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discovered five additional ones,
increasing the number of known planets
in the system to seven.
The new results were published
Wednesday in the journal Nature, and
announced at a news briefing at NASA
Headquarters in Washington.
Using Spitzer data, the team precisely
measured the sizes of the seven planets
and developed first estimates of the
masses of six of them, allowing their
density to be estimated.
NASA Telescope Reveals Largest Batch of EarthSize, Habitable-Zone Planets Around Single Star
NASA’s Spitzer Space Telescope has revealed the first known
system of seven Earth-size planets around a single star. Three
of these planets are firmly located in the habitable zone, the area
around the parent star where a rocky planet is most likely to have
liquid water.
The discovery sets a new record for greatest number of
habitable-zone planets found around a single star outside our
solar system. All of these seven planets could have liquid
water – key to life as we know it – under the right atmospheric
conditions, but the chances are highest with the three in the
habitable zone.
“This discovery could be a significant piece in the puzzle of
finding habitable environments, places that are conducive
to life,” said Thomas Zurbuchen, associate administrator of
the agency’s Science Mission Directorate in Washington.
“Answering the question ‘are we alone’ is a top science priority
and finding so many planets like these for the first time in the
habitable zone is a remarkable step forward toward that goal.”
At about 40 light-years (235 trillion miles) from Earth, the
system of planets is relatively close to us, in the constellation
Aquarius. Because they are located outside of our solar system,
these planets are scientifically known as exoplanets.
This exoplanet system is called TRAPPIST-1, named for
The Transiting Planets and Planetesimals Small Telescope
(TRAPPIST) in Chile. In May 2016, researchers using
TRAPPIST announced they had discovered three planets in the
system. Assisted by several ground-based telescopes, including
the European Southern Observatory’s Very Large Telescope,
Spitzer confirmed the existence of two of these planets and
Based on their densities, all of the
TRAPPIST-1 planets are likely to be
rocky. Further observations will not
only help determine whether they are
rich in water, but also possibly reveal
whether any could have liquid water on
their surfaces. The mass of the seventh and farthest exoplanet
has not yet been estimated – scientists believe it could be an icy,
“snowball-like” world, but further observations are needed.
“The seven wonders of TRAPPIST-1 are the first Earth-size
planets that have been found orbiting this kind of star,” said
Michael Gillon, lead author of the paper and the principal
investigator of the TRAPPIST exoplanet survey at the University
of Liege, Belgium. “It is also the best target yet for studying the
atmospheres of potentially habitable, Earth-size worlds.”
In contrast to our sun, the TRAPPIST-1 star – classified as an
ultra-cool dwarf – is so cool that liquid water could survive on
planets orbiting very close to it, closer than is possible on planets
in our solar system. All seven of the TRAPPIST-1 planetary
orbits are closer to their host star than Mercury is to our sun.
The planets also are
very close to each
other. If a person was
standing on one of
the planet’s surface,
they could gaze up
and potentially see
geological features or
clouds of neighboring
worlds, which would
sometimes appear
larger than the moon
in Earth’s sky.
The planets may also
be tidally locked
to their star, which
means the same
side of the planet is
always facing the star,
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Shasta Astronomy Club
Newsletter
therefore each side is either perpetual day or night. This could
mean they have weather patterns totally unlike those on Earth,
such as strong winds blowing from the day side to the night side,
and extreme temperature changes.
Spitzer, an infrared telescope that trails Earth as it orbits the sun,
was well-suited for studying TRAPPIST-1 because the star glows
brightest in infrared light, whose wavelengths are longer than the
eye can see. In the fall of 2016, Spitzer observed TRAPPIST-1
nearly continuously for 500 hours. Spitzer is uniquely positioned
in its orbit to observe enough crossing – transits – of the planets
in front of the host star to reveal the complex architecture of
the system. Engineers optimized Spitzer’s ability to observe
transiting planets during Spitzer’s “warm mission,” which began
after the spacecraft’s coolant ran out as planned after the first
five years of operations.
“This is the most exciting result I have seen in the 14 years of
Spitzer operations,” said Sean Carey, manager of NASA’s Spitzer
Science Center at Caltech/IPAC in Pasadena, California. “Spitzer
will follow up in the fall to further refine our understanding of
these planets so that the James Webb Space Telescope can follow
up. More observations of the system are sure to reveal more
secrets.”
Following up on the Spitzer discovery, NASA’s Hubble Space
Telescope has initiated the screening of four of the planets,
including the three inside the habitable zone. These observations
aim at assessing the presence of puffy, hydrogen-dominated
atmospheres, typical for gaseous worlds like Neptune, around
these planets.
