Storming the One-Meter-Per-Second Barrier

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Kitt Peak National Observatory mountain top at Dusk looking north. Visible in the picture are the NOAO 4-meter Mayall, the Steward Observatory 90-inch, the University of Arizona Lunar and Planetary Laboratory Spacewatch Telescopes, LOTIS, 0.4-meter Visitor Center Telescope, Case Western Reserve University Observatory and the SARA Observatory. Credit: P. Marenfeld (NOAO/AURA/NSF)
The Kitt Peak National Observatory, on the Tohono O’odham reservation outside Tucson, will be home to a next-generation spectrometer and related system which will allow astronomers to detect much smaller exoplanets through the radial velocity method.  P. Marenfeld (NOAO/AURA/NSF)

When the first exoplanet was identified via the radial velocity method, the Swiss team was able to detect a wobble in the star 51 Pegasi at a rate of 50 meters per second.   The wobble is the star’s movement back and forth caused by the gravitational pull of the planet, and in that first case it was dramatic — the effects of a giant Jupiter-sized planet orbiting extremely close to the star.

Many of the early exoplanet discoveries were of similarly large planets close to their host stars, but it wasn’t because there are so many of them in the cosmos.  Rather, it was a function of the capabilities of the spectrographs and other instruments used to view the star.  They were pioneering breakthroughs, but they didn’t have the precision needed to measure wobbles other than the large, dramatic ones caused by a close-in, huge planet.

That was the mid 1990s, and radial velocity astronomers have worked tirelessly since to “beat down” that 50 meters per second number.  And twenty years later, RV astronomers using far more precise instruments and more refined techniques have succeeded substantially:  1 meter per second of wobble is now achieved for the quietest stars.  That has vastly improved their ability to find smaller exoplanets further from their stars and is a major achievement.  But it has nonetheless been a major frustration for astronomers because to detect terrestrial exoplanets in the Earth-sized range, they have to get much more precise  — in the range of tens of centimeters per second.

A number of efforts to build systems that can get that low are underway, most notably the ESPRESSO spectrograph scheduled to begin work on the High Accuracy Radial Vlocity Planet Searcher (HARPS) in Chile next year. Then earlier this month an ambitious NASA-National Science Foundation project was awarded to Penn State University to join the race.  The next-generation spectrograph is scheduled to be finished in 2019 and installed at the Kitt Peak National Observatory in Arizona, and its stated goal is to reach the 20 to 30 centimeters per second range.

Suvrath Mahadevan, an assistant professor at Penn State, is principal investigator for the project.  It is called NEID, which means ‘to see’ in the language of the Tohono O’odham, on whose land the Kitt Peak observatory is located.

“For many reasons, the (radial velocity) community has been desperate for an instrument that would allow for detections of smaller planets, and ones in habitable zones,” he said.  “We’re confident that the instrument we’re building will — in time — provide that capability.”

Las Cumbres Observatory Global Telescope Network.
A illustration of how the radial velocity method of planet hunting works.  The wobble of the stars is far away miniscule in galactic terms, making extreme precision essential in measuring the movement. (Las Cumbres Observatory Global Telescope Network)

Project scientist Jason Wright, associate professor of astronomy and astrophysics at Penn State, put it this way:  “NEID will be more stable than any existing spectrograph, allowing astronomers around the world to make the precise measurements of the motions of nearby, Sun-like stars.”  He said his Penn State team will use the instrument “to discover and measure the orbits of rocky planets at the right distances from their stars to host liquid water on their surfaces.”

NASA and the NSF wanted the new spectrograph built on an aggressive timetable to meet major coming opportunities and needs, Mahadevan said.

The speedy three-year finish date is a function of the role that radial velocity detection plays in exoplanet research.  While many planets have been, and will be, first detected through the technique, it is also essential in the confirming of candidate planets identified by NASA space telescopes such as Kepler, the soon-to-be launched TESS (the Transiting Exoplanet Survey Satellite) and others into the future.  There is a huge backlog of planets to be confirmed, and many more expected in the relatively near future.

What’s more, as Mahadevan explained, an instrument like NEID could significantly help NASA’s planning for a possible 2030s Flagship space telescope mission focused on exoplanets.  Two of the four NASA contenders under study are in that category — LUVOIR (Large Ultraviolet Visible Infrared) Surveyor and Hab-Ex — and their capabilities, technologies, timetables and cost are all now under consideration.

