OSIRIS-REx CONFIRMS WATER ON ASTEROID
NASA
Early data from the Origins, Spectral Interpretation, Resource
Identification, Security-Regolith Explorer (OSIRIS-REx) mission revealed
water locked inside Bennu. Data collected by the probe's two spectrometers,
OVIRS and OTES, revealed the presence of hydroxyls, molecules featuring
bonded oxygen and hydrogen atoms. Scientists believe that those hydroxyl
groups exist across the asteroid in water-bearing clay minerals, suggesting
that, at some point, Bennu's rocky surface interacted with water.
OSIRIS-REx arrived at its asteroid target earlier this month. Shortly after
its rendezvous, the probe's instruments began surveying the asteroid. In
addition to studying the chemical composition of Bennu's surface, the
spacecraft's instruments are helping scientists map the asteroid's shape and
contours. OSIRIS-REx's surveying efforts will continue for the next year.
Over the next several months, the probe will execute a series of fly-bys to
get a closer look at some of Bennu's features. The spacecraft will swoop by
the asteroid's equator and poles. Some of the approaches will put the probe
within 4.4 miles of the asteroid's surface. With each fly-by, the maps of
Bennu will become more detailed. Scientists will also use OSIRIS-REx's
observations to refine estimates of the asteroid's mass and spin rate. The
new data will help scientists to understand better how asteroids form and
evolve. Updated maps will also help OSIRIS-REx to perfect its orbit around
the asteroid, as well as to identify points of interest. The data will also
help scientists choose where OSIRIS-REx will reach down with its robotic arm
and scoop up regolith -- rocks and dust -- from Bennu's surface. The
earliest observations show that Bennu has a balanced mix of heavily
bouldered regions and relatively smooth areas. The third New Frontiers
planetary science mission (following Juno and New Horizons), OSIRIS-REx is
expected to return to Earth with a collected specimen in 2023 September.
EVIDENCE FOR CARBON-RICH SURFACE ON CERES
Southwest Research Institute
Astronomers have concluded that the surface of dwarf planet Ceres is rich in
organic matter. Data from the Dawn spacecraft indicate that Ceres's surface
may contain several times the concentration of carbon that is present in the
most carbon-rich primitive meteorites found on Earth. Ceres is believed to
have originated about 4.6 billion years ago at the dawn of our Solar System.
Dawn data previously revealed the presence of water and other volatiles,
such as ammonium derived from ammonia, and now a high concentration of
carbon. That chemistry suggests that Ceres formed in a cold environment,
perhaps outside the orbit of Jupiter. An ensuing shake-up in the orbits of
the large planets would have pushed Ceres to its current location in the
main asteroid belt, between the orbits of Mars and Jupiter. Geophysical,
compositional and collisional models based on Dawn data revealed that Ceres'
partially differentiated interior has been altered by fluid processes.
Dawn's Visible and Infrared Mapping Spectrometer has shown that the overall
low albedo of Ceres' surface is a combination of rock--water interaction
products such as phyllosilicates and carbonates and a significant amount of
spectrally neutral darkening agents, such as magnetite, an iron oxide.
Because Dawn's Gamma Ray and Neutron Detector limits magnetite to only
a few per cent by mass, the data point to the presence of an additional darkening
agent, probably amorphous carbon. Interestingly, specific organic compounds
have also been detected near a 31-mile-wide impact crater named Ernutet,
giving further support to the notion of widespread presence of organics in
Ceres' shallow subsurface. The new study also finds that 50-60 per cent of
Ceres' upper crust may have a composition similar to that of primitive
carbonaceous chondrite meteorites. That material is compatible with contam-
ination from infalling carbonaceous asteroids, a possibility supported by
Ceres' battered surface.
THE MYSTERY OF ULTIMA THULE
Spaceweather.com
When NASA's New Horizons spacecraft flew past Pluto three years ago, mission
scientists watching the first close-up images were shocked. Despite being
stuck in the deep freeze of the Solar System 6 billion km from the Sun,
Pluto was not the frozen world that many expected it to be. It was alive
with mountain ranges, windswept dunes, bladed terrain and much more. In one
quick fly-by, New Horizons turned planetary science on its head. New
Horizons is now less than 2 weeks away from a new world even less known than
Pluto. Its name is 'Ultima Thule' (2014 MU69), which means means 'beyond
the borders of the known world'. Indeed, the little space rock is
profoundly unknown. Located almost a billion kilometres farther from the
Sun than Pluto, Ultima Thule has never been much more than a faint speck of
light in telescopes. It inhabits the distant Kuiper Belt. On New Year's
Eve and New Year's Day, New Horizons will swoop three times closer to Ultima
Thule than it flew past Pluto in July 2015, shattering previous records for
the most distant body explored by a spacecraft. First images will be posted
on a web site set up by the New Horizons' team: SeeUltimaThuleNow.com .
