IRREGULAR HEARTBEAT OF SUN
RAS
A new model of the solar cycle is producing accurate predictions
of irregularities within the Sun's 11-year cycle. The model draws on
dynamo effects in two layers of the Sun, one close to the surface and
one deep within its convection zone. Predictions from the model
suggest that solar activity will fall by 60 per cent during the 2030s
to conditions last seen during the 'mini ice age' that began in 1645.
It is 172 years since a scientist first noticed that the Sun's
activity varies over a cycle lasting around 10 to 12 years. But every
cycle is a little different, and none of the models of causes to date
has fully explained the fluctuations. Many solar physicists have
attributed the solar cycle to a dynamo caused by convecting fluid
deep within the Sun. Now, astronomers have found that adding a second
dynamo, close to the surface, completes the picture with surprising
accuracy. The researchers found magnetic wave components appearing in
pairs, originating in two different layers in the Sun's interior.
They both have a frequency of approximately 11 years, although their
frequencies are slightly different, and they are offset in time. Over
the cycle, the waves fluctuate between the northern and southern
hemispheres of the Sun. When the two waves were combined and compared
with real data for the current solar cycle, their predictions showed
an accuracy of 97%.
The team derived its model by a technique called 'principal component
analysis' of the magnetic-field observations from the Wilcox Solar
Observatory in California. They examined three solar cycles' worth of
magnetic-field activity, covering the period 1976-2008. In addition,
they compared the predictions with average sunspot numbers, another
strong marker of solar activity. All the predictions and observations
were closely matched. Looking ahead to the next solar cycles, the
model predicts that the pair of waves become increasingly offset
during Cycle 25, which peaks in 2022. During Cycle 26, which covers
the decade 2030-2040, the two waves will become exactly out of sync,
and that will cause a significant reduction in solar activity. In
cycle 26, the two waves exactly mirror each other -- peaking at the
same time but in opposite hemispheres of the Sun. Their interaction
will be disruptive -- they will nearly cancel one another. The team
predicts that that will lead to the properties of a 'Maunder minimum'.
Effectively, when the waves are approximately in phase, they can show
strong reinforcement, or resonance, and we have strong solar activity.
When they are out of phase, we have solar minimum. When there is full
phase separation, we have the conditions last seen during the Maunder
minimum, 370 years ago.
NEW HORIZONS AT PLUTO
BBC News
Now that the New Horizons probe has successfully flown past Pluto and
confirmed that it is all in one piece, researchers can look forward to
a cornucopia of images and data from the strange, distant world over
the next 16 months. But even though only a few of pictures have been
transmitted so far, scientists are learning more from them than they
have in years of telescopic observations. For 60 years scientists
have known that there was a bright mass on Pluto, but it was only the
high resolution provided by the cameras on New Horizons that detailed
its distinctive heart shape which is believed to have been caused by
an impact. Researchers believe that the crater is filled with frozen
gases from the atmosphere -- nitrogen, methane and carbon dioxide.
The initial image had a reddish hue, something that scientists have
long known. It is very different from the other red planet, Mars,
in that Pluto's colour is probably caused by hydrocarbon molecules,
called tholins, that are formed when solar ultraviolet light and
cosmic rays interact with methane in Pluto's atmosphere and on its
surface. Pluto's reddening process occurs even on the night side
where there is no sunlight, and in the depths of winter when the Sun
remains below the horizon for decades at a time.
New Horizons has provided more accurate information on the size of
Pluto. It is slightly (about 80 km) bigger than expected, making it
around two-thirds the size of our Moon. The increased dimensions mean
that Pluto is likely to be made of less rock and more ice beneath its
surface, according to members of the mission team. The revision makes
Pluto now officially bigger than Eris, one of hundreds of thousands
of mini-planets and comet-like objects circling beyond Neptune in a
region called the Kuiper Belt. The relative lack of impact craters on
Pluto could be an indication that the surface is being renewed, either
by internal or atmospheric activity, such as erosion. There is
evidence of surface activity, a tantalizing hint of Earth-like
tectonics in its past or even its present. NASA has dubbed one of the
strange, darker regions of Pluto the 'whale'. Researchers say it is
unusual to have contrasting bright and dark surfaces on objects in our
Solar System, reflecting the fact that Pluto is far more complex than
previously thought. Surface temperatures on Pluto are extremely cold,
ranging from -172 to -238 degrees C depending on where it is in its
248-year orbit of the Sun. Since it passed perihelion in 1989,
experts assumed that since then it should have been cooling. Pluto
has strong atmospheric cycles: it snows on the surface, and then the
snow sublimates and goes back into the atmosphere in the course of
each 248-year orbit. Little light has so far been shed on the moons
of Pluto, but an image indicates that Charon, the biggest, is covered
with red material around its pole. Scientists believe that that stuff
may be tholins that have escaped from Pluto's atmosphere. Experts
believe that the mottled colours at lower latitudes point to a
diversity of land forms on Charon. So far little detail has emerged
about the other moons except more accurate measurements of their
sizes. Retrieving all the data from the brief fly-past of Pluto will
take almost 16 months.
