SMALL ASTEROID IS THE EARTH'S CONSTANT COMPANION
NASA
A small asteroid has been discovered in an orbit around the Sun that
keeps it as a constant companion of the Earth, and it will remain so for
centuries to come. As it orbits the Sun, the new-found asteroid,
designated 2016 HO3, appears to circle around the Earth as well. It is
too distant to be considered a true satellite of our planet, but it is
the best and most stable example to date of a near-Earth companion.
Since 2016 HO3 loops around our planet, but never ventures very far away
as we both go round the Sun, we refer to it as a quasi-satellite of
Earth. One other asteroid -- 2003 YN107 -- followed a similar orbital
pattern for a while over 10 years ago, but it has since departed from
our vicinity. The new asteroid is much more locked onto us. Calcula-
tions indicate 2016 HO3 has been a stable quasi-satellite of the Earth
for almost a century. In its yearly orbit round the Sun, the asteroid
spends about half the time closer to the Sun than the Earth is, and
passes ahead of our planet, and the other half of the time farther away,
causing it to fall behind. Its orbit is also tilted a little, causing
it to pass up and then down once each year through the Earth's orbital
plane.
The asteroid's orbit also undergoes a slow, back-and-forth twist over
multiple decades. The asteroid's loops around the Earth drift a little
ahead or behind from year to year, but when they drift too far forward
or backward, the Earth's gravity is just strong enough to reverse the
drift and hold onto the asteroid so that it never wanders farther away
than about 100 times the distance of the Moon. The same effect also
prevents it from ever approaching much closer than about 38 times the
distance of the Moon. In effect, the small asteroid is caught in a
little dance with the Earth. Asteroid 2016 HO3 was first observed on
2016 April 27, by the Pan-STARRS 1 asteroid survey telescope in Hawaii.
The size of the object has not yet been firmly established, but it is
probably between 40 and 100 metres.
EXTREME TRANS-NEPTUNIAN OBJECTS AND PLANET 9
Plataforma SINC
In an effort to discover a ninth planet in the Solar System (Pluto no
longer having that distinction, being demoted), scientists in various
countries have been trying to calculate its orbit from the paths
followed by small bodies that move well beyond Neptune. Now,
astronomers from Spain and Cambridge University have confirmed, with
new calculations, that the orbits of the six extreme trans-Neptunian objects
that served as a reference to announce the existence of Planet Nine are
not as stable as it was thought. At the beginning of this year, astronomers
announced that they had found evidence of the existence of a giant planet
with a mass ten times larger than the Earth's in the confines of the Solar
System. Moving in an unusually elongated orbit, the planet would take
between 10,000 and 20,000 years to complete one revolution around the
Sun. To arrive at that conclusion, the team ran computer simulations with
input data based on the orbits of six extreme trans-Neptunian objects
(ETNOs): Sedna, 2012 VP113, 2004 VN112, 2007TG422, 2013 RF98
and 2010 GB174. Now, however, the team has considered the question
the other way round: how would the orbits of those six ETNOs evolve if a
Planet Nine, such as the one proposed, really did exist? With the orbit
indicated by the Caltech astronomers for Planet Nine, calculations show
that the six ETNOs would move in lengthy, unstable orbits. Those objects
would escape from the Solar System in less than 1.5 billion years, and in
the case of 2004 VN112, 2007 TG422 and 2013 RF98 they could
abandon it in less than 300 million years; what is more important, their
orbits would become unstable in just 10 million years, a really short time in
astronomical terms.
According to the new study, based on numerical (N-body) simulations, the
orbit of the new planet would have to be modified slightly so that the
orbits of the six ETNOs analysed would be really stable for a long time.
Those results also lead to a new question: are the ETNOs a transient and
unstable population or, on the contrary, are they permanent and stable?
