MOON'S ORBIT EXPLAINED
University of Maryland
The Moon is among the strangest planetary bodies in the Solar System.
Its orbit has a surprisingly large tilt. Planetary scientists have
struggled to piece together a scenario that accounts for that and
other related characteristics of the Earth--Moon system. A new
research paper, based on numerical models of the Moon's explosive
formation and the evolution of the Earth--Moon system, comes closer to
tying up all the loose ends than any previous explanation. The work
suggests that the impact that formed the Moon also caused major
changes to the Earth's rotation and the tilt of its spin axis. The
impact sent the Earth spinning much faster, and at a much steeper
tilt, than it does today. In the several thousand million years since
that impact, complex interactions between the Earth, Moon and Sun have
smoothed out many of those changes, resulting in the Earth--Moon
system that we have today. In that scenario, the remaining anomalies
in the Moon's orbit are relics of the Earth--Moon system's explosive
past. Evidence suggests that a major impact blasted off a huge amount
of material that formed the Moon. The material would have formed a
ring of debris first, then the ring would have aggregated to form the
Moon. But that model does not quite work if the Earth's spin axis was
tilted at the 23.5-degree angle that it has today.
Collisional physics calls for the ring of debris -- and thus the
Moon's orbit immediately after formation -- to lie in the Earth's
equatorial plane. As tidal interactions between the Earth and the
Moon drove the Moon further away, the Moon's orbit should have shifted
from the Earth's equatorial plane to the ecliptic plane -- that of the
Earth's orbit around the Sun. But today, instead of being in line
with the ecliptic plane, the Moon's orbit is tilted five degrees away
from it. Such tilt is not to be expected; until now, there has not
been a good explanation, but we can understand it if the Earth had a
more dramatic early history than we previously suspected. Astronomers
have proposed many different scenarios, but the most successful ones
involve a Moon-forming impact that set the Earth spinning extremely
fast -- as much as twice the rate predicted by other models. The
impact also knocked the Earth's tilt far off, to somewhere between 60
and 80 degrees. The team already suspected that the Earth must have
spun especially fast after the impact. An early high tilt would
enables our planet to lose its excess spin more readily. The model
also suggests that the newly-formed Moon started off very close to the
Earth, but then drifted away to nearly 15 times its initial distance.
As it did so, the Sun began to exert a more powerful influence over
the Moon's orbit. According to the researchers, both factors -- a
highly tilted, fast-spinning Earth and an outwardly-migrating Moon --
contributed to establishing the Moon's current weird orbit. The new-
born Moon's orbit most likely followed the equator, tilted at a steep
60-80-degree angle that matched the Earth's tilt.
One finding of the new research is that, if the Earth were indeed
tilted by more than 60 degrees after the Moon formed, the Moon could
not make a gradual transition from the equatorial plane to the
ecliptic one. Instead, the transition would be abrupt and leave the
Moon with a large tilt relative to the ecliptic -- much larger than
is observed today. As the Moon moved outward, the Earth's steep tilt
made for a more chaotic transition as the Sun became a greater
influence. Subsequently, and over thousands of millions of years,
the Moon's tilt slowly decayed down to the five degrees we see today.
So today's five-degree tilt may be seen as a relic and a signature
of a much steeper tilt in the past.
ELUSIVE BROWN DWARF PINPOINTED
NASA
The Spitzer and Swift space telescopes joined forces to observe a
micro-lensing event -- one in which a distant star brightens owing
to the gravitational field of a foreground cosmic object. That
technique is useful for finding low-mass bodies orbiting stars, such
as planets. In this case, the observations revealed a brown dwarf.
Brown dwarfs are thought to be the missing link between planets and
stars, with masses up to 80 times that of Jupiter, but their centres
are not hot or dense enough to generate energy through nuclear fusion
in the way that stars do. Curiously, scientists have found that, for
stars roughly the mass of our Sun, less than 1% have a brown dwarf
orbiting within 3 AU. That absence is called the 'brown dwarf
desert'. The newly discovered brown dwarf, which orbits a host star,
may inhabit such a desert. Spitzer and Swift observed the micro-
lensing event after being tipped off by ground-based micro-lensing
surveys, including the Optical Gravitational Lensing Experiment
(OGLE). The discovery of the brown dwarf, with the unwieldy name
OGLE-2015-BLG-1319, marks the first time the two space telescopes
have collaborated to observe a micro-lensing event. Astronomers want
to understand how brown dwarfs form around stars, and why there is a
gap in where they are found relative to their host stars.
