EARTH-MASS GAS PLANET
Harvard-Smithsonian Center for Astrophysics
Astronomers have discovered the first Earth-mass planet that transits
(passes in front of) its host star. KOI-314c has the smallest mass of
any planet (outside the Solar System) to have both its mass and
physical size measured. Surprisingly, although the planet has the
same mass as the Earth, it is 60% larger in diameter, so it is
certainly not Earth-like; it seems that there is no clear dividing
line between rocky planets like ours and fluffier ones like gas
giants. The team divined the planet's characteristics from data
obtained by the Kepler spacecraft. KOI-314c orbits a dim red-dwarf
star about 200 light-years away. It circles its star every 23 days.
The team estimates its temperature to be 105C. KOI-314c is only 30%
denser than water, which suggests that the planet is enveloped by a
significant atmosphere of hydrogen and helium hundreds of miles thick.
It might have begun as a mini-Neptune and lost some of its atmospheric
gases over time, boiled off by the intense radiation of its star.
Finding the mass of such a small planet was a challenge. Astronomers
usually determinee the mass of an exoplanet by measuring the tiny
motion induced in the parent star by the planet's gravity. That
method is extremely difficult for a planet with the Earth's mass. The
previous record for a planet with a measured mass (Kepler-78b) was 70%
more than the Earth. For KOI-314c, the team relied on a different
technique known as transit timing variations (TTV), a method that can
be used only when more than one planet orbits a star. The two planets
interact gravitationally, slightly changing the times that they
transit their star. By repeatedly measuring the times at which the
transits occurred, they were able to infer that the two planets are
locked in what is called a dynamical resonance. The second planet in
the system, KOI-314b, is about the same size as KOI-314c but
significantly denser, being about 4 times the mass of the Earth. It
orbits the star every 13 days, in a 5-to-3 resonance with the outer
planet. TTV is a quite a new method of finding and studying
exoplanets, first used successfully in 2010. The planet was
discovered by chance by the team as it scoured the Kepler data not for
exoplanets, but for exomoons. The 'Hunt for Exomoons with Kepler'
(HEK) project scans through Kepler's planet haul looking for TTV,
which can also be a signature of an exomoon. When astronomers noticed
that the planet showed transit timing variations, the signature was
clearly because of the other planet in the system and not a moon. At
first they were disappointed that it wasn't a moon but they soon
realized that it was nevertheless an interesting measurement.
NEW TYPE OF CELESTIAL OBJECT
University of Toronto
An object located near and probably orbiting a very young star about
440 light-years away is leading astrophysicists to believe that there
is not an easy-to-define line between planets and stars. Astronomers
have detailed measurements of the object spanning seven years, even a
spectrum revealing its gravity, temperature, and molecular
composition. Still they can't yet determine whether it is a planet or
a failed star -- a brown dwarf. Depending on what measurement you
consider, the answer could be either. Named ROXs 42Bb for its
proximity to the star ROXs 42B, the object is approximately nine times
the mass of Jupiter, below the limit most astronomers use to separate
planets from brown dwarfs, which are more massive. However, it is
located 30 times further away from the star than Jupiter is from the
Sun. Most astronomers believe that gas-giant planets like Jupiter and
Saturn formed by core accretion, whereby they form from a solid core
that then accretes a massive gaseous envelope. Core accretion
operates most efficiently closer to the parent star owing to the
length of time required to form the core in the first place. An
alternate theory proposed for forming gas-giant planets is disc
instability -- a process by which a fragment of a disc of gas
surrounding a young star collapses under its own gravity into a
planet. That mechanism works best farther away from the parent star.
Of the dozen or so other young objects observed by the team and having
masses appropriate to planets, some have planet-to-star mass ratios
less than about 10 times that of Jupiter and are located within about
15 times Jupiter's distance from the Sun. Others have much higher
mass ratios and/or are located at more than 50 times Jupiter's orbital
radius, properties that are similar to much more massive objects
widely accepted not to be planets. The first group would be planets
formed by core accretion, and the second group probably formed just
like stars and brown dwarfs. In between those two populations is a big
gap separating true planets from other objects. Astronomers say that
the new object starts to blur that distinction between planets and
brown dwarfs, and may lie within and begin to fill the gap. It is
hard to understand how the object could have formed in the way that
Jupiter is supposed to have done, but also it seems to have too low a
mass to be a typical brown dwarf; disc instability might just work at
its distance from the star. It may represent a new class of planets
or it may just be a rare very-low-mass brown dwarf formed like other
stars and brown dwarfs: a 'planet-mass' brown dwarf.
