[meteorite-list] OT: Plutonian Planets, Undiscovered Nearby Stars

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Sun Jul 31 18:55:57 2005
Message-ID: <42ED56DA.45911DF1_at_bhil.com>

Hi,

    An assortment of stuff about near(er)by stars, KBO's, and other
topics of interest to somebody...

    A "zoomable" 3-D map of (known) stars within 12.5 light years. You
can zoom it out to the entire galaxy in steps. Very neat.
<http://anzwers.org/free/universe/12lys.html>

    Hipparchos data suggest:
"a value of 11.7 +/- 1.3 stellar encounters per Myr within one pc of
the Sun." or about one every 80,000 to 100,000 years.

    I poo-poohed a big KBO being an extra-solar object, but not
everybody does. These guys say a 10% chance. A planet from another
star?!
Stellar encounters as the origin of
distant solar system objects
in highly eccentric orbits by:
Kenyon, Scott J ; Bromley, Benjamin C.
    "Abstract: The discovery of Sedna places new constraints on the
origin and evolution of our solar system. Here we investigate the
possibility that a close encounter with another star produced the
observed edge of the Kuiper belt, at roughly 50 AU, and the highly
elliptical orbit of Sedna. We show that a passing star probably
scattered Sedna from the Kuiper Belt into its observed orbit. The
likelihood that a planet at 60-80 AU can be scattered into Sedna's orbit
is roughly 50%; this estimate depends critically on the geometry of the
flyby. Even more interesting, though, is the roughly 10% chance that
Sedna was captured from the outer disk of the passing star. Most
captures have very high inclination orbits; detection of these objects
would confirm the presence of extrasolar planets in our own Solar
System."
    Notice that they "thought" the edge of the KB was at 50 AU, Whoops!
2003 UB313 at 97, and 2003 EL61 at 51.


    Closest star passage in the future?
Close Approaches of Stars
to the Solar System, by
P. R. Weissman, J. Garcia-Sanchez,
R. A. Preston, D. L. Jones
(Jet Propulsion Laboratory),
J.-F. Lestrade Observatoire de Paris-Meudon/CNRS),
D. W. Latham (Harvard-Smithsonian CfA)
    "Only one star, Gliese 710, is found with a predicted closest
approach distance <100,000 AU (0.5 parsecs), although several stars
come within about 1 parsec during a 8.5 Myr interval. The predicted
minimum distance for Gliese 710 is 53,000 to 71,000 AU, approximately
1.0 to 1.4 Myr in the future. Gliese 710 is a late-type dwarf star (dM1
or K7 V) with an estimated mass of 0.42 solar masses, and is currently
about 19 parsecs from the Sun. The star may be a binary."


    Planets at all?
Are stars with planets anomalous?
Guillermo Gonzalez
    "The chemical-dynamical properties of stars with giant planets are
compared to those of a nearby star sample within the framework of a
stellar orbital diffusion model. The stars-with-planets sample includes
recently discovered extrasolar planets and the Sun. We find that the
planet-bearing stars, 14 Her, rho-1 Cnc and tau Boo, are much more
metal-rich than stars of similar age and this cannot be easily explained
by orbital diffusion. We also confirm previous claims that the motion of
the Sun relative to the local standard of rest is very small compared to
other G dwarfs of similar age, and we offer a possible explanation for
this apparent anomaly."


    There's good news and bad news...

The Close Approach of Stars in the Solar Neighbourhood Quarterly Journal
of the Royal Astronomical Society 35 1-9 1994:
    "At present, 58 stars are known to lie within a radius of about 5
parsecs of the Sun, and thus within the so-called "Solar Neighbourhood".
In this paper, I calculate the trajectories and distances of those
making the closest approach to the Sun over the next 50,000 years. I
find that Proxima Centauri has been the closest star to the Sun for the
last 32,000 years, but will lose this status to the dwarf star Ross 248
in 33,000 years' time. We are approaching a period relatively rich in
stellar encounters, with six stars coming closer to the Sun that
Proxima's current distance within the next 45,000 years. Only the close
approach of Alpha Centauri A/B - which has a combined mass more than
twice that of our Sun - will have any noticeable dynamical effects,
however. In particular, it has already begun to perturb the outer Oort
Cloud of comets, and will put around 100,000 comets into potentially
Earth-impacting orbits."

    100,000 comets in Earth-impacting orbits? You did say 100,000,
didn't you? I thought so. Do I start digging the shelter now?

    Update on Earth Trojans (subject of an earlier thread):
<http://www.rssd.esa.int/SA-general/Projects/GAIA_files/LATEX2HTML/node118.html>

    They'll be searching Venus Trojan points for the first time ever,
among other things.
    The same site about the dynamic properties of KBO's:
<http://www.rssd.esa.int/SA-general/Projects/GAIA_files/LATEX2HTML/node119.html>

    This group hoped to find Pluto-sized KBO's. Good idea, but too late.
They haven't launched yet. They explain the difficulties of finding them
with earth-based telescopes, which are considerable.
    Brown did just fine, though...

    About the frequency of L class stars:
    "Class T and L could be more common than all the other classes
combined, if recent research is accurate. From studying the number of
proplyds (protoplanetary discs, clumps of gas in nebulae from which
stars and solar systems are formed) then the number of stars in the
galaxy should be several orders of magnitude higher than what we know
about. It's theorised that these proplyds are in a race with each other.
The first one to form will become a proto-star, which are very violent
objects and will disrupt other propylids in the vicinity, stripping them
of their gas. The victim propylids will then probably go on to become
main sequence stars or brown dwarf stars of the L and T classes, but
quite invisible to us. Since they live so long (no star below 0.8 solar
masses has ever died in the history of the galaxy) then these smaller
stars will accumulate over time."


    They're looking for that L class near the Sun, apparently:
Announcement of New Spectral Class of Stars: L Dwarfs, by
J. D. Kirkpatrick, R. M. Cutri, B. Nelson, C. A. Beichman (IPAC,
Caltech), I. N. Reid (Caltech), J. Liebert (U.Arizona), C. C. Dahn, D.
G. Monet (U.S.Naval Observatory, Flagstaff), M. F. Skrutskie
(U.Massachusetts, Amherst)
    "Summary: A new spectral class of stars, L Dwarfs, has been defined
that extends the previously-defined spectral classes of normal stars to
cooler objects. 20 new sources have been found in only 1% of the 2MASS
data, which was enough to define a temperature sequence with 9
subdivisions for the L spectral class, L0-L8. At least 6 of these
sources are brown dwarfs, objects formed like stars but which will never
sustain hydrogen burning, and hence will fade from view much more
rapidly than normal stars.
    The L Dwarfs do not contribute much matter to the Galaxy since they
individually weigh typically perhaps one-twentieth the mass of the sun.
However, they probably outnumber all other spectral classes of stars
combined. This directly implies that there is a good chance that an L
dwarf is the closest source to the Solar System, beating out Proxima
Centauri, an M5 star 1.3 pc (4.3 light-years) distant. Further 2MASS
work will find out whether such a source exists."

    Keep looking...


Sterling K. Webb
Received on Sun 31 Jul 2005 06:55:22 PM PDT