Some Spectacular Images (And Science) From The Year Past

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A rose made of galaxies

This is a golden era for space and planetary science, a time when discoveries, new understandings, and newly-found mysteries are flooding in.  There are so many reasons to find the drama intriguing:  a desire to understand the physical forces at play, to learn how those forces led to the formation of Earth and ultimately us, to explore whether parallel scenarios unfolded on planets far away, and to see how our burgeoning knowledge might set the stage for exploration.

But always there is also the beauty; the gaudy, the stimulating, the overpowering spectacle of it all.

Here is a small sample of what came in during 2016:

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The Small Magellanic Cloud, a dwarf galaxy that is a satellite of our Milky Way galaxy, can be seen only in the southern hemisphere.  Here, the Hubble Space Telescope captured two nebulas in the cloud. Intense radiation from the brilliant central stars is heating hydrogen in each of the nebulas, causing them to glow red.

Together, the nebulas are called NGC 248 and are 60 light-years long and 20 light-years wide. It is among a number of glowing hydrogen nebulas in the dwarf satellite galaxy, which is found approximately 200,000 light-years away.

The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE). Astronomers are using Hubble to probe the Milky Way satellite to understand how dust is different in galaxies that have a far lower supply of heavy elements needed to create that dust.  {NASA.ESA, STSci/K. Sandstrom (University of California, San Diego), and the SMIDGE team}

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope.

Probably the biggest exoplanet news of the year, and one of the major science stories, involved the discovery of an exoplanet orbiting Proxima Centauri, the star closest to our own.

This picture combines a view of the southern skies over the European Space Observatory’s 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left).

The planet Proxima Centauri b is thought to lie within the habitable zone of its star.  Learning more about the planet, the parent star and the two other stars in the Centauri system has become a focus of the exoplanet community.

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We all know about auroras that light up our far northern skies, but there’s no reason why they wouldn’t exist on other planets shielded by a magnetic field — such as Jupiter.  Astronomers using the Hubble Space Telescope have found them on the poles of our solar system’s  largest planet, and produced far ultraviolet light images taken as the Juno spacecraft approached the planet.

Auroras are formed when charged particles in the space surrounding the planet are accelerated to high energies along the planet’s magnetic field. When the particles hit the atmosphere near the magnetic poles, they cause it to glow like gases in a fluorescent light fixture. Jupiter’s magnetosphere is 20,000 times stronger than that of Earth.

The full-color disk of Jupiter in this image was separately photographed at a different time by Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project that annually captures global maps of the outer planets.

Inside the Crab Nebula

Peering deep into the core of the Crab Nebula, this close-up image reveals the heart of one of the most historic and intensively studied remnants of a supernova, an exploding star. The inner region sends out clock-like pulses of radiation and tsunamis of charged particles embedded in magnetic fields.

The neutron star at the very center of the Crab Nebula has about the same mass as the sun but compressed into an incredibly dense sphere that is only a few miles across. Spinning 30 times a second, the neutron star shoots out detectable beams of energy that make it look like it’s pulsating.

The NASA Hubble Space Telescope image is centered on the region around the neutron star (the rightmost of the two bright stars near the center of this image) and the expanding debris surrounding it. Intricate details of glowing gas are shown in red and the blue glow is radiation given off by electrons spiraling at nearly the speed of light in the powerful magnetic field around the crushed stellar core.

Observations of the Crab supernova were recorded by Chinese astronomers in 1054 A.D. The nebula, bright enough to be visible in amateur telescopes, is located 6,500 light-years away in the constellation Taurus.  (NASA, ESA)

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The Gemini Planet Imager provides some of the earliest high-resolution, high-contrast direct imaging of exoplanets.  Using a coronagraph inside the telescope to block out the light of the star, the GPI can then allow researchers to see the region surrounding that star — in other words, where exoplanets might be.

This image includes a wide-angle view of the star HD 106906 taken by the Hubble Space Telescope and a close-up view from the Planet Imager, which operates on the Gemini South telescope in Chile’s Atacama Desert.  The image reveals a disturbed system of comets near the star, which may be responsible for the orbit of the the unusually distant giant planet (upper right).

The GPI Exoplanet Survey is operated by a team of astronomers from the University of California at  Berkeley and 23 other institutions, and is targeting 600 young stars to understand how planetary systems evolve over time.

Paul Kalas of UC Berkeley is responsible for the image and led the team that wrote about it. That paper actually came out in the Astrophysical Journal in late 2015 but, hey, that’s almost 2016.

Astronomers have regularly found a galaxy or star that is the furthest from us ever to be detected.  But the record is there to be broken, and in 2016 it was astronomers from the Great Observatories Origins Deep Survey (GOODS) who made the discovery.

Galaxy GN-z11, shown in the inset, was imaged as it was 13.4 billion years in the past, just 400 million years after the big bang.  That means the universe was only three percent of its current age when the light left that galaxy.

The galaxy has many blue stars that are bright and young, but it looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe.

(NASA, ESA, P. Oesch (Yale University), G. Brammer ( STScI)), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)

Biggest announce of discovred exoplanets by Kepler. (No, those are not real images, but still...)

No, these are not images of actual exoplanets, but they represent the continuing work of one of NASA’s most pioneering and productive missions, the Kepler Space Telescope. In May the Kepler team announced the detection of 1284 more planets or planet candidates as part of its newest catalog, the largest number announced at once in the mission.

To date, Kepler has identified unconfirmed 4,696 planet candidates, 2,331 confirmed planets, and 21 confirmed small planets in a habitable zone. In addition, the follow-on K2 mission has identified 458 candidate planets and 173 confirmed.

The Kepler spacecraft stared fixedly at a small portion of the sky for four years, looking to identify miniscule dimmings in the brightness of stars that would indicate that a planet was passing between the telescope and the star. In this way, Kepler has established a census of exoplanets that has been extrapolated to show the presence of billions and billions of planets around other stars.

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The 21-foot array that will collect photons for the James Webb Space Telescope was finished and put on display in November at the Goddard Space Flight Center. It will be the largest mirror to go into space, and will likely make the JWST into the most powerful and far-seeing observatory ever.

It will observe in the infrared portion of the spectrum because its goals include peering deep into the past of the universe, which is now most visible in the infrared. This means the JWST will have to be cooled to -364 degrees F, just 50 degrees above absolute zero.  To achieve that temperature, it’s insulated from the sun by five membrane layers, each no thicker than a human hair. Placing those membranes was finished in November, marking an end to construction of the telescope “mirror.”

The project has been enormously ambitious, and with that has come long delays and budget overruns that almost resulted in it being scrapped. Just this month, some early vibrating tests – designed to simulate launch conditions – experienced an anomaly that NASA engineers are working on now.  The JWST is scheduled to launch in late 2018.

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This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position of Jupiter’s moon Europa. The plumes, photographed by NASA’s Hubble’s Space Telescope Imaging Spectrograph, were seen in silhouette as the moon passed in front of Jupiter.