The behaviour of those objects in one way or the other affects the
evolution of their orbits and also the numerical modelling. If the ETNOs
are transient, they are being continuously ejected and must have a
stable source located beyond 1,000 astronomical units (in the Oort
cloud) where they come from. But if they are stable in the long term,
then there could be many in similar orbits although we have not observed
them yet. In any case, the statistical and numerical evidence obtained
by the authors, both through this investigation and previous work, leads
them to suggest that the most stable picture is one in which there is
not just one planet, but rather several more beyond Pluto, in mutual
resonance. The situation is reminiscent of the one leading to the
discovery of Neptune, in which the French mathematician Urbain Le
Verrier was the first to "discover" a new planet by means of laborious
hand calculations based on the positions of Uranus, whereupon the German
astronomer J. G Galle directly observed it. If Neptune was the first
planet discovered by pen and paper, Planet Nine could be the first to
be discovered entirely from computerized numerical calculations.
STAR MAY HOLD CLUES TO PLANET FORMATION
NASA
In 1936, the young star FU Orionis began devouring material from its
surrounding disc of gas and dust with a sudden voracity. During a
three-month binge, the star became 100 times brighter, heating the disc
around it to temperatures of up to 7,000°K. FU Orionis is still
devouring gas to this day, although not as quickly. Its brightening is
the most extreme event of its kind that has been confirmed around a star
the size of the Sun, and may have implications for how stars and planets
form. The intense baking of the star's surrounding disc probably
changed its chemistry, permanently altering material that could one day
turn into planets. Our own Sun may have gone through a similar
brightening, which would have been a crucial step in the formation of
the Earth and other planets in the Solar System. Visible-light
observations of FU Orionis, which is about 1,500 light-years distant,
have shown astronomers that the star's extreme brightness began slowly
fading after its initial 1936 outburst. But astronomers wanted to know
more about the relationship between the star and surrounding disc. Is
the star still gorging on it? Is its composition changing? When will
its brightness return to pre-outburst levels? To answer those
questions, scientists needed to observe the star's brightness at
infrared wavelengths to provide temperature measurements. The team
compared infrared data obtained with the Stratospheric Observatory for
Infrared Astronomy (SOFIA) to observations made with the Spitzer space
telescope. By combining data collected from the two telescopes over a
12-year interval, scientists were able to gain a perspective on the
star's behaviour over time. Using those observations and other
historical data, researchers found that FU Orionis had continued its
rapid accretion after the initial brightening event -- it has accreted
the equivalent of 18 Jupiters in the last 80 years.
The recent measurements provided by SOFIA inform researchers that the
total amount of visible and infrared light energy coming out of the
FU Orionis system decreased by about 13% over the 12 years since the
Spitzer observations. Researchers found that the decrease has been
caused by dimming of the star at short infrared wavelengths, but not at
longer wavelengths. That means up to 13% of the hottest material of the
disc has disappeared, while the cooler material has remained intact. A
decrease in the hottest gas means that the star is eating the innermost
part of the disc, but the rest of the disc has essentially not changed
in the last 12 years. That result is consistent with computer models,
but for the first time we are able to confirm the theory with
observations. Astronomers predict, partly on the basis of the new
results, that FU Orionis will run out of hot material to consume within
the next few hundred years. At that point, it will return to the state
it was in before the dramatic 1936 brightening event. Scientists are
unsure what the star was like before or what set off the feeding frenzy.
The material falling into the star is like water from a hose that is
slowly being pinched off, and eventually the water will stop. If the
Sun ever had a brightening event like FU Orionis did in 1936, it could
explain why certain elements are more abundant on Mars than on Earth. A
sudden 100-fold brightening would have altered the chemical composition
of material close to the star, but not as much farther from it. Because
Mars formed farther from the Sun, its component material would not have
been heated up as much as the Earth's was. At a few hundred thousand
years old, FU Orionis is a newborn in relation to the typical lifespan
of a star. The 80 years of brightening and fading since 1936 represent
only a tiny fraction of the star's existence so far, but those changes
have happened to occur at a time when astronomers exist and could
observe. It is surprising that an entire protoplanetary disc can change
on such a short time-scale, within a human lifetime.
MILKY WAY'S MISSING RED GIANTS
Georgia Institute of Technology
New computer simulations provide a conclusive test for a hypothesis of
why the centre of the Milky Way appears to be filled with young stars
but has very few old ones. According to the theory, the remnants of
older, red-giant stars are still there, but they are not bright enough
to be detected with telescopes. The simulations investigate the
possibility that the red giants were dimmed after they were stripped of
a large percentage of their mass millions of years ago during repeated
collisions with an accretion disc at the Galactic Centre. The very
existence of the young stars, seen in astronomical observations today,
is an indication that such a gaseous accretion disc was present at the
Galactic Centre, because the young stars are thought to have formed from
it as recently as a few million years ago. The study is the first to
run computer simulations on the theory, which was introduced in 2014.
The team created models of red giants similar to those that are
supposedly missing from the Galactic Centre -- stars that are more than
a billion years old and dozens of times larger in size than the Sun.
They put them through a computerized version of a wind tunnel to
simulate collisions with the gaseous disc that once occupied much of the
space within half a parsec of the Galactic Centre. They varied orbital
velocities and the disc's density to find the conditions required to
cause significant damage to the red-giant stars.
Red giants could have lost a significant portion of their mass only if
the disc were very massive and dense. So dense that gravity would have
already fragmented the disc on its own, helping to form massive clumps
that became the building blocks of a new generation of stars. The
simulations suggest that each of the red-giant stars orbited its way
into and through the disc as many as dozens of times, sometimes taking
as long as days to weeks to complete a single pass-through. Mass was
stripped away with each collision as the star blistered the fragmenting
disc's surface. It is a process that would have taken place 4 to 8
million years ago, which is the same age as the young stars seen in the
centre of the Milky Way today. The only way for that scenario to take
place within that relatively short time frame would be if, to begin
with, the disc that fragmented had a much larger mass than all the young
stars that eventually formed from it -- at least 100 to 1,000 times more
mass. The impacts also probably lowered the kinetic energy of the red
giant stars by at least 20--30%, shrinking their orbits and pulling them
closer to the Milky Way's black hole. At the same time, the collisions
may have torqued the surface and spun up the red giants, which are
otherwise known to rotate relatively slowly in isolation.
SMALL PLANETS HIDING IN GIANT CLOAKS
RAS
Hazes and clouds high up in the atmospheres of exo-planets may make
them appear bigger than they really are, according to new research by
astronomers at the Space Research Institute (IWF) of the Austrian
Academy of Sciences. Since the first confirmed discovery in 1993,
astronomers have found more than 3,000 planets in orbit around stars
other than our Sun. A key goal now is to characterize known planets by
mass, size and composition, in the effort to understand the evolution of
planetary systems, and the prospects for 'Earthlike' planets that might
support life. In 2014 the team used ESA's CoRoT space telescope to
study the upper atmospheres of two low-mass planets that are regularly
seen to transit in front of the star they orbit. The two planets orbit
their star in 5 and 12 days, appear to be around 4 and 5 times the
diameter of the Earth, and have respective masses of less than 6, and
28, times that of the Earth. The outer, more massive planet, CoRoT-24c,
is similar in mass to Neptune; the inner planet, CoRoT-24b, is less than
a quarter as massive, but is similar in size, so seems to have a very
low density. With orbits of such short periods, both planets must be
close to the star and experience dramatic heating. The team modelled
that, and found that the lower-mass planet would see its atmosphere
evaporate within 100 million years, if it really is as big as is
suggested. But the star is billions of years old, so the planet should
have lost its atmosphere long ago. The solution seems to be that the
planet is only about half as big as has been thought. It is suggested
that an extended, very thin, atmosphere surrounds a relatively compact
planet, but has high-altitude features that confuse observations. The
radius is based on what we see when the planet makes its transit. The
result is probably falsified by clouds and haze high in the atmosphere,
in a region where the atmospheric pressure is very low. Such an effect
needs to be considered by future exo-planet missions, like the ESA
CHaracterising ExOPlanets Satellite (CHEOPS) mission that is due to be
launched in late 2017. Results for some planets found by the Kepler
observatory may also need to be re-evaluated. Since Kepler has also
discovered several similar low-density and low-mass planets, it is very
likely that the sizes measured for many of them also differ from the
true values, so there could be a bias in the results. If the Austrian
team is right, its conclusion has considerable implications, for example
in the studies of planet populations and how the masses of planets
relate to their sizes.