If NEID can identify some clearly Earth-sized planets in habitable zones, he said, then the planning for LUVOIR or Hab-Ex could be more focused (and the proposal potentially less costly.)  This is because the observatory could be designed to look at a limited number of exoplanets and their host stars, rather than scanning the skies for a clearly Earth-like planet.

“Right now we have no definite Earth-sized planets in a habitable zone, so a LUVOIR or Hab_ex design would have to include a blind search.  But if we know of maybe 15 planets we’re pretty sure are in their habitable zones, the targets get more limited and the project becomes a lot cheaper.”

Suvrath Mahadevan, assistant professor of Astronomy and Astrophysics at Penn State, and principal investigator for a new-generation high precision spectrometer. (Penn State)
Suvrath Mahadevan, assistant professor of Astronomy and Astrophysics at Penn State, and principal investigator for a new-generation high precision spectrometer. (Penn State)

These possibilities, however, are for the future.  Now, Mahadevan said, the Penn State team has to build a re-considered spectrograph, a significant advance on what has come before.  With its track record of approaching their work through interdisciplinary collaboration, the Penn State team will be joined by collaborators from NASA Goddard Space Flight Center, University of Colorado, National Institute of Standards and Technology, Macquarie University in Australia, Australian Astronomical Observatory, and Physical Research Laboratory in India.  Much of the work will be done over the next three years at Penn State, but some at the partner institutions as well.

Key to their assembly approach is that the instrument will be put together in vacuum-sealed environment and will have no vibrating or moving parts.  This design stability will prevent, or minimize, instrument-based misreadings of the very distant starlight being analyzed.

A major issue confronting radial velocity astronomers is that light from stars can fluctuate for many reasons other than a nearby planet — from sunspots, storms, and other magnetic phenomena.  The NEID instrument will try to minimize these stellar disruptors by providing the broadest wavelength coverage so far in an exoplanet spectrograph, Mahadevan said, collecting light from well into the blue range of the spectrum to almost the end of the red.

“We’re not really building a spectorograph but a radial velocity system, he said.  That includes upgrades to the telescope port, the data pipeline and more.

This is how Lori Allen, Associate Director for Kitt Peak, described that new “system”: “The extreme precision (of NEID) results from numerous design factors including the extreme stability of the spectrometer environment, image stabilization at the telescope, innovative fiber optic design, as well as state-of-the-art calibration and data reduction techniques”.

 

The new generation spectrograph will be installed on the 3.5 meter WYN telescope at Kitt Peak. Operated by National Optical Astronomy Observatory, the $10 million project is a collaboration of NASA and the National Science Foundation.
The new generation spectrograph will be installed on the 3.5 meter WYN telescope at Kitt Peak. The site is managed by the National Optical Astronomy Observatory, and $10 million spectrograph project is a collaboration of NASA and the National Science Foundation.

Sixteen teams ultimately competed to build the spectrograph, and the final two contenders were Penn State and MIT.  Mahadevan said that, in addition to its spectrograph design, he believed several factors helped the Penn State proposal prevail.

His team has worked for several years on another advanced spectrograph for the Hobby-Eberly Telescope in Texas, one that required complex vacuum-sealed and very cold temperature construction.  Although the challenges slowed the design, the team ultimately succeeded in demonstrating the environmental stability in the lab.  So Penn State had a track record. What’s more, the school and its Center for Exoplanets and Habitable Worlds have a history of working in an interdisciplinary manner, and have been part of several NASA Astrobiology Institute projects. (The instrument has a blog of its own: NEID.)

The Kitt Peak observatory, which saw first light in 1994, has been the sight of many discoveries, but in recent years has faced cutbacks in NSF funding.  There was some discussion of reducing its use, and the NASA-NSF decision t0 upgrade the spectrograph was in part an effort to make it highly relevant again.  And given the scientific need to confirm so many planets — a need that will grow substantially after TESS launches in 2017 or 2018 and begins sending back information on thousands of additional transiting exoplanets — enhancing the capabilities of the Kitt Peak 3.5 meter telescope made sense.