While the plumes spitting out of Saturn’s moon Enceladus are much better known now — the Cassini spacecraft flew through them in 2015, after all — the growing scientific consensus that Europa also has some plumes may be of even greater importance.  That moon is much larger, its ice-covered oceans have been determined to hold more water than all the oceans of Earth, and those oceans have clearly been around for a long time.

Hubble’s ultraviolet sensitivity allowed for the detection of the plumes, which rise more than 100 miles above Europa’s icy surface. The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions. (NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center.)

compounds being created in the xxx nebula

How the fundamentals needed for life are created in space has been a longstanding mystery.  The cosmos, after all, began with hydrogen and helium, and that was about it.  But life needs carbon atoms connected to hydrogen, oxygen, nitrogen and other elements

Astronomers and astrochemists have been making progress in recent years and now understand the basics of how the heavier elements are formed in space.  New data from the European Space Agency’s Herschel Space Observatory has gone further and has established that ultraviolet light from stars plays a key role in creating these molecules.  Previously, scientists thought that turbulence created by “shock” events was the driving force.

This image is of the Orion nebula, where scientists studied carbon chemistry of a major star-forming region. Herschel probed an area of the electromagnetic spectrum — the far infrared, associated with cold objects — that no other space telescope has reached before so it could take into account the entire Orion Nebula instead of individual stars.

The result was a better understanding of how carbon and hydrogen reach the states necessary to bond and form the basic carbon chemistry of the cosmos (and of life.)

Within the inset image, the emission from ionized carbon atoms (C+), overlaid in yellow, was isolated and mapped out from spectrographic data.

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Following a successful close flyby of Enceladus, the NASA-ESA Cassini spacecraft captured this image of the moon with Saturn’s rings beyond.

The image was taken in visible light with the Cassini spacecraft wide-angle camera when it was about 106,000 miles away from Enceladus. That flyby turned into a fly-through as well, when Cassini entered the plumes of water vapor and dust that shoot out of the bottom of the moon.

Scientists already know that an array of organic and other chemicals are in the plumes, but the field is awaiting word about the presence (or absence) of molecular hydrogen, which is formed when water comes into contact with rocks in hydrothermal vents.  Many think that Enceledus is habitable and should be tested for signs of life because biosignatures could potentially exist in the relatively easy-to-access geysers.

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While Yuri Beletsky is a staff astronomer at the Las Campanas Observatory in Chile, he is also a noted astrophotographer who specializes in capturing the beauty of nighttime scenes — usually connecting the celestial with the terrestrial.

In this 2016 photo, the moon is surrounded by a halo caused by the presence of millions of ice crystals in the upper atmosphere.  Great conditions for an astrophotographer, but pretty much useless for an astronomer.

The star within the halo is Regulus, brightest object in the constellation Leo the Lion. On the left outside the halo is Procyon from Canis Minor and on the right is the planet Jupiter.

As is so often the case in this line of endeavor, it’s quite a sight to see.

 

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Ranking Exoplanet Habitability

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The Virtual Planetary Lab at the University of Washington has been working to rank exoplanets (or exoplanet candidates) by how likely they are to be habitable. (Rory Barnes)
The Virtual Planetary Lab at the University of Washington has been working to rank exoplanets (or exoplanet candidates) by how likely they are to be habitable. (Rory Barnes)

 

Now that we know that there are billions and billions of planets beyond our solar system, and we even know where thousands of confirmed and candidate planets are located, where should we be looking for those planets that could in theory support extraterrestrial life, and might just possibly support it now?

The first order answer is, of course, the habitable zone — that region around a host star that would allow orbiting planets to have liquid water on the surface at least some of the time.

That assertion is by definition a theoretical one — at this point we have no detection of an exoplanet with liquid water orbiting a distant star — and it is actually a rather long-held view.

For instance, this is what William Whewell, the prominent British natural philosopher-scientist-theologian (and Master of Trinity College at Cambridge) wrote in 1853:

William Whewell was
William Whewell was an early proponent of a region akin to a habitable zone.  He also coined the words “scientist” and “physicist.”

“The Earth is really the domestic hearth of this solar system; adjusted between the hot and fiery haze on one side, the cold and watery vapour on the other.  This region is fit to be the seat of habitation; and in this region is placed the largest solid globe of our system; and on this globe, by a series of creative operations…has been established, in succession, plants, and animals, and man…The Earth alone has become a World.”

Whewell wrongly limited his analysis to our solar system, but he was pretty much on target regarding the crude basics of a habitable zone. His was followed over the decades by other related theoretical assessments, including in more modern times Steven Dole for the Rand Corporation in 1964 and NASA’s Michael Hart in 1979.  All pretty much based on an Earth-centric view of habitable zones throughout the cosmos.

It was this approach, even in its far more sophisticated modern versions, that got some of the scientists at the University of Washington’s Virtual Planetary Laboratory thinking three years ago about how they might do better.  What they wanted to do was to join the theory of the habitable (or more colloquially, the “Goldilocks zone”) with actual data now coming in from measurements of transiting exoplanets.

Although the measurements remain pretty limited, the group was convinced that the process could come up with the beginnings of a “Habitability Index” that would rate — based on evidence-based calculations and models — which exoplanets had the best chance of being able to support life.

“We certainly are constrained by the observations being made, but we do have some important physical measurements to work with,” said Rory Barnes, a astrophysical theorist with the VPL.  “And what we’ve done is to connect the possibility of life with the fundamental observables we do have….This really hasn’t been done before.”

Of the 1,030 confirmed planets from Kepler, a dozen are less than twice the size of Earth and reside in the habitable zone of their host star. The sizes of the exoplanets are represented by the size of each sphere. These are arranged by size from left to right, and by the type of star they orbit, from the M stars that are significantly cooler and smaller than the sun, to the K stars that are somewhat cooler and smaller than the sun, to the G stars that include the sun. The sizes of the planets are enlarged by 25X compared to the stars. The Earth is shown for reference. NASA Ames/JPL-CalTech/R. Hurt
Of the 1,030 confirmed planets from Kepler, a dozen are less than twice the size of Earth and reside in the habitable zone of their host star. They are arranged by by size and by the type of star they orbit — from the M stars that are significantly cooler and smaller than the sun, to the K stars that are somewhat cooler and smaller than the sun, to the G stars that include the sun. The sizes of the planets are enlarged by 25 times compared to the stars. The Earth is shown for reference. (NASA Ames/JPL-CalTech/R. Hurt)

The result was a detailed paper in the Astrophysical Journal that showed observations and modeling that can be harnessed together to come up with a list of the 10 exo-objects most likely to support life.   I specifically didn’t write “exoplanets” because nine of the ten remain  “candidate” planets detected by the Kepler Space Telescope as transiting objects that block out a small bit of light from the host star.  But they have not yet been confirmed through other detection techniques.

And why do the hard work of teasing out the potentially most habitable planets (objects) from the many thousands of others identified?  Clearly, it’s not because the data will point to some planet/objects that have a very good chance of being habitable.  The information available just won’t allow for that.

