STScI Scientists Surprised to Find Brightness ‘Gap’ in Ancient Star Cluster

Euclid image of NGC 6397

This Euclid image of globular cluster NGC 6397 is speckled with hundreds of thousands of stars, which vary in size and color. Most stars are located at the cluster’s center, where they are bound together by gravity. Scientists studying NGC 6397 found that when they grouped the cluster’s stars by brightness and color they observed a thin brightness “gap” of expected but missing low-mass stars called red dwarfs. This gap is thought to be linked to changes occurring within some stars’ interiors. This is the first time the gap feature was discovered in a globular cluster.Credits Image: ESA, NASA, Euclid Consortium - Image Processing: Jean-Charles Cuillandre (CEA-Saclay), Giovanni Anselmi (ESA)

Globular Cluster NGC 6397 Brightness "Gap" Feature

This graph shows the brightness gap that scientists found using Euclid when they grouped the globular cluster NGC 6397’s stars by brightness and color. What they observed was a thin “gap” of expected but missing low-mass stars called red dwarfs. The observations fit well with their model prediction. This gap is thought to be linked to changes occurring within some stars’ interiors, giving astronomers a glimpse at processes happening inside stars even from thousands of light-years away. This is the first time the gap feature was discovered in a globular cluster. Credits Illustration: Massimo Griggio (STScI), Leah Hustak (STScI)

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Scientists from the Space Telescope Science Institute (STScI) in Baltimore, Maryland, sought to study one stellar subject and ended up finding something even more exciting.

Using data from the European Space Agency’s (ESA’s) Euclid space telescope and NASA’s Hubble Space Telescope, the team planned to analyze the motions of stars within an ancient collection of stars called a globular cluster. But what they found when they grouped the cluster’s stars by brightness and color as observed by Euclid was a thin “gap” of expected but missing low-mass stars called red dwarfs. This gap is thought to be linked to changes occurring within some stars’ interiors, giving astronomers a glimpse at processes happening inside stars even from thousands of light-years away.

This is the first time the gap feature was discovered in a globular cluster. “The discovery was serendipitous,” said STScI’s Andrea Bellini, one of the research paper’s primary authors. “We were not looking for the gap, but we found it.”

Understanding the Gap

The presence of this gap in relatively nearby stars was discovered in 2018 by scientists analyzing data from ESA’s Gaia observatory. That team plotted nearly 250,000 stars from the Gaia archive on a Hertzsprung-Russell (HR) diagram, one of the most important tools in stellar studies. This is the graph that astronomers use to classify stars and trace their life cycles.

On the HR diagram, stellar luminosities are plotted against their colors, which serve as a proxy for their temperatures. The positions of stars on the diagram reveal specific stellar evolutionary stages. Perhaps the most distinctive feature is the swath of main-sequence stars that cuts diagonally across the diagram.

As the precision and sensitivity of modern astronomy improves, astronomers can place stars more accurately on the plot. The Gaia data revealed a previously unknown feature — a narrow, diagonal slice of mostly missing stars through the main sequence in the middle of the red dwarf region.

So what causes this gap? It appears that in some red dwarf stars, fuel built up in their centers can trigger an energy burst that results in structural instability in a star’s interior. Between 0.34 and 0.36 times the mass of the Sun, red dwarfs undergo small variations that change their size, brightness, and temperature. Because only a small number of stars are undergoing these changes, there is a dearth of red dwarfs with these specific brightnesses. This is reflected in the HR diagram as a gap.

Enabling More Accurate Distance Estimates

In the Gaia case, stars were at a multitude of different distances and had varying ages, histories, and chemical compositions. In contrast, stars within a globular cluster share a common history, having formed in the same environment at roughly the same point in cosmic time.

“Globular clusters are the ideal laboratories to study stellar evolution and stellar populations,” said STScI’s Massimo Griggio, the principal author on the research paper. “In this globular cluster, the stars are basically at the same distance and have approximately the same age.”

The STScI team used Euclid to study NGC 6397, one of the closest globular clusters to Earth. Located approximately 8,000 light-years away in the southern constellation Ara, it contains hundreds of thousands of stars and is estimated to be 13.4 billion years old.

“Because we can determine the brightness where the gap is with very high precision and know for what stellar masses it occurs, we can use this information to estimate the cluster’s distance,” said STScI’s Russell Ryan, another of the primary researchers.

Gaia found the gap while viewing stars in the local neighborhood, which are typically younger than stars in globular clusters. Now, the Euclid team found the exact same process happening in more distant stellar interiors.

Hubble Tools Pave the Way for New Discoveries

This finding would not have been possible without the software and techniques originally developed at STScI for NASA’s Hubble Space Telescope over more than two decades. The team used these tools, which were pioneered primarily by STScI’s Jay Anderson, to make the high-precision measurements needed to detect this feature in the extremely crowded environment of a globular cluster. Though Hubble’s field of view is much, much smaller, when these tools were coupled with Euclid’s panoramic view, the gap clearly appeared.

“With these tools, we show that we can push the limits of Euclid, and in the future, the Roman Space Telescope, across a wide field of view,” said team member Mattia Libralato, formerly of STScI and currently with the Italian National Institute for Astrophysics (INAF) in Padova, Italy.  “Further investigations with Euclid and, in the future, Roman, will hopefully allow us to better characterize this feature also in other globular clusters.”

The team’s results published today in Astronomy & Astrophysics.

The Space Telescope Science Institute is expanding the frontiers of space astronomy by hosting the science operations center of the Hubble Space Telescope, the science and mission operations centers for the James Webb Space Telescope, and the science operations center for the Nancy Grace Roman Space Telescope. STScI also houses the Barbara A. Mikulski Archive for Space Telescopes (MAST) which is a NASA-funded project to support and provide to the astronomical community a variety of astronomical data archives, and is the data repository for the Hubble, Webb, Roman, Kepler, K2, TESS missions and more. STScI is operated by the Association of Universities for Research in Astronomy in Washington, D.C.

Source: Space Telescope Science Institute (STScI)/News

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Euclid: Early Release Observations – Internal kinematics and the convective-transition gap of NGC 6397

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Webb Narrows Atmospheric Possibilities for Earth-sized Exoplanet TRAPPIST-1 d

TRAPPIST-1 d (Artist’s Concept)

This artist’s concept depicts planet TRAPPIST-1 d passing in front of its turbulent star, with other members of the closely packed system shown in the background. The TRAPPIST-1 system is intriguing to scientists for a few reasons. Not only does the system have seven Earth-sized rocky worlds, but its star is a red dwarf, the most common type of star in the Milky Way galaxy. If an Earth-sized world can maintain an atmosphere here, and thus have the potential for liquid surface water, the chance of finding similar worlds throughout the galaxy is much higher. In studying the TRAPPIST-1 planets, scientists are determining the best methods for separating starlight from potential atmospheric signatures in data from NASA’s James Webb Space Telescope. The star TRAPPIST-1’s variability, with frequent flares, provides a challenging testing ground for these methods. Credits/Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

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The exoplanet TRAPPIST-1 d intrigues astronomers looking for possibly habitable worlds beyond our solar system because it is similar in size to Earth, rocky, and resides in an area around its star where liquid water on its surface is theoretically possible. But according to a new study using data from NASA’s James Webb Space Telescope, it does not have an Earth-like atmosphere.