SEDNA IS POSSIBLE EXO-PLANET
CosmosUp
Astronomers at Leiden University suspect that the dwarf planet Sedna,
discovered in 2003, actually originated from another star. With a
diameter of approximately 1000 km, Sedna is a relatively large Kuiper-
belt object -- only Pluto and Eris are larger. Sedna has a very
elongated orbit around the Sun: the point of closest approach to the
Sun is 76 AU (76 times the Earth-Sun distance) but the farthest point
(aphelion) is estimated at 937 AU (31 times Neptune's distance).
Sedna completes an orbit every 11,400 years, making it one of the most
distant objects in the Solar System. Some astronomers think that,
more than 4 billion years ago, a possible encounter with another star
could have led to ice dwarfs being gravitationally captured into
Sedna-like orbits. The passing star would have been 80% as massive as
the Sun and would have passed through the Kuiper Belt and affected the
outer edge of the Solar System. Its passage must have occurred before
the so-called 'late heavy bombardment' which occurred approximately 4
billion years ago. During that interval a large number of asteroids
apparently collided with the early terrestrial planets in the inner
Solar System. The reconstruction of the near-collision suggests that
about 2,000 planetesimals, including Sedna and 2012 VP113, were
captured into our Solar System, and that the passing star would itself
have stolen hundreds of Solar-System ice dwarfs, and hundreds more
would have been lost into interstellar space.
FIVE-STAR DOUBLY ECLIPSING STAR SYSTEM
RAS
Astronomers have discovered for the first time a quintuple star system
containing two eclipsing binary stars. About a third of all stars are
found in pairs or multiple systems. The quintuple system was first
detected in archived data from the SuperWASP (Wide Angle Search for
Planets) project, which uses relatively small and low-cost cameras in
the Canary Islands and South Africa to image almost the whole sky
every few minutes. Over many years, its measurements of the bright-
nesses of individual stars have been assembled into light-curves for
some 30 million sources in the Milky Way. Regular small dips in a
light-curve can reveal the presence of orbiting planets, when they
cross or transit the face of their host star, and SuperWASP has been
extremely successful in finding such 'exo-planets' since it began
operating in 2003. Light-curves also enable eclipsing binary syatems
to be discovered. As seen from the Earth, each star will pass in
front of its companion once in every orbit and eclipse some or all of
its light. That produces a regular pattern of pairs of dips in the
binary's light-curve, whose depths and shapes give indications of the
physical properties of the two stars.
The light-curve of the new quintuple system, designated as 1SWASP
J093010.78+533859.5, initially revealed the presence of a contact
eclipsing binary -- a system in which the two stars are orbiting so
close together that they share an outer atmosphere. Contact binaries
are quite common, but that particular system is notable because its
orbital period is so short, just under six hours. Then it was noted
that the light-curve contained some additional unexpected eclipses,
and the data were re-analysed to reveal a second eclipsing binary at
the same location on the sky. The new binary is detached -- its
component stars are well separated by a distance of about 3 million
km, or about twice the diameter of the Sun -- and it has a longer
orbital period of one and a third days. The two sets of stars are
separated by about 21 (US)-billion km (more than three times Pluto's
distance from the Sun). Spectroscopy then unexpectedly revealed the
presence of a fifth star, up to 2 billion km away from the detached
binary, but not apparently producing any additional eclipses. By
combining the data from the five stars' light-curves and their
spectra, researchers have been able to confirm that they are all
gravitationally bound together in a single system, around 250 light-
years away from us in the constellation of Ursa Major. The data also
let the team determine the stars' masses, sizes and temperatures. All
the stars are rather smaller and cooler than the Sun, but collectively
the system is bright enough (9th magnitude) to be visible in small
telescopes, and amateur astronomers could see the eclipses for
themselves. One particularly interesting finding is that the two
binaries seem to be orbiting in the same plane. That suggests that
they may originally have formed from a single disc of gas and dust,
which broke up as gravity concentrated it into clumps.