Rather, the next-generation James Webb Space Telescope is scheduled to launch in 2018, and it will be able to measure the components of exoplanets and their atmospheres in a whole new way.But access to a telescope like the JWST is costly and the observing and analyzing is and time-consuming.  And so the Virtual Planetary Laboratory’s index is designed to help fellow astronomers identify which worlds might have the best chance of hosting life, and so are worthy of all the necessary time and money.

Is the Habitability Index that much more useful than the more traditional habitable zone assessments based on a planet’s proximity to a particular star of a particular strength?  And is it more predictive than some related assessments such as the Earth Similarity Index, created by Abel Mendez at the University of Puerto Rico at Arecibo.

Because it takes into account so much more information, it certainly seems likely that it is more predictive, especially as new and better information is added to the system.  While the traditional habitable zone points to a locations, the Habitability Index identifies distinctions within a habitable zone that would make an exoplanet more or less likely to support life.

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Rory Barnes is a theorist in the Virtual Planetary Laboratory primarily interested in the formation and evolution of habitable planets.
Rory Barnes is a theorist in the Virtual Planetary Laboratory primarily interested in the formation and evolution of habitable planets.

The new index is more nuanced, producing a continuum of values that astronomers can punch into a Virtual Planetary Laboratory Web form to arrive at the single-number habitability index.

In creating the index, the researchers factored in estimates of a planet’s rockiness, rocky planets being the more Earth-like. They also accounted for a phenomenon called “eccentricity-albedo degeneracy,” which comments on a sort of balancing act between the a planet’s albedo — the energy reflected back to space from its surface — and the circularity of its orbit, which affects how much energy it receives from its host star.

The two counteract each other. The higher a planet’s albedo, the more light and energy are reflected off to space, leaving less at the surface to warm the world and aid possible life. But the more non-circular or eccentric a planet’s orbit, the more intense is the energy it gets when passing close to its star in its elliptic journey.

A life-friendly energy equilibrium for a planet near the inner edge of the habitable zone — in danger of being too hot for life — Barnes said, would be a higher albedo, to cool the world by reflecting some of that heat into space. Conversely, a planet near the cool outer edge of the habitable zone would perhaps need a higher level of orbital eccentricity to provide the energy needed for life.

These are the kinds of measurements being analyzed as well by the NASA’s Kepler Habitable Zone Working Group, a collection of scientists within the Kepler team with the task of identifying some of the most promising targets for future observation.

Stephen Kane is leading the group, and expects to come out with an assessment this summer.

Barnes, Meadows and Evans ranked in this way planets so far found by the Kepler Space Telescope, in its original mission as well as its “K2” follow-up mission. They found that the best candidates for habitability and life are those planets that get about 60 percent to 90 percent of the solar radiation that the Earth receives from the sun, which is in keeping with current thinking about a star’s habitable zone.

The research is part of the ongoing work of the Virtual Planetary Laboratory to study faraway planets in the ongoing search for life, and was funded by the NASA Astrobiology Institute.

“This innovative step allows us to move beyond the two-dimensional habitable zone concept to generate a flexible framework for prioritization that can include multiple observable characteristics and factors that affect planetary habitability,” said Meadows.

“The power of the habitability index will grow as we learn more about exoplanets from both observations and theory.”

 

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Shredding Exoplanets, And The Mysteries They May Unravel

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In this artist’s conception, a tiny rocky object vaporizes as it orbits a white dwarf star. Astronomers have detected the first planetary object transiting a white dwarf using data from the K2 mission. Slowly the object will disintegrate, leaving a dusting of metals on the surface of the star. (NASA)
In this artist’s conception, a small planet or planetesimal vaporizes as it orbits close to a white dwarf star. The detection of several of these disintegrating planets around a variety of stars has led some astronomers to propose intensive study of their ensuing dust clouds as a surprising new way to learn about the interiors of  exoplanet.  (NASA)

One of the seemingly quixotic goals of exoplanet scientists is to understand the chemical and geo-chemical compositions of the interiors of the distant planets they are finding.   Learning whether a planet is largely made up of silicon or magnesium or iron-based compounds is essential to some day determining how and where specific exoplanets were formed in their solar systems, which ones might have the compounds and minerals believed to be necessary for  life, and ultimately which might actually be hosting life.

Studying exoplanet interiors is a daunting challenge for sure, maybe even more difficult in principle than understanding the compositions of exoplanet atmospheres.  After all, there’s still a lot we don’t know about the make-up of planet interiors in our own solar system.

An intriguing pathway, however, has been proposed based on the recent discovery of exoplanets in the process of being shredded.  Generally orbiting very close to their suns, they appear to be disintegrating due to intense radiation and the forces of gravity.

And the result of their coming apart is that their interiors, or at least the dust clouds from their crusts and mantles, may well be on display and potentially measurable.

“We know very little for sure about these disintegrating planets, but they certainly seem to offer a real opportunity,” said Jason Wright, an astrophysicist at Pennsylvania State University with a specialty in stellar astrophysics.  No intensive study of the dusty innards of a distant, falling-apart exoplanet has been done so far,  he said, but in theory at least it seems to be possible.

Artist’s impression of disintegrating exoplanet KIC 12255 (C.U Keller, Leiden University)
Artist’s impression of disintegrating exoplanet KIC 12557548, the first of its kind ever detected. (C.U Keller, Leiden University)

And if successful, the approach could prove broadly useful since astronomers have already found at least four of disintegrating planets and predict that there are many more out there.  The prediction is based on, among other things, the relative speed with which the planets fall apart.  Since the disintegration has been determined to take only tens of thousands to a million years (a very short time in astronomical terms) then scientists conclude that the shreddings must be pretty common  –based on the number already caught in the act.

Saul Rappaport, professor emeritus of physics at MIT, led the team that first identified a disintegrating planet around KIC 12557548, using data from transit light curves collected by the Kepler Space Telescope.  The transits clearly did not indicate the usual small but detectable blockage by a solid body planet,  but were nonetheless intriguing because they were showing that something interesting was crossing (or occulting) the star and trailing an orbiting object.

Rappaport said he was definitely not searching for a dust trail from a disintegrating planet.

“Nobody had suggested that and we weren’t looking for it,” he said. “It took us completely by surprise.  Actually, after we found it, we spent many weeks trying to model it as a collection of solid bodies or something other than a disintegrating planet.  But ultimately we had to face up to what it is – occultation by dust emanating from a planet.”

Four years after his first paper was published, Rappaport said he is now 99 percent certain that KIC 12557548 is a close-in planet slowly disintegrating via the emission of dusty materials, as are three other similar objects subsequently detected.

Rappaport said that speaking generally, measurements of the size of the dust particles coming from those decaying planets would provide very valuable information to scientists, as would any insights into their chemical composition.  But he said that good data will be challenging to collect and equally difficult to interpret.