“Ultimately, we want to know if something like the environment we enjoy on Earth can exist elsewhere, and under what conditions. While NASA’s James Webb Space Telescope is giving us the ability to explore this question in Earth-sized planets for the first time, at this point we can rule out TRAPPIST-1 d from a list of potential Earth twins or cousins,” said Caroline Piaulet-Ghorayeb of the University of Chicago and Trottier Institute for Research on Exoplanets (IREx) at Université de Montréal, lead author of the study published in The Astrophysical Journal.

Planet TRAPPIST-1 d

The TRAPPIST-1 system is located 40 light-years away and was revealed as the record-holder for most Earth-sized rocky planets around a single star in 2017, thanks to data from NASA’s retired Spitzer Space Telescope and other observatories. Due to that star being a dim, relatively cold red dwarf, the “habitable zone” or “Goldilocks zone” – where the planet’s temperature may be just right, such that liquid surface water is possible – lies much closer to the star than in our solar system. TRAPPIST-1 d, the third planet from the red dwarf star, lies on the cusp of that temperate zone, yet its distance to its star is only 2 percent of Earth’s distance from the Sun. TRAPPIST-1 d completes an entire orbit around its star, its year, in only four Earth days.

Webb’s NIRSpec (Near-Infrared Spectrograph) instrument did not detect molecules from TRAPPIST-1 d that are common in Earth’s atmosphere, like water, methane, or carbon dioxide. However, Piaulet-Ghorayeb outlined several possibilities for the exoplanet that remain open for follow-up study.

“There are a few potential reasons why we don’t detect an atmosphere around TRAPPIST-1 d. It could have an extremely thin atmosphere that is difficult to detect, somewhat like Mars. Alternatively, it could have very thick, high-altitude clouds that are blocking our detection of specific atmospheric signatures — something more like Venus. Or, it could be a barren rock, with no atmosphere at all,” Piaulet-Ghorayeb said.

The Star TRAPPIST-1

No matter what the case may be for TRAPPIST-1 d, it’s tough being a planet in orbit around a red dwarf star. TRAPPIST-1, the host star of the system, is known to be volatile, often releasing flares of high-energy radiation with the potential to strip off the atmospheres of its small planets, especially those orbiting most closely. Nevertheless, scientists are motivated to seek signs of atmospheres on the TRAPPIST-1 planets because red dwarf stars are the most common stars in our galaxy. If planets can hold on to an atmosphere here, under waves of harsh stellar radiation, they could, as the saying goes, make it anywhere.

“Webb’s sensitive infrared instruments are allowing us to delve into the atmospheres of these smaller, colder planets for the first time,” said Björn Benneke of IREx at Université de Montréal, a co-author of the study. “We’re really just getting started using Webb to look for atmospheres on Earth-sized planets, and to define the line between planets that can hold onto an atmosphere, and those that cannot.”

The Outer TRAPPIST-1 Planets

Webb observations of the outer TRAPPIST-1 planets are ongoing, which hold both potential and peril. On the one hand, Benneke said, planets e, f, g, and h may have better chances of having atmospheres because they are further away from the energetic eruptions of their host star. However, their distance and colder environment will make atmospheric signatures more difficult to detect, even with Webb’s infrared instruments.

“All hope is not lost for atmospheres around the TRAPPIST-1 planets,” Piaulet-Ghorayeb said. “While we didn’t find a big, bold atmospheric signature for planet d, there is still potential for the outer planets to be holding onto a lot of water and other atmospheric components.”

“As NASA leads the way in searching for life outside our solar system, one of the most important avenues we can pursue is understanding which planets retain their atmospheres, and why,” said Shawn Domagal-Goldman, acting director of the Astrophysics Division at NASA Headquarters in Washington. “NASA’s James Webb Space Telescope has pushed our capabilities for studying exoplanet atmospheres further than ever before, beyond extreme worlds to some rocky planets – allowing us to begin confirming theories about the kind of planets that may be potentially habitable. This important groundwork will position our next missions, like NASA’s Habitable Worlds Observatory, to answer a universal question: Are we alone?”

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

To learn more about Webb, visit: https://science.nasa.gov/webb

Source: NASA's James Webb Space Telescope/News

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Hannah Braun
Space Telescope Science Institute, Baltimore

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Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• The University of Montreal Press Release
• More about the TRAPPIST-1 system
• Changing views on the “habitable zone”

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NASA's Webb Lifts Veil on Common but Mysterious Type of Exoplanet

Hot Sub-Neptune Exoplanet Illustration
Credits/Illustration: NASA, ESA, CSA, Dani Player (STScI)

Hot Sub-Neptune Spectrum
Credits/Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

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Though they don’t orbit around our Sun, sub-Neptunes are the most common type of exoplanet, or planet outside our solar system, that have been observed in our galaxy. These small, gassy planets are shrouded in mystery…and often, a lot of haze. Now, by observing exoplanet TOI-421 b, NASA’s James Webb Space Telescope is helping scientists understand sub-Neptunes in a way that was not possible prior to the telescope’s launch.

“I had been waiting my entire career for Webb so that we could meaningfully characterize the atmospheres of these smaller planets,” said principal investigator Eliza Kempton of the University of Maryland, College Park. “By studying their atmospheres, we’re getting a better understanding of how sub-Neptunes formed and evolved, and part of that is understanding why they don't exist in our solar system.”

Small, Cool, Shrouded in Haze

The existence of sub-Neptunes was unexpected before they were discovered by NASA’s retired Kepler space telescope in the last decade. Now, astronomers are trying to understand where these planets came from and why are they so common.

Before Webb, scientists had very little information on them. While sub-Neptunes are a few times larger than Earth, they are still much smaller than gas-giant planets and typically cooler than hot Jupiters, making them much more challenging to observe than their gas-giant counterparts.

A key finding prior to Webb was that most sub-Neptune atmospheres had flat or featureless transmission spectra. This means that when scientists observed the spectrum of the planet as it passed in front of its host star, instead of seeing spectral features – the chemical fingerprints that would reveal the composition of the atmosphere – they saw only a flat-line spectrum. Astronomers concluded from all of those flat-line spectra that at least certain sub-Neptunes were probably very highly obscured by either clouds or hazes.

