VERY DARK EXO-PLANET
RAS
Astronomers have discovered a remarkably dark exo-planet -- a distant,
Jupiter-sized gas giant known as TrES-2b. It orbits the star GSC
03549-02811, about 750 light-years away in the constellation Draco.
TrES-2b was discovered in 2006 by the Trans-Atlantic Exoplanet Survey
(TrES). TrES-2b apparently reflects less than 1% of the starlight
falling on it, making it blacker than coal or any planet or moon in
our Solar System. In our Solar System, Jupiter is swathed in bright
clouds of ammonia that reflect more than a third of the sunlight
reaching them, whereas TrES-2b lacks reflective clouds owing to its
high temperature. It orbits at a distance of only five million
kilometres from its star, which heats it to more than 1000°C. Its
atmosphere contains light-absorbing chemicals like vaporized sodium
and potassium, or gaseous titanium oxide. Yet none of those chemicals
fully explains the extreme blackness of TrES-2b.
Astronomers used data from the Kepler spacecraft, which is designed to
measure the brightnesses of stars with extreme precision, to estimate
the reflectivity of TrES-2b. They monitored the brightness of the
TrES-2 system as the planet orbited its star. They detected a subtle
dimming and brightening due to the planet's changing phase. TrES-2b
is believed to be tidally locked like our Moon, so one side of the
planet always faces the star and the planet shows changing phases as
it orbits the star, causing the total brightness of the star plus
planet to vary slightly. By combining the data from Kepler over 50
orbits, the team detected a minute change in brightness of 6 parts per
million. The extreme smallness of the fluctuations indicated that
TrES-2b is incredibly dark.
INTERSTELLAR CRASHES COULD THROW OUT HABITABLE PLANETS
RAS
Our Solar System, where planets have a range of sizes and move in
near-circular paths, may be rather unusual, according to a German-
British team of the University of Bonn. The astronomers find that, in
the course of formation, planetary systems may be knocked around by
crashes with nearby clumps of material, leading to systems where
planets have highly inclined orbits and where the smaller (and
potentially habitable) ones are thrown out completely. The planets in
our Solar System, including the Earth, travel around the Sun in the
same direction as the Sun spins, mostly move in paths not very
different from circles, and are also more or less lined up into a
plane not tilted very much with respect to the solar equator. But
planets around other stars can be very different, with some moving in
the opposite direction to the spin of their stars and with highly
inclined orbits. For the first time the astronomers think that they
have a model that explains such radically different systems.
Both the shape of and direction of travel of planets in our Solar
System were thought to result entirely from the formation of the Sun
and planets more than 4600 million years ago. Our local planetary
system is believed to have formed as a cloud of gas and dust (a
nebula) that collapsed into a rotating disc under the influence of
gravity. The planets then grew from clumps of material within that
proto-planetary disc. The new work suggests that oddly shaped orbits
may result from a rather less smooth process. The team thinks that if
the proto-planetary disc enters another cloud of material, it can draw
off up to about 30 times the mass of Jupiter from the cloud. Adding
that extra gas and dust tilts the disc and hence the angle of the
final orbits. Most planetary systems are thought to form in clusters
of stars, where the member stars are fairly close together, so
encounters may be very common.
Computer simulations show that as well as tilting over, loading the
proto-planetary disc with material can even reverse its spin and cause
it to rotate in the opposite sense to its parent star. At the same
time, the encounter compresses the inner region of the disc, possibly
speeding up the planetary formation process. In those circumstances,
the simulation suggests that any planets that form will be in highly
inclined or even retrograde orbits. In some cases the orbits may even
be tilted with respect to one another, leading to a highly unstable
system. One by one, the least-massive planets will be ejected
completely, leaving behind a small number of 'hot Jupiters', massive
planets that move in orbits extremely close to their star. In less
extreme cases, the disc may collect only a small amount of additional
gas and dust and change its tilt by a small amount. That may be what
happened in our own Solar System, where the weighted average tilt of
planetary orbits to the Sun's equator is about 7 degrees.