Spitzer observed the binary system containing the brown dwarf in 2015
July, during the last fortnight of the telescope's micro-lensing
campaign for that year. While Spitzer is over 1 AU away from the
Earth in an Earth-trailing orbit round the Sun, Swift is in a low
orbit around our planet. Swift also saw the binary system in late
June last year through micro-lensing, representing the first time that
that telescope had observed a micro-lensing event. But Swift is not
far enough away from ground-based telescopes to get a significantly
different view of the event, so no parallax could be measured between
the two. That draws scientists' attention to the limits of the
telescope's capabilities for certain types of objects and distances.
Simulations suggest that Swift could measure parallaxes for nearby,
less-massive objects, including 'free-floating' planets, which do not
orbit stars. By combining data from the space-based and ground-based
telescopes, researchers determined that the newly discovered brown
dwarf is between 30 and 65 Jupiter masses. They also found that it
orbits a K dwarf, a type of star that tends to have about half the
mass of the Sun. They have already written a paper about it (a paper
having almost 100 authors!), although they have not yet managed to
decide between two very different possible distances between the brown
dwarf and its host star, 0.25 and 45 AU. The 0.25-AU distance would
put the system in the 'brown-dwarf desert'.
GRAVITATIONAL LENS MAKES DISTANT GALAXY VISIBLE
Max Planck Institute for Physics
Never before have astrophysicists measured light of such high energy
from a celestial object so far away. Around 7 billion years
ago, a huge explosion occurred at the black hole in the centre of a
galaxy. That was followed by a burst of high-intensity gamma rays.
A number of telescopes, 'MAGIC' included, has succeeded in capturing
that light. As an added bonus it was possible to confirm once again
Einstein's General Theory of Relativity, as the light rays encount-
ered a less-distant galaxy on their route to the Earth -- and were
deflected by that gravitational lens. The object, QSO B0218+357, is
a blazar, a specific type of black hole. Researchers now assume that
there is a super-massive black hole at the centre of every galaxy.
Black holes into which matter is currently plunging are called active
black holes. They emit extremely bright jets. If such jets point
towards the Earth, the term blazar is used. The event with which
this article is concerned took place 7000 million years ago, when the
Universe was not even half its present age. The blazar was discovered
initially on 2014 July 14 by the Large Area Telescope (LAT) of the
Fermi satellite. The gamma-ray telescopes on Earth immediately
observed the blazar. One of them, MAGIC, on La Palma in the Canary
Islands, specializes in high-energy gamma-rays. It can capture
photons whose energy is 10 to the power 11 times higher than photons
of visible light and a thousand times higher than those measured by
Fermi-LAT. The MAGIC scientists were initially out of luck, however,
because a Full Moon prevented the telescope from operating during the
time in question.
Eleven days later, MAGIC got a second chance, as the gamma-rays
emitted by QSO B0218+357 did not take the direct route to the Earth:
a thousand million years after setting off on their journey, they
reached the galaxy B0218+357G. That is where the theory of relativity
came into play. That states that a large mass in the Universe,
a galaxy, for example, deflects the light of an object behind it.
In addition, the light is focused as if by a gigantic optical lens --
to a distant observer, the object appears to be much brighter, but
also distorted. The light beams also need different lengths of time
to pass through the lens, depending on the angle of observation.
The gravitational lens was the reason that MAGIC was able, after all,
to measure QSO B0218+357 -- and thus the most distant object in the
high-energy gamma-ray spectrum. Astronomers knew from observations
undertaken by the Fermi space telescope and radio telescopes in 2012
that the photons that took the longer route would arrive 11 days
later. This was the first time that they were able to observe that
high- energy photons were deflected by a gravitational lens. The fact
that gamma-rays of such high energy from a distant celestial body can
reach the Earth's atmosphere is anything but obvious. Many gamma-rays
are lost when they interact with photons which originate from galaxies
or stars and have a lower energy. The fact that the light arrived on
the Earth at the time calculated might disturb a few theories on the
structure of the vacuum -- further investigations, however, are
required to confirm that.
