LOST ASTEROID RETURNS TO EARTH
Spaceweather.com
Last Monday the near-Earth asteroid 2010 WC9 moved across the constellation
Hercules. On May 15, it flew through the Earth-Moon system, splitting the
distance between our planet and the Moon. At its closest approach to us
(203,000 km), the asteroid shone like an 11th-magnitude star as it raced
through the southern constellation Pavo. 2010 WC9 is known as the 'lost
asteroid' because astronomers lost track of it soon after it was discovered
in 2010 November. The asteroid receded from the Earth and did not return
for nearly 8 years ... until now. Estimates of 2010 WC9's size range from
60 to 130 m. That puts it in the same class as the Tunguska impactor, which
levelled a forest in Siberia in 1908. And it is at least 3 times as large
as the Chelyabinsk meteoroid, which exploded in the morning sky over Russia
on 2013 Feb. 15, shattering windows and knocking people to the ground.
There was no danger of a collision this time, though. Analysts are certain
2010 WC9 will not hit the Earth in the foreseeable future. New observations
of the asteroid in recent days have extended our knowledge of its orbit and
eliminated the threat of collision for at least the next 100 years.
NEW MAGNETIC PROCESS IN TURBULENT SPACE
NASA/Goddard Space Flight Center
Though close to home, the space immediately around Earth is full of hidden
secrets and invisible processes. Scientists working with the Magnetospheric
Multiscale spacecraft -- MMS -- have uncovered a new type of magnetic event
in our near-Earth environment by using an innovative technique to squeeze
extra information out of the data. Magnetic reconnection is one of the most
important processes in the space -- filled with charged particles known as
plasma -- around the Earth. That fundamental process dissipates magnetic
energy and propels charged particles, both of which contribute to a dynamic
space-weather system that scientists want to understand better, and even one
day predict, as we do terrestrial weather. Reconnection occurs when crossed
magnetic-field lines snap, explosively flinging away nearby particles at
high speeds. The new discovery found reconnection where it has never been
seen before -- in turbulent plasma. Magnetic reconnection has been observed
innumerable times in the magnetosphere -- the magnetic environment around
the Earth -- but usually under calm conditions. The new event occurred in a
region called the magnetosheath, just outside the outer boundary of the
magnetosphere, where the solar wind is extremely turbulent. Previously,
scientists did not even know whether reconnection could occur there, as the
plasma is highly chaotic in that region. MMS found that it does, but on
scales much smaller than previous spacecraft could probe.
Even though the instruments aboard MMS are incredibly fast, they are still
too slow to capture turbulent reconnection in action, which requires
observing narrow layers of fast-moving particles hurled by the recoiling
field lines. Compared to standard reconnection, in which broad jets of ions
stream out from the site of reconnection, turbulent reconnection ejects
narrow jets of electrons only a couple of miles wide. Magnetic reconnection
occurs throughout the Universe, so that when we learn about it around our
planet -- where of course it is easiest for us to examine it -- we can apply
that information to other processes farther away. The finding of reconnec-
tion in turbulence has implications, for example, for studies of the Sun.
It may help scientists understand the role magnetic reconnection plays in
heating the inexplicably hot solar corona -- the Sun's outer atmosphere --
and accelerating the supersonic solar wind. NASA's upcoming Parker Solar
Probe mission is to be launched directly to the Sun in the summer of 2018 to
investigate exactly those questions -- and that research is all the better
armed the more we understand about magnetic reconnection nearer home.
WHAT WILL HAPPEN WHEN THE SUN DIES?
University of Manchester
Scientists agree that the Sun will die in approximately 10 billion
years, but they were not sure what would happen next ... until now.
A team of international astronomers predicts that it will turn into a
massive ring of luminous, interstellar gas and dust, known as a planetary
nebula.
Such nebulae mark the ends of 90% of all stars' active lives and trace a
star's transition from a red giant to a degenerate white dwarf. But for
years, scientists were not sure whether the Sun would follow that fate:
it was thought to have too low mass to create a visible planetary nebula.
To find out, the team developed a new stellar model that predicts the life
cycle of stars. The model was used to predict the brightness (or lumin-
osity) of the ejected envelope, for stars of different masses and ages.
When a star dies it ejects a mass of gas and dust -- known as its envelope
-- into space. The envelope can be as much as half the star's mass. That
reveals the star's core, which by that point in the star's life is running
out of fuel, eventually turning off before finally dying. It is only then
that the hot core makes the ejected envelope shine brightly for around
10,000 years -- a brief period in astronomy. That is what makes the
planetary nebula visible. Some are so bright that they can be seen from
extremely large distances, tens of millions of light-years, whereas the
star itself would be much too faint to see.
The model also solves another problem that has been perplexing astronomers
for a quarter of a century. Approximately 25 years ago astronomers
discovered that if you look at planetary nebulae in another galaxy, the
brightest ones always have the same brightness. It was found that it was
possible estimate the distance of a galaxy just from the appearance of its
brightest planetary nebulae. In theory it worked in any of type of galaxy.