Kitt Peak is unusual in being open to all comers with a great proposal, whether they’re from the U.S. or abroad.  The Penn State team and partners will get a certain number of dedicated night to observe, but many others will be allocated through competitive reviews.  And so when NEID is completed, astronomers from around will have a shot at using this state-of-the-art planet finder.

 

 

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Hunting for Exoplanets Via TESS

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The TESS satellite, which will launch in 2017, will use four cameras to search for exoplanets around bright nearby stars. MIT
The TESS satellite, which will launch in 2017, will use four cameras to search for exoplanets around bright nearby stars. MIT initially proposed the mission, and it was approved in 2013.  (MIT)

Seven years ago this month the Kepler spacecraft launched into space – the first NASA mission dedicated to searching for planets around distant stars. The goal was to conduct a census of these exoplanets, to learn whether planets are common or rare. And in particular, to understand whether planets like Earth are common or rare.

With the discovery and confirmation of over 1,000 exoplanets (and thousands more exoplanet candidates that have not yet been confirmed), Kepler has taught us that planets are indeed common, and scientists have been able to make new inferences about how planetary systems form and evolve. But the planets found by Kepler are almost exclusively around distant, faint stars, and the observations needed to further study and characterize these planets are challenging. Enter TESS.

The Transiting Exoplanet Survey Satellite (TESS) is a NASA Explorer mission designed to search for new exoplanets around bright, nearby stars. The method that TESS will use is identical to that used by Kepler – it looks for planets that transit in front of their host star. Imagine that you’re looking at a star, and that star has planets around it.

If the orbit of the planet is aligned correctly, then once per “year” of the planet (i.e. once per orbit), the planet will pass in front of the star. As the planet moves in front of the star, it blocks a small fraction of the light, so the star appears to get slightly fainter. As the planet moves out of transit, the star returns to normal brightness. We can see an example of this in our own solar system on May 9, 2016, as Mercury passes in front of the Sun.

Tranit
A small dip in the amount of light emanating from a star tells astronomers that a planet may well be crossing in front of it.

We can learn a lot from observing the transits of a planet. First, we can learn the size of a planet – the bigger the planet, the more light it will block, and the larger the “dip” in the brightness of the host star. Second, we can learn how long the planet’s year is – since it only passes in front of the star once per orbit, the time between transits is the planet’s year.

The duration of the year, in combination with the properties of the host star, also allows us to determine if a planet might be habitable. With high precision measurements, we can also infer much more about the orbit of the planet (e.g., the eccentricity of the orbit). And, in fact, in some cases, we can look at small changes in the apparent year of the planet to discover additional planets in the system that do not transit (Transit Timing Variations).

To observe these transits, TESS will use four identical, extremely precise cameras mounted behind four identical 8-inch telescopes. Each one of these cameras will be sensitive to changes in the brightness of a star as small as about 40 parts per million, allowing TESS to detect planets even smaller than our planet.

Earth, transiting the sun, would produce a dip of about 100 parts per million. Each of the four cameras has a field-of-view of 24°×24°, and the fields of the four cameras are adjacent so that TESS will instantaneously observe a 24°×96° swath of the sky (referred to as an observation sector). Within this field, TESS will collect “postage stamp” images of about 8,000 stars every two minutes – the postage stamps are small sub-images, nominally about 10×10 pixels.

Over the course of two years, TESS will survey nearly the entire sky looking for transiting exoplanets. Each observing sector covers a patch of sky 24°×96° for 27 days; where sectors overlap, TESS will be able to observe planets for a long as nearly a year.
Over the course of two years, TESS will survey nearly the entire sky looking for transiting exoplanets. Each observing sector covers a patch of sky 24°×96° for 27 days; where sectors overlap, TESS will be able to observe planets for a long as nearly a year. (Ricker et al)

TESS will stare continuously at each of these observation sectors for 27 days before moving to the next sector; over the course of one year, this will give TESS coverage of almost one entire hemisphere, with postage stamp data on approximately 100,000 stars. In the second year of the TESS mission, 13 additional sectors will cover the other hemisphere of the sky, resulting in observations of about 200,000 stars.

The method used for these postage stamp-sized observations is very similar to that used for Kepler, but the survey itself is different. While TESS is conducting an all-sky survey (about 40,000 square degrees), Kepler looked at only a relatively small patch of the sky (115 square degrees). But with a telescope seven times larger than those on TESS, Kepler was able to look much further away – TESS surveys stars within only about 200 light years, compared to 3,000 light years for Kepler.

This underscores the difference in the underlying philosophy of the two missions. The goal of Kepler was to understand the statistics of exoplanets, to conduct a census to understand the population as a whole.

Artist's rendering of a Jupiter-sized exoplanet and its host, a star slightly more massive than our sun. Image credit: ESO
Artist’s rendering of a Jupiter-sized exoplanet and its host, a star slightly more massive than our sun. Image credit: ESO

TESS, on the other hand, is about finding planets around bright, nearby stars –planets that will be well-suited to follow-up observations from both the ground and from space. On average, the stars observed by TESS will be between 30 and 100 times brighter than those observed by Kepler. These brighter targets will allow for follow-up observations that will be critical for understanding the nature of the newly discovered planets – more on that in a moment.

In raw numbers, what do we expect from TESS?

Former MIT graduate student Peter Sullivan conducted detailed simulations of the mission to make a prediction on what it might discover, and these results are incredible. With TESS, we expect to find over 1,600 new exoplanets within the postage stamp data, with about 70 of those being about the size of the Earth (within 25% of the Earth’s diameter), and almost 500 “super-Earth” planets (less than twice the diameter of Earth).

Perhaps most exciting is the likelihood that TESS will discover a handful of Earth-sized planets in the habitable zones of their host stars.

Finding an Earth-sized planet in a distant habitable zone is a top goal of TESS, and of the exoplanet community as a whole. (NASA/Chester Harman)
Finding an Earth-sized planet in a distant habitable zone is a top goal of TESS, and of the exoplanet community as a whole. (NASA/Chester Harman)

In addition, while TESS obtains the postage stamp data every two minutes, it also obtains a full-frame image – a picture of the entire observing sector – every thirty minutes.

In those data, we expect to find over 20,000 additional planets. The majority of those will be large (Jupiter-size) planets, but there will also be about 1,400 additional super-Earths discovered. The sheer number of planets that will be found is amazing, but more important than the number is the fact that all of these planets will be orbiting bright, nearby stars. This is a fantastic leap relative to where we were just 25 years ago, when not a single exoplanet was known.

One of the challenges of transit measurements is that they can produce false positives. Stellar activity can cause quasi-periodic dips in the brightness of a star. An eclipsing binary star in the background could mimic the dip from a transiting planet. With careful analysis, most of these effects can be accounted for, but it remains important to follow a transit observation with a confirmation — making a secondary measurement to ensure that what was observed is, in fact, a planet.

The most straightforward way to confirm a transiting exoplanet is with a radial velocity (RV) measurement. The RV method takes advantage of the reflex motion of the star; as a planet orbits a star, the star itself doesn’t remain stationary. In fact, both the planet and the star orbit the center of mass of the system. So, if one looks at spectral lines from the host star, it is possible to measure the Doppler shift of those lines as the star does it’s little pirouette around the center of mass.

From this data, astronomers can measure the mass and the year (orbital period) of the exoplanet. This confirms the orbital period observed from the transit data, and the combination of radius (observed from the transit) and the mass (observed from the RV) gives us the bulk density of the planet. With that, we can make inferences about the composition of the planet – is it a rock, like Earth? A water-world or a ball of ice? A gas giant?

Measurements of the TESS space telescope. (NASA)
Measurements of the TESS space telescope. (NASA)

Making the RV measurement, while straightforward, is not an easy one – less than 10% of the exoplanet candidates found by Kepler have been confirmed with RV measurements, largely because the host stars themselves are faint. For TESS, however, because the host stars are nearby and bright, it will be possible to make follow-up observations on nearly all of the stars that host small planets – the only major limitation will be due to the noise from the stars themselves (i.e. flares, starspots).

Further, because these host stars are bright, they will also be excellent targets for transit spectroscopy. Imagine, for a moment, that there is a transiting planet with a very large atmosphere, and that this atmosphere is transparent in red and blue, but completely opaque in the green. Then, if you observe the planet in red light (or blue light), only the “rock” part of the planet will block light from the star. In green light, however, the rock and the atmosphere will both block light – in the green, the planet appears to be larger than at other wavelengths.