When an Earth-size planet passes in front of a star, it creates a symmetric dip in the star's light that's shaped like the red curve here. But astronomers detected the strange-looking, blue dip in light from the white dwarf 1145+017. The team suspects the signal comes from a tiny disintegrating planet or asteroid and its comet-like dusty tail. The black dots are measurements recorded by the Kepler spacecraft during its K2 mission. CfA / A. Vanderburg - See more at: http://www.skyandtelescope.com/astronomy-news/white-dwarf-eats-planet2610201523/#sthash.p9521Fxi.dpuf
When an Earth-size planet passes in front of a star, it creates a symmetric dip in the star’s light that’s shaped like the red curve here. But astronomers detected the strange-looking, blue dip in light from the white dwarf 1145+017. The team suspects the signal comes from a tiny disintegrating planet or asteroid and its comet-like dusty tail. (CfA /A. Vanderburg)

Unrelated to Rappaport’s work, Wright and a Penn State team, although with from the Arizona State University astrophysicist Steve Desch and others, have just sent a proposal into NASA to fund  disintegrating exoplanet research using ground-based telescopes and the Hubble Space Telescope.

The collaboration originated at a meeting of the Nexus for Exoplanet Systems Science (NExSS), a five-year NASA initiative to bring together exoplanet scientists from a variety of disciplines with the goal of having them work together across disciplines.  Organized by Mary Voytek, NASA’s senior scientist for astrobiology, it aims to bring the highly interdisciplinary model of astrobiology to the field of characterizing exoplanets.

“This is a project that really calls for, in fact requires, an interdisciplinary approach,” Desch said.  “This is where astronomy and astrophysics meet planetary science and geology, and that should be a very fruitful place.”

Is a measure of the interdisciplinary effort, their team also includes Casey Lisse at the Johns Hopkins University Applied Physics Laboratory.  He’s a comet scientist with a specialty in planet formation and astromineralogy.

Jason Wright, associate professor at Penn State University, initiated the collaboration to use disintegrating planets as a pathway to understanding exoplanet interiors. (Gudmundur Stefansson)
Jason Wright, associate professor at Penn State University, initiated the collaboration to use disintegrating planets as a pathway to understanding exoplanet interiors. (Gudmundur Stefansson)

Wright and Desch want to focus on the unusual transit signals from five stars — three M dwarf identified by Kepler, one a burned-out but super-dense white dwarf and other made famous last fall when a substantial and currently impossible-to-explain dust cloud was detected nearby it.  All the known explanations to explain it were deemed inadequate, which led to (last option) suggestions that perhaps it was an alien “megastructure” or Dyson swarm built by intelligent beings.

Wright was part of the group trying to explain the vast cloud around the star — KIC 8462852 or “Tabby’s star,” named after Yale University post-doc and co-founder Tabetha Boyajian) and now suspects that a disintegrating planet could be a source (though he says that Desch was the first to make the case.)

KIC 8462852, informally known as Tabby’s Star, is a magnitude +11.7 F-type main-sequence star located in the constellation Cygnus approximately 1,480 light-years from Earth. Data from NASA’s Kepler space telescope shows that the star displays aperiodic dimming of 20 percent and more. KIC 8462852 is shown here in infrared (2MASS survey, left) and ultraviolet (GALEX). Image credit: IPAC/NASA (infrared); STScI/NASA (ultraviolet).
KIC 8462852, informally known as Tabby’s Star, is a magnitude +11.7 F-type main-sequence star located in the constellation Cygnus approximately 1,480 light-years from Earth. Data from NASA’s Kepler space telescope shows that the star displays unexplained periodic dimming of 20 percent and more. KIC 8462852 is shown here in infrared (2MASS survey, left) and ultraviolet (GALEX) IPAC/NASA (infrared); STScI/NASA (ultraviolet)

The object that orbits a white dwarf star at a distance about the same as between Earth and the moon.  When its discovery was announced last year by Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, he said that something unique had been found:  “We’re watching a solar system get destroyed.”

The planet (or planetesimal) orbits its white dwarf, WD 1145+017, once every 4.5 hours. This orbital period places it extremely close to the super-dense star, and that speeds the shredding and evaporating of the planet. But makes it a theoretically easier target to observe.  Each time it orbits is a potentially detectable transit to be captured and studied.

White dwarf stars have also served as an earlier destination for those looking for information about potential insides of planets, but via a more indirect approach.  Because of their greatly heightened gravity, white dwarfs have surfaces covered only with light elements of helium and hydrogen. For years, researchers have found evidence that some white dwarf atmospheres are polluted with traces of heavier elements such as calcium, silicon, magnesium and iron. Scientists have long suspected that the source of this pollution has been asteroids or, what was then theoretical, a small planet being torn apart.

Steven Desch, an astrophysicist at ASU, sees a frequent gap between the work of astronomers and planetary scientists, and hopes to help bridge it.
Steve Desch, a theoretical astrophysicist at ASU, sees a frequent gap between in the exoplanet work of astronomers and of planetary scientists, and hopes to help bridge it. (ASU News)

Another prime target for disintegrating-planet research is the first one identified,  KIC 12557548 b.  Because it is so small — no bigger than Mercury — it’s an object that would never be detected by telescopes looking for transits across a star.  It is, after all, 1500 light years away.  But the dust cloud is much bigger and blocks as much as 1 percent of the light from the star every time it orbits.  To compare, our Jupiter would block about the same amount of the sun’s light in a similar scenario seen from afar.

The team leaders said that while their goal is to collect data that will help them understand the grain size and chemical composition of the dusty planetary remains, they also aim to refine the observing and spectrographic techniques for future observations — most especially on the James Webb Space Telescope.

The JWST, which launches in 2018, will have the capacity to collect information about the disintegrating planets that current instruments cannot.  But time on the telescope will be very costly and competitive, so Wright said the team will be doing the groundwork needed to make disintegrating planets an appealing subject for research.

“A lot of the observational technique has to be invented,” said Wright.  “JWST will be prime time for new science, but before that we need a lot of ground-based pre-study to make the case.”

The proposal also calls for extensive modeling of the dynamics of how dust grains would be released under the pressure of intense gravity and radiation pressure.

Coincidentally, a paper that models exoplanetary interiors authored by Li Zeng of the Harvard-Smithsonian Center for Astrophysics (CfA) and others, has been accepted for publication by The Astrophysical Journal.

Making sure it first could reproduce the Preliminary Reference Earth Model (PREM) — the standard model for Earth’s interior — Zeng and his team modified their planetary interior code to predict the structure of exoplanets with different masses and compositions, and applied it to six known rocky exoplanets with well-measured masses and radii.

They found that the other planets, despite their different masses and presumably different chemical makeup, nevertheless all appear to have a iron/nickel cores containing about 30% of the planet’s mass, very similar to the 32% of the Earth’s mass found in the Earth’s core. The remainder of each planet would be mantle and crust, just as with Earth.

The model, however, does not add new information about the observed make-up of exoplanet interiors.  That’s where the disintegration of close-in exoplanets just might come in.