Mapping the family tree of stars
Astronomers are borrowing principles applied in biology and
archaeology to build a family tree of the stars in the galaxy. By
studying chemical signatures found in the stars, they are piecing
together these evolutionary trees looking at how the stars formed
and how they are connected to each other. The signatures act
as a proxy for DNA sequences. It’s akin to chemical tagging of
stars and forms the basis of a discipline astronomers refer to as
galactic archaeology.
It was Charles Darwin, who, in 1859 published his revolutionary
theory that all life forms are descended from one common
ancestor. This theory has informed evolutionary biology ever
since but it was a chance encounter between an astronomer and a
biologist over dinner at King’s College in Cambridge that got the
astronomer thinking about how it could be applied to stars in the
Milky Way.
Writing in Monthly Notices of the Royal Astronomical Society,
Dr. Paula Jofré, of the University of Cambridge’s Institute of
Astronomy, describes how she set about creating a phylogenetic
“tree of life” that connects a number of stars in the galaxy.
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“The use of algorithms to identify families of stars is a science
that is constantly under development. Phylogenetic trees add an
extra dimension to our endeavours which is why this approach is
so special. The branches of the tree serve to inform us about the
stars’ shared history,” she says.
The team picked 22 stars, including the Sun, to study. The
chemical elements have been carefully measured from data
coming from ground-based high-resolution spectra taken with
large telescopes located in the north of Chile. Once the families
were identified using the chemical DNA, their evolution was
studied with the help of their ages and kinematical properties
obtained from the space mission Hipparcos, the precursor of
Gaia, the spacecraft orbiting Earth that was launched by the
European Space Agency and is almost halfway through a 5-year
project to map the sky.
Stars are born from violent explosions in the gas clouds of the
galaxy. Two stars with the same chemical compositions are
likely to have been born in the same molecular cloud. Some
will live longer than the current age of the universe and serve as
fossil records of the composition of the gas at the time they were
formed. The oldest star in the sample analysed by the team is
estimated to be almost ten billion years old, which is twice as old
as the Sun. The youngest is 700 million years old.
In evolution, organisms are linked together by a pattern of
descent with modification as they evolve. Stars are very
different from living organisms, but they still have a history of
shared descent as they are formed from gas clouds, and carry
that history in their chemical structure. By applying the same
phylogenetic methods that biologists use to trace descent in
plants and animals it is possible to explore the ‘evolution’ of stars
in the galaxy.
“The differences between stars and animals is immense, but
they share the property of changing over time, and so both can
be analysed by building trees of their history,” says Professor
Robert Foley, of the Leverhulme Centre for Human Evolutionary
Studies at Cambridge.
With an increasing number of datasets being made available
from both Gaia and more advanced telescopes on the ground,
and on-going and future large spectroscopic surveys,
astronomers are moving closer to being able to assemble one tree
that would connect all the stars in the Milky Way.
Astronomers discover a new satellite for the Milky
Way
Phil Plait
Galaxies are immense structures. Composed of gas, dust, dark
matter, and billions of stars, big ones can be a hundred thousand
light-years across — a million trillion kilometers — and have
masses equaling trillions of Suns.
Our own Milky Way fits those numbers pretty well. It formed
not long after the Universe, itself, did, probably a billion or
so years after the Big Bang, collapsing from a vast cloud of
hydrogen and helium gas. It wasn’t alone, though: Two other big
galaxies were born along with it (the Andromeda Galaxy and
Triangulum), and a handful of smaller ones that are all bound by
their mutual gravity, forming what we call the Local Group.
Some of these galaxies are actually satellites of the Milky Way,
in a similar way that the Moon is a satellite of Earth. The two
biggest are the Large and Small Magellanic Clouds, with about
10 billion and a few hundred million stars in them respectively,
but we know of a few dozen very small dwarf galaxies also in
orbit around us. Most of them are extremely faint and hard to
detect, and we’re not really sure how many there are in total.
That’s actually important to know. Different theories and models
of how galaxies form predict different numbers and distributions
of dwarf satellite galaxies. To differentiate them, astronomers
scan the skies looking for more Milky Way companions.
These surveys are paying off: Nine dwarf candidate (meaning as
yet unconfirmed) satellites were found in 2015. Late last year, in
2016, another was discovered, and it’s pretty cool.
It was found using the Hyper Suprime-Cam instrument on the
gigantic Subaru 8.2 meter telescope. The HSC is itself a bit of a
monster; it’s over two meters long, weighs three tons, and takes
enormous 870 megapixel images that cover 1.5° of the sky on a
side. The Moon is about 0.5°, so this covers an area nearly ten
times the area of the Moon.
Astronomers aimed it at five separate regions of the sky,
covering a total of 100 square degrees (that’s a lot). They mapped
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Shasta Astronomy Club
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where all the objects were in the fields, separated stars from distant background galaxies (stars are point sources, whereas most
galaxies are slightly extended), and then looked for places where there were more stars than expected — hoping some might be faint
Milky Way satellites.
