Topic: Early June Astronomy Bulletin

[Clive]

FIRST INTERSTELLAR IMMIGRANT FOUND IN SOLAR SYSTEM
RAS
 
A new study has discovered the first known permanent immigrant to our Solar
System.  The asteroid, currently nestling in Jupiter's orbit, is the first
asteroid known to have been captured from another star system.  An object
known as 'Oumuamua was the last interstellar interloper to hit the headlines,
in 2017.  However, it was just a tourist passing through, whereas the new
exo-asteroid -- given the catchy name (514107) 2015 BZ509 -- is a long-term
resident.  All of the planets in the Solar System, and the vast majority of
other objects as well, travel around the Sun in the same direction.  But
2015 BZ509 is different -- it moves in the opposite direction, in what is
known as a 'retrograde' orbit.  How the asteroid came to move in that way
while sharing Jupiter's orbit has until now been unknown.  If 2015 BZ509
were a native of our system, it should have had the same original direction
as all of the other planets and asteroids, inherited from the cloud of gas
and dust that formed them.  However, the team ran simulations to trace the
location of 2015 BZ509 right back to the birth of our Solar System, 4.5
billion years ago when the era of planet formation ended.  They show that
2015 BZ509 has always moved in that way, and so could not have been there
originally and must have been captured from another system.
 
Asteroid immigration from other star systems occurs because the Sun
initially formed in a tightly-packed star cluster, where every star had
its own system of planets and asteroids.  The close proximity of the stars,
aided by the gravitational forces of the planets, helped those systems
attract, remove and capture asteroids from one another.  The discovery of
the first permanent asteroid immigrant in the Solar System has important
implications for the open problems of planet formation, Solar-System
evolution, and possibly the origin of life itself.  Understanding exactly
when and how 2015 BZ509 settled in the Solar System may provide clues about
the Sun's original star nursery, and about the potential enrichment of our
early environment with components necessary for the appearance of life on
Earth.


CURIOSITY IS COLLECTING MARS ROCKS
NASA

Engineers working with NASA's 'Curiosity' Mars rover have been hard at work
testing a new way for the rover to drill rocks and extract powder from them.
That effort has produced the first drilled sample on Mars in more than a
year.  Curiosity tested percussive drilling, penetrating about 50 mm into a
rock called 'Duluth'.  NASA has been testing that drilling technique since
a mechanical problem took Curiosity's drill offline in 2016 December.  The
technique, called 'Feed Extended Drilling', keeps the drill's bit extended
out past two stabilizer posts whose original purpose was to steady the drill
against Martian rocks.  It lets Curiosity drill using the force of its
robotic arm, a little more like the way a human would drill into a wall at
home.  Drilling is a vitally important part of Curiosity's capabilities to
study Mars.  Inside the rover are two laboratories that are able to conduct
chemical and mineralogical analyses of rock and soil samples.  The samples
are acquired from Gale Crater, which the rover has been exploring since
2012.


COSMOCHEMICAL MODEL FOR PLUTO'S FORMATION 
Southwest Research Institute
 
Scientists have developed what they call 'the giant comet' cosmochemical
model of Pluto's formation.  At the heart of the research is the nitrogen-
rich ice in Sputnik Planitia, a large glacier that forms the left lobe of
the bright Tombaugh Regio feature on Pluto's surface.  Researchers found an
intriguing consistency between the estimated amount of nitrogen inside the
glacier and the amount that would be expected if Pluto were formed by the
agglomeration of roughly a billion comets or other Kuiper-Belt objects
similar in chemical composition to 67P, the comet explored by Rosetta.  In
addition to the comet model, scientists also investigated a solar model,
with Pluto forming from very cold ices that would have had a chemical
composition that more closely matches that of the Sun.  Scientists needed to
understand not only the nitrogen present in Pluto now -- in its atmosphere
and in glaciers -- but also how much of that volatile element potentially
could have leaked out of the atmosphere and into space over the aeons. 
They then needed to reconcile the proportion of carbon monoxide to nitrogen
to get a more complete picture.  Ultimately, the low abundance of carbon
monoxide in Pluto points to burial in surface ices or to destruction from
liquid water.  The research suggests that Pluto's initial chemical makeup,
inherited from cometary building blocks, was chemically modified by liquid
water, perhaps even in a sub-surface ocean.  However, the solar model also
satisfies some constraints.  While the research pointed to some interesting
possibilities, many questions remain to be answered.  The research builds
upon the success of the New Horizons and Rosetta missions to expand our
understanding of the origin and evolution of Pluto.  Using chemistry as a
detective's tool, scientists were able to trace certain features we see on
Pluto today to formation processes from long ago.  That leads to a new
appreciation of the richness of Pluto's 'life story', which we are only
now starting to grasp.