This is the core idea behind transit spectroscopy. By measuring how the apparent size of a transiting planet varies with wavelength, we can infer the composition (and potentially the structure) of the planetary atmosphere. This technique has been used successfully on a very small number of exoplanets to date, but with the large number of planets that TESS will find, and the fact that they will all be around bright, nearby stars, it will be possible to use the James Webb Space Telescope and the next generation of large ground-based telescopes to make these observations.

TESS is expected to add 2,000 new exoplanets to the already long list of the ones alrday detected. (NASA)
TESS is expected to monitor more than 200,000 stars and add 1,500 new exoplanets to the already long list of those confirmed or awaiting confirmation.  (NASA)

For the first time, astronomers will actually be able to study not only individual exoplanets, but will be able to study enough of them to make comparisons and draw conclusions about how planets form and evolve.

For me, TESS is endlessly exciting. The sheer quantity of new exoplanets is stunning. The ability to use follow-up observations to characterize these planets will create new paths for scientific investigation. And the discoveries made will help define the science that will be pursued by future missions such as WFIRST, and perhaps more ambitious missions in the future. But, perhaps most exciting, TESS is in part about making “Exoplanets for Everyone.”

In a few years, it will be possible for everyone to go outside to a dark location, point at a star that you can see with the naked eye, and say “there is a planet around that star.” And the night sky may never feel quite the same again.

Video link: TESS Trailer — https://youtube/ZsPStvGgNuk

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The Pale Red Dot Campaign

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Alpha and Beta Centauri are the bright stars; Proxima Centauri is the small, faint one circles in red.
Alpha Centauri A and B are the bright stars; Proxima Centauri, a red dwarf star, is the small, faint one circled in red. (NASA, Julia Figliotti)

Astronomers have been trying for decades to find a planet orbiting Proxima Centauri, the star closest to our sun and so a natural and tempting target.  Claims of an exoplanet discovery have been made before, but so far none have held up.

Now, in a novel and very public way, a group of European astronomers have initiated a focused effort to change all that with their Pale Red Dot Campaign.  Based at the La Silla Observatory in Chile, and supported by  networks of smaller telescopes around the world, they will over the next three months observe Proxima and its environs and then will spend many more months analayzing all that they find.  And in an effort to raise both knowledge and excitement, the team will tell the world what they’re doing and finding over Twitter, Facebook, blogs and other social and traditional media of all kind.

“We have reason to be hopeful about finding a planet, but we really don’t know what will happen,” said Guillem Anglada-Escudé  of Queen Mary University, London, one of the campaign organizers.  “People will have an opportunity to learn how astronomers do their work finding exoplanets, and they’ll be able to follow our progress.  If we succeed, that would be wonderful and important.  And if no planet is detected, that’s very important too.”

The Pale Blue Dot, as photographed by Voyager 1 (NASA)
The Pale Blue Dot, as photographed by Voyager 1 (NASA)

The name of the campaign is, of course, a reference to the iconic “Pale Blue Dot” image of Earth taken by the Voyager 1 spacecraft in 1990, when it was well beyond Pluto.  The image came to symbolize our tiny but precious place in the galaxy and universe.

But rather than potentially finding a pale blue dot, any planet orbiting the red dwarf star Proxima Centauri would reflect the reddish light of the the star, which lies some 4.2 light years away from our solar system.  Proxima — as well as 20 of the 30 stars in our closest  neighborhood — is reddish because it is considerably smaller and less luminous than a star like our sun.

Anglada-Escudé said he is cautiously optimistic about finding a planet because of earlier Proxima observations that he and colleagues made at the same observatory.  That data, he said, suggested the presence of a planet 1.2 to 1.5 times the size of Earth, within the habitable zone of the star.

“We did not and are not making claims in terms of having discovered a planet,”  he said.  “We’re saying that we detected signals that could mean there is a planet.  This is why we’ve planned this campaign — to see if the signal is telling us something real.”  He described the campaign as a “partnership between scientists involved in the observations and European Southern Observatory.”

Even without a previous signal, it’s a reasonable bet that Proxima does have at least one planet orbiting it.  Based on the results of the Kepler Space Telescope survey in particular, there is a consensus of sorts in the astronomy community that on average, every star has at least one planet circling it.

