keck Observatory

Read more 



__________________
1 2 37  >  Last»  | Page of 7  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard