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Overlooked Treasure: The First Evidence of Exoplanets

Pasadena CA (JPL)

Nov 02, 2017

Beneath an elegant office building with a Spanish-style red tiled roof in Pasadena, California, three timeworn storerooms safeguard more than a century of astronomy. Down the stairs and to the right is a basement of wonder. There are countless wooden drawers and boxes, stacked floor to ceiling, with telescope plates, sunspot drawings and other records. A faint ammonia-like smell, reminiscent of old film, fills the air. Guarding one storeroom is a short black door with a sign saying “This door to be kept closed.”

Carnegie Observatories hosts 250,000 photographic plates taken at Mount Wilson, Palomar and Las Campanas observatories, spanning more than 100 years. In their heydays, the Mount Wilson 60-inch and 100-inch telescopes – the bigger saw its first light on Nov. 1, 1917 – were the most powerful instruments of their kind.

Each indelibly changed humanity’s understanding of our place in the cosmos. But these technological marvels were ahead of their time – in one case, capturing signs of distant worlds that wouldn’t be recognized for a century.

Mount Wilson is the site where some of the key discoveries about our galaxy and universe were made in the early 20th century. This is where Edwin Hubble realized that the Milky Way cannot be the extent of our universe, because Andromeda (or M31) is farther away than the most distant reaches of our galaxy. The photographic plate from the 100-inch Hooker Telescope from 1923, which captured this monumental realization, is blown up as a huge poster outside the Carnegie storerooms.

Hubble and Milton Humason, whose Mount Wilson career began as a janitor, worked together to explore the expanding nature of the universe. Using the legendary telescopes, as well as data from Lowell Observatory in Flagstaff, Arizona, they recognized that clusters of galaxies are traveling away from each other – and the more distant galaxies move away from each other at greater speeds.

But there is a far lesser known, 100-year-old discovery from Mount Wilson, one that was unidentified and unappreciated until recently. It’s actually: The first evidence of exoplanets.

A detective story

It started with Ben Zuckerman, professor emeritus of astronomy at the University of California, Los Angeles. He was preparing a talk about the compositions of planets and smaller rocky bodies outside our solar system for a July 2014 symposium at the invitation of Jay Farihi, whom he had helped supervise when Farihi was a graduate student at UCLA. Farihi had suggested that Zuckerman talk about the pollution of white dwarfs, which are faint, dead stars composed of mainly hydrogen and helium.

By “pollution,” astronomers mean heavy elements invading the photospheres – the outer atmospheres – of these stars. The thing is, all those extra elements shouldn’t be there – the strong gravity of the white dwarf should pull the elements into the star’s interior, and out of sight.

The first polluted white dwarf identified is called van Maanen’s Star (or “van Maanen 2” in the scientific literature), after its discoverer Adriaan van Maanen. Van Maanen found this object in 1917 by spotting its subtle motion relative to other stars between 1914 and 1917. Astronomer Walter Sydney Adams, who would later become director of Mount Wilson, captured the spectrum – a chemical fingerprint – of van Maanen’s Star on a small glass plate using Mount Wilson’s 60-inch telescope.

Adams interpreted the spectrum to be of an F-type star, presumably based on the presence and strength of calcium and other heavy-element absorption features, with a temperature somewhat higher than our Sun. In 1919, van Maanen called it a “very faint star.”

Today, we know that van Maanen’s Star, which is about 14 light-years away, is the closest white dwarf to Earth that is not part of a binary system.

“This star is an icon,” Farihi said recently. “It is the first of its type. It’s really the proto-prototype.”

While preparing his talk, Zuckerman had what he later called a “true ‘eureka’ moment.” Van Maanen’s Star, unbeknownst to the astronomers who studied it in 1917 and those who thought about it for decades after, must be the first observational evidence that exoplanets exist.

What does this have to do with exoplanets?

Heavy elements in the star’s outermost layer could not have been produced inside the star, because they would immediately sink due to the white dwarf’s intense gravitational field. As more white dwarfs with heavy elements in their photospheres were discovered in the 20th century, scientists came to believe that the exotic materials must have come from the interstellar medium – in other words, elements floating in the space between the stars.

But in 1987, more than 70 years after the Mount Wilson spectrum of van Maanen’s Star, Zuckerman and his colleague Eric Becklin reported an excess of infrared light around a white dwarf, which they thought might come from a faint “failed star” called a brown dwarf. This was, in 1990, interpreted to be a hot, dusty disk orbiting a white dwarf. By the early 2000s, a new theory of polluted white dwarfs had emerged: Exoplanets could push small rocky bodies toward the star, whose powerful gravity would pulverize them into dust. That dust, containing heavy elements from the torn-apart body, would then fall on the star.

“The bottom line is: if you’re an asteroid or comet, you can’t just change your address. You need something to move you,” Farihi said. “By far, the greatest candidates are planets to do that.”

NASA’s Spitzer Space Telescope has been instrumental in expanding the field of polluted white dwarfs orbited by hot, dusty disks. Since launch in 2004, Spitzer has confirmed about 40 of these special stars. Another space telescope, NASA’s Wide-field Infrared Survey Explorer, also detected a handful, bringing the total up to about four dozen known today. Because these objects are so faint, infrared light is crucial to identifying them.

“We can’t measure the exact amount of infrared light coming from these objects using telescopes on the ground,” Farihi said. “Spitzer, specifically, just burst this wide open.”

Supporting the new “dusty disk” theory of pulled white dwarfs, in 2007, Zuckerman and colleagues published observations of a white dwarf atmosphere with 17 elements – materials similar to those found in the Earth-Moon system. (The late UCLA professor Michael Jura, who made crucial contributions to the study of polluted white dwarfs, was part of this team.)

This was further evidence that at least one small, rocky body – or even a planet – had been torn apart by the gravity of a white dwarf. Scientists now generally agree that a single white dwarf star with heavy elements in its spectrum likely has at least one rocky debris belt – the remnants of bodies that collided violently and never formed planets – and probably at least one major planet.

So, heavy elements that happened to be floating in the interstellar medium could not account for the observations. “About 90 years after van Maanen’s discovery, astronomers said, ‘Whoa, this interstellar accretion model can’t possibly be right,'” Zuckerman said.

Chasing the spectrum

Inspired by Zuckerman, Farihi became enamored with the idea that someone had taken a spectrum with the first evidence of exoplanets in 1917, and that a record must exist of that observation. “I got my teeth in the question and I wouldn’t let go,” he said.

Farihi reached out to the Carnegie Observatories, which owns the Mount Wilson telescopes and safeguards their archives. Carnegie Director John Mulchaey put volunteer Dan Kohne on the case. Kohne dug through the archives and, two days later, Mulchaey sent Farihi an image of the spectrum.

“I can’t say I was shocked, frankly, but I was pleasantly blown out of my seat to see that the signature was there, and could be seen even with the human eye,” Farihi said.

The spectrum of van Maanen’s Star that Farihi had requested is now located in a small archival sleeve, labeled with the handwritten date “1917 Oct 24” and a modern yellow sticky note: “possibly 1st record of an exoplanet.”

Cynthia Hunt, an astronomer who serves as chair of Carnegie’s history committee, took the glass plate out of the envelope and placed it onto a viewer that lit it up. The spectrum itself just about 1/6th of an inch, or a bit over 0.4 centimeters.

Though the plate seems unremarkable at first glance, Farihi saw two obvious “fangs” representing dips in the spectrum. To him, this was the smoking gun: Two absorption lines from the same calcium ion, meaning there were heavy elements in the photosphere of the white dwarf – indicating it likely has at least one exoplanet. He wrote about it in 2016 in New Astronomy Reviews.

Exoplanets and debris disks

Scientists have long thought the gravity of giant planets could be keeping debris belts in place, especially in young planetary systems. A recent study in The Astrophysical Journal showed that young stars with disks of dust and debris are more likely to have giant planets orbiting at great distance from their parent star than those without disks.

A white dwarf is not a young star – on the contrary, it forms when a low-to-medium-mass star has already burned all of the fuel in its interior. But the principle is the same: The gravitational pull of giant exoplanets could throw small, rocky bodies into the white dwarfs.

Our own Sun will become a red giant in about 5 billion years, expanding so much it may even swallow Earth before it blows off its outer layers and becomes a white dwarf. At that point, Jupiter’s large gravitational influence may be more disruptive to the asteroid belt, flinging objects toward our much-dimmer Sun. This kind of scenario could explain the heavy elements at van Maanen’s Star.

Spitzer’s observations of van Maanen’s Star have not found any planets there so far. In fact, to date, no exoplanets have been confirmed orbiting white dwarfs, although one does have an object thought to be a massive planet. Other compelling evidence has emerged just in the last couple of years. Using the W. M. Keck Observatory in Hawaii, scientists, including Zuckerman, recently announced that they had found evidence of a Kuiper-Belt-like object having been eaten by a white dwarf.

Scientists are still exploring polluted white dwarfs and looking for the exoplanets they may host. About 30 percent of all white dwarfs we know about are polluted, but their debris disks are harder to spot. Jura put forward that with lots of asteroids coming in and colliding with debris, dust may be converted into gas, which would not have the same highly detectable infrared signal as dust.

Farihi was thrilled about how his Mount Wilson archive detective work turned out. In 2016, he described the historical find in the context of a review paper about polluted white dwarfs, arguing that white dwarfs are “compelling targets for exoplanetary system research.”

Who knows what other overlooked treasures await discovery in the archives of great observatories – the sky-watching records of a cosmos rich in subtlety. Surely, other clues will be found by those motivated by curiosity who ask the right questions.

“It’s personal interaction with data that can really spur us to get invested in the questions that we’re asking,” Farihi said.

Source: Space Daily.

Link: http://www.spacedaily.com/reports/Overlooked_Treasure_The_First_Evidence_of_Exoplanets_999.html.

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Atmosphere around super-earth detected

Heidelberg, Germany (SPX)

Apr 07, 2017

Astronomers have detected an atmosphere around the super-Earth GJ 1132b. This marks the first detection of an atmosphere around a low-mass super-Earth, in terms of radius and mass the most Earth-like planet around which an atmosphere has yet been detected. Thus, this is a significant step on the path towards the detection of life on an exoplanet.

The team, which includes researchers from the Max Planck Institute for Astronomy, used the 2.2-m ESO/MPG telescope in Chile to take images of the planet’s host star, GJ 1132, and measured the slight decrease in brightness as the planet and its atmosphere absorbed some of the starlight while passing directly in front of their host star.

While it’s not the detection of life on another planet, it’s an important step in the right direction: the detection of an atmosphere around the super-Earth GJ 1132b marks the first time an atmosphere has been detected around a planet with a mass and radius close to Earth’s mass and radius (1.6 Earth masses, 1.4 Earth radii).

Astronomers’ current strategy for finding life on another planet is to detect the chemical composition of that planet’s atmosphere, on the lookout for certain chemical imbalances that require the presence of living organisms as an explanation. In the case of our own Earth, the presence of large amounts of oxygen is such a trace.

We’re still a long way from that detection though. Until the work described in this article, the (few!) observations of light from exoplanet atmospheres all involved planets much more massive than Earth: gas giants – relatives of our own solar system’s Jupiter – and a large super-Earth with more than eight times the Earth’s mass. With the present observation, we’ve taken the first tentative steps into analyzing the atmosphere of smaller, lower-mass planets that are much more Earth-like in size and mass.

The planet in question, GJ 1132b, orbits the red dwarf star GJ 1132 in the southern constellation Vela, at a distance of 39 light-years from us. Recently, the system has come under scrutiny by a team led by John Southworth (Keele University, UK).

The project was conceived, and the observations coordinated, by Luigi Mancini, formerly of the Max Planck Institute for Astronomy (MPIA) and now working at the University of Rome Tor Vergata. Additional MPIA team members were Paul Molliere and Thomas Henning.