A Different Kind of Sub-Neptune?

“Why did we observe this planet, TOI-421 b? It's because we thought that maybe it wouldn't have hazes,” said Kempton. “And the reason is that there were some previous data that implied that maybe planets over a certain temperature range were less enshrouded by haze or clouds than others.”

That temperature threshold is about 1,070 degrees Fahrenheit. Below that, scientists hypothesized that a complex set of photochemical reactions would occur between sunlight and methane gas, and that would trigger the haze. But hotter planets shouldn't have methane and therefore perhaps shouldn't have haze.

The temperature of TOI-421 b is about 1,340 degrees Fahrenheit, well above the presumed threshold. Without haze or clouds, researchers expected to see a clear atmosphere – and they did!

A Surprising Finding

“We saw spectral features that we attribute to various gases, and that allowed us to determine the composition of the atmosphere,” said the University of Maryland’s Brian Davenport, a third-year Ph.D. student who conducted the primary data analysis. “Whereas with many of the other sub-Neptunes that had been previously observed, we know their atmospheres are made of something, but they're being blocked by haze.”

The team found water vapor in the planet’s atmosphere, as well as tentative signatures of carbon monoxide and sulfur dioxide. Then there are molecules they didn’t detect, such as methane and carbon dioxide. From the data, they can also infer that a large amount of hydrogen is in TOI-421 b’s atmosphere.

The lightweight hydrogen atmosphere was the big surprise to the researchers. “We had recently wrapped our mind around the idea that those first few sub-Neptunes observed by Webb had heavy-molecule atmospheres, so that had become our expectation, and then we found the opposite,” said Kempton. This suggests TOI-421 b may have formed and evolved differently from the cooler sub-Neptunes observed previously.

Is TOI-421 b Unique?

The hydrogen-dominated atmosphere is also interesting because it mimics the composition of TOI-421 b's host star. “If you just took the same gas that made the host star, plopped it on top of a planet's atmosphere, and put it at the much cooler temperature of this planet, you would get the same combination of gases. That process is more in line with the giant planets in our solar system, and it is different from other sub-Neptunes that have been observed with Webb so far,” said Kempton.

Aside from being hotter than other sub-Neptunes previously observed with Webb, TOI-421 b orbits a Sun-like star. Most of the other sub-Neptunes that have been observed so far orbit smaller, cooler stars called red dwarfs.

Is TOI-421b emblematic of hot sub-Neptunes orbiting Sun-like stars, or is it just that exoplanets are very diverse? To find out, the researchers would like to observe more hot sub-Neptunes to determine if this is a unique case or a broader trend. They hope to gain insights into the formation and evolution of these common exoplanets.

“We've unlocked a new way to look at these sub-Neptunes,” said Davenport. “These high-temperature planets are amenable to characterization. So by looking at sub-Neptunes of this temperature, we're perhaps more likely to accelerate our ability to learn about these planets.”

The team’s findings appear May 5 in The Astrophysical Journal Letters.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

To learn more about Webb, visit:  https://science.nasa.gov/webb

Source: NASA's James Webb Space Telescope/News

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Space Telescope Science Institute, Baltimore

Hannah Braun
Space Telescope Science Institute, Baltimore

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Webb Rules Out Thick Carbon Dioxide Atmosphere for Rocky Exoplanet

Rocky Exoplanet TRAPPIST-1 c (Artist Concept)
Credit: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)
Science: Sebastian Zieba (MPI-A), Laura Kreidberg (MPI-A)

TRAPPIST-1 c Light Curve
Credit: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)
Science: Sebastian Zieba (MPI-A), Laura Kreidberg (MPI-A)

TRAPPIST-1 c Emission Spectra
Credit: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)
Science: Sebastian Zieba (MPI-A), Laura Kreidberg (MPI-A)

Release Images

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An international team of researchers has used NASA’s James Webb Space Telescope to calculate the amount of heat energy coming from the rocky exoplanet TRAPPIST-1 c. The result suggests that the planet’s atmosphere – if it exists at all – is extremely thin.

With a dayside temperature of roughly 380 kelvins (about 225 degrees Fahrenheit), TRAPPIST-1 c is now the coolest rocky exoplanet ever characterized based on thermal emission. The precision necessary for these measurements further demonstrates Webb’s utility in characterizing rocky exoplanets similar in size and temperature to those in our own solar system.

The result marks another step in determining whether planets orbiting small red dwarfs like TRAPPIST-1 – the most common type of star in the galaxy – can sustain atmospheres needed to support life as we know it.

“We want to know if rocky planets have atmospheres or not,” said Sebastian Zieba, a graduate student at the Max Planck Institute for Astronomy in Germany and first author on results being published today in Nature. “In the past, we could only really study planets with thick, hydrogen-rich atmospheres. With Webb we can finally start to search for atmospheres dominated by oxygen, nitrogen, and carbon dioxide.”

“TRAPPIST-1 c is interesting because it’s basically a Venus twin: It’s about the same size as Venus and receives a similar amount of radiation from its host star as Venus gets from the Sun,” explained co-author Laura Kreidberg, also from Max Planck. “We thought it could have a thick carbon dioxide atmosphere like Venus.”

TRAPPIST-1 c is one of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth. Although the planets are similar in size and mass to the inner, rocky planets in our own solar system, it is not clear whether they do in fact have similar atmospheres. During the first billion years of their lives, M dwarfs emit bright X-ray and ultraviolet radiation that can easily strip away a young planetary atmosphere. In addition, there may or may not have been enough water, carbon dioxide, and other volatiles available to make substantial atmospheres when the planets formed.

To address these questions, the team used MIRI (Webb’s Mid-Infrared Instrument) to observe the TRAPPIST-1 system on four separate occasions as the planet moved behind the star, a phenomenon known as a secondary eclipse. By comparing the brightness when the planet is behind the star (starlight only) to the brightness when the planet is beside the star (light from the star and planet combined) the team was able to calculate the amount of mid-infrared light with wavelengths of 15 microns given off by the dayside of the planet.

This method is the same as that used by another research team to determine that TRAPPIST-1 b, the innermost planet in the system, is probably devoid of any atmosphere.

The amount of mid-infrared light emitted by a planet is directly related to its temperature, which is in turn influenced by atmosphere. Carbon dioxide gas preferentially absorbs 15-micron light, making the planet appear dimmer at that wavelength. However, clouds can reflect light, making the planet appear brighter and masking the presence of carbon dioxide.

In addition, a substantial atmosphere of any composition will redistribute heat from the dayside to the nightside, causing the dayside temperature to be lower than it would be without an atmosphere. (Because TRAPPIST-1 c orbits so close to its star – about 1/50th the distance between Venus and the Sun – it is thought to be tidally locked, with one side in perpetual daylight and the other in endless darkness.)