MATERIALS TO BUILD EARTH-LIKE PLANETS FOUND IN EVERY PLANETARY SYSTEM
RAS
Earth-like planets orbiting other stars in the Milky Way are three
times more likely to have the same type of minerals as the Earth than
astronomers had previously thought. In fact, conditions for making
the building blocks of Earth-like rocks are ubiquitous throughout the
Milky Way. Minerals made from carbon, oxygen, magnesium and silicon
are thought to control the landscapes of rocky planets that form in
planetary systems around Sun-like stars. A subtle difference in
mineralogy can have a big effect on plate tectonics, heating and
cooling of a planet's surface, all of which can affect whether a
planet is ultimately habitable. Until now, astronomers thought that
rocky planets fell into three distinct groups: those with a set of
building blocks to similar to the Earth's, those that had a much
richer concentration of carbon, and those that had significantly more
silicon than magnesium. The ratio of elements on the Earth has led to
the chemical conditions favourable for life.
Researchers have constructed a simulation of the chemical evolution of
the Milky Way, which results in an accurate recreation of the Milky
Way as we see it today. That has allowed them to examine the
chemistry of processes such as planetary formation in detail. Their
findings came as something of a surprise. At first, they thought that
the model was wrong. As an overall representation of the Milky Way,
everything seemed very good. Everything was in the right place; the
rates of stars forming and stars dying, individual elements and
isotopes all matched observations of what the Milky Way is really
like. But when they looked at planetary formation, every system they
looked at had the same elemental building blocks as the Earth, and not
just one in three. They could not find any fault with the model, so
they went back and checked the observations. They found some
uncertainties that were causing the one-in-three result. When those
were removed, observations agreed with predictions that the same
elemental building blocks are found in every exo-planet system,
wherever it is in the Galaxy. The cloud out of which the Solar System
formed has approximately twice as many atoms of oxygen as carbon, and
roughly five atoms of silicon for every six of magnesium. Observers
trying to ascertain the chemical make-up of planetary systems have
tended to look at large planets orbiting very bright stars, which can
lead to uncertainties of 10 or 20 per cent. In addition, historically
the spectra of oxygen and nickel have been hard to differentiate.
Improvements in spectroscopic techniques have cleaned up the oxygen
spectra, providing data that match the team's estimates. Even with
the right chemical building blocks, not every planet will be just like
the Earth, and conditions allowing for liquid water to exist on the
surface are needed for habitability. We need only to look to Mars and
Venus to see how differently terrestrial planets can evolve. However,
if the building blocks are there, then it is more likely that
Earth-like planets will form -- and three times more likely than had
previously been thought.
PEBBLES POISED TO MAKE PLANETS
RAS
A team of astronomers has announced the discovery of a ring of rocks
circling a very young star. Planets are thought to form from the dust
and gas in discs that encircle young stars. Over time, dust particles
stick together, until they build up bigger clumps. Eventually, the
clumps have enough mass for gravity to become significant, and over
millions of years the clumps crash together to make planets and moons.
In our own Solar System, that process took place about 4500 million
years ago, with the giant planet Jupiter the first to form. Since the
1990s, astronomers have found discs both of gas and dust, and nearly
2000 fully formed planets, but the intermediate stages of formation
are harder to detect. The team used the e-MERLIN array of radio
telescopes that is centred at Jodrell Bank and stretches across
England as an interferometer, mimicking the resolution of a single
large telescope. They observed DG Tauri, a star only 2.5 million
years old and 450 light-years away in the constellation Taurus.
At radio wavelengths, they discovered a faint glow characteristic of
rocks in orbit around the newly formed star. Astronomers knew that
DG Tauri has jets of hot gas flowing off its poles -- a beacon for
stars still in the process of forming -- so they had an idea of what
to look for.
The team was surprised to see also, with only a fraction of the data
it hopes to acquire, a belt of pebbles. The fine detail that could be
seen with the e-MERLIN telescopes was the key to that discovery.
Astronomers could zoom in to a region as small as the orbit of Jupiter
is in the Solar System. They found a belt of pebbles strung along a
very similar orbit -- just where they would be needed if a planet were
to grow in the next few million years. The e-MERLIN observations were
made at a wavelength of 4.6 cm. To give off such radio waves, rocky
chunks at least a centimetre in size are needed, and the shape of the
belt confirms the rocks as the source of the radio waves. By imaging
the rocky belts of many stars, the team will look for clues as to how
often planets form, and where, around stars that will evolve into
objects like the Sun. The ultimate aim is to zoom in and see
'extra-solar Earths' being born, five times closer in to their host
stars than Jupiter's orbit. Upgrades to e-MERLIN's capabilities in
the next few years, as well as the construction of the new Square-
Kilometre Array (with its HQ at Jodrell Bank), make that a real
possibility.
Topic: Late July Astronomy Bulletin Part 1 (Read 1394 times)