In the constellation of Virgo, they found such a clump. It’s unlikely to be a random fluctuation in the distribution of Milky Way stars
masquerading as a physical clump; it’s better than 99% certain to be an actual object. To make sure, the astronomers did something
clever. In an old dwarf satellite galaxy, it’s reasonable to assume all the stars in it were born at the same time; these galaxies tend to
form stars right as the galaxy, itself, forms, then run out of gas to make any more. If the stars instead belong to our Milky Way they
would have all different ages, since we’re still actively churning them out.
Using models of how stars change color as they age, the astronomers were able to show that the stars in the clump do look to be about
the same age —about 13 billion years. Not only that, if they throw away the stars that don’t match that age, the statistical significance
of the clump being real jumps up to near certainty.
So, this appears to be a real galaxy, which they’ve dubbed Virgo I. The distance (measured by looking at the brightness of the stars in
it) is about 280,000 light years away; three times the width of the Milky Way, itself. The size is a bit difficult to determine; galaxies
aren’t solid objects and fade with distance from their centers. But it appears this object is roughly 300 light years across.
That, in itself, is interesting. First, that’s tiny. Second, there are objects called globular clusters, which are magnificent collections of
hundreds of thousands of stars in a ball, all orbiting their common center of mass like bees buzzing around a hive. About 150 of them
are known to orbit the Milky Way. While the numbers of stars in a typical globular cluster is similar to Virgo I, the latter is much
bigger than what you’d expect for a globular at that distance, making it even more likely this is, indeed, a galaxy.
So, this looks to be a legit dwarf galaxy, likely a satellite of the Milky Way, so small and faint it’s escaped detection until now. Now,
here’s a fun fact: The astronomers looked at 100 square degrees of sky and found one such object. But there are over 40,000 square
degrees of sky, so extrapolating from that means there may be hundreds of these dinky galaxies yet to find!
Happily, the survey that found Virgo I is ongoing, so hopefully they’ll start finding more. It’s rather amazing to me that we can see
galaxies billions of light years way, nearly to the edge of the observable Universe, but there can be galaxies literally orbiting our own
that have gone unnoticed. Of course, the ones we see at fantastic distances are huge and bright, and the nearby ones small and faint.
But still, it shows you that, sometimes, treasures can be found on your doorstep if you just look more carefully.
A map of the number of stars seen in the region of Virgo I (left) shows a clump
at its location, whereas extended galaxies (right) does not. Credit: Homma et al.
virgoi_map.jpg
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teaming up with private spaceflight companies, a model that is
expected to be utilized in the administration in general.
Along with the Webb telescope, NASA has two telescopes
based on modified versions of the Hubble design donated by the
National Reconnaissance Office. One such mission, the Wide
Field Infrared Survey Telescope, will be utilized as an exoplanet
and dark matter hunter to be launched in the mid-2020s. Plans
for the other telescope have not yet been announced.
Meteorites Date Demise of Solar Nebula
Another Hubble repair mission could be on the way
By: David Dickinson
Preliminary reports suggest the Trump administration
may team up with Sierra Nevada to bring new life to
an old telescope.
A study of ancient meteorites has refined the date for the
dissolution of the solar nebula, the cloud of dust and gas that
shrouded our Sun in its earliest days.
By John Wenz
The Hubble Space Telescope, launched in 1990, has provided
a wellspring of information about our universe over the last 27
years. Some of those discoveries required five upgrades to the
system.
And now, according to a Wall Street Journal report, there could
be a sixth. According to the report, the servicing would provide
an “insurance policy” in case the James Webb Space Telescope,
which will perch itself far from low-Earth orbit (and even beyond
the Moon) at a stable point called L2.
With the space shuttle program ending in 2011, there isn’t a
vehicle to complete the mission. Yet. But Sierra Nevada, a
private spaceflight company, has worked for years on a miniature
space shuttle called the Dream Chaser, based on older designs
generated in the early days of NASA. Right now, the craft is
only cleared for automated flights and may resupply the ISS as
soon as 2019. The project would require a human-piloted variant
relying on infrastructure that already exists in the ship’s design.
According to the WSJ report, the possibility is currently in the
(very) preliminary stages. It would represent a public-private
venture that would drive down federal government costs by
What would we see in our solar system if we could go back
billions of years? Much of what transpired during the solar
system’s formation is lost to time. But as we explore worlds
outside our own system, it would be valuable to know just how
common — or rare — the our solar system is in the grand drama
of the Universe.
Now, a recent study by a Massachusetts Institute of Technology
(MIT) team has pinpointed a key period during our solar
system’s formation when the Sun had blown away the cloud of
dust and gas enshrouding it.