Although these initial measurements do not provide definitive information about the nature of TRAPPIST-1 c, they do help narrow down the likely possibilities. “Our results are consistent with the planet being a bare rock with no atmosphere, or the planet having a really thin CO2 atmosphere (thinner than on Earth or even Mars) with no clouds,” said Zieba. “If the planet had a thick CO2 atmosphere, we would have observed a really shallow secondary eclipse, or none at all. This is because the CO2 would be absorbing all of the 15-micron light, so we wouldn’t detect any coming from the planet.”

The data also show that it is unlikely the planet is a true Venus analog with a thick CO2 atmosphere and sulfuric acid clouds.

The absence of a thick atmosphere suggests that the planet may have formed with relatively little water. If the cooler, more temperate TRAPPIST-1 planets formed under similar conditions, they too may have started with little of the water and other components necessary to make a planet habitable.

The sensitivity required to distinguish between various atmospheric scenarios on such a small planet so far away is truly remarkable. The decrease in brightness that Webb detected during the secondary eclipse was just 0.04 percent: equivalent to looking at a display of 10,000 tiny light bulbs and noticing that just four have gone out.

“It is extraordinary that we can measure this,” said Kreidberg. “There have been questions for decades now about whether rocky planets can keep atmospheres. Webb’s ability really brings us into a regime where we can start to compare exoplanet systems to our solar system in a way that we never have before.”

This research was conducted as part of Webb’s General Observers (GO) program 2304 , which is one of eight programs from Webb’s first year of science designed to help fully characterize the TRAPPIST-1 system. This coming year, researchers will conduct a follow-up investigation to observe the full orbits of TRAPPIST-1 b and TRAPPIST-1 c. This will make it possible to see how the temperatures change from the day to the night sides of the two planets and will provide further constraints on whether they have atmospheres or not.

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency), and CSA (Canadian Space Agency). MIRI was contributed by NASA and ESA, with the instrument designed and built by a consortium of nationally funded European Institutes (the MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona.

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Space Telescope Science Institute, Baltimore, Maryland

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• The science paper by S. Zieba et al.

Source: NASA's James Webb Space Telescope/News

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The Case of the Missing Jupiters: Gas Giant Planets are a No-Show around Small Red Stars

Artist conception of a Jupiter-like planet around a small red dwarf star. A new study shows that these systems are rare.
Credit: Melissa Weiss, CfA. Hi-res Image

The dearth of Jupiters suggests that potentially habitable, Earth-like planets might not readily emerge around red dwarf stars.

Cambridge, Mass. – Astronomers have revealed that the smallest and most common kinds of stars in the universe, called red dwarfs, very rarely host big, Jupiter-like planets. This absence of Jupiter analogs could have major impacts on the development of Earth-like planets around red dwarfs and in the search for worlds capable of supporting alien life.

Befitting its distinction as the locally largest planet, Jupiter has played a dominant role in the evolution of our Solar System. Scientists think Jupiter ultimately set the stage for Earth becoming habitable, influencing our world's formation, size, and composition. Thus, the lack of hulking gas giants in red dwarf planetary systems suggests that any resident rocky worlds may not have evolved into particularly Earthly, life-friendly places.

"We have shown that the least massive stars don't have Jupiters, meaning Jupiter-mass planets that receive similar amounts of starlight as Jupiter receives from our Sun," says Emily Pass, a researcher at the Center for Astrophysics | Harvard & Smithsonian  (CfA) and lead author of a new study to be published in The Astronomical Journal conveying the results. "While this discovery suggests truly Earth-like planets might be in short supply around red dwarfs, there still is so much we don't yet know about these systems, so we must keep our minds open."

The findings have additional importance because many red dwarfs are among our nearest cosmic neighbors. That proximity, coupled with the fact that cool, dim red dwarfs do not overwhelm their planets in glare, has established them as the most amenable targets for investigating the atmospheres of exoplanets—a key research priority now and for the next few decades.

"The pipsqueak red dwarf stars that we looked at for this study are our most immediate cosmic neighbors, which means their planets are ideal candidates for detailed examination by the James Webb Space Telescope," says study co-author David Charbonneau, a professor at Harvard University and a member of the Center for Astrophysics | Harvard & Smithsonian. "But now that we have very strong evidence of cold gas giants like Jupiter and Saturn being exceedingly rare around these stars, the temperate rocky planets we end up studying could diverge greatly from our terrestrial expectations."

To gauge the frequency of Jupiter planets, Pass and colleagues examined an unprecedently large population of 200 small red dwarfs, each only 10% to 30% of the mass of the Sun. Such tiny red dwarfs are the cosmic norm, vastly outnumbering Sun-sized stars in our galaxy. The observations were gathered between 2016 and 2022 primarily from the Fred Lawrence Whipple Observatory, located in Arizona, as well as the Cerro Tololo Inter-American Observatory in Chile.

The researchers relied on the radial-velocity technique to suss out any large exoplanets in their stellar dataset. As planets orbit their host stars, the bodies' interacting gravities cause the stars to "wobble" ever so slightly, an effect discernible in detailed starlight readouts.

Across the entire sample of stars, the researchers did not detect a single Jupiter-equivalent planet. Based on inherent statistical uncertainties, the researchers can safely say that Jupiters occur in less than 2% of low-mass red dwarf planetary systems.

The findings starkly contrast with similar surveys of mid-sized stars like our Sun, which commonly sport massive planets at Jupiter-like distances. The tremendous masses of these worlds—Jupiter alone contains more mass than all the other planets put together—translates to tremendous gravity, and tremendous gravity translates to far-reaching influence on other celestial bodies.

"In the Solar System, Jupiter is the bully," says Charbonneau. "A lot of what makes Earth the way it is traces back to what Jupiter was doing in the early phases of the Solar System's history."

Among the most significant events is Jupiter's migration in the first few hundred million years of the Solar System's existence. After formation in the far reaches of the Solar System, Jupiter, along with the other outer planets, is theorized to have moved inward toward the Sun. In the process, hefty Jupiter's gravity scattered loads of ice-rich cometary bodies onto collision courses with the four rocky worlds in the inner Solar System.

As a large number of those icy bodies impacted on our young planet, they delivered copious amounts of water, potentially along with organic (carbon-containing) molecules. The waters pooled on our world's surface, creating the oceans, within which organic molecules are thought to have gone on to mix together for millions of years. Eventually, the molecules evolved complexity and began self-replicating, having transitioned to what we refer to as life.

Sans Jupiter, these conditions might not have come to be, and the journey to life might never have gotten underway.

