arXiv:1807.02960 -- Outer solar system possibly shaped by a stellar fly-by

Paper: Outer solar system possibly shaped by a stellar fly-by
Authors: Susanne Pfalzner, Asmita Bhandare, Kirsten Vincke, Pedro Lacerda

Abstract: The planets of our solar system formed from a gas-dust disk. However, there are some properties of the solar system that are peculiar in this context. First, the cumulative mass of all objects beyond Neptune (TNOs) is only a fraction of what one would expect. Second, unlike the planets themselves, the TNOs do not orbit on coplanar, circular orbits around the Sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. This implies that some process restructured the outer solar system after its formation. However, some of TNOs, referred to as Sednoids, move outside the zone of influence of the planets. Thus external forces must have played an important part in the restructuring of the outer solar system. The study presented here shows that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density outside 30 AU and excite the TNOs onto eccentric, inclined orbits, including the family of Sednoids. In the past it was estimated that such close fly-bys are rare during the relevant development stage. However, our numerical simulations show that such a scenario is much more likely than previously anticipated. A fly-by also naturally explains the puzzling fact that Neptune has a higher mass than Uranus. Our simulations suggest that many additional Sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet X.

My Comment: Fun discussion of solar system shaping mechanism and conducted further work to show plausibility of a fly-by during very early (10Myr) Solar System. Got me thinking about the Tisserand parameter with respect to Neptune, and once again am very happy to have astro-twitter folks willing to point papers and ideas out to me!

My Scrawling Notes:

Further investigation of changes in cometary rotation: arXiv:1806.11158

Paper: Further investigation of changes in cometary rotation
Authors: Beatrice E. A. Mueller, Nalin H. Samarasinha

Abstract: Samarasinha & Mueller (2013) related changes of cometary rotation to other physical parameters for four Jupiter family comets defining a parameter X  , which is approximately constant within a factor of two irrespective of the active fraction of a comet. Two additional comets are added to this sample in this paper and the claim of a nearly constant parameter X  for these six comets is confirmed, albeit with a larger scatter. Taking the geometric mean of X  for all the comets above excluding 2P/Encke (as X  for each comet was determined with respect to that of 2P/Encke), the expected changes in the rotation periods for a sample of 24 periodic comets are derived. We identify comets from this sample that are most likely to show observationally detectable changes in their rotation periods. Using this sample and including the six comets used to determine X  , we find a correlation between the parameter ζ  (i.e. the total water production per unit surface area per orbit approximated by that inside of 4 au) and the perihelion distance q  ; specifically we derive ζ  ∝  q −0.8   and provide a theoretical basis for this in Appendix A. This relationship between ζ  and q  enables ready comparisons of activity due to insolation between comets. Additionally, a relationship between the nuclear radius R  and the rotation period P  is found. Specifically, we find that on average smaller nuclei have smaller rotation periods compared to the rotation periods of larger nuclei. This is consistent with expectations for rotational evolution and spin-up of comet nuclei, providing strong observational evidence for sublimation-driven rotational changes in comets.

My Comment: The empirical law given seems to work on a factor of a few, which is better than the order of magnitude spanning effects being modeled. This paper does not justify its creation, with the details being presented in an earlier work from the authors in 2013.

My Scrawling Notes:

Special cases : moons, rings, comets, trojans; arXiv:1806.10032

Paper: Special cases: moons, rings, comets, trojans
Authors: Juan Cabrera, Maria Fernandez Jimenez, Antonio Garcia Munoz, Jean Schneider
Abstract: Non-planetary bodies provide valuable insight into our current under- standing of planetary formation and evolution. Although these objects are challeng- ing to detect and characterize, the potential information to be drawn from them has motivated various searches through a number of techniques. Here, we briefly review the current status in the search of moons, rings, comets, and trojans in exoplanet systems and suggest what future discoveries may occur in the near future. .