In this Chandra image of ngc6388, researchers have found evidence that a white dwarf star may have ripped apart a planet as it came too close. When a star reaches its white dwarf stage, nearly all of the material from the star is packed inside a radius one hundredth that of the original star. Using several telescopes, including NASA’s Chandra X-ray Observatory, researchers have found evidence that a white dwarf star – the dense core of a star like the Sun that has run out of nuclear fuel – may have ripped apart a planet as it came too close. ( NASA)
In this Chandra image of globular cluster NGC 6388, researchers have found evidence that another white dwarf star may have ripped apart a planet as it came too close. When a star runs out of nuclear fuel and reaches its white dwarf stage, nearly all of its material from the star is packed inside a radius one hundredth that of the original star. The images was made with from images taken by several telescopes, including NASA’s Chandra X-ray Observatory. (NASA)
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How Will We Know What Exoplanets Look Like, and When?

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An earlier version of this article was accidently published last week before it was completed.  This is the finished version, with information from this week’s AAS annual conference.

This image of a pair of interacting galaxies called Arp 273 was released to celebrate the 21st anniversary of the launch of the NASA/ESA Hubble Space Telescope. The distorted shape of the larger of the two galaxies shows signs of tidal interactions with the smaller of the two. It is thought that the smaller galaxy has actually passed through the larger one.
This image of a pair of interacting galaxies called Arp 273 was released to celebrate the 21st anniversary of the launch of the NASA/ESA Hubble Space Telescope. The distorted shape of the larger of the two galaxies shows signs of tidal interactions with the smaller of the two. It is thought that the smaller galaxy has actually passed through the larger one.

Let’s face it:  the field of exoplanets has a significant deficit when it comes to producing drop-dead beautiful pictures.

We all know why.  Exoplanets are just too small to directly image, other than as a miniscule fraction of a pixel, or perhaps some day as a full pixel.  That leaves it up to artists, modelers and the travel poster-makers of the Jet Propulsion Lab to help the public to visualize what exoplanets might be like.  Given the dramatic successes of the Hubble Space Telescope in imaging distant galaxies, and of telescopes like those on the Cassini mission to Saturn and the Mars Reconnaissance Orbiter, this is no small competitive disadvantage.  And this explains why the first picture of this column has nothing to do with exoplanets (though billions of them are no doubt hidden in the image somewhere.)

The problem is all too apparent in these two images of Pluto — one taken by the Hubble and the other by New Horizons telescope as the satellite zipped by.

image

Pluto image taken by Hubble Space Telescope (above) and close up taken by New Horizons in 2015. (NASA)
Pluto image taken by Hubble Space Telescope (above) and close up taken by New Horizons in 2015. (NASA)

Pluto is about 4.7 billion miles away.  The nearest star, and as a result the nearest possible planet, is 25 trillion miles  away.  Putting aside for a minute the very difficult problem of blocking out the overwhelming luminosity of a star being cross by the orbiting planet you want to image,  you still have an enormous challenge in terms of resolving an image from that far away.

While current detection methods have been successful in confirming more than 2,000 exoplanets in the past 20 years (with another 2,000-plus candidates awaiting confirmation or rejection),  they have been extremely limited in terms of actually producing images of those planetary fireflies in very distant headlights.  And absent direct images — or more precisely, light from those planets — the amount of information gleaned about the chemical makeup of their atmospheres  as been limited, too.

But despite the enormous difficulties, astronomers and astrophysicist are making some progress in their quest to do what was considered impossible not that long ago, and directly image exoplanets.

In fact, that direct imaging — capturing light coming directly from the sources — is pretty uniformly embraced as the essential key to understanding the compositions and dynamics of exoplanets.  That direct light may not produce a picture of even a very fuzzy exoplanet for a very long time to come, but it will definitely provide spectra that scientists can read to learn what molecules are present in the atmospheres, what might be on the surfaces and as a result if there might be signs of life.

This diagram illustrates how astronomers using NASA's Spitzer Space Telescope can capture the elusive spectra of hot-Jupiter planets. Spectra are an object's light spread apart into its basic components, or wavelengths. By dissecting light in this way, scientists can sort through it and uncover clues about the composition of the object giving off the light. To obtain a spectrum for an object, one first needs to capture its light. Hot-Jupiter planets are so close to their stars that even the most powerful telescopes can't distinguish their light from the light of their much brighter stars. But, there are a few planetary systems that allow astronomers to measure the light from just the planet by using a clever technique. Such "transiting" systems are oriented in such a way that, from our vantage point, the planets' orbits are seen edge-on and cross directly in front of and behind their stars. In this technique, known as the secondary eclipse method, changes in the total infrared light from a star system are measured as its planet transits behind the star, vanishing from our Earthly point of view. The dip in observed light can then be attributed to the planet alone. To capture a spectrum of the planet, Spitzer must observe the system twice. It takes a spectrum of the star together with the planet (first panel), then, as the planet disappears from view, a spectrum of just the star (second panel). By subtracting the star's spectrum from the combined spectrum of the star plus the planet, it is able to get the spectrum for just the planet (third panel). This ground-breaking technique was used by Spitzer to obtain the first-ever spectra of two planets beyond our solar system, HD 209458b and HD 189733b. The results suggest that the hot planets are socked in with dry clouds high up in the planet's stratospheres. In addition, HD 209458b showed hints of silicates, indicating those high clouds might be made of very fine sand-like particles.
This diagram illustrates how astronomers using NASA’s Spitzer Space Telescope can capture the elusive spectra of hot-Jupiter planets. Spectra are an object’s light spread apart into its basic components, or wavelengths. By dissecting light in this way, scientists can sort through it and uncover clues about the composition of the object giving off the light. (NASA/JPL-Caltech)

There has been lots of technical and scientific debate about how to capture that light, as well as debate about how to convince Congress and NASA to fund the search.  What’s more, the exoplanet community has a history of fractious internal debate and competition that has at times undermined its goals and efforts, and that has been another hotly discussed subject.  (The image of a circular firing squad used to be a pretty common one for the community.)

But a seemingly much more orderly strategy has been developed in recently years and was on display at the just-completed American Astronomical Society annual meeting in Florida.  The most significant breaking news was probably that NASA has gotten additional funds to support a major exoplanet direct imaging mission in the 2020s, the Wide Field Infrared Survey Telescope (WFIRST), and that the agency is moving ahead with a competition between four even bigger exoplanet or astrophysical missions for the 2030s. The director of NASA Astrophysics, Paul Hertz, made the formal announcements during the conference, when he called for the formation of four Science and Technology Definition Teams to assess in great detail the potentials and plausibilities of the four possibilities.

Paul Hertz, Director of the Astrophysics Division of NASA's Science Mission Directorate.
Paul Hertz, Director of the Astrophysics Division of NASA’s Science Mission Directorate.

Putting it into a broader perspective, astronomer Natalie Batalha, science lead for the Kepler Space Telescope, told a conference session on next-generation direct imaging that  “with modern technology, we don’t have the capability to image a solar system analog.”  But, she said, “that’s where we want to go.”