Although the new findings do suggest that the circumstances that led to at least one world in our Solar System becoming habitable are not likely to be matched in solar systems hosted by tiny red stars, the door is far from closed when it comes to extraterrestrial life in these systems.

"We don't think that the absence of Jupiters necessarily means rocky planets around red dwarfs are uninhabitable," says Charbonneau.

The conspicuous absence of Jupiter-esque mega-planets means more raw material should be available for building up smaller, rocky bodies, because this material wasn't incorporated into Jupiter-like worlds. Indeed, other studies have shown that red dwarfs' solid worlds tend to be correspondingly larger in size than those around Sunlike stars.

Relatedly, rocky planets seem to form in greater numbers around red dwarfs versus Sunlike stars. For instance, the famous TRAPPIST-1 planet system packs seven rocky worlds into orbits much closer to the host red dwarf star than Mercury is to our Sun.

In a word, red dwarf planetary systems are just different from ours. And that difference could perhaps lead to rich habitability possibilities we have not yet realized.

"Our work implies that rocky worlds with masses similar to Earth and orbiting red dwarfs were born and raised in a very different environment from that of our own planet," says Pass. "We're excited to see what exactly that means as we forge ahead in remotely exploring the planets in our cosmic neighborhood."

Other members of the research team include Jennifer Winters (CfA and Williams College), Jonathan Irwin (CfA and the University of Cambridge, UK), and David Latham, Perry Berlind, Michael Calkins, Gilbert Esquerdo, and Jessica Mink (CfA).

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The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask—and ultimately answer—humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.

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Hubble Follows Shadow Play Around Planet-Forming Disk

Concentric Gas-and-Dust Disks Around Star TW Hydrae (Artist's Concept)
Credits: Artwork: NASA, AURA/STScI for ESA, Leah Hustak (STScI)

TW Hydrae Disk
Credits: Image: NASA, ESA, STScI, John Debes (AURA/STScI for ESA)
Image Processing: Joseph DePasquale (STScI)

Releasse Images

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The young star TW Hydrae is playing "shadow puppets" with scientists observing it with NASA's Hubble Space Telescope.

In 2017, astronomers reported discovering a shadow sweeping across the face of a vast pancake-shaped gas-and-dust disk surrounding the red dwarf star. The shadow isn't from a planet, but from an inner disk slightly inclined relative to the much larger outer disk – causing it to cast a shadow. One explanation is that an unseen planet's gravity is pulling dust and gas into the planet's inclined orbit.

Now, a second shadow – playing a game of peek-a-boo – has emerged in just a few years between observations stored in Hubble's MAST archive. This could be from yet another disk nestled inside the system. The two disks are likely evidence of a pair of planets under construction.

TW Hydrae is less than 10 million years old and resides about 200 light-years away. In its infancy, our solar system may have resembled the TW Hydrae system, some 4.6 billion years ago. Because the TW Hydrae system is tilted nearly face-on to our view from Earth, it is an optimum target for getting a bull's-eye-view of a planetary construction yard.

The second shadow was discovered in observations obtained on June 6, 2021, as part of a multi-year program designed to track the shadows in circumstellar disks. John Debes of AURA/STScI for the European Space Agency at the Space Telescope Science Institute in Baltimore, Maryland, compared the TW Hydrae disk to Hubble observations made several years ago.

"We found out that the shadow had done something completely different," said Debes, who is principal investigator and lead author of the study published in The Astrophysical Journal. "When I first looked at the data, I thought something had gone wrong with the observation because it wasn't what I was expecting. I was flummoxed at first, and all my collaborators were like: what is going on? We really had to scratch our heads and it took us a while to actually figure out an explanation."

The best solution the team came up with is that there are two misaligned disks casting shadows. They were so close to each other in the earlier observation they were missed. Over time they've now separated and split into two shadows. "We've never really seen this before on a protoplanetary disk. It makes the system much more complex than we originally thought," he said.

The simplest explanation is that the misaligned disks are likely caused by the gravitational pull of two planets in slightly different orbital planes. Hubble is piecing together a holistic view of the architecture of the system.

The disks may be proxies for planets that are lapping each other as they whirl around the star. It's sort of like spinning two vinyl phonograph records at slightly different speeds. Sometimes labels will match up but then one gets ahead of the other.

"It does suggest that the two planets have to be fairly close to each other. If one was moving much faster than the other, this would have been noticed in earlier observations. It's like two race cars that are close to each other, but one slowly overtakes and laps the other," said Debes.

The suspected planets are located in a region roughly the distance of Jupiter from our Sun. And, the shadows complete one rotation around the star about every 15 years – the orbital period that would be expected at that distance from the star.

Also, these two inner disks are inclined about five to seven degrees relative to the plane of the outer disk. This is comparable to the range of orbital inclinations inside our solar system. "This is right in line with typical solar system style architecture," said Debes.

The outer disk that the shadows are falling on may extend as far as several times the radius of our solar system's Kuiper belt. This larger disk has a curious gap at twice Pluto's average distance from the Sun. This might be evidence for a third planet in the system.

Any inner planets would be difficult to detect because their light would be lost in the glare of the star. Also, dust in the system would dim their reflected light. ESA's Gaia space observatory may be able to measure a wobble in the star if Jupiter-mass planets are tugging on it, but this would take years given the long orbital periods.

The TW Hydrae data are from Hubble's Space Telescope Imaging Spectrograph. The James Webb Space Telescope's infrared vision may also be able to show the shadows in more detail.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

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About This Release

Credits

Media Contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Science Contact:Contact: John Debes
AURA/STScI for the European Space Agency, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents:

• Science Paper: The science paper by J. Debes, et al. (ApJ), PDF (1.94 MB)
• NASA's Hubble Portal
• ESAHubble.org's Release
• University of Warwick's Release
• Rochester Institute of Technology's Release
• Carnegie Institute for Science's Release
• George Mason University's Release
• University of Leicester's Release

Source: HubbleSite/News

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Webb Finds Water Vapor, But From a Rocky Planet or Its Star?

Exoplanet GJ 486 b (Artist Concept)
Credits: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI), Leah Hustak (STScI)

Exoplanet GJ 486 b (Transmission Spectrum)
Credits: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

Science: Sarah E. Moran (University of Arizona), Kevin B. Stevenson (APL), Ryan MacDonald (University of Michigan), Jacob A. Lustig-Yaeger (APL)

Release Images

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The most common stars in the universe are red dwarf stars, which means that rocky exoplanets are most likely to be found orbiting such a star. Red dwarf stars are cool, so a planet has to hug it in a tight orbit to stay warm enough to potentially host liquid water (meaning it lies in the habitable zone). Such stars are also active, particularly when they are young, releasing ultraviolet and X-ray radiation that could destroy planetary atmospheres. As a result, one important open question in astronomy is whether a rocky planet could maintain, or reestablish, an atmosphere in such a harsh environment.