We already know one thing about Ultima Thule. Its shape is elongated and
strange. In 2017, astronomers watched a distant star pass behind Ultima
Thule. Starlight winked in and out in a pattern suggesting two lobes with
diameters of 20 and 18 km, respectively. Ultima Thule could be a small
binary system. Ultima Thule is 100 times smaller than Pluto, but its
scientific value is incalculable. From everything we know, it was formed
4.5 or 4.6 billion years ago, 4 billion miles from the Sun. It has been
remained at that enormous distance from the Sun, at a temperature of nearly
absolute zero, ever since, so it probably represents the best sample of the
ancient solar nebula ever studied.
MOST-DISTANT SOLAR-SYSTEM OBJECT OBSERVED
Carnegie Institution for Science
A team of astronomers has discovered the most-distant body ever observed in
our Solar System. It is the first known Solar-System object that has been
detected at a distance that is more than 100 times farther than the Earth is
from the Sun. The new object has been given the provisional designation
2018 VG18. 2018 VG18, nicknamed 'Farout' by the discovery team for its
extremely distant location, is at about 120 astronomical units (AU). The
second-most-distant observed Solar-System object is Eris, at about 96 AU.
Pluto is currently at about 34 AU, making 2018 VG18 more than three and a
half times more distant than the Solar System's most-famous dwarf planet.
2018 VG18 was discovered as part of the team's continuing search for
extremely distant Solar-System objects, including the suspected Planet X,
which is sometimes also called Planet 9. In October, the same group of
researchers announced the discovery of another distant Solar-System object,
called 2015 TG387 and nicknamed 'The Goblin' because it was first seen near
Halloween. The Goblin was discovered at about 80 AU and has an orbit that
is consistent with its being influenced by an unseen Super-Earth-sized
Planet X on the Solar System's very distant fringes. The existence of a
ninth major planet at the fringes of the Solar System was first proposed by
that same research team in 2014 when they discovered 2012 VP113, nicknamed
Biden, which is currently near 84 AU.
2015 TG387 and 2012 VP113 never get close enough to the Solar System's giant
planets, like Neptune and Jupiter, to have significant gravitational
interactions with them. That means that those extremely distant objects can
be probes of what is happening in the Solar System's outer reaches. The
team does not know 2018 VG18's orbit very well yet, so it has not been able
to determine if it shows signs of being shaped by Planet X. 2018 VG18 is
much more distant and slower-moving than any other observed Solar-System
object, so it will take a few years to determine its orbit fully. But it
was found in a similar location in the sky to the other known extreme Solar
System objects, suggesting that it might have the same type of orbit that
most of them do. The orbital similarities shown by many of the known small,
distant Solar-System bodies was the catalyst for the original assertion that
there is a distant, massive planet at several hundred AU shepherding those
smaller objects. All that we currently know about 2018 VG18 is its extreme
distance from the Sun, its approximate diameter, and its colour. Because
2018 VG18 is so distant, it orbits very slowly, probably taking more than
1,000 years to take one trip around the Sun. The discovery images of 2018
VG18 were taken by the Japanese Subaru 8-m telescope on Mauna Kea in
Hawaii on 2018 November 10. Once 2018 VG18 was found, it needed to
be re-observed to confirm its very distant nature. (It takes multiple nights
of observing to determine an object's distance.) 2018 VG18 was seen for
the second time in early December at the Magellan telescope at Las Campanas
Observatory in Chile. The Magellan observations confirmed that 2018 VG18
is at around 120 AU, making it the first Solar-System object observed beyond
100 AU. Its brightness suggests that it is about 500 km in diameter. It has a
pinkish hue, a colour generally associated with ice-rich objects.
WHERE DID ALL THE NEPTUNES GO?