And the road to discovering exoplanets that might actually sustain life may well require a space-based telescope in the range of eight to twelve meters in radius, she and others are convinced.  Considering that a very big challenge faced by the engineers of the James Webb Space Telescope (scheduled to launch in 2018) was how to send a 6.5 meter-wide mirror into space, the challenges (and the costs) for a substantially larger space telescope will be enormous.

We will come back in following post to some of these plans for exoplanet missions in the decades ahead, but first let’s look at a sample of the related work done in recent years and what might become possible before the 2020s.  And since direct imaging is all about “seeing” a planet — rather than inferring its existence through dips in starlight when an exoplanet transits, or the wobble of a sun caused by the presence of  an orbiting ball of rock (or gas)  — showing some of the images produced so far seems appropriate.  They may not be breath-taking aesthetically, but they are remarkable.

There is some debate and controversy over which planets were the first to be directly imaged. But all agree that a major breakthrough came in 2008 with the imaging of the HR8799 system via ground-based observations.

NASA/JPL-Caltech/Palomar Observatory - http://www.nasa.gov/topics/universe/features/exoplanet20100414-a.html This image shows the light from three planets orbiting a star 120 light-years away. The planets' star, called HR8799, is located at the spot marked with an "X." This picture was taken using a small, 1.5-meter (4.9-foot) portion of the Palomar Observatory's Hale Telescope, north of San Diego, Calif. This is the first time a picture of planets beyond our solar system has been captured using a telescope with a modest-sized mirror -- previous images were taken using larger telescopes. The three planets, called HR8799b, c and d, are thought to be gas giants like Jupiter, but more massive. They orbit their host star at roughly 24, 38 and 68 times the distance between our Earth and sun, respectively (Jupiter resides at about 5 times the Earth-sun distance).
This 2010 image shows the light from three planets orbiting HR8799, 120 light-years away.  The three planets, called HR8799b, c and d, are thought to be gas giants like Jupiter, but more massive. (NASA/JPL-Caltech/Palomar Observatory)

First, three Jupiter-plus gas giants were identified using the powerful Keck and Gemini North infrared telescopes on Mauna Kea in Hawaii by a team led by Christian Marois of the National Research Council of Canada’s Herzberg Institute of Astrophysics. That detection was followed several years later the discovery of a fourth planet and then by the release of the surprising image above, produced with the quite small (4.9 foot) Hale telescope at the Palomar Observatory outside of San Diego.

As is the case for all planets directly imaged, the “pictures” were not taken as we would with our own cameras, but rather represent images produced with information that is crunched in a variety of necessary technical ways before their release.  Nonetheless, they are images in a way similar the iconic Hubble images that also need a number of translating steps to come alive.

Because light from the host star has to be blocked out for direct imaging to work, the technique now identifies only planets with very long orbits. In the case of HR8799, the planets orbit respectively at roughly 24, 38 and 68 times the distance between our Earth and sun.  Jupiter orbits at about 5 times the Earth-sun distance.

In the same month as the HR8799 announcement, another milestone was made public with the detection of a planet orbiting the star Formalhaut.  That, too, was done via direct imagining, this time with the Hubble Space Telescope.

The Hubble images were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. This false-color composite image, taken with the Hubble Space Telescope, reveals the orbital motion of the planet Fomalhaut b. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit. The planet will appear to cross a vast belt of debris around the star roughly 20 years from now. If the planet's orbit lies in the same plane with the belt, icy and rocky debris in the belt could crash into the planet's atmosphere and produce various phenomena. The black circle at the center of the image blocks out the light from the bright star, allowing reflected light from the belt and planet to be photographed. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute)
The Hubble images the the star Formalhaut and planet Formalhaut b were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. This false-color composite image reveals the orbital motion of the Fomalhaut b. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit. The black circle at the center of the image blocks out light from the very bright star, allowed reflected light from the belt and planet to be captured.  Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute)

Signs of the planet were first detected in 2004 and 2006 by a group headed by Paul Kalas at the University of California, Berkeley, and they made the announcement in 2008.  The discovery was confirmed several years later and tantalizing planetary dynamics began to emerge from the images (all in false color.) For instance, the planet appears to be on a path to cross a vast belt of debris around the star roughly 20 years from now.  If the planet’s orbit lies in the same plane with the belt, icy and rocky debris could crash into the planet’s atmosphere and cause interesting damage.

The region around Fomalhaut’s location is black because astronomers used a coronagraph to block out the star’s bright glare so that the dim planet could be seen. This is essential since Fomalhaut b is 1 billion times fainter than its star. The radial streaks are scattered starlight. Like all the planets detected so far using some form of direct imaging,  Fomalhaut b if far from its host star and completes an orbit every 872 years.

Adaptive optics of the Gemini Planet Imager, at the Gemini South Observatory in Chile, has been successful in imaging exoplanets as well.  The GPI grew out of a proposal by the Center for Adaptive Optics, now run by the University of California system, to inspire and see developed innovative optical technology.  Some of the same breakthroughs now used in treating human eyes found their place in exoplanet astronomy.

 

Discovery image of 51 Eri b with the Gemini Planet Imager taken in the near-infrared light on December 18, 2014. The bright central star has been mostly removed by a hardware and software mask to enable the detection of the exoplanet one million times fainter. Credits: J. Rameau (UdeM) and C. Marois (NRC Herzberg).
Discovery image of 51 Eri b with the Gemini Planet Imager taken in the near-infrared light on December 18, 2014. The bright central star has been mostly removed by a hardware and software mask to enable the detection of the exoplanet one million times fainter. Credits: J. Rameau (UdeM) and C. Marois (NRC Herzberg).

The Imager, which began operation in 2014, was specifically created to discern and evaluate dim, newer planets orbiting bright stars using a different kind of direct imaging. It is adept at detecting young planets, for instance, because they still retain heat from their formation, remain luminous and visible. Using the GPI to study the area around the y0ung (20-million-year-old) star 51 Eridiani, the team made their first exoplanet discovery in 2014.

By studying its thermal emissions, the team gained insights into the planet’s atmospheric composition and found that — much like Jupiter’s — it is dominated by methane.  To date, methane signatures have been weak or absent in directly imaged exoplanets.

James Graham, an astronomer at the University of California, Berkeley, is the project leader for a three-year GPI survey of 600 stars to find young gas giant planets, Jupiter-size and above.

“The key motivation for the experiment is that if you can detect heat from the planet, if you can directly image it, then by using basic science you can learn about formation processes for these planets.”  So by imaging the planets using these very sophisticated optical advances, scientists go well beyond detecting exoplanets to potentially unraveling deep mysteries (even if we still won’t know what the planets “look like” from an image-of-the-day perspective.