The team used the GROND imager at the 2.2-m ESO/MPG telescope of the European Southern Observatory in Chile to observe the planet simultaneously in seven different wavelength bands. GJ 1132b is a transiting planet: From the perspective of an observer on Earth, it passes directly in front of its star every 1.6 days, blocking some of the star’s light.

The size of stars like GJ 1132 is well known from stellar models. From the fraction of starlight blocked by the planet, astronomers can deduce the planet’s size – in this case around 1.4 times the size of the Earth. Crucially, the new observations showed the planet to be larger at one of the infrared wavelengths than at the others.

This suggests the presence of an atmosphere that is opaque to this specific infrared light (making the planet appear larger) but transparent at all the others.

Different possible versions of the atmosphere were then simulated by team members at the University of Cambridge and the Max Planck Institute for Astronomy. According to those models, an atmosphere rich in water and methane would explain the observations very well.

The discovery comes with the usual exoplanet caveats: while somewhat larger than Earth, and with 1.6 times Earth’s mass (as determined by earlier measurements), observations to date do not provide sufficient data to decide how similar or dissimilar GJ 1132b is to Earth. Possibilities include a “water world” with an atmosphere of hot steam.

The presence of the atmosphere is a reason for cautious optimism. M dwarfs are the most common types of star, and show high levels of activity; for some set-ups, this activity (in the shape of flares and particle streams) can be expected to blow away nearby planets’ atmospheres.

GJ 1132b provides a hopeful counterexample of an atmosphere that has endured for billion of years (that is, long enough for us to detect it). Given the great number of M dwarf stars, such atmospheres could mean that the preconditions for life are quite common in the universe.

In any case, the new observations make GJ 1132b a high-priority target for further study by instruments such as the Hubble Space Telescope, ESO’s Very Large Telescope, and the James Webb Space Telescope slated for launch in 2018.

Source: Space Daily.

Link: http://www.spacedaily.com/reports/Atmosphere_Around_Super_Earth_Detected_999.html.

Possible Venus twin discovered around dim star

Mountain View CA (SPX)

Apr 07, 2017

Astronomers using NASA’s Kepler space telescope have found a planet 219 light-years away that seems to be a close relative to Venus. This newly discovered world is only slightly larger than Earth and orbits a low-temperature star called Kepler-1649 that’s one-fifth the diameter of our Sun.

The planet tightly embraces its dim home star, encircling it every 9 days. The tight orbit causes the flux of sunlight reaching the planet to be 2.3 times as great as the solar flux on Earth. For comparison, the solar flux on Venus is 1.9 times the terrestrial value.

The discovery will provide insight into the nature of planets around M dwarf stars, by far the most common type in the universe. While such stars are redder and dimmer than the Sun, recent exoplanet discoveries have revealed instances in which Earth-sized worlds circle an M dwarf in orbits that would place them in their star’s habitable zone. But such worlds might not inevitably resemble Earth, with its salubrious climate. They could just as well be analogs of Venus, with thick atmospheres and scalding temperatures.

According to SETI Institute scientist Isabel Angelo, the study of planets similar to the Venus analog Kepler-1649b is “becoming increasingly important in order to understand the habitable zone boundaries of M dwarfs.

“There are several factors, like star variability and tidal effects, that make these planets different from Earth-sized planets around Sun-like stars.”

It’s said that Venus is Earth’s sister planet, but in many ways it’s not a close sibling. Despite being the same size as Earth, and only 40 percent closer to the Sun, its atmosphere and surface temperature are wildly different from our own. If we wish to find life on other Earth-sized worlds, we should take a cue from “The Music Man” and get to know the territory.

Elisa Quintana, from the SETI Institute and NASA Goddard Space Flight Center, and a member of the Kepler 1649b discovery team, notes, “Many people are hung up on finding other Earths. But Venus analogs are just as important.

“Since new telescopes coming down the pike will allow us to probe atmospheres, focusing on both Earth and Venus analogs may help decipher why, in our solar system, one planet allows life to thrive, and one does not, despite having similar masses, comparable densities, etc.”

