WHAT EXPLODED OVER RUSSIA?
NASA
When the Sun rose over Russia's Ural Mountains on Friday, Feb. 15,
some of the residents of Chelyabinsk already knew that a space rock
was coming: later that day, an asteroid named 2012 DA14 would pass by
the Earth, only 17,200 miles above Indonesia. There was no danger of
a collision, NASA assured the public. So when the morning sky lit up
with a second Sun and a shock wave shattered windows in hundreds of
buildings around Chelyabinsk, not many people recognized what had
happened right away -- it was not a crashing plane or a rocket attack,
but a meteor strike, the most powerful since the Tunguska event of
1908. In a coincidence that still has NASA experts shaking their
heads, a small asteroid completely unrelated to 2012 DA14 struck the
Earth only hours before the publicized event. The impactor arrived
from the direction of the Sun where no telescope could see it coming,
and took everyone by surprise.
Researchers have since pieced together what happened. The most
telling information came from a network of infrasound sensors operated
by the Comprehensive Test Ban Treaty Organization (CTBTO). Their
purpose is to monitor nuclear explosions. Infrasound is a type of
very-low-frequency sound wave that only elephants and a few other
animals can hear. Meteors entering the atmosphere create infrasound,
and by analyzing records of it it is possible to discover how long a
meteor was in the air, in which direction it travelled, and how much
energy it released. The Russian meteor's infrasound signal was the
strongest ever detected by the CTBTO network. The furthest station to
record it was 15,000 km away in Antarctica. Analysis has shown the
asteroid to be about 17 metres in diameter and weighing approximately
10,000 tons. It struck the atmosphere at about 20 km/s (40,000 mph)
and broke apart at about 12 to 15 miles altitude. The energy
of the resulting explosion exceeded 470 kilotons of TNT. For
comparison, the first atomic bombs produced 'only' 15 to 20 kilotons.
The meteor's trajectory shows that it came from the asteroid belt,
about 2.5 times farther from the Sun than the Earth is, but its orbit
was nothing like that of 2012 DA14. The fact that the two came on the
same day appears to be a complete coincidence. The infrasound records
show that the meteor entered the atmosphere at a shallow angle of
about 20 degrees and lasted more than 30 seconds before it exploded.
The loud report, which was heard and felt for hundreds of miles,
marked the beginning of a scientific scavenger hunt. Lots of
fragments of the meteor must lie scattered across the Ural country-
side, and a few have already been found. Preliminary reports suggest
that the asteroid was made mostly of stone with a bit of iron.
NEW GREEK OBSERVATORY SHEDS LIGHT ON OLD STAR
RAS
Continuing a tradition stretching back more than 25 centuries,
astronomers have used the new 2.3-m 'Aristarchos' telescope, sited at
Helmos Observatory (2340 m high) in the Peloponnese Mountains in
Greece, to determine the distance to and history of an enigmatic
stellar system, finding it to be probably a binary star hidden
within a nebula. Stars of a mass similar to the Sun's end their
careers by ejecting much of their outer atmospheres into space,
leaving behind a remnant core that eventually becomes a white dwarf.
The shells of ejected material sometimes have the superficial
appearance of planets, so were named planetary nebulae. Astronomers
can study the motion and appearance of the material in planetary
nebulae to deduce how the remnant stars have changed over time. In
the 1950s the planetary nebula KjPn8 was discovered on Palomar
Observatory Sky Survey plates. Follow-up work in the 1990s by Mexican
astronomers at the San Pedro Martir Observatory led to the discovery
of large clouds of nebular material visible around the system, a
quarter of a degree across, while in 2000 a central star was finally
discerned by the Hubble telescope.
Two researchers have been studying the system with the Aristarchos
telescope, measuring the expansion of the nebula. By measuring the
velocity and the increasing size of the expanding material, the
scientists were able to deduce the distance to the system and date the
history of three successive ejections. They found that KjPn8 is
around 6000 light-years away and that the material was thrown out in
three brief episodes 3200, 7200 and 50000 years ago. The inner lobe
of material is expanding at more than 300 km/s, high enough to suggest
that it originates in what is called an 'Intermediate-Luminosity
Optical Transient' (ILOT) event. The expression 'intermediate' refers
to the scale of the outburst event, being intermediate between that of
an ordinary nova and a supernova, which differ in characteristic
energy release by a factor of the order of a million. ILOTs are
thought to be caused by the sudden transfer of a substantial mass of
material from a massive star onto a main-sequence companion, as a
result of some sort of catastrophe in the former. The astronomers
therefore had to postulate that the core of KjPn8 is a binary system,
where ILOT events have three times led to the ejection of material at
high speed.