KEPLER FOCUSES ON STAR CLUSTERS
NASA

The Kepler planet-hunting spacecraft began the 18th observing campaign of
its extended mission, K2, on May 12.  For the next 82 days, Kepler will
stare at clusters of stars, faraway galaxies, and a handful of Solar-System
objects, including comets, objects beyond Neptune, and an asteroid.  The
Kepler spacecraft is expected to run out of fuel within several months.
Campaign 18 is a familiar patch of space, as it is approximately the same
region of sky that Kepler observed during Campaign 5 in 2015.  One of the
advantages of observing a field again is that planets outside the Solar
System, called exoplanets, may be found orbiting farther from their stars.
Astronomers hope not only to discover new exoplanets during this campaign,
but also to confirm candidates that were previously identified. 

Open star clusters are regions where many stars formed at roughly the same
time; they include Messier 67 and Messier 44, the latter also known as
Praesepe or the Beehive cluster.  Home to six known exoplanets, Praesepe
will be searched anew for objects that are transiting, or crossing, around
the same or other stars.  At approximately 800 million years old, the stars
in Praesepe are young in comparison with the Sun.  Many of those youthful
stars are active and have large spots that can reveal information about the
star's magnetic field, a fundamental component of a star that drives flaring
and other activity.  By comparing brightness data collected in Campaigns 18
and 5, scientists hope to learn more about how a star's spots cycle over
time.

At several billion years, the Messier 67 cluster is much older and has many
Sun-like stars.  It is one of the best-studied open clusters in the sky.
[The moderator of these Bulletins was among the authors in the 1980s of
papers that gave radial velocities for no fewer than 170 stars in the M67
field and spectroscopic orbits for 22 of them.]  Astronomers will continue
their studies of stellar astrophysics by analyzing M67's stars for changes
in brightness.  They will search for the signatures of exoplanets, observe
the pulsations of evolved stars, and measure the rotation rates of many
other stars in the cluster.  Beyond the star clusters, Kepler will observe
blazars, the energetic nuclei of faraway galaxies with black holes in their
centres.  Those objects propel jets of hot plasma towards the Earth (though
they are far too distant to affect us).  The most notable of the targets is
OJ 287, a system hosting two black holes in orbit around each other, one of
which is 18 billion times the mass of the Sun!  Even closer to home,
Kepler will look at Solar-System objects, including comets, trans-Neptunian
objects, and the near-Earth asteroid 99942 Apophis.  That 1,000-foot chunk
of rock will pass within 20,000 miles of the Earth in the year 2029 -- close
astronomically but still far enough away not to pose any danger to the Earth.


VAST IONIZED HYDROGEN CLOUD IN M51
Case Western Reserve University

Astronomers have been observing M51, the Whirlpool Galaxy, since the 1800s;
its signature spiral structure informed the earliest debates over the nature
of galaxies and the cosmos at large.  But no one -- not with the naked eye
or with increasingly powerful modern telescopes -- had ever seen what
astronomers first observed with a refurbished 75-year-old telescope in the
mountains of southwest Arizona.  What it was turned out to be a massive
cloud of ionized hydrogen gas spewed from a nearby galaxy and then
essentially 'cooked' by radiation from the galaxy's central black hole. 
The discovery of the giant gas cloud, first observed in 2015, potentially
provides astronomers with an unexpected 'front-row seat' to view the
behaviour of a black hole and the associated galaxy as it consumes and
'recycles' hydrogen gas.  We know of a few clouds like it in distant
galaxies, but not in one so 'close' to us.  It gives astronomers a great
opportunity to study up 'close' how gas is ejected from galaxies and how
black holes can influence large regions of space around those galaxies. 
The astronomers used the Burrell Schmidt telescope of the Warner & Swasey
Observatory, now at Kitt Peak.  Although older and smaller than most
telescopes on Kitt Peak, the telescope is constructed in such a way as to
provide a wide field of view, while also keeping out unwanted stray light.
That allows astronomers to see things that other telescopes don't: diffuse
patches of light that are "over 100 times fainter than the blackest night
sky you can imagine".  What the telescope really does well is measure very
diffuse, low-surface-brightness light emitted by gas or stars around a
galaxy.