DETECTION OF METHYL ALCOHOL IN PROTOPLANETARY DISC
ESO
The organic molecule methyl alcohol (methanol) has been found by the
Atacama Large Millimetre/Submillimetre Array (ALMA) in the TW Hydrae
protoplanetary disc. This is the first such detection of the compound
in a young planet-forming disc. Methanol is the only complex organic
molecule that unambiguously derives from an icy form and that has been
detected in discs. Its detection helps astronomers to understand the
chemical processes that occur during the formation of planetary systems
and that ultimately lead to the creation of the ingredients for life.
The protoplanetary disc around the young star TW Hydrae is the closest
known example to Earth, at a distance of about 170 light-years. The
system resembles what astronomers think the Solar System must have
looked like during its formation more than four thousand million years
ago. Furthermore, methanol is itself a building block for more complex
compounds of pre-biotic importance, like amino-acid compounds. As a
result, methanol plays a vital role in the creation of the rich organic
chemistry needed for life. Gaseous methanol in a protoplanetary disc
has a unique importance in astrochemistry. While other species detected
in space are formed by gas-phase chemistry alone, or by a combination of
both gas- and solid-phase generation, methanol is a complex organic
compound which is formed solely in the ice phase via surface reactions
on dust grains. The observation of methanol in the gas phase, combined
with information about its distribution, implies that methanol formed on
the disc's icy grains, and was subsequently released in gaseous form.
This first observation helps to clarify the puzzle of the methanol
ice--gas transition, and more generally the chemical processes in
astrophysical environments.
UNIVERSE'S FIRST LIFE BORN ON CARBON PLANETS?
Harvard-Smithsonian Center for Astrophysics
Our Earth consists of silicate rocks and an iron core with a thin veneer
of water and life. But the first potentially habitable planets to form
might have been very different. New research suggests that planet
formation in the early Universe might have created carbon planets
consisting of graphite, carbides, and diamond. Astronomers might find
such diamond planets by searching a rare class of stars. The primordial
Universe consisted mostly of hydrogen and helium, and lacked chemical
elements like carbon and oxygen necessary for life as we know it. Only
after the first stars exploded as supernovae and seeded the second
generation did planet formation and life become possible. Astronomers
examined a particular class of old stars known as carbon-enhanced
metal-poor stars, or CEMP stars. Those anaemic stars contain only one
hundred-thousandth as much iron as the Sun; evidently they formed before
interstellar space had been widely seeded with heavy elements. Such
stars are fossils from the young Universe. By studying them, we can
look at how planets, and possibly life, got started. Although lacking
in iron and other heavy elements compared to the Sun, CEMP stars have
more carbon than would be expected given their age. That relative
abundance would influence planet formation, as fluffy carbon dust grains
clump together to form tar-black planets. From a distance, carbon
planets would be difficult to tell apart from more Earth-like ones.
Their masses and physical sizes would be similar. Astronomers would
have to examine their atmospheres for signs of their true nature. Gases
like carbon monoxide and methane would envelop those unusual planets.
A dedicated search for planets around CEMP stars can be done by the
transit technique.