To help answer that question, astronomers used NASA’s James Webb Space Telescope to study a rocky exoplanet known as GJ 486 b. It is too close to its star to be within the habitable zone, with a surface temperature of about 800 degrees Fahrenheit (430 degrees Celsius). And yet, their observations using Webb’s Near-Infrared Spectrograph (NIRSpec) show hints of water vapor. If the water vapor is associated with the planet, that would indicate that it has an atmosphere despite its scorching temperature and close proximity to its star. Water vapor has been seen on gaseous exoplanets before, but to date no atmosphere has been definitively detected around a rocky exoplanet. However, the team cautions that the water vapor could be on the star itself – specifically, in cool starspots – and not from the planet at all.

“We see a signal and it’s almost certainly due to water. But we can’t tell yet if that water is part of the planet’s atmosphere, meaning the planet has an atmosphere, or if we’re just seeing a water signature coming from the star,” said Sarah Moran of the University of Arizona in Tucson, lead author of the study.

“Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science. But we must be careful and make sure that the star is not the culprit,” added Kevin Stevenson of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, principal investigator on the program.

GJ 486 b is about 30% larger than the Earth and three times as massive, which means it is a rocky world with stronger gravity than Earth. It orbits a red dwarf star in just under 1.5 Earth days. It is expected to be tidally locked, with a permanent day side and a permanent night side.

GJ 486 b transits its star, crossing in front of the star from our point of view. If it has an atmosphere, then when it transits starlight would filter through those gasses, imprinting fingerprints in the light that allow astronomers to decode its composition through a technique called transmission spectroscopy.

The team observed two transits, each lasting about an hour. They then used three different methods to analyze the resulting data. The results from all three are consistent in that they show a mostly flat spectrum with an intriguing rise at the shortest infrared wavelengths. The team ran computer models considering a number of different molecules, and concluded that the most likely source of the signal was water vapor.

While the water vapor could potentially indicate the presence of an atmosphere on GJ 486 b, an equally plausible explanation is water vapor from the star. Surprisingly, even in our own Sun, water vapor can sometimes exist in sunspots because these spots are very cool compared to the surrounding surface of the star. GJ 486 b’s host star is much cooler than the Sun, so even more water vapor would concentrate within its starspots. As a result, it could create a signal that mimics a planetary atmosphere.

“We didn’t observe evidence of the planet crossing any starspots during the transits. But that doesn’t mean that there aren’t spots elsewhere on the star. And that’s exactly the physical scenario that would imprint this water signal into the data and could wind up looking like a planetary atmosphere,” explained Ryan MacDonald of the University of Michigan in Ann Arbor, one of the study’s co-authors.

A water vapor atmosphere would be expected to gradually erode due to stellar heating and irradiation. As a result, if an atmosphere is present, it would likely have to be constantly replenished by volcanoes ejecting steam from the planet’s interior. If the water is indeed in the planet’s atmosphere, additional observations are needed to narrow down how much water is present.

Future Webb observations may shed more light on this system. An upcoming Webb program will use the Mid-Infrared Instrument (MIRI) to observe the planet’s day side. If the planet has no atmosphere, or only a thin atmosphere, then the hottest part of the day side is expected to be directly under the star. However, if the hottest point is shifted, that would indicate an atmosphere that can circulate heat.

Ultimately, observations at shorter infrared wavelengths by another Webb instrument, the Near-Infrared Imager and Slitless Spectrograph (NIRISS), will be needed to differentiate between the planetary atmosphere and starspot scenarios.

“It’s joining multiple instruments together that will really pin down whether or not this planet has an atmosphere,” said Stevenson.

The study is accepted for publication in The Astrophysical Journal Letters.

The James Webb Space Telescope is the world’s premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

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About This Release:

Credits:

Media Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Sarah E. Moran (University of Arizona), Kevin B. Stevenson (APL), Ryan MacDonald (University of Michigan), Jacob A. Lustig-Yaeger (APL)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents:

Science Paper: "High Tide or Rip-Tide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ 486b from JWST Observations", PDF (4.74 MB)

Source:NASA's James Webb Space Telescope/News

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Super-Earth Skimming Habitable Zone of Red Dwarf

Schematic diagram of the newly discovered Ross 508 planetary system. The green region represents the habitable zone where liquid water can exist on the planetary surface. The planetary orbit is shown as a blue line. Ross 508 b skims the inner edge of the habitable zone (solid line), possibly crossing into the habitable zone for part of the orbit (dashed line). (Credit: Astrobiology Center) Original size (100KB) 

A super-Earth planet has been found near the habitable zone of a red dwarf star only 37 light-years from the Earth. This is the first discovery by a new instrument on the Subaru Telescope and offers a chance to investigate the possibility of life on planets around nearby stars. With such a successful first result, we can expect that the Subaru Telescope will discover more, potentially even better, candidates for habitable planets around red dwarfs.

Red dwarfs, stars smaller than the Sun, account for three-quarters of the stars in the Milky Way Galaxy, and are abundant in the neighborhood around the Sun. As such, they are important targets in the search for nearby extra-solar planets and extraterrestrial life. But red dwarfs are cool and don’t emit much visible light compared to other types of stars, making it difficult to study them.

In the infrared wavelengths red dwarfs are brighter. So the Astrobiology Center in Japan developed an infrared observational instrument mounted on the Subaru Telescope to search for signs of planets around red dwarf stars. The instrument is called IRD for Infrared Doppler, the observational method used in this search.

The first fruits of this search are signs of a super-Earth four times the mass of the Earth circling the star Ross 508, located 37 light-years away in the constellation Serpens. This planet, Ross 508 b, has a year of only 11 Earth-days, and lies at the inner edge of the habitable zone around its host star. Interestingly, there are indications that the orbit is elliptical, which would mean that for part of the orbit the planet would be in the habitable zone, the region where conditions would be right for liquid water to exist on the surface of the planet. Whether or not there is actually water or life are questions of further study.

To have the very first planet discovered by this new method be so tantalizingly close to the habitable zone seems too good to be true and bodes well for future discoveries. Bun’ei Sato, a Professor at the Tokyo Institute of Technology and the principal investigator in this search comments, “It has been 14 years since the start of IRD’s development. We have continued our development and research with the hope of finding a planet exactly like Ross 508 b.”

These results appeared as Harakawa et al. “A Super-Earth Orbiting Near the Inner Edge of the Habitable Zone around the M4.5-dwarf Ross 508” in Publication of the Astronomical Society of Japan on June 30, 2022.