TRIPLE-STAR SYSTEM COULD CHECK THEORY OF GRAVITY
BBC News
Astronomers have discovered a triple-star system which might reveal
more of the nature of gravity. They found a pulsar with two white
dwarfs all packed into a space smaller than the Earth's orbit of the
Sun. The unusually close orbits allow precise measurements of gravity
and could resolve difficulties with gravitational theories. The
triple system represents a cosmic laboratory better than any found
before for learning exactly how such three-body systems work and
testing how well general-relativity theory holds up under extreme conditions.
Pulsars are formed after a supernova explodes and a remnant collapses
to a dense, highly magnetised ball of neutrons. They emit lighthouse-
like beams of radio waves that rapidly sweep through space as the
stars spin on their axes. Using the Green Bank Telescope, the
astronomers discovered a pulsar 4,200 light-years from Earth, spinning
nearly 366 times per second. Such rapidly-spinning bodies are called
millisecond pulsars -- and are used by astronomers as precise tools
for studying gravitational effects and other phenomena. Subsequent
observations showed the pulsar to be in a close orbit with a white-
dwarf star, and that that pair is in orbit with another, more-distant
white dwarf. Three-body systems are of interest because they allow
competing theories of gravity to be tested, but until now the only
known triple system containing a millisecond pulsar was one with a
planet as the outer companion, causing only weak gravitational
interactions. The gravitational perturbations imposed on each member
of the new system by the others are relatively strong. By precise
timing of the arrival of the pulses, the scientists were able to
calculate the geometry of the system and the masses of the stars. The
pulsar's inner white-dwarf companion has an orbital period of less
than two days, while the outer one has a period of almost a year. The
system gives the scientists the best opportunity yet to look for
violations of the equivalence principle described by Einstein -- which
states that the effect of gravity on a body does not depend on the
nature or internal structure of that body. That was famously
illustrated by Galileo's dropping of two balls of different weights
from the Leaning Tower of Pisa, and Apollo 15 Commander Dave Scott's
dropping of a hammer and a falcon feather while standing on the Moon
in 1971. Rather than drifting to the ground, the feather plummeted,
falling as fast as the hammer. With no air resistance to slow the
feather, both objects hit the lunar dust at the same time. While
Einstein's theory of general relativity has so far been confirmed by
every experiment, it is not compatible with quantum theory. Because
of that, physicists expect that it will break down under extreme
conditions. High-precision timing of the pulsar's 'lighthouse'
flashes may let astronomers hunt for deviations in the equivalence
principle at a sensitivity much greater than ever before.
ALMA OBSERVES SUPERNOVA DUST FACTORY ESO
Galaxies can be remarkably dusty, and supernovae are thought to be a
primary source of the dust, especially in the early Universe. But
direct evidence of a supernova's dust-making capabilities has been
slim up to now, and could not account for the copious amount of dust
detected in young, distant galaxies. But now observations with ALMA
are changing that. An international team of astronomers used ALMA to
observe the glowing remains of Supernova 1987A , which is in the Large
Magellanic Cloud, a dwarf galaxy orbiting the Milky Way about 160,000
light-years away. SN 1987A is the closest observed supernova
explosion since Kepler's observation of a supernova inside the Milky
Way in 1604. Astronomers predicted that as the gas cooled after the
explosion, large amounts of dust would form as atoms of oxygen,
carbon, and silicon bonded together in the cold central regions of the
remnant. However, earlier observations of SN 1987A with infrared
telescopes, made during the first 500 days after the explosion,
detected only a small amount of hot dust. Using ALMA, the research
team was able to image the far more abundant cold dust, which glows
brightly at millimetre and sub-millimetre wavelengths. The
astronomers estimate that the remnant now contains about a quarter of
a solar mass of newly formed dust. They also found that significant
amounts of carbon monoxide and silicon monoxide have formed.
Supernovae, however, can both create and destroy dust grains. As the
shock wave from the initial explosion radiated out into space, it
produced bright glowing rings of material, as seen in earlier
observations with the Hubble telescope. After hitting the envelope of
gas, which was thrown off by the progenitor red-giant star as it
neared the end of its life, a portion of the powerful explosion
rebounded back towards the centre of the remnant. At some point, the
rebounding shock wave will slam into the clumps of freshly minted dust
and it is likely that some fraction of the dust will be disrupted at
that point. If a good fraction of it survives and makes its way into
interstellar space, that would be a process that could account for the
copious amounts of dust that astronomers detect in the early Universe.