Our solar system formed about 4.6 billion years ago, when a
giant, magnetized cloud of dust and molecular hydrogen gas
collapsed to form the Sun and, not long thereafter, its attendant
planets. However, once the Sun ignited fusion within its core, it
began to shine and the pressure from its radiation and solar wind
started slowly lifting the curtain of dust and gas pervading the
inner solar system. The solar nebula that had fed the infant star
soon dispersed.
We have witnessed other “proto-solar systems,” such as the
proplyds dotting the Orion Nebula, in the act of formation today.
Going off of such snapshots of infant systems, astronomers
gauged the lifetime of the early solar nebula at 1 to 10 million
years. The recent MIT study, published in the February 9th
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The Wild Times of the Solar System’s Youth
The early years of the solar system were wild and chaotic, with
the solar nebula’s gravitational forces driving planets’ migrations
about the system.
“When the solar nebula is present, it exerts a gravitational force
on the giant planets.” says Weiss. “This [force] can cause the
planets’ orbits to change rapidly, typically evolving inward
toward the Sun.” This may also explain the proliferation of “hotJupiters,” or exoplanets seen in tight orbits around their host stars
that have since migrated inward.
The nebula’s dissipation after 3.8 million years would have
ended most of this disorder, giving rise to an arrangement of
planets familiar to us today.
Proplyds (insets) dot the stellar nursery of the Orion Nebula (M42), located
1,350 light-years away. NASA / ESA / M. Robberto (Space Telescope Science
Institute/ESA) / Hubble Space Telescope Orion Treasury Project Team and L.
Ricci (ESO) heic0917ab.jpg
Science, refines these estimates, putting the end of the solar
nebula at 3 to 4 million years.
“Our solar nebula’s lifetime appears to be right in the middle
of what is observed for Sun-like stars,” says Benjamin Weiss
(MIT).
The team arrived at their estimate by looking at some of the
oldest meteorites on Earth, known as angrites, including
meteorites collected from Antarctica, the Sahara, Brazil, and
Argentina. The Argentine D’Orbiny meteorite in particular has a
storied history, as the rock was found while a farmer was tilling
his field and resided by his farmhouse for 20 years before it was
analyzed and identified as a rare angrite meteorite — the largest
specimen discovered.
These rocks contain a high amount of uranium, whose steady
decay enables researchers to pinpoint the rocks’ formation at
4.653 billion years ago. Also, the rocks’ magnetism was frozenin during their formation, giving researchers a record of what the
magnetic field was like at the time.
The team tested the angrites using a precision magnetometer
at the MIT Paleomagnetism Laboratory and found remnant
magnetism so weak, it could have only been produced in an
extremely weak magnetic field of no more than 0.6 microteslas
about 3.8 million years after the solar system’s formation. By
contrast, back in 2014 the same team had looked at even older
meteorites, which had formed 2 to 3 million years after the
solar system, and found evidence for a magnetic field of 5 to 50
microteslas pervading the early solar system.
The more than tenfold drop in the strength of the solar nebula’s
magnetic field indicates that the nebula itself had all but
dissipated by 3.8 million years after the solar system’s birth.
This result also throws another piece of evidence into the planet
formation ring, where two scenarios vie to explain the formation
of Jupiter and Saturn. In the two-stage scenario known as core
accretion, bits of rock fused together to form these gas giants’
cores, which then attracted huge shrouds of gas. The opposing
scenario, called gravitational collapse, proposes that the gas
giants formed all at once, much as the Sun did.
The two scenarios happen on
vastly different timescales:
gravitational collapse would
have occurred over about
100,000 years, while core
accretion would have taken
millions of years. The
persistence of the solar nebula
over 3 to 4 million years
means the core accretion
hypothesis remains viable, but
it also constrains the length of
time that mechanism would
have been allowed to operate.
The refined age of the solar nebula puts one more piece into
place in the puzzle of our solar system’s formation. Looking
out at other exoplanetary systems at various stages will give us
further insight into how the process unfolds. Missions like the
Transiting Exoplanet Survey Satellite (TESS) and the James
Webb Space Telescope (JWST), for example, are set to up the
tally of known worlds, which currently stands at 3,576.
Also, sample return missions such as JAXA’s Hayabusa 2 and
Osiris-REX may confirm or refute the findings gathered from
meteorites found here on Earth. Finally, NASA’s Juno spacecraft
is currently probing the interior of Jupiter, and we may soon
know if it has a rocky core at its very heart, or if it’s pure
metallic hydrogen all the way through.
Get ready for a renaissance in planetary science, as the mystery
of the solar system’s formation continues to unfold.
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Shasta Astronomy Club
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March 2017
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