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Related Links

• Can a Super-Earth around a Low-Mass Star Harbor Life? (Subaru Telescope)
• Can a Super-Earth around a Low-Mass Star Harbor Life? (Astrobiology Center)
• New IR Instrument Searches for Habitable Planets (July 2, 2018)

Source: National Astronomical Observatory of Japan (NAOJ)/News

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CU Boulder scientists bring stellar flares into clearer focus

At the top of the page: An artist’s impression of a superflaring star (NASA’s Goddard Space Flight Center). Above: This animation shows how a dip in the observed brightness of a star may indicate the presence of a planet passing in front of it, an occurrence known as a transit (NASA's Goddard Space Flight Center).

In work that has implications for the search for life elsewhere in the galaxy, scientists analyze data from 440 stellar flares and find them to be not just common and powerful, but also more complex than previously thought

Armed with a new statistical analysis of stellar flares on hundreds of distant stars, scientists are beginning to understand the likelihood that remote “exoplanets” might sustain life in our galaxy, research at the University of Colorado Boulder suggests.

The most-intense flares, which are more complex than previously observed, could have implications for the viability of life on nearby planets.

Ward Howard, a postdoctoral researcher who led the study, and Meredith MacGregor, assistant professor of astrophysical and planetary sciences at CU Boulder, conducted the first large-scale analysis of solar-flare data collected at 20-second intervals from NASA’s TESS mission. Their findings are soon to be published in The Astrophysical Journal.

TESS—the Transiting Exoplanet Survey Satellite—was launched in 2018 to search for planets outside of our solar system, including those that could support life.

The satellite detects those planets when they periodically block part of the light as they pass in front of their host stars, events called “transits.” The stars in question are M dwarf stars, which compose about 70% of the stars in our galaxy. Those stars are cooler and dimmer than Earth’s sun but are prone to explosive superflares—10 to 1,000 times larger than flares from our sun.

Superflares could destroy a nearby planet’s atmosphere, particularly because exoplanets in the “habitable zone” of these stars can be 20 times closer to their stars than we are to the sun.

“The sun is very well behaved,” Howard said. “Many of these red dwarf stars can emit flares 1,000 times larger than those from the sun, and you can only imagine what that might do to a planet or to life on the surface.”

The 20-second TESS data reveal the building blocks of the flare emission and informs how much radiation reaches the planets during the brief peaks of the flares.

By analyzing data from 440 large stellar flares from TESS, scientists are starting to “pull back the curtain” on questions of which exoplanets might have atmospheres that are conducive to life, and which would be “dead rocks,” Howard said.

Additionally, the new CU Boulder analysis of the flares shows the flares to be “super complicated, MacGregor said. “They have all sorts of weird structure in the light curves, which indicates that some of them are bursting multiple times.”

“We have historically had a very simple picture of stellar activity, where one loop breaks and we have one outburst of energy, and then it slowly dies away, and then we think about the frequency of that,” she continued. “That's the model that's been fed into everything we think about stars and their impact on planets, and it’s clearly just flat-out wrong.”

Although TESS’s primary mission is to detect exoplanets, the fact that TESS stares at certain parts of the sky for a month at a time also allows the instrument to detect stellar flares and superflares, which are rare and random events.

Solar and stellar flares result from entangled magnetic fields, and they release huge bursts of radiation and charged particles.

“Our sun does this, and we can get beautiful images where you see these loops of emission protruding out of the surface of the sun, and then they break and stream out into space,” MacGregor said. When those particles and radiation hit the Earth’s upper atmosphere, they can dissociate atmospheric molecules, causing the aurora borealis in northern latitudes and aurora australis in the southern.

“So we see beautiful lovely green lights,” MacGregor said. “What we're actually observing is the effect of our sun splitting apart molecules in our atmosphere and then the release of energy from that splitting of things like ozone and water.”

As originally deployed, TESS captured data every two minutes, a frequency sufficient to detect exoplanets but insufficient to gather detailed data on the incidence of stellar flares affecting those planets.

“It allows us to kind of have a statistical understanding of how often do certain things occur,” Howard said, adding that scientists have never before been able to determine how much radiation reaches planets during the peak of the superflares and how much complexity the flares have.

The James Webb Space Telescope, launched in December, is poised to further probe these questions, MacGregor and Howard said. In addition to seeking information about the earliest stages of the universe, it will look for atmospheres on exoplanets, aiming to determining what kind of atmospheres they have and whether they might support life.

“This field of astrobiology and exoplanet research is changing so quickly right now, that it makes it a really exciting area to work in,” MacGregor said.

By Clint Talbott

Source: University of Colorado Boulder (Colorado Arts and Sciences Magazine)

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NASA's Webb Will Seek Atmospheres around Potentially Habitable Exoplanets

This artist’s concept portrays the seven rocky exoplanets within the Trappist-1 system, located 40 light-years from Earth. Astronomers will observe these worlds with Webb in an effort to detect the first atmosphere of an Earth-sized planet beyond our solar system. Credits: NASA and JPL/Caltec. Release Images

This month marks the third anniversary of the discovery of a remarkable system of seven planets known as TRAPPIST-1. These seven rocky, Earth-size worlds orbit an ultra-cool star 39 light-years from Earth. Three of those planets are in the habitable zone, meaning they are at the right orbital distance to be warm enough for liquid water to exist on their surfaces. After its 2021 launch, NASA’s James Webb Space Telescope will observe those worlds with the goal of making the first detailed near-infrared study of the atmosphere of a habitable-zone planet.

To find signs of an atmosphere, astronomers will use a technique called transmission spectroscopy. They observe the host star while the planet is crossing the face of the star, known as a transit. The light of the star filters through the planet’s atmosphere, which absorbs some of the starlight and leaves telltale fingerprints in the star’s spectrum.

Finding an atmosphere around a rocky exoplanet — the word scientists use for planets beyond our solar system — won’t be easy. Their atmospheres are more compact than those of gas giants, while their smaller size means they intercept less of the star’s light. TRAPPIST-1 is one of the best available targets for Webb since the star itself is also quite small, meaning the planets’ size relative to the star is larger.

“The atmospheres are harder to detect but the reward is higher. It would be very exciting to make the first detection of an atmosphere on an Earth-sized planet,” said David Lafrenière of the University of Montreal, principal investigator on one of the teams examining TRAPPIST-1.

Red dwarf stars like TRAPPIST-1 tend to have violent outbursts that could make the TRAPPIST-1 planets inhospitable. But determining whether they have atmospheres, and if so, what they're made of, is the next step to finding out whether life as we know it could survive on these distant worlds.

A coordinated effort

More than one team of astronomers will study the TRAPPIST-1 system with Webb. They plan to use a variety of instruments and observing modes to tease out as many details as they can for each planet in the system.

“It’s a coordinated effort because no one team could do everything we wanted to do with the TRAPPIST-1 system. The level of cooperation has been really spectacular,” explained Nikole Lewis of Cornell University, the principal investigator on one of the teams.