Source: Space Daily.

Link: http://www.spacedaily.com/reports/Possible_Venus_Twin_Discovered_Around_Dim_Star_999.html.

Ultracool Dwarf and the Seven Planets

Munich, Germany (SPX)

Feb 22, 2017

Astronomers have found a system of seven Earth-sized planets just 40 light-years away. Using ground and space telescopes, including ESO’s Very Large Telescope, the planets were all detected as they passed in front of their parent star, the ultracool dwarf star known as TRAPPIST-1.

According to the paper appearing in the journal Nature, three of the planets lie in the habitable zone and could harbor oceans of water on their surfaces, increasing the possibility that the star system could play host to life. This system has both the largest number of Earth-sized planets yet found and the largest number of worlds that could support liquid water on their surfaces.

Astronomers using the TRAPPIST-South telescope at ESO’s La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world, have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth.

Dips in the star’s light output caused by each of the seven planets passing in front of it – events known as transits – allowed the astronomers to infer information about their sizes, compositions and orbits. They found that at least the inner six planets are comparable in both size and temperature to the Earth.

Lead author Michael Gillon of the STAR Institute at the University of Liege in Belgium is delighted by the findings: “This is an amazing planetary system – not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!”

With just 8% the mass of the Sun, TRAPPIST-1 is very small in stellar terms – only marginally bigger than the planet Jupiter – and though nearby in the constellation Aquarius (The Water Carrier), it appears very dim. Astronomers expected that such dwarf stars might host many Earth-sized planets in tight orbits, making them promising targets in the hunt for extraterrestrial life, but TRAPPIST-1 is the first such system to be found.

Co-author Amaury Triaud expands: “The energy output from dwarf stars like TRAPPIST-1 is much weaker than that of our Sun. Planets would need to be in far closer orbits than we see in the Solar System if there is to be surface water. Fortunately, it seems that this kind of compact configuration is just what we see around TRAPPIST-1!”

The team determined that all the planets in the system are similar in size to Earth and Venus in the Solar System, or slightly smaller. The density measurements suggest that at least the innermost six are probably rocky in composition.

The planetary orbits are not much larger than that of Jupiter’s Galilean moon system, and much smaller than the orbit of Mercury in the Solar System. However, TRAPPIST-1’s small size and low temperature mean that the energy input to its planets is similar to that received by the inner planets in our Solar System; TRAPPIST-1c, d and f receive similar amounts of energy to Venus, Earth and Mars, respectively.

All seven planets discovered in the system could potentially have liquid water on their surfaces, though their orbital distances make some of them more likely candidates than others. Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces.

The orbital distance of the system’s outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbour liquid water – assuming no alternative heating processes are occurring. TRAPPIST-1e, f, and g, however, represent the holy grail for planet-hunting astronomers, as they orbit in the star’s habitable zone and could host oceans of surface water.

These new discoveries make the TRAPPIST-1 system a very important target for future study. The NASA/ESA Hubble Space Telescope is already being used to search for atmospheres around the planets and team member Emmanuel Jehin is excited about the future possibilities: “With the upcoming generation of telescopes, such as ESO’s European Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope, we will soon be able to search for water and perhaps even evidence of life on these worlds.”

Source: Space Daily.

Link: http://www.spacedaily.com/reports/Ultracool_Dwarf_and_the_Seven_Planets_999.html.

Seven Terrestrial Exoplanets Around a Nearby Star

Bern, Switzerland (SPX)

Feb 22, 2017

TRAPPIST-1 is the name of the small, ultracool star that is the new hot topic in astronomy and the search for life outside our solar system. Observing the star with telescopes from the ground and space during an extensive campaign, an international team found that there are at least seven terrestrial planets around TRAPPIST-1. Their temperatures are low enough to make possible liquid water on the surfaces, as the researchers report in the journal Nature.

“Looking for life elsewhere, this system is probably our best bet as of today,” says Brice-Olivier Demory, professor at the University of Bern’s Center for Space and Habitability and one of the authors of the Nature paper.

The configuration of these exoplanets orbiting a dwarf star makes it possible to study their atmospheric properties with current and future telescopes. “The James Webb Space Telescope, Hubble’s successor, will have the possibility to detect the signature of ozone if this molecule is present in the atmosphere of one of these planets,” explains Demory.

“This could be an indicator for biological activity on the planet.” But the astrophysicist warns that we must remain extremely careful about inferring biological activity from afar and that everything could be different than expected.

Observing from All Over the World and Space

A year ago, the astronomers had already detected three Earth-sized planets orbiting the star TRAPPIST-1. The planets pass in front of the star in so called transits and periodically dim the starlight by a small amount.

After this discovery the researchers observed the star for months with different telescopes in Chile, Morocco, Hawaii, La Palma and South Africa, and in September 2016, NASA’s Spitzer Space Telescope monitored TRAPPIST-1 for 20 days. Exploiting all the data the astronomers found that the TRAPPIST-1 system is a compact analogue of our inner solar system with at least seven planets.

Bernese Computer Simulations Confirmed

“My task was to make an independent analysis of the Spitzer data as well as a dynamic analysis of the system that allowed to compute the masses of these planets,” explains Demory. He found that some of the detected planets have densities similar to the Earth and most probably a rocky composition.

In a paper published in October 2016, Yann Alibert and Willy Benz, both astrophysics professors at the University of Bern as well, had already predicted based on their computer simulations that such planets around dwarf stars should be common.

Earth-like exoplanets orbiting dwarf stars are easier to observe than real Earth twins around solar-type stars. Since these dwarfs are also much cooler, the temperature zone that allows water to be liquid on the surface of the planet is much closer to the star. And exoplanets that are close to their host star revolve more rapidly and produce more transits in a given timeframe.

“About 15 percent of the stars in our neighbourhood are very cool stars like TRAPPIST-1,” says Brice-Olivier Demory. “We have a list of about 600 targets that we will observe in the future.”

To monitor the candidate stars in the northern hemisphere the Center for Space and Habitability (CSH) of the University of Bern is leading a consortium that builds a new telescope in Mexico.

Source: Space Daily.

Link: http://www.spacedaily.com/reports/Seven_Terrestrial_Exoplanets_Around_a_Nearby_Star_999.html.

Could Proxima Centauri b Really Be Habitable

Seattle WA (SPX)

Aug 31, 2016

The world’s attention is now on Proxima Centauri b, a possibly Earth-like planet orbiting the closest star, 4.22 light-years away. The planet’s orbit is just right to allow liquid water on its surface, needed for life. But could it in fact be habitable?

If life is possible there, the planet evolved very different than Earth, say researchers at the University of Washington-based Virtual Planetary Laboratory (VPL) where astronomers, geophysicists, climatologists, evolutionary biologists and others team to study how distant planets might host life.

Astronomers at Queen Mary University in London have announced discovery of Proxima Centauri b, a planet orbiting close to a star 4.22 light-years away. The find has been called “the biggest exoplanet discovery since the discovery of exoplanets.”

Rory Barnes, UW research assistant professor of astronomy, published a discussion about the discovery at palereddot.org, a website dedicated to the search for life around Proxima Centauri. His essay describes research under way through the UW planetary lab – part of the NASA Astrobiology Institute – to answer the question, is life possible on this world?

“The short answer is, it’s complicated,” Barnes writes. “Our observations are few, and what we do know allows for a dizzying array of possibilities” – and almost as many questions.

The Virtual Planetary Laboratory is directed by Victoria Meadows, UW professor of astronomy. UW-affiliated researchers include Giada Arney, Edward Schwieterman and Rodrigo Luger. Using computer models, the researchers studied clues from the orbits of the planet, its system, its host star and apparent companion stars Alpha Centauri A and B – plus what is known of stellar evolution to begin evaluating Proxima b’s chances.

Relatively little is known about Proxima:

* It’s at least as massive as Earth and may be several times more massive, and its “year” – the time it takes to orbit its star – is only 11 days.

* Its star is only 12 percent as massive as our Sun and much dimmer (so its habitable zone, allowing liquid water on the surface, is much closer in) and the planet is 25 times closer in than Earth is to our Sun.

* The star may form a third part of the Alpha Centauri binary star system, separated by a distance of 15,000 “astronomical units,” which could affect the planet’s orbit and history.

* The new data hint at the existence of a second planet in the system with an orbital period near 200 days, but this has not been proven.

Perhaps the biggest obstacle to life on the planet, Barnes writes, is the brightness of its host star. Proxima Centauri, a red dwarf star, is comparatively dim, but wasn’t always so.

“Proxima’s brightness evolution has been slow and complicated,” Barnes writes. “Stellar evolution models all predict that for the first one billion years Proxima slowly dimmed to its current brightness, which implies that for about the first quarter of a billion years, planet b’s surface would have been too hot for Earth-like conditions.”

Barnes notes that he and UW graduate student Rodrigo Luger recently showed that had modern Earth been in such a situation, “it would have become a Venus-like world, in a runaway greenhouse state that can destroy all of the planet’s primordial water,” thus extinguishing any chance for life.

Next come a host of questions about the planet’s makeup, location and history, and the team’s work toward discerning answers.

* Is the planet “rocky” like Earth? Most orbits simulated by the planetary lab suggest it could be – and thus can host water in liquid form, a prerequisite for life.

* Where did it form, and was there water? Whether it formed in place or farther from its star, where ice is more likely, VPL researchers believe it is “entirely possible” Proxima b could be water-rich, though they are not certain.

* Did it start out as a hydrogen-enveloped Neptune-like planet and then lose its hydrogen to become Earth-like? VPL research shows this is indeed possible, and could be a viable pathway to habitability.

* Proxima Centauri flares more often than our Sun; might such flares have long-since burned away atmospheric ozone that might protect the surface and any life? This is possible, though a strong magnetic field, as Earth has, could protect the surface. Also, any life under even a few meters of liquid water would be protected from radiation.

Another concern is that the planet might be tidally locked, meaning one side permanently faces its star, as the Moon does Earth. Astronomers long thought this to mean a world could not support life, but now believe planetwide atmospheric winds would transport heat around the planet.

“These questions are central to unlocking Proxima’s potential habitability and determining if our nearest galactic neighbor is an inhospitable wasteland, an inhabited planet, or a future home for humanity,” Barnes writes.

Planetary laboratory researchers also are developing techniques to determine whether Proxima b’s atmosphere is amenable to life.

“Nearly all the components of an atmosphere imprint their presence in a spectrum (of light),” Barnes writes. “So with our knowledge of the possible histories of this planet, we can begin to develop instruments and plan observations that pinpoint the critical differences.”

At high enough pressures, he notes, oxygen molecules can momentarily bind to each other to produce an observable feature in the light spectrum.

“Crucially, the pressures required to be detectable are large enough to discriminate between a planet with too much oxygen, and one with just the right amount for life.

As we learn more about the planet and the system, we can build a library of possible spectra from which to quantitatively determine how likely it is that life exists on planet b.”

Our own Sun is expected to burn out in about 4 billion years, but Proxima Centauri has a much better forecast, perhaps burning for 4 trillion years longer.

“If Proxima b is habitable, then it might be an ideal place to move. Perhaps we have just discovered a future home for humanity. But in order to know for sure, we must make more observations, run many more computer simulations and, hopefully, send probes to perform the first direct reconnaissance of an exoplanet,” Barnes writes. “The challenges are huge, but Proxima b offers a bounty of possibilities that fills me with wonder.”

Proxima Centauri b may be the first exoplanet to be directly characterized by powerful ground- and space-based telescopes planned for the future, and its atmosphere spectroscopically probed for active biology.

“Whether habitable or not,” Barnes concludes, “Proxima Centauri b offers a new glimpse into how the planets and life fit into our universe.”

Source: Space Daily.

Link: http://www.spacedaily.com/reports/Could_Proxima_Centauri_b_Really_Be_Habitable_999.html.

