Month: December 2017

Two Super-Earths Around Red Dwarf K2-18

New research using data collected by the European Southern Observatory (ESO) has revealed that a little-known exoplanet called K2-18b could well be a scaled-up version of Earth.

Just as exciting, the same researchers also discovered for the first time that the planet has a neighbor.

“Being able to measure the mass and density of K2-18b was tremendous, but to discover a new exoplanet was lucky and equally exciting,” says lead author Ryan Cloutier, a PhD student in U of T Scarborough’s Centre for Planet Science, U of T’s Department of Astronomy and Astrophysics, and Université de Montréal Institute for research on exoplanets (iREx).

Both planets orbit K2-18, a red-dwarf star located about 111 light years away in the constellation Leo. When the planet K2-18b was first discovered in 2015, it was found to be orbiting within the star’s habitable zone, making it an ideal candidate to have liquid surface water, a key element in harbouring conditions for life as we know it.

The data set used by the researchers came from the High Accuracy Radial Velocity Planet Searcher (HARPS) using the ESO’s 3.6m telescope at La Silla Observatory, in Chile. HARPS allows for measurements of radial velocities of stars, which can be affected by the presence of nearby planets, to be taken with the highest accuracy currently available. The instrument makes it possible to detect very small planets orbiting those stars.

In order to figure out whether K2-18b was a scaled-up version of Earth (mostly rock), or a scaled-down version of Neptune (mostly gas), researchers had to first figure out the planet’s mass, using radial velocity measurements taken with HARPS.

“If you can get the mass and radius, you can measure the bulk density of the planet and that can tell you what the bulk of the planet is made of,” says Cloutier.

After using a machine-learning approach to figure out the mass measurement, Cloutier and his team were able to determine the planet is either a mostly rocky planet with a small gaseous atmosphere — like Earth, but bigger — or a mostly water planet with a thick layer of ice on top of it.

“With the current data, we can’t distinguish between those two possibilities,” he says. “But with the James Webb Space Telescope (JWST) we can probe the atmosphere and see whether it has an extensive atmosphere or it’s a planet covered in water.”

The JWST, which will be launched in 2019, will be instrumental in collecting a range of data for studying the solar system, early universe and exoplanets.

“There’s a lot of demand to use this telescope, so you have to be meticulous in choosing which exoplanets to look at,” says René Doyon, a co-author on the paper who is also the principal investigator for NIRISS, the Canadian Space Agency instrument on board JWST.

“K2-18b is now one of the best targets for atmospheric study, it’s going to the near top of the list.”

It was while looking through the data of K2-18b that Cloutier noticed something unusual. In addition to a signal occurring every 39 days from the rotation of K2-18, and one taking place every 33 days from the orbit of K2-18b, he noticed a different signal occurring every nine days.

“When we first threw the data on the table we were trying to figure out what it was. You have to ensure the signal isn’t just noise, and you need to do careful analysis to verify it, but seeing that initial signal was a good indication there was another planet,” Cloutier says.

Cloutier collaborated with an international team of researchers from the Observatoire Astronomique de l’Universite? de Gene?ve, the Institute for research on exoplanets (iREx), Universite? de Grenoble, U of T Scarborough, and Universidade do Porto.

While the newly described planet K2-18c is closer to its star, and probably too hot to be in the habitable zone, like K2-18b it also appears to be a Super-Earth meaning it has a mass similar to Earth. Cloutier, who had set the goal of discovering a new exoplanet within his PhD, considers himself very lucky to have discovered it in this dataset.

“It wasn’t a eureka moment because we still had to go through a checklist of things to do in order to verify the data. Once all the boxes were checked it sunk in that, wow, this actually is a planet.”

Submarine Volcanoes Add To Ocean Soundscape

Most volcanoes erupt beneath the ocean, but scientists know little about them compared to what they know about volcanoes that eject their lava on dry land. Gabrielle Tepp of the Alaska Volcano Observatory and the U.S. Geological Survey thinks that with improved monitoring, scientists can learn more about these submarine eruptions, which threaten travel and alter the ocean soundscape.

During the 174th Meeting of the Acoustical Society of America, held Dec. 4-8, 2017, in New Orleans, Louisiana, Tepp will discuss the challenges and benefits of remote monitoring and what it can teach us about submarine volcanoes.

“It’s very difficult to study underwater volcanoes because it’s hard to put instruments in the water, especially long-term,” Tepp said.

Depending on the size and depth of an underwater eruption, gas and ash may never break the ocean surface, or the gas and ash could create a volcanic plume with the potential to interfere with air travel. “The ocean is a big place so it’s pretty unlikely that you’re going to have a situation where a ship haphazardly wanders over an eruption, but there are a few that have come close,” Tepp said. These unpredictable eruptions may also create a floating blanket of rocks, called a pumice raft, which can clog harbors and damage boats.