But while the data suggested that that was correct, the scientific models
claimed otherwise. Old, low-mass stars should make much fainter planetary
nebulae than young, more massive ones. The data said you could get bright
planetary nebulae from low-mass stars like the Sun, but the models said that
that was not possible, anything less than about twice the mass of the Sun
would give a planetary nebula too faint to see. The new models show that
after the ejection of the envelope, the stars heat up three times faster
than was found by older models. That makes it much easier for a low-mass
star, such as the Sun, to form a bright planetary nebula. The team found
that in the new models, the Sun is almost exactly the lowest-mass star that
still produces a visible, though faint, planetary nebula. Stars even a
few per cent smaller do not. The team found that stars with masses less
than 1.1 times the mass of the Sun produce fainter nebulae, and stars more
massive than 3 solar masses brighter nebulae, but for the rest the
predicted brightness is very close to what had been observed. Problem
solved, after 25 years! Not only do we now have a way to measure the
presence of stars of ages a few billion years in distant galaxies, which
is a range that is remarkably difficult to measure, we have even found out
what the Sun will do when it dies!
WATER PLUMES ON EUROPA?
NASA/Jet Propulsion Laboratory
Scientists re-examining data from an old mission bring new insights to the
tantalizing question of whether Jupiter's moon Europa has the ingredients
to support life. The data provide independent evidence that the moon's
sub-surface liquid-water reservoir may be venting plumes of water vapour
above its icy shell. Data collected by the Galileo spacecraft in 1997 were
put through new and advanced computer models to disentangle a mystery -- a
brief, localized bend in the magnetic field -- that had gone unexplained
until now. Previous ultraviolet images from the Hubble Space Telescope in
2012 suggested the presence of plumes, but this new analysis used data
collected much closer to the source and is considered strong, corroborating
support for plumes. At the time of the 1997 fly-by, about 200 km above
Europa's surface, the Galileo team did not suspect that the spacecraft
might be grazing a plume erupting from the icy moon. When they re-examined
the information gathered during that fly-by 21 years ago, sure enough, high-
resolution magnetometer data showed something strange. Drawing on what
scientists learned from exploring plumes on Saturn's moon Enceladus -- that
material in plumes becomes ionized and leaves a characteristic blip in the
magnetic field -- they knew what to look for. And there it was on Europa --
a brief, localized bend in the magnetic field that had never been explained.
Galileo carried a powerful Plasma Wave Spectrometer to measure plasma waves
caused by charged particles in the gases of Europa's atmosphere. The team
studied those data as well, and they also appeared to back the theory of a
plume. But numbers alone could not paint the whole picture. The team
layered the magnetometry and plasma-wave signatures into new 3D modelling
which simulated the interactions of plasma with Solar-System bodies. The
final ingredient was the data from Hubble that suggested the dimensions of
potential plumes. The result that emerged, with a simulated plume, was a
match to the magnetic field and plasma signatures that the team pulled
from the Galileo data. There now seem to be too many lines of evidence to
dismiss plumes at Europa. The findings are good news for the Europa
Clipper mission, which may be launched as 'soon' as 2022 June. From its
orbit of Jupiter, Europa Clipper will sail close by the moon in rapid,
low-altitude fly-bys. If plumes are indeed spewing vapour from Europa's
ocean or sub-surface lakes, Europa Clipper could sample the frozen liquid
and dust particles. The mission team is gearing up now to look at potential
orbital paths, and the new research will play into those discussions. If
plumes exist, and we can directly sample what's coming from the interior of
Europa, then we can more easily get at whether Europa has the ingredients
for life.
UNUSUAL ASTEROID DISCOVERED IN OUTER SOLAR SYSTEM
ESO
Astronomers have found that the Kuiper-Belt object 2004 EW95 is a carbon-
rich asteroid, the first of its kind to be confirmed in the cold outer
reaches of the Solar System. That curious object probably formed in the
asteroid belt between Mars and Jupiter and has been flung billions of
kilometres from its origin to its current home in the Kuiper Belt. The
early days of our Solar System were a tempestuous time. Theoretical models
of that period suggest that, after the gas giants formed, they rampaged
through the Solar System, ejecting small rocky bodies from the inner Solar
System to far-flung orbits at great distances from the Sun. In particular,
those models suggest that the Kuiper Belt -- a cold region beyond the orbit
of Neptune -- should contain a small fraction of rocky bodies from the inner
Solar System, such as carbon-rich asteroids, referred to as carbonaceous
asteroids. Now, a recent paper has presented evidence for the first
reliably-observed carbonaceous asteroid in the Kuiper Belt, providing
support for the theoretical models of our Solar System's troubled youth.
After taking measurements from multiple instruments at the Very Large
Telescope (VLT), a small team of astronomers was able to measure the
composition of the anomalous Kuiper-Belt object 2004 EW95, and thus
determined that it is a carbonaceous asteroid. That suggests that it
originally formed in the inner Solar System and must since have migrated
outwards. The peculiar nature of 2004 EW95 first came to light during
routine observations with the Hubble Space Telescope. The asteroid's
reflectance spectrum was different from that of similar small Kuiper-Belt
objects (KBOs), which typically have uninteresting, featureless spectra
that reveal little about their composition.