A star’s birth holds early clues to life-potential

Moffett Field CA (SPX)

Aug 19, 2016

Our solar system began as a cloud of gas and dust. Over time, gravity slowly pulled these bits together into the Sun and planets we recognize today. While not every system is friendly to life, astronomers want to piece together how these systems are formed.

A challenge to this research is the opacity of dust clouds to optical wavelengths (the ones that humans can see). So, astronomers are experimenting with different wavelengths, such as infrared light, to better see the center of dense dust clouds, where young stars typically form.

Recently, astronomers used data from NASA’s Spitzer Space Telescope – a powerful space observatory launched in 2003 that observes the Universe in infrared light – to look at a molecular cloud called L183, which is about 360 light-years away in the constellation Serpens Cauda (the serpent). Their goal was to see how light scattering affects the view of the cloud at the mid-infrared wavelength of 8 microns (um). Ultimately, the astronomers hope to use this data to get a better look inside the clouds.

“One thing we have to do is evaluate the mass that is sitting in the center of the cloud, which is ready to collapse to make a star,” said co-author Laurent Pagani, a researcher at the National Center for Scientific Research (CNRS) in Paris, France.

His former doctoral student, Charlene Lefevre, led the research. Their work was recently published in the journal Astronomy and Astrophysics under the title, “On the importance of scattering at 8?um: Brighter than you think.” Funding for the research came from CNRS and the French government.

Penetrating the dust

Dust clouds are tough to see through not only because of the dust itself, but also because the gases present are not very visible in telescopes observing in the infrared. Clouds are mainly made up of hydrogen and helium, which emit no radiation in the infrared or millimeter wavelengths. These two elements make up 98 percent of the mass of the cloud, meaning most of it is escaping any kind of measurement.

To get around this measurement problem, astronomers use proxies such as dust. Dust is roughly 1 percent of the cloud’s mass, but it is best measured at the edges of the cloud. Dust abundance can be inferred through the extinction of starlight. Since we can also measure the quantity of molecular hydrogen via ultraviolet absorption at the edge of the clouds, the dust abundance is derived with respect to molecular hydrogen. Once “calibrated,” the dust mass is measured throughout the cloud, providing the molecular hydrogen gas and the cloud mass.

For this project, Pagani and his team attempted to measure the amount of dust absorption at 8 microns for the cloud L183. It’s common to find light at this wavelength throughout the galaxy, making it a potential measuring tool for different clouds. By measuring the absorption, scientists can estimate how much light is coming from the front of the cloud to the back of the cloud; in other words, by how much the light from the background is diminished.

In so doing, astronomers hope to gain a better understanding about how young stars form. Other, unrelated studies of dust clouds are also looking at where elements – including those grouped in molecules associated with life, such as water – are situated in young solar systems.

More mysteries

The method appears to work, but there are limitations, the researchers concluded. Different types of dust clouds appear to be more or less sensitive to different wavelengths of light, making it difficult to see what is inside this region.

“There is not only absorption, but also scattering [in L183], and this scattering diminishes the contrast,” Pagani said. “You have the light that is absorbed by the dust, but the dust is also emitting or scattering light towards the observer. It looks less deep than it actually is, if you don’t take into account the scattering.”

Lefevre was able to use the 8-micron scattering model correctly to fit other observations of the cloud. However, if she tried to observe using other wavelengths – such as 100 microns or 200 microns – she saw a very different picture concerning dust absorption. It’s possible that some of the measurements were affected by ice on the dust, which was not accounted for by her radiative transfer model, Pagani said.

More work will be required. The two researchers (Lefevre is now a post-doctoral researcher at IRAM, the international Institute for Millimeter Radio-Astronomy but still working with Pagani) are using more grain types to try different methods to measure clouds at various wavelengths. “If this works, we know what kind of grains work in the clouds,” Pagani said. “If it doesn’t work, we have to talk to the theoreticians to modify [the models] to fit the observations.”

Source: Space Daily.

Link: http://www.spacedaily.com/reports/A_stars_birth_holds_early_clues_to_life_potential_999.html.

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