NAMES PROPOSED FOR NEW ELEMENTS
BBC News
Names have now been proposed for the four new chemical elements
added to the periodic table in January. They are nihonium (with the
symbol Nh), moscovium (Mc), tennessine (Ts), and oganesson (Og). Until
now, the quartet has been referred to simply by the number of protons in
each atom - 113, 115, 117 and 118, respectively. The elements are the
first to be added to the famous table since 2011, and complete its seventh
row. The names must go out to consultation for five months, but if
there are no objections their confirmation should be a formality. That
will come from the International Union of Pure and Applied Physics and
the International Union of Pure and Applied Chemistry. All four
elements are extreme -- the synthetic creations of scientists. None of
them exists outside the lab; they were made by bombarding two smaller
(albeit still very large) atomic nuclei together. Theory predicts that
there are 'islands of stability' in the high reaches of the periodic
table where certain combinations should stick and hold together -- but
even then that state is usually only fleeting.
Uranium (92 protons) is the heaviest naturally occurring element on
Earth in any significant abundance. Nonetheless, the exercise does
provide scientists with valuable insights into the structure of atomic
nuclei and the properties that stem from it. As is customary, the
discoverers of the new elements had the right to suggest a name. The
rules state that that can reflect a mythological concept, a mineral, a
place or country, a property or a scientist. The name also has to be
unique and maintain 'historical and chemical consistency'. That
explains why there is a lot of '-iums' in the table. Nihonium refers
to the Japanese name for Japan. The atom was discovered at the RIKEN
Nishina Centre for Accelerator Science. Moscovium was named after
the Moscow region, the location of the Joint Institute for Nuclear
Research in Dubna. Tennessine recognises the US state of Tennessee
and the local contributions made to the discovery by the Oak Ridge
National Laboratory and Vanderbilt University. Oganesson honours the
nuclear physicist Yuri Oganessian, who has played a leading role in the
search for new elements including the one that will now bear his name.
OBSERVATION OF MOST DISTANT OXYGEN
ESO
A team of astronomers has used the Atacama Large Millimetre/submilli-
metre Array (ALMA) to detect glowing oxygen in a distant galaxy seen
just 700 million years after the Big Bang. That is the most distant
galaxy in which oxygen has ever been unambiguously detected, and it is
most likely being ionized by powerful radiation from young giant stars.
That galaxy could be an example of one type of source responsible for
cosmic reionization in the early history of the Universe. The galaxy,
SXDF-NB1006-2, lies at a redshift of 7.2. The team was hoping to find
out about the heavy chemical elements present in that galaxy, as they
can tell us about the level of star formation, and hence provide clues
about the period in the history of the Universe known as cosmic
reionization. In the time before objects formed in it, the Universe was
filled with electrically neutral gas. But when the first objects began
to shine, a few hundred million years after the Big Bang, they emitted
powerful radiation that started to break up those neutral atoms and
ionize the gas. During that phase, known as cosmic reionization, the
whole Universe changed dramatically. But there is much debate about
what kinds of objects caused the reionization. Studying the conditions
in very distant galaxies may help to answer that question.
Before observing the distant galaxy, the researchers performed computer
simulations to predict how easily they could expect to see evidence of
ionized oxygen with ALMA. They also considered observations of similar
galaxies that are much closer to the Earth, and concluded that the
oxygen emission should be detectable, even at vast distances. They then
carried out high-sensitivity observations with ALMA and found light from
ionized oxygen in SXDF-NB1006-2, making that the most distant
unambiguous detection of oxygen ever obtained. It is firm evidence for
the presence of oxygen in the early Universe, only 700 million years
after the Big Bang. Oxygen in SXDF-NB1006-2 was found to be ten times
less abundant than it is in the Sun. The small abundance is expected
because the Universe was still young and had a short history of star
formation at that time. The team was unable to detect any emission from
carbon in the galaxy, suggesting that that young galaxy contains very
little un-ionized hydrogen gas, and also found that it contains only a
small amount of dust, which is made up of heavy elements. The detection
of ionized oxygen indicates that many very brilliant stars, several
dozen times more massive than the Sun, have formed in the galaxy and
are emitting the intense ultraviolet light needed to ionize the oxygen
atoms. The lack of dust in the galaxy allows the intense ultraviolet
light to escape and ionize vast amounts of gas outside the galaxy.
