SPIRAL ASTEROID
Spaceweather.com
The International Astronomical Union has announced the discovery of a
spiral structure around main-belt asteroid (596) Scheila. Astronomers
found the curious shape in images obtained on Dec. 11 through the
Catalina 0.68-m Schmidt telescope. Other observers have since
confirmed the phenomenon. It is possible that a small asteroid might
have hit 596 Scheila, raising a cloud of dust which forms a nebula
around the larger space rock. A 1-m-class impactor could be large
enough. Alternatively, 596 Scheila might be a rare main-belt comet, a
body with the orbital characteristics of an asteroid and the physical
characteristics of a comet. If so, a pocket of volatile ice might be
vaporizing to produce the spiralling tail.
EARTHLY GOLD CAME FROM ASTEROID BOMBARDMENT
University of Maryland
New findings appear to suggest that gold, platinum, palladium, and
other such elements found in the crusts and mantles of the Earth, the
Moon, and Mars arrived on mini-planet-sized impactors during the final
phase of planet formation in the Solar System. The massive collisions
occurred within tens of millions of years after the even bigger impact
that has in recent years been supposed to have produced our Moon.
Current understanding of the formation of the Earth and other planets
with iron cores and silicate mantles suggests that heavy elements are
pulled into the planet cores as they form. Thus, we should have an
Earth that has almost no gold or heavy-metal ores in its crust for us
to mine. The fact that we do has long suggested that something must
have happened to bring more heavy elements to the Earth after
completion of the separation of the metallic core and silicate mantle.
But it has been open to question whether such late accretion of
material occurred in big chunks over a relatively short period of time
or as a 'rain' of smaller pieces of material over a longer time.
Now, some astronomers have used numerical models to try to see what
size objects would best match the needed criteria. The criteria
include (1) providing the right amount of heavy metals to the Earth,
Moon and Mars; (2) being large enough to breach the crusts and mantles
of these bodies, creating local molten rock ponds from their impact
energy and efficiently mixing into the mantle; and (3) not being so
large as to cause a fragmenting and reformation of the planet cores,
which would result in most of the newly added elements being pulled
down into the cores. The best results were obtained if the late-
accretion population were dominated by a limited number of massive
projectiles. The largest Earth impactor would be roughly the size
of Pluto, while those hitting the Moon would be 250 to 300 km across.
The team asserts that those impactor sizes are consistent with
physical evidence such as the size distributions of present asteroids
and of ancient Martian impact scars.
ANOTHER NEW PLANET
University of California
Astronomers using the Keck II telescope in Hawaii say that a
planetary system in which they have obtained images showing a fourth
planet resembles an over-sized version of our Solar System. Besides
having four giant planets, both systems also contain two 'debris
belts' composed of small rocky or icy objects, along with lots of
dust. The planets orbit a sixth-magnitude star called HR 8799, which
is 40 parsecs away. The astronomers estimate that the combined mass
of the four giant planets may be 20 times greater than the mass of all
the planets in our Solar System, and the debris belts also contain
much more mass than our own. The newly discovered planet orbits
HR 8799 more closely than the other three, at a distance that would
correspond in the Solar System to between the orbits of Saturn and
Uranus.
'ZIRCONIUM STAR'
RAS
Astronomers from Armagh Observatory in Northern Ireland have found
what appears to be the most zirconium-rich star ever analysed. They
made the discovery while looking for chemical clues to explain why a
small group of stars known as helium-rich hot subdwarfs, which are
reaching the end of their lives, have much less hydrogen on their
surfaces than most otherwise similar stars. Using data obtained with
the Anglo-Australian Telescope at Siding Spring in New South Wales,
they looked at the evolved star LS IV -14° 116, 600 parsecs away
towards the border between the constellations of Capricornus and
Aquarius.
The spectrum of LS IV -14° 116 had the usual lines arising from common
elements, but other strong lines were less easy to identify. Four of
the lines proved to be due to Zr IV (triply-ionized zirconium), that
exists only at temperatures above 20 000°C and had never previously
been identified in an astronomical spectrum. The zirconium abundance
is about ten thousand times as high as in the Sun. Other spectral
lines proved to come from Sr II, Ge III and Y III (ionized strontium,
germanium and yttrium), and those elements are between one thousand
and ten thousand times more abundant than normal. The astronomers
argue that the unusual abundances in LS IV -14° 116 are caused by
stratification of elements in the star's atmosphere -- the only part
of a star that can be seen directly. A process called radiatively-
driven diffusion can concentrate certain elements, mainly metals
heavier than calcium, in the layer that we observe, even though their
overall abundances in the star as a whole may be near normal. It is
suggested that the star is shrinking from being a bright cool giant to
a faint hot subdwarf. As the star shrinks, different elements sink
down or float up in the atmosphere to a region where they become
highly visible, making the apparent composition very sensitive to
the star's recent history.
SUPER-EARTH ATMOSPHERE OBSERVED
ESO
Astronomers have confirmed the existence of an atmosphere around a
'super-Earth' exo-planet known as GJ 1214b, observed as it transited
in front of its parent star and some of the starlight passed through
its atmosphere. GJ 1214b is about 2.6 times as big as the Earth and
6.5 times as massive. It is about 12 parsecs away, towards Ophiuchus.
It is a faint star, but is also small, so the size of the planet is
not too small compared to the stellar disc, making it relatively easy
to study. The planet crosses the disc of its parent star once every
38 hours as it orbits at a distance of only two million kilometres --
70 times closer than the Earth is to the Sun. Although there is now
known to be an atmosphere around the planet, it has not been possible
to decide whether it is made mostly of water in the form of steam, or
is obscured, dominated by thick clouds or hazes.
VENUS PROBE MISSES TARGET
Science Daily
A Japanese probe bound for Venus has failed to reach orbit and is now
heading towards the Sun. It was designed to monitor volcanic activity
and provide data on the thick cloud cover and climate, including
whether the planet has lightning. It will be six years before the
Japanese Space Agency can make another attempt. Japan has never
succeeded in an interplanetary mission but has previously launched
several rockets into space; in 1998 it launched a Mars mission that
was plagued by technical glitches and was finally abandoned in 2003.
Topic: Mid December Astronomy Bulletin (Read 742 times)