BIGGEST TELESCOPE MAY SWAP CONTINENTS
BBC News
One of the world's biggest telescope projects might be forced to move
its location to a different continent. The Thirty-Metre Telescope
(TMT) was due to be built in Hawaii, but has run into opposition from
indigenous groups which consider its proposed site sacred. Now the
TMT's board says that a site in the Canary Islands could be a possible
alternative. The big project should enable experts to study the early
Universe and analyze the atmospheres of exo-planets. It is one of a
raft of big observatories -- along with the European Extremely Large
Telescope (E-ELT) and space-based James Webb telescope -- intended to
serve astronomy into the 2020s and beyond. Cloud-free Pacific skies,
low atmospheric water vapour and other attributes make conditions on
Mauna Kea, Hawaii, among the best in the world for astronomy. The
site intended for the TMT was just below the 4,207-m summit of the
dormant volcano. Opposition to the construction of observatories on
Mauna Kea has existed for decades. To many native Hawaiians, Mauna
Kea is considered the most sacred of all mountains on the island, with
a special connection to their religion's deities. So continued
development is considered a desecration. But others who are against
the project cite environmental and conservation concerns. As con-
struction was due to begin on the project in 2015 April, protesters
blocked access roads to keep crews off the site, resulting in several
arrests. But opponents were also pursuing their complaint through
the courts. Last December, the Hawaii State Supreme Court rescinded
a 2011 construction permit for the telescope. It said that the permit
had been issued before opponents had had an opportunity to state their
case. That meant that the TMT project would have to seek a new permit
if it wanted to proceed with construction on Mauna Kea.
Earlier this month, the board of governors met to discuss progress
on the TMT project in Hawaii and to consider potential alternative
locations. After careful deliberation, the board identified the
Observatorio del Roque de los Muchachos (ORM) on La Palma as the
primary alternative to Hawaii. The site on La Palma is already home
to several telescopes. But Mauna Kea is higher and even more remote
than La Palma, which, in some opinions, gives it the edge over the
Canary Islands in terms of cloud-free skies, good seeing, low water
vapour and lack of light pollution. However, those advantages could
be offset by inconvenience and the cost of access as well as working
conditions. Altitude sickness remains an issue on Mauna Kea, even
though most observing is now done remotely -- without astronomers
physically visiting the telescopes. A move from the Pacific to the
Atlantic would also result in major upheaval for the project, which
has been in development for the past 15 years. The TMT board said
that it would continue its efforts to gain approval for construction
on Hawaii, but if those efforts continue to meet resistance, it is
conceivable that astronomers will have to fall back on La Palma.
NEW TECHNIQUE PARTLY SOLVES BEAGLE 2 MYSTERY
University of Leicester
Scientists have moved a step closer to understanding exactly what
happened to the ill-fated Mars Lander Beagle 2, thanks to an innov-
ative research technique. The probe was identified on the surface of
Mars in 2014 November, but uncertainty surrounded what had caused its
failure to communicate with the Earth. Now, a collaboration between
De Montfort University and the University of Leicester has used 3D
modelling technology to reveal that Beagle 2 deployed at least three,
and possibly all four, of the solar panels that it was supposed to
unfurl after touching down on the planet's surface. (It had been
thought that perhaps only two of the four solar panels had deployed.)
Beagle 2 was part of the ESA 'Mars Express' mission launched in 2003
June. Mars Express is still orbiting Mars and returning scientific
data on the planet. Beagle 2 was successfully ejected from the Mars
Express spacecraft on 2003 December 19 but failed to send a signal on
Christmas Day -- the day that it was scheduled land on Mars. It was
presumed lost until more than a decade later, when it was seen in
images taken by the Mars Reconnaissance Orbiter (MRO). Although it
was detected, owing to the small size of the lander and the limited
resolution of the camera on the MRO, the exact configuration of the
lander on Mars was not clear, despite the collection of 8 images of
the lander and the use of image-processing techniques.
Now researchers have come up with the concept of 'reflection analysis'
-- of matching simulated and real images of Beagle 2. The technique
is based on simulating possible configurations of the lander on the
surface and comparing the light of the Sun reflected by the simulated
lander with the unprocessed images available from MRO's camera at a
number of different Sun angles. Commercially available software used
for 3D modelling, animation, visual effects and simulation design was
adapted to suit such an analysis. The visual comparison between the
real and simulated images could then begin to identify which landing
configuration (1, 2, 3 or 4 deployed solar panels) was the best fit.
It was originally just a proof-of-principle project, but the team
reached the conclusion that Beagle 2 did not crash but landed properly
and probably deployed most of its panels. That goes some way towards
solving a long-standing mystery, but in reality we may never know
exactly what caused the lander's failure to communicate after what
has now been construed as a successful landing. The work shows that
Beagle 2 came frustratingly close to working as intended on Mars.
Topic: Late November Astronomy Bulletin (Read 1549 times)