The GPI has also detected a second exoplanet, shown here at different stages of its orbit:

 

The animation is a series of images taken between November 2013 and April 2015 with the Gemini Planet Imager (GPI) on the Gemini South telescope in Chile, and shows the exoplanet β Pictoris b, which is more than 60 lightyears from Earth. The star is the black area on the left edge of the frame and is hidden by the Gemini Planet Imager’s coronagraph. We are looking at the planet’s orbit almost edge-on, with the planet closer to the Earth than the star. (M. Millar-Blanchaer, University of Toronto; F. Marchis, SETI Institute)
The animation is a series of images taken between November 2013 and April 2015 with the Gemini Planet Imager (GPI) on the Gemini South telescope in Chile, and shows the exoplanet β Pictoris b, which is more than 60 lightyears from Earth. The star is the black area on the left edge of the frame and is hidden by the Gemini Planet Imager’s coronagraph. (M. Millar-Blanchaer, University of Toronto; F. Marchis, SETI Institute)

A next big step in direct imaging of exoplanets will come with the launch of the James Webb Space Telescope in 2018.  While not initially designed to study exoplanets — in fact, exoplanets were just first getting discovered when the telescope was under early development — it does now include a coronagraph which will substantially increase its usefulness in imaging exoplanets.

As explained by Joel Green, a project scientist for the Webb at the Space Telescope Science Institute in Baltimore, the new observatory will be able to capture light — in the form of infrared radiation– that will be coming from more distant and much colder environments than what Hubble can probe.

“It’s sensitive to dimmer things, smaller planets that are more earth-sized.  And because it can see fainter objects, it will be more help in understanding the demographics of exoplanets.  It uses the infrared region of the spectrum, and so it can look better into the cloud levels of the planets than any telescope so far and see deeper.”

James Webb Space Telescope mirror being inspected at Goddard Space Flight Center, as it nears completion.  The powerful, sophisticated and long-awaited telescope is scheduled to launch in 2018.
James Webb Space Telescope mirror being inspected at Goddard Space Flight Center, as it nears completion. The powerful, sophisticated and long-awaited telescope is scheduled to launch in 2018.

These capabilities and more are going to be a boon to exoplanet researchers and will no doubt advance the direct imaging effort and potentially change basic understandings about exoplanets.  But it is not expected produce gorgeous or bizarre exoplanet pictures for the public, as Hubble did for galaxies and nebulae.  Indeed, unlike the Hubble — which sees primarily in visible light —  Webb sees in what Green said is, in effect, night vision.   And so researchers are still working on how they will produce credible images using the information from Webb’s infrared cameras and translating them via a color scheme into pictures for scientists and the public.

Another compelling exoplanet-imaging technology under study by NASA is the starshade, or external occulter, a metal disk in the shape of a sunflower that might some day be used to block out light from host stars in order to get a look at faraway orbiting planets.  MIT’s Sara Seager led a NASA study team that reported back on the starshade last year in a report that concluded it was technologically possible to build and launch, and would be scientifically most useful.  If approved, the starshade — potentially 100 feet across — could be used with the WFIRST telescope in the 2020s.  The two components would fly far separately, as much as 35,000 miles away from each other, and together could produce breakthrough exoplanet direct images.

An artist's depiction of a sunflower-shaped starshade that could help space telescopes find and characterize alien planets. Credit: NASA/JPL/Caltec
An artist’s depiction of a sunflower-shaped starshade that could help space telescopes find and characterize alien planets.  Credit: NASA/JPL/Caltech

Here is a link to an animation of the starshade being deployed: http://planetquest.jpl.nasa.gov/video/15

The answer, then, to the question posed in the title to this post — “How Will We Know What Exoplanets Look Like, and When?”– is complex, evolving and involves a science-based definition of what “looking like” means.  It would be wonderful to have images of exoplanets that show cloud formations, dust and maybe some surface features, but “direct imaging” is really about something different.  It’s about getting light from exoplanets that can tell scientists about the make-up of those exoplanets and their atmospheres, and ultimately that’s a lot more significant than any stunning or eerie picture.

And with that difference between beauty and science in mind, this last image is one of the more striking ones I’ve seen in some time.

Moon glow over Las Campanas Observatory, run by the Carnegie Institution of Science, in Chile. (Yuri Beretsky)
Moon glow over Las Campanas Observatory, operated by the Carnegie Institution of Science, in Chile. (Yuri Beretsky)

It was taken at the Las Campanas Observatory in Chile last year, during a night of stargazing.  Although the observatory is in the Atacama Desert, enough moisture was present in the atmosphere to create this lovely moon-glow.

But working in the observatory that night was Carnegie’s pioneer planet hunter Paul Butler, who uses the radial velocity method to detect exoplanets.  But to do that he needs to capture light from those distant systems.  So the night — despite the beautiful moon-glow — was scientifically useless.

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Faint Worlds On the Far Horizon

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Faintest distant galaxy ever detected, formed only 400 million years after the Big Bang. NASA, ESA, and L. Infante (Pontificia Universidad Catolica de Chile)
Faintest distant galaxy ever detected, formed only 400 million years after the Big Bang. NASA, ESA, and L. Infante (Pontificia Universidad Catolica de Chile)

For thinking about the enormity of the canvas of potential suns and exoplanets, I find images like this and what they tell us to be an awkward combination of fascinating and daunting.

This is an image that, using the combined capabilities of NASA’s Hubble and Spitzer space telescopes, shows what is being described as the faintest object, and one of very oldest, ever seen in the early universe.  It is a small, low mass, low luminosity and low size protogalaxy as it existed some 13.4 billion years ago, about 4oo million years after the big bang.

The team has nicknamed the object Tayna, which means “first-born” in Aymara, a language spoken in the Andes and Altiplano regions of South America.

Though Hubble and Spitzer have detected other galaxies that appear to be slightly further away, and thus older, Tayna represents a smaller, fainter class of newly forming galaxies that until now have largely evaded detection. These very dim bodies may offer new insight into the formation and evolution of the first galaxies — the “lighting of the universe” that occurred after several hundred million years of darkness following the big bang and its subsequent explosion of energy.

This is an illustration by Adolf Schaller from the Hubble Gallery (NASA). It is public domain. It shows colliding protogalaxies less than 1 billion years afer the big bang.
This is an illustration by Adolf Schaller from the Hubble Gallery and shows
colliding protogalaxies less than 1 billion years after the big bang. (NASA)

Detecting and trying to understand these earliest galaxies is somewhat like the drive of paleo-anthropologists to find older and older fossil examples of early man. Each older specimen provides insight into the evolutionary process that created us, just as each discovery of an older, or less developed, early galaxy helps tease out some of the hows and whys of the formation of the universe.

Leopoldo Infante, an astronomer at Pontifical Catholic University of Chile, is the lead author of last week’s Astrophysical Journal article on the faintest early galaxy.  He said there is good reason to conclude there were many more of these earliest protogalaxies than the larger ones at the time, and that they were key in the “reionization” of the universe — the process through which the universe’s early “dark ages” were gradually ended by the formation of more and more luminous stars and galaxies..

But the process of detecting these very early protogalaxies is only beginning, he said, and will pick up real speed only when the NASA’s James Webb Space Telescope (scheduled to be launched in 2018) is up and operating.  The Webb will be able to see considerably further back in time than the Hubble or Spitzer.

Estimates of how many galaxies might exist in the universe are in flux, with recent studies producing results ranging from 100 to 225 billion.  On average a galaxy will have some 100 billion stars, giving the universe a low-end estimate of 10,000,000,000,000,000,000,000 stars.