BLOB ILLUMINATED FROM WITHIN
ESO
A team of astronomers has used the Very Large Telescope (VLT) to
study an object called a Lyman-alpha blob -- a rare and very luminous
structure seen in certain regions of the early Universe where matter
is concentrated. Lyman-alpha blobs are some of the biggest objects in
the Universe: clouds of hydrogen gas that can reach diameters of a few
hundred thousand light-years (a few times the size of the Milky Way),
and which look as bright as the brightest galaxies. They are
typically found at large distances, so we see them as they were when
the Universe was only a few billion years old. They might therefore
be important to our understanding of how galaxies formed and evolved
when the Universe was younger. But the source of their luminosity,
and the actual nature of the blobs, has remained unclear. The team
studied one of the first and brightest of these blobs to be found; it
is known as LAB-1 and was discovered in 2000. It is so far away that
its light has taken about 11.5 billion years to reach us (redshift
3.1). With a diameter of about 300 000 light-years it is also one of
the largest known, and has several primordial galaxies inside it,
including an active galaxy.
There are various theories to explain Lyman-alpha blobs. One idea
is that they shine when cool gas is pulled in by the blob's powerful
gravity, and heats up. Another is that they are shining because of
brilliant objects inside them -- galaxies undergoing vigorous star
formation, or containing voracious black holes engulfing matter. The
new observations show that it is embedded galaxies, and not gas being
pulled in, that power LAB-1. The team tested the two theories by
seeing whether the light from the blob was polarised. By studying how
light is polarised astronomers can find out about the physical
processes that produced the light, or what has happened to it between
its origin and its arrival at Earth. If it is reflected or scattered
it becomes polarised. To measure polarisation of the light from a
Lyman-alpha blob is, however, a challenging observation, because of
the great distance. By observing it for about 15 hours with the VLT,
the team found that the light from LAB-1 was polarised in a ring
around the central region, and that there was no polarisation in the
centre. That effect would be almost impossible to produce if the
light simply came from gas falling into the blob under gravity, but it
is just what would be expected if the light originally came from
galaxies embedded in the central region, before being scattered by the
gas. The astronomers now plan to look at more such objects to see if
the results obtained for LAB-1 are true of other blobs.
DONORS HELP RE-OPEN TELESCOPES
BBC News
Telescopes looking for extra-terrestrial intelligence may re-open
within weeks after donors replaced income lost in public-funding cuts.
In April the 'Search for Extraterrestrial Intelligence' (SETI)
Institute had to shut the Allen Telescope Array, which consists of 42
radio telescopes in northern California that search for potential
signals from alien life forms. Actress Jodie Foster was one of more
than 2,400 people who contributed to the fund to save the array. She
played the leading role of an astronomer looking for evidence of
aliens in the 1997 film 'Contact'. Another donor was the Apollo-8
astronaut Bill Anders. The SETI Institute says that the fund should
be enough to keep the telescopes operating until the end of the year,
though the plan is still dependent on the institute receiving
additional money from the US Air Force to track space debris that
could damage satellites. The array began operating in 2007 and is
named after its major benefactor, Paul Allen, co-founder of Microsoft.
SETI is hoping to raise more money to contribute to the £1.5m annual
operating and staffing costs of the telescopes and keep them going
beyond the end of this year.
NASA PLANS TO VISIT A NEAR-EARTH ASTEROID
NASA
The OSIRIS-REx1 spacecraft, targeted for launch in 2016 September,
will intercept asteroid 1999 RQ36, orbit it for a year, and then
approach the surface and, without landing, stretch out a robotic arm
equipped with a sample collector. The asteroid's surface will be
agitated with ultra-pure nitrogen to stir up material for capture.
Observations by ground-based telescopes suggest that asteroid 1999
RQ36 has various carbon-based compounds but do not identify them
as specifically as would be possible if a sample were brought home.
Upon reaching 1999 RQ36 in 2019, the spacecraft's suite of cameras and
instruments will photograph the asteroid and measure its surface
topography, composition, and thermal emissions while its radio
provides mass and gravity-field maps. That information should
increase our understanding of asteroids as well as help the mission
team select the most promising sample site.
Topic: Late August Astronomy Bulletin (Read 744 times)