Researchers had originally been imaging the Whirlpool to map the faint
streamers of starlight torn off by the collision between the galaxies.
Thinking that there might also be gas in those streamers, the team fitted
the telescope with a special filter to see hot, ionized hydrogen gas,
which emits a specific wavelength of light.  Finding stars is relatively
straightforward, but gas does not shine at all wavelengths.  That is one
of several reasons why no one had ever seen that before -- earlier studies
using such hydrogen filters to look for ionized gas could not detect
emission so faint and over such a wide area around the Whirlpool.  But
there was still one thing to double-check: the team worried that they were
actually seeing a diffuse cloud of gas right in front of us in our own
galaxy and it wasn't really part of M51.  The astronomers called on the
nearby WIYN Observatory to confirm the cloud's association with M51.  The
WIYN 3.5-m telescope was equipped with an instrument capable of taking a
detailed spectrum of the cloud to measure its velocity.  Once the WIYN
people had taken the spectrum of the cloud, they were able to tell how fast
it was moving away from us, and it became immediately apparent that it was
part of M51, not something nearer to us.  The discovery's role in  under-
standing nmore clearly how galaxies eject and 'recycle' their gas and
stars will be determined in the coming years as more researchers dig into
information that had been there all along -- even if unseen until now.


STARS FORMING 250 MILLION YEARS AFTER THE BIG BANG
ESO
 
Astronomers have used observations from the Atacama Large Millimeter/sub-
millimeter Array (ALMA) and the Very Large Telescope (VLT) to determine
that star formation in the very distant galaxy MACS 1149-JD1 started at
an unexpectedly early stage, 'only' 250 million years after the Big Bang.
That discovery also represents the most distant oxygen ever detected in
the Universe and the most distant galaxy ever observed by ALMA or the VLT. 
The team detected a very faint glow emitted by ionized oxygen in the
galaxy.  As that infrared light travelled across space, the expansion of the
Universe stretched it to wavelengths more than ten times longer by the time
it reached the Earth and was detected by ALMA.  The team inferred that the
signal was emitted 13.3 billion years ago (or 500 million years after the
Big Bang), making it the most distant oxygen ever detected.  The presence
of oxygen is a clear sign that there must have been even earlier generations
of stars in that galaxy.  In addition to the glow from oxygen picked up by
ALMA, a weaker signal of hydrogen emission was also detected by ESO's Very
Large Telescope (VLT).  The distance to the galaxy determined from that
observation is consistent with the distance from the oxygen observation.

That makes MACS 1149-JD1 the most distant galaxy with a precise distance
measurement and the most distant galaxy ever observed with ALMA or the VLT.
For a period after the Big Bang there was no oxygen in the Universe; it was
created by the fusion processes of the first stars and then released when
those stars died.  The detection of oxygen in MACS 1149-JD1 indicates that
those earlier generations of stars had already been formed and expelled
oxygen by just 500 million years after the beginning of the Universe. 
But when did that earlier star formation occur?  To find out, the team
reconstructed the earlier history of MACS 1149-JD1 using infrared data taken
with the Hubble and Spitzer space telescopes.  They found that the observed
brightness of the galaxy is well explained by a model where the onset of
star formation corresponds to 'only' 250 million years after the Universe
began.  The maturity of the stars seen in MACS 1149-JD1 raises the question
of when the very first galaxies emerged from total darkness, an epoch
astronomers romantically term 'cosmic dawn'.  By establishing the age of
MACS 1149-JD1, the team has effectively demonstrated that galaxies existed
earlier than those that we can currently detect directly.