Universite de Geneve
"But where did the hot Neptunes go?" That is a question astronomers have
been asking for a long time, faced with the mysterious absence of planets
the size of Neptune very close to their stars. A team of researchers has
just discovered that one such planet is losing its atmosphere at a frantic
pace. That observation strengthens the theory that hot Neptunes have lost
much of their atmospheres and turned into smaller planets called
super-Earths, which are much more numerous. Fishermen would be puzzled if
they netted only big and little fish, but few medium-sized fish. That is
similar to what happens to astronomers hunting exoplanets. They found a
large number of hot planets the size of Jupiter and numerous others a little
larger than the Earth (called super-Earths, whose diameters do not exceed
1.5 times that of the Earth), but no planets close to their star the size of
Neptune. The mysterious 'desert' of hot Neptunes suggests two explanations:
either such worlds are rare, or that they were plentiful at one time, but
have since disappeared. A few years ago, UNIGE astronomers using NASA's
Hubble Space Telescope discovered that a warm Neptune on the edge of the
desert, GJ 436b, was losing hydrogen from its atmosphere. The loss is not
enough to threaten the atmosphere of GJ 436b, but suggested that Neptunes
receiving more energy from their star could evolve more dramatically. That
has just been confirmed by the same astronomers, members of the national
research centre PlanetS. They observed with Hubble that another warm
Neptune at the edge of the desert, named GJ 3470b, is losing its hydrogen
100 times faster than GJ 436b. The two planets reside about 3.7 million
kilometres from their star, one-tenth the distance between Mercury and the
Sun, but the star hosting GJ 3470b is much younger and energetic. The team
estimates that GJ 3470b has already lost more than a third of its mass.
Observing the evaporation of two warm Neptunes is encouraging, but team
members know that they need to study more of them to confirm their
predictions. Unfortunately, the hydrogen that escapes from these planets
cannot be detected if they are more than 150 light-years from Earth
(GJ 3470b is 97 light-years away), because hydrogen is then hidden by
interstellar gas. Researchers thus plan to use Hubble to look for other
traces of atmospheric escape, because hydrogen could drag upwards heavier
elements such as carbon. The solution could also come from helium, whose
infrared radiation is not blocked by the interstellar medium.
DID SUPERNOVAE KILL OFF LARGE OCEAN ANIMALS?
University of Kansas
About 2.6 million years ago, an oddly bright light arrived in the pre-
historic sky and lingered there for weeks or months. It was a supernova
some 150 light-years away. Within a few hundred years, long after the
strange light in the sky had dwindled, a tsunami of cosmic energy from that
same shattering star explosion could have reached our planet and pummelled
the atmosphere, touching off climate change and triggering mass extinctions
of large ocean animals, including a shark species that was the size of a
school bus. Recent papers revealing ancient seabed deposits of iron-60
isotopes provided the compelling evidence of the timing and distance of
supernovae. Because iron-60 is radioactive, if it had formed with the Earth
it would be long gone by now. So it had to have been rained down on us.
There is some debate about whether there was only one supernova really
nearby or a whole chain of them. Studies of iron-60 residue reveal that
there is a huge spike 2.6 million years ago, but there is excess scattered
clear back 10 million years. According to astronomers, other evidence for a
series of supernovae is found in the very architecture of the local
Universe. We have the Local Bubble in the interstellar medium and we are
right on its edge. It is a giant region about 300 light-years long. It is
basically very hot, very low-density gas -- nearly all the gas clouds have
been swept out of it. The best way to manufacture a bubble like that is a
number of supernovae that blow it bigger and bigger, and that seems to fit
well with idea of a chain. Calculations are based on the idea that one
supernova that goes off, and its energy sweeps by Earth, and it's over.
But with the Local Bubble, the cosmic rays bounce off the sides and the
cosmic-ray bath would last 10,000 to 100,000 years. That way, one could
imagine a whole series of these things feeding more and more cosmic rays
into the Local Bubble and giving us cosmic rays for millions of years.
Whether or not there was one supernova or a series of them, the supernova
energy that spread layers of iron-60 all over the world also caused
penetrating particles called muons to shower the Earth, causing cancers and
mutations -- especially to larger animals. The best description of a muon
would be a very heavy electron -- but muons are a couple of hundred times
more massive than electrons. They are very penetrating. Even normally,
there are lots of them passing through us. Nearly all of them pass through
harmlessly, yet about one-fifth of our radiation dose comes by muons. But
when the wave of cosmic rays hits, multiply those muons by a few hundred.