SXDF-NB1006-2 must be an example of the type of light sources
responsible for the cosmic reionization.
CHIRAL MOLECULE DETECTED IN INTERSTELLAR SPACE
National Radio Astronomy Observatory
Like a pair of human hands, certain organic molecules have mirror-image
versions of themselves, a chemical property known as chirality. Those
so-called 'handed' molecules are essential for biology and have
intriguingly been found in meteorites on Earth and comets in the Solar
System. None, however, has been detected in interstellar space, until
now. The molecule, propylene oxide (CH3CHOCH2), was found near the
centre of the Galaxy in an enormous star-forming cloud of dust and gas
known as Sagittarius B2 (Sgr B2). The research was undertaken primarily
with the Green Bank Telescope (GBT) in West Virginia as part of the
'Prebiotic Interstellar Molecular Survey'. Additional supporting
observations were taken with the Parkes radio telescope in Australia.
This is the first molecule detected in interstellar space that has the
property of chirality, making it an advance in our understanding of how
prebiotic molecules are made in the Universe and the effects they may
have on the origins of life. Propylene oxide is among the most complex
and structurally intricate molecules detected so far in space. Detect-
ing that molecule opens the door for further experiments determining how
and where molecular handedness emerges and why one form may be slightly
more abundant than the other. Complex organic molecules form in inter-
stellar clouds like Sgr B2 in several ways. The most basic pathway is
through gas-phase chemistry, in which particles collide and merge to
produce ever more complex molecules. Once organic compounds as
large as methanol (CH3OH) are produced, however, the process
becomes much less efficient.
Astronomers believe that to form more complex molecules, like propylene
oxide, thin mantles of ice on dust grains help link small molecules into
longer and larger structures. Those molecules can then evaporate from
the surface of the grains and further react in the gas of the surround-
ing cloud. To date, more than 180 different molecules have been detected
in space. Each molecule, as it naturally tumbles and vibrates in the
near-vacuum interstellar medium, gives off a distinctive signature, a
series of telltale spikes that appear in the radio spectrum. Larger and
more complex molecules have correspondingly more complex signatures,
making them harder to detect. To claim a definitive detection,
scientists must observe multiple spectral lines associated with the same
molecule. In the case of propylene oxide, the research team detected
two such lines with the GBT. The third was at a frequency difficult to
observe from the northern hemisphere owing to satellite radio
interference. Scientists used the Parkes telescope to tease out the
final spectral line needed to verify their results. The current data,
however, do not distinguish between the left- and right-handed versions
of the molecule. In addition to the same chemical composition, chiral
molecules have the same melting, boiling, and freezing points, and the
same spectra. Those spectra are like your hands' shadows. It is
impossible to tell if a right hand or a left hand is casting the shadow.
That presents a challenge to researchers trying to determine if one
version of propylene oxide is more abundant than the other. Every
living thing on Earth uses one, and only one, handedness of many types
of chiral molecules. That trait, called homochirality, is critical for
life and has important implications for many biological structures,
including DNA's double helix. Scientists do not yet understand how
biology came to rely on one handedness and not the other. The answer,
the researchers speculate, may be found in the way these molecules
naturally form in space before being incorporated into asteroids and
comets and later deposited on young planets. The researchers believe
that it may eventually be possible to determine if there is an excess of
one handedness of propylene oxide over the other by examining how
polarized light interacts with the molecules in space.
Topic: Early July Astronomy Bulletin (Read 1531 times)