The team observed 2004 EW95 with the X-Shooter and FORS2 instruments on the VLT. The sensitivity of those spectrographs allowed the team to obtain more
detailed spectra of light reflected from the asteroid and thus to infer its
composition. However, even with the light-collecting power of the VLT, 2004
EW95 was still difficult to observe. Although the object is 300 kilometres
across, it is currently four billion kilometres from the Earth, making
gathering data from its dark, carbon-rich surface a demanding scientific
challenge. Two features of the object's spectra were particularly eye-
catching and corresponded to the presence of phyllosilicates and ferric
oxides. The presence of those materials had never before been confirmed in
a KBO, and they strongly suggest that 2004 EW95 formed in the inner Solar
System. Given 2004 EW95's present-day abode in the icy outer reaches of the
Solar System, that implies that it was flung out into its present orbit by
a migratory planet in the early days of the Solar System. While there have
been previous reports of other (atypical) Kuiper-Belt-object spectra, none
was confirmed to this level of quality. The discovery of a carbonaceous
asteroid in the Kuiper Belt is a key verification of one of the fundamental
predictions of dynamical models of the early Solar System.
HELIUM DETECTED IN ATMOSPHERE OF EXOPLANET
ESA/Hubble Information Centre
As far back as the year 2000, it was predicted that helium would be one
of the most readily-detectable gases on giant exoplanets, but until now
searches for it were unsuccessful. Now, astronomers using the Hubble
telescope have detected it in the atmosphere of the exoplanet WASP-107b.
Helium is the second-most-common element in the Universe after hydrogen.
It is also one of the main constituents of Jupiter and Saturn in our Solar
System. However, up till now helium had not been detected on exoplanets,
despite searches for it. The team made the detection by analysing the
infrared spectrum of the atmosphere of WASP-107b. Previous detections of
extended exoplanet atmospheres have been made by studying the spectrum at
ultraviolet and optical wavelengths; this detection therefore demonstrates
that exoplanet atmospheres can also be studied at longer wavelengths. The
strong signal measured from helium demonstrates a new technique to study
upper layers of exoplanet atmospheres in a wider range of planets. Current
methods, which use ultraviolet light, are limited to the closest exoplanets.
We know that there is helium in the Earth's upper atmosphere, and this new
technique may help us to detect atmospheres around Earth-sized exoplanets --
which is otherwise very difficult with current technology. WASP-107b is one
of the lowest-density planets known: while the planet is about the same size
as Jupiter, it has only 12% of Jupiter's mass. It is about 200 light-years
away and takes less than six days to orbit its host star. The amount of
helium detected in the atmosphere of WASP-107b is so large that its upper
atmosphere must extend tens of thousands of kilometres out into space. It
is the first time that such an extended atmosphere has been discovered at
infrared wavelengths. Since its atmosphere is so extended, the planet must
be losing a significant amount of its atmospheric gases into space -- from
0.1 to 4% of its atmosphere's total mass every billion years.
FASTEST-GROWING BLACK HOLE
Astronomical Society of Australia
Supermassive black holes at the centres of galaxies can get absurdly huge,
sometimes reaching masses billions of times greater than that of the Sun.
The rate at which black holes grow can vary, but Australian astronomers
have detected one such object with an unusually intense appetite, making it
the fastest-growing black hole ever detected. That bloated supermassive
black hole has an equally bloated name, QSO SMSS J215728.21-360215.1, or
J2157-3602 for short. As it is 12 billion light-years away, we are
observing this bright behemoth not as it is today, but as it existed
nearly four billion years after the Big Bang. Astronomers with the
Australian National University (ANU) used three different instruments to
observe the black hole, or quasi-stellar object (QSO) as it is also called:
ESA's Gaia satellite, the ANU Siding Spring Observatory, and NASA's Wide-
field Infrared Survey Explorer satellite. Observations show that J2157-3602
is the size of about 20 billion suns, and is growing at a rate of 1% every
million years. Every two days, that black hole devours a mass equivalent to
our Sun, gobbling up dust, gas, bits of celestial debris, and whatever else
it can suck in with its powerful gravitational influence. Astronomers have
observed fast-growing QSOs before, but this one is a record-setter, making
it the fastest-growing and the brightest-glowing black hole ever detected.
The influx of gases is producing a tremendous amount of friction and heat,
resulting in the high luminosity.
The black hole is also shining ultraviolet light and X-rays at a rate that
is rendering the entire galaxy sterile. If we had this monster sitting at
the centre of our Milky Way galaxy, it would appear ten times brighter than
the Full Moon. It would appear as an incredibly bright pinpoint star that
would make the sky so bright as almost to wash out all the other stars.
Supermassive black holes came into existence as early as 800 million years
after the Big Bang, but how they grew so big and so quickly after the Big
Bang remains a mystery. Scientists are now hoping to find black holes that
are growing even faster than J2157-3602. Work in that area could tell us
more about what the conditions were like in the early Universe, how elements
were formed (especially metals), and how the early black holes may have
ionized gases around them, making the Universe more transparent.
Topic: Late May Astronomy Bulletin (Read 1059 times)