Only a small fraction of them will interact in any way, but when the number
is so large and their energy so high, you get increased mutations and cancer
-- those would be the main biological effects. Scientists have estimated
that the cancer rate would go up about 50% for something the size of a human
-- and the bigger you are, the worse it is. For an elephant or a whale, the
radiation dose is much larger. A supernova 2.6 million years ago may be
related to a marine megafaunal extinction at the Pliocene-Pleistocene
boundary where 36 per cent of the genera were estimated to have become
extinct. The extinction was concentrated in coastal waters, where larger
organisms would catch a greater radiation dose from the muons. Indeed, one
of the extinctions that happened 2.6 million years ago was Megalodon, a
famously large and fierce marine animal inhabiting shallow waters. Damage
from muons would extend down hundreds of metres into ocean waters, becoming
less severe at greater depths. High-energy muons can reach deeper in the
oceans, being the more relevant agent of biological damage as depth
increases.
LARGE POPULATION OF YOUNG PLANETS
University of Nevada, Las Vegas
Astronomers have catalogued nearly 4,000 exoplanets in orbit around distant
stars. Though the discovery of those new-found worlds has taught us much,
there is still a great deal that we do not know about the birth of planets
and the precise cosmic recipes that spawn the wide array of planetary bodies
that we have already uncovered, including so-called hot Jupiters, massive
rocky worlds, icy dwarf planets, and -- hopefully some day soon -- distant
analogues of the Earth. To help answer those and other intriguing
questions, a team of astronomers has conducted the first large-sample,
high-resolution survey of protoplanetary discs, the belts of dust and gas
around young stars. Using the Atacama Large Millimetre/submillimetre Array
(ALMA) telescope, researchers have obtained high-resolution images of 20
nearby protoplanetary discs and given astronomers new insights into the
variety of features they contain and the speed with which planets can
emerge. It appears that in other parts of our Milky Way there is
potentially a large population of young planets -- similar in mass to
Neptune or Jupiter -- in wide orbits, that are not detectable by other
current planet-searching techniques. That implies that many extra-solar
systems may be similar to our Solar System in the sense that they also have
planets like Uranus and Neptune at the outer disc.
Understanding how the Earth was formed 4 billion years ago in our Solar
System is difficult because the Solar System finished the planet-formation
processes long ago. On the other hand, we can observe young stars in other
parts of the Milky Way where young stars and young planets are currently
being assembled. Since the young stars are far away from us, we need
powerful telescopes, like ALMA, to study those systems. When stars are
young, they are surrounded by flat discs made of gas and dust. Those discs,
called protoplanetary discs, are where young planets are born (that is also
why planetary orbits in the Solar System are coplanar, lying in a common
plane around our Sun). It is very challenging, but, when we drop a pebble
into a pond, it will lead to ripples in the pond, which are more visible.
Similarly, when a young planet is present in its water pond (the proto-
planetary disc), it will excite waves too. If the planet is massive enough,
the waves become a tsunami and cause damage to the disc, forming a gap along
the planet's orbit in the disc. ALMA can detect tiny ripples and gaps in
protoplanetary discs.
FOSSIL FROM THE BIG BANG
W. M. Keck Observatory
A relic cloud of gas, orphaned after the Big Bang, has been discovered in
the distant Universe by astronomers using the world's most powerful optical
telescope, the W. M. Keck Observatory on Mauna Kea. The discovery of such a
rare fossil offers new information about how the first galaxies in the
Universe formed. Everywhere we look, the gas in the Universe is polluted by
waste heavy elements from exploding stars, but this particular cloud seems
pristine, unpolluted by stars even 1.5 billion years after the Big Bang. If
it has any heavy elements at all, it must be less than 1/10,000th of the
proportion we see in the Sun. That is extremely low; the most compelling
explanation is that it is a true relic of the Big Bang. The team used two
of Keck Observatory's instruments -- the Echellette Spectrograph and Imager
(ESI) and the High-Resolution Echelle Spectrometer (HIRES) -- to observe the
spectrum of a quasar behind the gas cloud. The quasar, which emits a bright
glow of material falling into a super-massive black hole, provides a light
source against which the spectral shadows of the hydrogen in the gas cloud
can be seen. The team targeted quasars where previous researchers had only
seen shadows from hydrogen and not from heavy elements in lower-quality
spectra. That allowed astronomers to discover such a rare fossil quickly
with the precious time on the Keck Observatory's twin telescopes. The only
two other fossil clouds known were discovered in 2011. The first two were
serendipitous discoveries but until now no one has discovered anything
similar -- they are clearly very rare and difficult to see.
Topic: Early January Astronomy Bulletin (Read 1107 times)