“With seven planets to choose from, we can each have a piece of the cake,” added Lafrenière.

Lafrenière’s program will target TRAPPIST-1d and -1f in an effort to not only detect an atmosphere but determine its basic composition. They expect to be able to distinguish between an atmosphere dominated by water vapor, or one composed mainly of nitrogen (like Earth) or carbon dioxide (like Mars and Venus).

Lewis’s program will observe TRAPPIST-1e with similar goals. TRAPPIST-1e is one of the planets beyond our solar system that has the most in common with Earth in terms of its density and the amount of radiation that it receives from its star. That makes it a great candidate for habitability — but scientists need to know more to find out.

A broad variety of planets

While the TRAPPIST-1 planets hold particular appeal from a standpoint of potential habitability, Lafrenière’s program will target a variety of planets — from rocky to mini-Neptunes to Jupiter-sized gas giants — at a variety of distances from their stars. The goal is to learn more about how, and where, these planets form.

In particular, astronomers continue to debate how gaseous planets can be found very close to their stars. Most believe that such a planet must have formed farther out in the protoplanetary disk — the disk around a star where planets are born — since more material is available far from the star, and then migrated inward. However, other scientists theorize that even large gas giants can form relatively close to their star.

“Also, maybe they formed farther out, but how much farther out?” asked Lewis.

To help inform the debate, astronomers will look at the ratio of carbon to oxygen in an assortment of exoplanets. This ratio can serve as a tracer of where a planet formed, because it varies with the distance from the star.

Weather maps

In addition to examining planets using transmission spectroscopy, the teams will also employ a technique known as a phase curve. This involves observing a planet over the course of an entire orbit, which is only practical for the hottest worlds with the shortest orbital periods.

A planet circling its star very close becomes tidally locked, meaning that it always shows the same face to the star, as the Moon does to Earth. As a result, distant observers watching the planet will see it go through various phases, since different sides of the planet are visible at different points in its orbit.

By measuring the planet at various times, astronomers can build up a map of the atmospheric temperature as a function of longitude. This technique was pioneered by NASA’s Spitzer Space Telescope, which made the first “weather map” of an exoplanet in 2007.

In addition, by observing the planet’s own heat emission, astronomers can model the atmosphere’s vertical structure.

“With a phase curve, we can build a complete 3D model of a planet’s atmosphere,” explained Lafrenière.

This work is being conducted as part of a Webb Guaranteed Time Observations (GTO) program. This program is designed to reward scientists who helped develop the key hardware and software components or technical and interdisciplinary knowledge for the observatory.

The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Source: NASA's James Webb Space Telescope/News

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Mini-Flares Potentially Jeopardize Habitability of Planets Circling Red Dwarf Stars

Flaring Red Dwarf Star (Artist's Illustration)

Credit: NASA, ESA, and G. Bacon (STScI)

 Release image

Cool dwarf stars are hot targets for exoplanet hunting right now. The discoveries of planets in the habitable zones of the TRAPPIST-1 and LHS 1140 systems, for example, suggest that Earth-sized worlds might circle billions of red dwarf stars, the most common type of star in our galaxy. But, like our own sun, many of these stars erupt with intense flares. Are red dwarfs really as friendly to life as they appear, or do these flares make the surfaces of any orbiting planets inhospitable?

To address this question, a team of scientists has combed 10 years of ultraviolet observations by the Galaxy Evolution Explorer (GALEX) spacecraft looking for rapid increases in the brightnesses of stars due to flares. Flares emit radiation across a wide swath of wavelengths, with a significant fraction of their total energy released in the ultraviolet bands where GALEX observed. At the same time, the red dwarfs from which the flares arise are relatively dim in the ultraviolet. This contrast, combined with the time resolution of the GALEX detectors, allowed the team to measure events with less total energy than many previously detected flares. This is important because, although individually less energetic and therefore less hostile to life, smaller flares might be much more frequent and add up over time to produce an inhospitable environment.

“What if planets are constantly bathed by these smaller, but still significant, flares?” asked Scott Fleming of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “There could be a cumulative effect.”

To detect and accurately measure these flares, the team had to slice the GALEX data into very high time resolution. From images with exposure times of nearly half an hour, the team was able to reveal stellar variations lasting just seconds.

First author Chase Million of Million Concepts in State College, Pennsylvania, led a project called gPhoton that reprocessed more than 100 terabytes of GALEX data held at the Mikulski Archive for Space Telescopes (MAST), located at STScI. The team then used custom software developed by Million and Clara Brasseur (STScI) to search several hundred red dwarf stars and detected dozens of flares.

“We have found dwarf star flares in the whole range that we expected GALEX to be sensitive to, from itty bitty baby flares that last a few seconds, to monster flares that make a star hundreds of times brighter for a few minutes,” said Million.

The flares GALEX detected are similar in strength to flares produced by our own sun. However, because a planet would have to orbit much closer to a cool, red dwarf star to maintain a temperature friendly to life as we know it, such planets would be subjected to more of a flare’s energy than Earth.

Large flares can strip away a planet’s atmosphere. Strong ultraviolet light from flares that penetrates to a planet’s surface could damage organisms or prevent life from arising.

Currently, team members Rachel Osten (STScI) and Brasseur are examining stars observed by both the GALEX and Kepler missions to look for similar flares. The team expects to eventually find hundreds of thousands of flares hidden in the GALEX data.

"These results show the value of a survey mission like GALEX, which was instigated to study the evolution of galaxies across cosmic time and is now having an impact on the study of nearby habitable planets," said Don Neill, research scientist at Caltech in Pasadena, California, who was part of the GALEX collaboration. "We did not anticipate that GALEX would be used for exoplanets when the mission was designed."

New and powerful instruments like the James Webb Space Telescope, scheduled for launch in 2018, ultimately will be needed to study atmospheres of planets orbiting nearby red dwarf stars and search for signs of life. But as researchers pose new questions about the cosmos, archives of data from past projects and missions, like those held at MAST, continue to produce exciting new scientific results.

These results were presented in a press conference at a meeting of the American Astronomical Society in Austin, Texas.

The GALEX mission, which ended in 2013 after more than a decade of scanning the skies in ultraviolet light, was led by scientists at Caltech. NASA's Jet Propulsion Laboratory, also in Pasadena, California, managed the mission and built the science instrument. JPL is managed by Caltech for NASA.

The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble Space Telescope science operations and is the mission and science operations center for the James Webb Space Telescope. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

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Contacts

Christine Pulliam / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4366 / 410-338-4514
cpulliam@stsci.edu / villard@stsci.edu

Chase Million
Million Concepts, State College, Pennsylvania
765-914-5336
chase.million@gmail.com

Source: HubbleSite