When it comes to planets, a consensus of sorts has formed around the conclusion that in the Milky Way, and perhaps elsewhere, there is on average at least one planet per star.  So assuming that the planetary dynamics of our galaxy are similar to those of others, that’s an awful lot of potential exoplanets.

PSR B1620-26 b is an extrasolar planet located approximately 12,400 light-years away from Earth in the constellation of Scorpius. It bears the unofficial nicknames "Methuselah" and "the Genesis planet" due to its extreme age
PSR B1620-26 b is an extrasolar planet located approximately 12,400 light-years away from Earth in the constellation of Scorpius. It bears the unofficial nicknames “Methuselah” and “the Genesis planet” due to its extreme age. (NASA and G. Bacon, STScI)

All this has significant implications for the field of exoplanet research.

“We know that basically, planets form at about the same time as their stars from all the leftover dust and gas kicked up,” said Joel Green, Project Scientist at Space Telescope Science Institute’s Office of Public Outreach (STScI.)  The Institute operates the science for the Hubble Space Telescope as an international observatory.

“The earliest planets may have been very different kinds of planets because there was not as much metallicity (heavier elements) in those stars.  But as soon as you have stars, you have planets.”

He said that in theory, that means that when the very earliest stars formed — during a time when the universe was essentially dark — planets were formed too. “They don’t need a universe of light to form; they need one star.”

The most ancient exoplanet detected so far (PSR B1620-26 b) has had a rather unusual history, first born 12.7 billion years ago outside of a “globular cluster”  of stars (a comparatively older, compact group of up to a million old stars, held together by mutual gravitation), it then migrated closer to the cluster and into a rough astrophysical neighborhood. As viewed today, it orbits a pair of burned-out stars in the crowded core of a globular star cluster. It was first identified as a possible planet in 1992 — before the detection of 51 Pegasi b — but it took more than a decade to confirm that it is.

The oldest known exoplanet solar system is Kepler -444, formed 11.2 billion years ago in the Milky Way, itself 13.2 billion years old. Located in the constellation Lyra  116 light-years away, it hosts five rocky planets, all orbiting close to their sun.

Kepler-444 hosts five Earth-sized planets in very compact orbits. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist's conception. Credit: Tiago Campante/Peter DevineKepler-444 is a metal-poor Sun-like star located in the constellation Lyra, 116.4 light-years away. Also known as HIP 94931, KIC 6278762, KOI-3158, and LHS 3450, this pale yellow-orange star is very bright and can be easily seen with binoculars. It was formed 11.2 billion years ago, when the Universe was less than 20 percent its current age. It is approximately 25 percent smaller than the Sun and substantially cooler.
Kepler-444 hosts five Earth-sized planets in very compact orbits. A metal poor sun (composed largely of hydrogen and helium), it is very bright and easily seen with binoculars. (Tiago Campante/Peter Devine)

The discovery of a solar system with rocky planets of this age (more than twice the age of our solar system’s rocky planet quartet), opens the door to the prospect of an early universe with many more rocky planets than once thought.  That means there could be vast numbers of very ancient Earth-like planets out there.

Returning to the faintest protogalaxy, it is described as being comparable in size to the Large Magellanic Cloud (LMC), a very small satellite galaxy of our Milky Way seen in the southern hemisphere. Tayna is rapidly making stars at a rate ten times faster than the LMC, and is likely the growing core of what will evolve into a full-sized galaxy.

This faintest ancient galactic find is part of a discovery of 22 young galaxies at ancient times located nearly at the observable horizon of the universe, research that substantially increases in the number of known very distant galaxies.

“The big unanswered question is how and when did the stars and galaxies turn on to end those Dark Ages,” said Green.  “There was a point when they started popping like popcorn.  With Hubble we can go back only so far and can’t see anymore, but the James Webb can go significantly further and see back to the Dark Ages.”

Massive cosmic objects, from single stars to galaxy clusters, bend and focus the light that flows around them with their gravity, acting like giant magnifying glasses. This effect is called gravitational lensing or, when it is detected on tiny patches on the sky, microlensing. Credit: ESA/ATG medialab Read more at: http://phys.org/news/2015-07-astronomers-cosmic-gravity-black-hole-scope.html#jCp
Massive cosmic objects, from single stars to galaxy clusters, bend and focus the light that flows around them with their gravity, acting like giant magnifying glasses. This effect is called gravitational lensing or, when detected on distant plants and faint galaxies, microlensing. (ESA/ATG medialab)

Ironically, Infante and his team were able to find the faintest distant galaxy so far without having it be the hardest to see.  That’s because they were able to use a technique of observing first proposed by Albert Einstein.  As described on the HubbleSite:

The small and faint galaxy was only seen thanks to a natural “magnifying glass” in space. As part of its Frontier Fields program, Hubble observed a massive cluster of galaxies, MACS J0416.1-2403, located roughly 4 billion light-years away and weighing as much as a million billion suns. This giant cluster acts as a powerful natural lens by bending and magnifying the light of far-more-distant objects behind it. Like a zoom lens on a camera, the cluster’s gravity boosts the light of the distant protogalaxy to make it look 20 times brighter than normal. The phenomenon is called gravitational lensing and was proposed by Einstein as part of his General Theory of Relativity.

While gravitational lensing uses a galaxy cluster as its magnifying glass, “microlensing” takes advantage of the same physics but uses a single star in our galaxy as the lens.  That technique is the only known method capable of discovering planets at truly great distances from the Earth. Radial velocity searches look for planets in our immediate galactic neighborhood, up to 100 light years from Earth, transit photometry can potentially detect planets at a distance of hundreds of light-years, but only microlensing can find planets orbiting stars near the center of the galaxy, thousands of light-years away.

And in the spirit of the wonder that microlensing tends to engender, let me leave you with another of those defining astronomical images that are impossible to ignore or forget.

This is the third version of the Hubble Ultra Deep Field, first assembled from 2003-2004 images, upgraded to the Hubble eXtreme Deep Field (XDF) image in 2012 and then enhanced further in 2014 and returned to the original Hubble Ultra Deep Field name.  Both the XDF and the 2014 version capture a patch of sky at the center of the original Hubble Ultra Deep Field.  That initial effort, which looked back in time approximately 13 billion years, picked up many unintentionally microlensed galaxies.

The newer images feature about 5,500 galaxies even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness of what the human eye can see; just imagine that ratio for a single star or a planet.

So while there undoubtedly are an untold numbers of planets in the field, they will remain hidden for a very long time to come.

Hubble Ultra Deep from 2014. using full range of ultraviolet to near infrared, includes some of the most distant galaxies imaged by an optical telescope.
Hubble Ultra Deep Field from 2014. using full range of ultraviolet to near infrared, includes some of the most distant galaxies imaged by an optical telescope.  It is the third iteration of the Hubble Ultra Deep Field image, and combines more than 10 years of Hubble photographs taken of a patch of sky at the center of the original creation. (NASA)
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