My Comment: Nice quick review - actually an (intro?) chapter for a larger review. Although posted to astro-ph today, the article is only current through mid 2017, and makes many references to the other chapters of the larger review series. Takeaway: we are in an era where smaller than planetary objects (rings, comets, moons, etc) may potentially be found around other star systems, but it is going to be a monumental task to cleanly separate an unambiguous signal of such from various systematics of the observations, and the fickleness of stars.

My Scrawling Notes:

The first polluted white dwarf from Gaia DR2: the cool DAZ GaiaJ1738−0826; arXiv:1806.09056

Paper: The first polluted white dwarf from Gaia DR2: the cool DAZ GaiaJ1738−0826
Authors: Carl Melis, B. Zuckerman, P. Dufour, I. Song, B. Klein
Abstract: We present the first metal-polluted single white dwarf star identified through Gaia DR2. GaiaJ1738-0826, selected from color and absolute magnitude cuts in the Gaia DR2 data, was discovered to have strong Ca~II absorption in initial spectroscopic characterization at Lick Observatory. Notably, GaiaJ1738-0826 resembles in many ways the first confirmed metal-polluted hydrogen atmosphere white dwarf, the DAZ G74-7.

My Comment: Really short article - mainly just an observation confirmation, but it makes use of GAIA DR2 to identify a candidate "weird" object, and then confirms what it is with follow-up observations, in this case spectra. I love this stuff, and wanted to grab a short GAIA DR2 paper to get started thinking about science that can be done with the data. Hint: it is a lot. Very a lot.

My Scrawling Notes:

The New Horizons Kuiper Belt Extended Mission - arXiv:1806.08393

Paper: The New Horizons Kuiper Belt Extended Mission 
Authors: S.A. Stern, H.A. Weaver, J.R. Spencer, H.A. Elliott, the New Horizons Team
Abstract: The central objective of the New Horizons prime mission was to make the first exploration of Pluto and its system of moons. Following that, New Horizons has been approved for its first extended mission, which has the objectives of extensively studying the Kuiper Belt environment, observing numerous Kuiper Belt Objects (KBOs) and Centaurs in unique ways, and making the first close flyby of the KBO 486958 2014 MU69. This review summarizes the objectives and plans for this approved mission extension, and briefly looks forward to potential objectives for subsequent extended missions by New Horizons.

My Comment: Two and a half days before closest encounter, the extended mission target 2014 MU69 will finally be 2 pixels on the LORRI instrument. That's um... rather quick!

My Scrawling Notes:

Page 1

Page 2

Page 3

Back again.

It has been a long time since I updated this dead blog, but I think that will change, at least for a little bit. To get back into the swing of professional astronomy again, instead of just job and home hunting, I’ve made a commitment to myself to read and take notes on one astro-ph article that comes out each day. Will I always succeed? No, but I’m going to make this a habit. To that end I’ll be posting links to some of the papers I look at, a favorite bit of the article, and my hand-scrawled notes to this blog. That favorite bit might not always be sciencey, it might just be a comment or stat that I found rather amusing or fun.

As I get back into this habit I hope to also get back to writing a bit of stuff for this blog, but for now this should at least get the ball rolling on my current plan.

A year long Curiosity

Just a few quick thoughts.  This week marks the one year anniversary of the Mars Science Laboratory Rover, Curiosity, landing in Gale Crater on the surface of Mars.  A year ago we deposited a ton of nuclear-powered robot on the surface of another world. 

NASA/JPL-Caltech

Since then it is have been roving, scooping, dusting, vaporizing rocks, and just sciencing the heck out of the red planet.  36,700 images, 76,000 rock-zapping laser shots, and 1.6 kilometers driven so far.  It still has about an 8 km drive to go to get to the lower layers of the 5.5 km tall Mt. Sharp.  Just in it’s first year Curiosity has already a world that looks downright “habitable” in the distant past – spectacularly finding the remains of a pebbled riverbed.

NASA / JPL-Caltech / MSSS / PSI

So happy “birthday” to the MSL Rover Curiosity – may there be many more rocks to bother in your future.