Alpha Centauri A and Alpha Centauri B are a binary pair, while Proxima Centauri is far away but is xxx
Alpha Centauri A, Alpha Centauri B and Proxima Centauri make up a three-star system, although Proxima Centauri is a distant .2 lightyears away rom the other two.  (Ian Morrison)

Paul Butler, a pioneer in planet hunting at the Carnegie Institution of Washington who has done extensive observing of Proxima with his team at Las Campanas Observatory in Chile, will be providing data to the Pale Red Dot campaign.  Proxima search results from the ESO’s Very Large Telescope at Paranal, Chile, will also be provided to campaign.

Butler said that in some ways Proxima “is the most exciting star in the sky.  It’s the very nearest star and so the discovery of a planet there would be huge – front page of the paper around the world.”

What’s more, he said, such a discovery could be enormously helpful in motivating Congress and taxpayers to spend the money needed for what is considered the holy grail of planet hunting — building a space-based exoplanet observatory that could directly image exoplanets.  “We have to give people a clear reasons to spend all that money and finding a potentially habitable planet around Proxima, that would be it.”

 Hubble Space Telescope image is our closest stellar neighbour: Proxima Centauri, just over four light-years from Earth. Although it looks bright through the eye of Hubble, Proxima Centauri -- with only about one eight the mass of our sun -- is not visible to the naked eye.Shining brightly in this Hubble image is our closest stellar neighbour: Proxima Centauri. Proxima Centauri lies in the constellation of Centaurus (The Centaur), just over four light-years from Earth. Although it looks bright through the eye of Hubble, as you might expect from the nearest star to the Solar System, Proxima Centauri is not visible to the naked eye. Its average luminosity is very low, and it is quite small compared to other stars, at only about an eighth of the mass of the Sun. However, on occasion, its brightness increases. Proxima is what is known as a “flare star”, meaning that convection processes within the star’s body make it prone to random and dramatic changes in brightness. The convection processes not only trigger brilliant bursts of starlight but, combined with other factors, mean that Proxima Centauri is in for a very long life. Astronomers predict that this star will remain middle-aged — or a “main sequence” star in astronomical terms — for another four trillion years, some 300 times the age of the current Universe. These observations were taken using Hubble’s Wide Field and Planetary Camera 2 (WFPC2). Proxima Centauri is actually part of a triple star system — its two companions, Alpha Centauri A and B, lie out of frame. Although by cosmic standards it is a close neighbour, Proxima Centauri remains a point-like object even using Hubble’s eagle-eyed vision, hinting at the vast scale of the Universe around us.
A Hubble Space Telescope image of Proxima Centauri, just over four light-years from Earth. Proxima Centauri — with only about one eight the mass of our sun — is not visible to the naked eye. Its average luminosity is very low but, on occasion, its brightness increases. Proxima is what is known as a “flare star” — where convection processes within the star’s make it prone to random and dramatic changes in brightness. (NASA)

Proxima and the other Alpha Centauri stars are also an especially appealing target because they have loomed so large in science fiction.  From Robert Heinlein’s “Ophans of the Sky” stories of crews traveling to Proxima to Isaac Asimov’s “Foundation and Earth ” set around Alpha Centauri and more recently to the James Cameron’s movie “Avatar,” also set in the Centauri neighborhood, these closer-by have been a frequent and logical destination.

While Alpha Centauri B has gotten much scientific attention in recent years with a reported but still unconfirmed and now often dismissed planet candidate, Proxima Centauri has been the object of much observation, too, and that has begun to define what kinds of planets might and might not be present.

So far, the work of Butler’s team has not found any particularly promising signs of a planetary-caused Proxima wobble.  But he said nothing established so far about Proxima rules out the presence of a small planet relatively close to the sun — the very time-consuming observations needed to potentially detect that size planet just haven’t been done.

Similarly, the Very Large Telescope results ruled out the presence of Saturn-size planets with many-year orbits and Neptune-size planets with orbits less than about 40 day, and no planets more than 6 to 10 Earths in the habitable zone.  This is actually promising news, since the absence of larger planets in the habitable zone leaves the field open for smaller ones.

Two other teams are now focused on Proxima as well.  One is led by David Kipping of Columbia University  using the Canadian Microvariability & Oscillations of STars space telescope (MOST) to search for transits.  The other is led by Kailash Sahu of the Space Science Telescope Institute in Baltimore, using the Hubble Space Telescope for microlensing of the star. The stars are aligned for the microlensing event this month.