ISS LIFE TO BE EXTENDED BBC News
NASA has won White House backing to extend the life of the
International Space Station for a further four years, until 2024.
Construction of the ISS began in 1998 and is a joint venture between
the US, Russia, Canada, Japan, and states in the European Space Agency
(ESA). For the extension to happen, it is likely to need the
partners' support. Their current commitments run to 2020, but many
engineers believe that the station could work safely until at least
2028. NASA says that it would be feasible to continue operating the
ISS if some partners decided not to stay on board [pun?!], but it
expects them all to offer full support, even if the agreements take a
few years to put in place. Certainly, Germany, Europe's biggest
contributor to the ISS project, is keen to see the $100bn orbiting
platform operate for many years into the future.
At the moment, the station is entirely reliant on Russian Soyuz
capsules to exchange the platform's six-person crew. NASA is
therefore collaborating with American companies to help them design
and build alternatives. A proposed mini-shuttle known as the Dream
Chaser would be launched by an Atlas rocket from Cape Canaveral in
Florida. It is envisaged that the vehicle will make its maiden voyage
into orbit autonomously in 2016 and fly its first manned mission the
next year. The Ariane 5 was originally conceived as a manned
launcher, and Europe spent considerable funds designing its own
mini-shuttle called Hermes to go on top of the rocket, but budgetary
constraints eventually led to the Hermes project being cancelled.
NASA SPACECRAFT FINDS ITS FIRST NEW ASTEROID
NASA
The 'Near-Earth-Object Wide-field Infrared Survey Explorer' (NEOWISE)
spacecraft has discovered a never-before-seen asteroid -- its first
such discovery since coming out of hibernation last year. NEOWISE was
originally called the Wide-field Infrared Survey Explorer (WISE),
which had made the most comprehensive survey to date of asteroids and
comets. It discovered more than 34,000 asteroids and characterized
158,000 throughout the Solar System during its prime mission in 2010
and early 2011. It was re-activated in September followed 31 months
in hibernation, re-named and given a new mission, which is to assist
efforts to identify the population of 'potentially hazardous'
near-Earth objects (NEOs). NEOWISE can also assist in characterizing
previously detected asteroids that could be considered potential
targets for future exploration missions. NEOWISE's first discovery in
its renewed mission came on Dec. 29 -- a near-Earth asteroid
designated 2013 YP139. The mission's software picked out the moving
object against the background of stars. As NEOWISE circled the Earth
scanning the sky, it observed the asteroid several times over half a
day before the object moved beyond its view. 2013 YP139 was about 43
million kilometres away. From its infrared brightness, scientists
estimate it to be roughly 650 metres in diameter and extremely dark,
like a piece of coal. The asteroid is in an elliptical orbit inclined
to the plane of the Solar System and is classified as 'potentially
hazardous'. It is possible for its orbit to bring it as close as
300,000 miles from the Earth, a little more than the distance to the
Moon. However, it will not come so close within the next century.
COUNTDOWN TO PLUTO
NASA
One of the fastest spacecraft ever built -- 'New Horizons' -- is
hurtling along at nearly a million miles per day. Launched in 2006,
it has been in transit longer than some missions last, and it is
nearing its destination, Pluto. Closest approach is scheduled for
2015 July when New Horizons will pass only 10,000 km from Pluto, but
the spacecraft will be busy long before then. The first step, in 2015
January, is an intensive campaign of photography by the 'Long-Range
Reconnaissance Imager' (LORRI). LORRI will photograph the (former)
planet against known background star fields. The images will be used
to refine knowledge of the spacecraft's position with respect to
Pluto, which is uncertain by a few thousand kilometres, and allow
mission controllers to make any necessary corrections to its
trajectory. At first, Pluto and its large moon Charon will be little
more than distant pinpricks -- but soon they will swell into resolved
objects with their own personalities. By late April in 2015, the
approaching spacecraft should be taking pictures that surpass the best
images from Hubble. By closest approach in 2015 July, whole new
worlds will be opened up to the spacecraft's cameras. If New Horizons
passed the Earth at the same distance, it could see individual
buildings and their shapes.
Topic: January astronomy bulletin (Read 936 times)