KEPLER DISCOVERS A SYSTEM OF TINY PLANETS
NASA
Kepler-mission scientists have discovered a system with three planets
that include the smallest one yet found around a star similar to
the Sun. The planets are in a system called Kepler 37, about 210
light-years away in the constellation Lyra. The smallest planet,
Kepler 37b, is slightly larger than our Moon, measuring about one-
third the size of the Earth. The Kepler mission is trying to find
Earth-sized planets in or near the 'habitable zone' (an expression
intended to conjure up unwarranted implications of 'little green men'
but actually meaning only a region where liquid water (as opposed to
ice or steam) might exist on the surface of an orbiting planet).
However, while the star in Kepler 37 may be similar to our Sun, the
system appears quite unlike the Solar System. Astronomers think
Kepler 37b has no atmosphere and could not support life as we know it.
The tiny planet is almost certainly rocky in composition. Kepler 37c,
the closer neighbouring planet, is slightly smaller than Venus,
measuring almost three-quarters the size of the Earth, and 37d, the
farther one, is twice the Earth's size. All three planets orbit their
star at less than the distance Mercury is from the Sun, so they must
be very hot -- 'inhospitable' would be an understatemen! Kepler-37b
orbits every 13 days at less than one-third Mercury's distance from
the Sun, while 37c and 37d orbit in 21 days and 40 days, respectively.
BIRTH OF A GIANT PLANET?
ESO
Astronomers using the Very Large Telescope have obtained what may be
the first direct observation of a forming planet still embedded in a
thick disc of gas and dust. The team has studied the disc that
surrounds the young star HD 100546, some 300 light-years away, and
found what seems to be a planet in the process of being formed,
still embedded in the disc. The candidate planet would be a
gas giant similar to Jupiter. HD 100546 is a well-studied object,
and it has already been suggested that a giant planet orbits about
six times farther from the star than the Earth is from the Sun. The
new candidate is located in the outer regions of the system, about
ten times further out. It was detected as a faint blob by a
coronagraph in the 'NACO' adaptive-optics instrument, which operates
at near-infrared wavelengths and suppresses the brilliant light
coming from the star at the location of the proto-planet candidate.
According to current theory, giant planets grow by capturing some of
the gas and dust that remains after the formation of a star. The
astronomers have seen features in the image of the HD 100546 disc that
support the proto-planet hypothesis. However, although a proto-
planet seems to be the most likely explanation for the observations,
follow-up observations are required to confirm the existence of the
planet and to refute other plausible explanations.
HERSCHEL SPACE TELESCOPE TO GO BLIND
BBC News
The European Space Agency (ESA) is about to lose the use of one of its
flagship satellites -- the billion-euro Herschel infrared telescope,
which was launched almost four years ago and sent to an observing
position 1.5 million km away from the Earth. It is equipped with a
3.5-m mirror -- the largest monolithic mirror ever flown -- and three
instruments sensitive to long wavelengths of light, in the far-
infrared and sub-millimetre range (55 to 672 microns). That
technology has allowed Herschel to study the processes at play as
large clouds of gas and dust collapse to form new stars, and has
helped to trace how galaxies have changed through cosmic time. But
the infrared detectors have to be cooled to close to absolute zero
(-273.15C). The cooling system uses liquid helium, more than 2,000
litres of which were loaded into the telescope at launch. The helium
has gradually boiled off during the course of the mission, and the
latest forecast is that it will be gone entirely towards the end of
this month. Once the detectors start to warm from their ultra-frigid
state, they will stop working. The end, when it happens, will be quite
sudden. The satellite will then be put into a slow drift around the
Sun. Researchers are now running through a final list of desired
observations. Thousands of pictures have already been deposited in a
Herschel archive, which will constitute an important reference source
for the future.
Topic: March Astronomy Bulletin (Read 1931 times)