A ring of telescopes at ESO's La Silla observatory. La Silla, in  the  southern part of the Atacama desert, 600 km north of  Santiago de  Chile,  was ESO's first observation site. The telescopes are 2400 metres  above  sea level, providing excellent observing conditions. ESO  operates the 3.6-m telescope, the  New Technology Telescope (NTT), and   the 2.2-m Max-Planck-ESO telescope  at La Silla. La Silla also hosts  national telescopes, such as the 1.2-m  Swiss  Telescope and the 1.5-m  Danish Telescope.
A ring of telescopes at ESO’s La Silla observatory. La Silla, in the southern part of the Atacama desert, 600 km north of Santiago de Chile, was ESO’s first observation site. The telescopes are 2400 metres above sea level, providing excellent observing conditions. ESO operates the 3.6-m telescope, the New Technology Telescope (NTT), and the 2.2-m Max-Planck-ESO telescope at La Silla. La Silla also hosts national telescopes, such as the 1.2-m Swiss Telescope and the 1.5-m Danish Telescope. (ESO)

The Pale Red Dot observing began last week and will run for two and a half month using the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph at the European Southern Observatory (ESO) telescope at La Silla, Chile. The observations — like those made at the Magellan and at Paranal — look for tiny wobbles in the star’s motion created by the gravitational pull of an orbiting planet. (More on how the radial velocity method works, as well as other connections to and details about the campaign can be found at:  https://palereddot.org/introduction/)

The campaign is the beneficiary of a substantial amount of HARPS observing time — 25 minutes of observing for 60 nights in a row — which is essential to confidently detect the presence of a small, Earth-sized planet.

Other robotic telescopes — including the Burst Optical Observer and Transient Exploring System,  the Las Cumbres Observatory Global Telescope Network and the Astrograph for the Southern Hemisphere II — will participate.  The role of these automated telescopes is to measure the brightness of Proxima each night, a backup that will help astronomers determine whether the wobbles of the star detected via radial velocity are the tug of an orbiting planet or activity on the surface of the star. Anglada-Escudé said that after a full analysis, the findings will offered to a peer-reviewed journal and published.

While the goal of the campaign is definitely to detect a planet orbiting our closest stellar neighbor, it is also very consciously a public outreach effort for astronomy and exoplanets.  Everything about the campaign will be made public, and often immediately via Twitter and other social media.  It will provide a window, said Anglada-Escudé, into how planet-hunting astronomy works.

Guillem Anglada-Escude
Guillem Anglada-Escudé is leading the Pale Red Dot campaign.

“We think this to be a good way to explain things that are not obvious to the public, to show them that looking for planets is not always excitement and ‘eurekas.’   We’ll show life at the observatory, how our observations are made, what happens as we analyze the data.  And if in the end we don’t find evidence of a planet, we will have shown how we search for such tiny objects so far away, and do it with a pretty amazing precision.”

Involving the public so early and often definitely brings risks, since the campaign could certainly come up empty-handed.  But in terms of real-life planet hunting, that result is hardly unusual.  An awful lot of planet-hunting campaigns end without a detection.

When red dwarf stars, also called M dwarfs, are found with orbiting planets, they tend to be much closer in than with more massive stars, and their habitable zones are also much more narrow.  Initially, red dwarfs were not considered good candidates for habitable planets because they are so relatively small — between 50 to 5 percent the mass of our sun.  Any planets orbiting close to a red dwarf would likely be tidally locked as well, with only one side ever facing the sun.  The pull of the host star causes the locking.

These issues and more earlier led scientists to dismiss red dwarf exoplanets as unlikely to be habitable. That unpromising view has changed with the creation of models for tidally locked planets that could be habitable, and with the discovery of many exoplanets orbiting around the red dwarfs.  These small suns actually  constitute more than 70 percent of the stars in the sky, although very few of the ones you can see without a telescope.

So the time seems ripe for a substantial exoplanet campaign at Proxima — one that just might find a planet and that certainly has a lot to teach the public.

Sites where you can follow the campaign:
Twitter: @Pale_red_dot #palereddot
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 Artist rendering of a cold desert on a planet orbiting Proxima Centauri. (Vladimir Romanyuk, Space Engine)
Artist rendering of a cold desert on a planet orbiting Proxima Centauri. (Vladimir Romanyuk, Space Engine)
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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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