Tepp is presenting observations from two submarine volcanoes: Ahyi, a seamount in the Northern Mariana Islands in the Pacific Ocean, and Bogoslof, a shallow submarine volcano in the Aleutian Islands. The volcanoes made very different sounds, suggesting that different processes occurred during eruption. In 2014, Ahyi erupted for two weeks, with short, repetitive gunshotlike explosions every few minutes. In 2016 and 2017, Bogoslof had more sustained eruptions, lasting minutes to hours, which occurred every few days.

Evidence of these eruptions showed up on distant seismometers, which measure waves passing through the ground to record earthquakes, and hydrophone arrays that pick up underwater sound to detect covert nuclear detonations. When volcanoes erupt directly into the water, the sounds can travel for thousands of miles before dissipating.

Questions remain, however, such as if seismometers are sufficient for remote monitoring or if the more accurate information provided by cabled hydrophone arrays is worth the greater expense. Researchers are also interested in how the movement of waves from water into rock, and vice versa, affects signal detection.

Tepp and colleagues at National Oceanic and Atmospheric Administration and USGS recently deployed a hydrophone array in the Northern Mariana Islands. They will collect the data next summer and hope to determine where and how often local volcanoes erupt to see if the area needs better hazard monitoring.

Due to the long distances that eruption signals travel, they likely show up as anomalies on far-off monitoring devices used to study earthquakes, land-based volcanoes or even whale songs.

“Eruptions that create a loud enough sound, in the right location, can travel pretty far, even from one ocean to another,” Tepp said. “It makes you wonder, how many of these signals have we seen on distant instruments where nobody knew what they were, and it’s a submarine volcano from halfway around the world?”

Cyclone Lashes Southern India, Killing at Least 21

NEW DELHI — A powerful cyclone sweeping through southern India has killed at least 21 fishermen and stranded more than 90 others at sea, according to a government official in the state of Kerala.

The storm, Cyclone Ockhi, caught many fishermen off guard over the weekend after it formed quickly in the Arabian Sea and began lashing the Lakshadweep Islands and coastlines in the states of Kerala and Tamil Nadu.

On Monday afternoon, the cyclone was about 480 miles southwest of Surat, a city in Gujarat State. The storm was expected to hit the coast near Surat by Tuesday evening, and lose some of its intensity.

The extent of the damage was still unclear on Monday, but Mohammed Faizal, a member of Parliament representing Lakshadweep, said the losses from damage on the islands exceeded $77 million.

The India Meteorological Department classified it as a “very severe cyclonic storm,” a designation for tempests with wind speeds reaching 137 miles an hour.

Cyclones occur in the South Pacific and Indian Ocean; in the Atlantic and Northeast Pacific, such severe storms are called hurricanes.

“There was no forewarning,” Sekhar Lukose Kuriakose, of the Kerala State Disaster Management Authority, said by telephone. “There was no scientific means of establishing that this was going to become a cyclone.”

But fishermen, saying the government had been slow to notify people of the storm, organized protests on Saturday in Kerala and in Tamil Nadu, blocking roads and pooling resources and boats to try to locate the missing.

Speaking to the families of missing fishermen in Tamil Nadu villages, India’s defense minister, Nirmala Sitharaman, said on Sunday that the country’s navy, air force and coast guard were doing everything possible to try to find the missing fishermen.

“I speak with folded hands,” she told the crowd, in which wives of the missing fishermen wept. “We have not stopped searching for them.”

Several hundred fishermen have been rescued, the Kerala disaster management agency said. The state has announced compensation payments of about $15,000 each for the families of those who have died.

Mr. Kuriakose said that some of the missing fishermen had already been out at sea days before the cyclone formed.

Before gathering force, the storm killed at least 13 people last week in neighboring Sri Lanka, uprooting trees, forcing schools to shut and disrupting air travel.

The India Meteorological Department said the cyclone was expected to weaken gradually in the next couple of days as it moved north toward the states of Maharashtra and Gujarat.

Heavy rainfall was forecast for the area on Tuesday and officials have advised fishermen in southern Gujarat and northern Maharashtra to stay on shore.

Trickle-Down Is The Solution (To The Planetary Core Formation Problem)

Scientists have long pondered how rocky bodies in the solar system — including our own Earth — got their metal cores. According to research conducted by The University of Texas at Austin, evidence points to the downwards percolation of molten metal toward the center of the planet through tiny channels between grains of rock.

The finding calls into question the interpretation of prior experiments and simulations that sought to understand how metals behave under intense heat and pressure when planets are forming. Past results suggested that large portions of molten metals stayed trapped in isolated pores between the grains. In contrast, the new research suggests that once those isolated pores grow large enough to connect, the molten metal starts to flow, and most of it is able to percolate along grain boundaries. This process would let metal trickle down through the mantle, accumulate in the center, and form a metal core, like the iron core at the heart of our home planet.

“What we’re saying is that once the melt network becomes connected, it stays connected until almost all of the metal is in the core,” said co-author Marc Hesse, an associate professor in the UT Jackson School of Geosciences Department of Geological Sciences, and a member of UT’s Institute for Computational Engineering and Sciences.

The research was published on Dec. 4 in the Proceedings of the National Academy of Sciences. The work was the doctoral thesis of Soheil Ghanbarzadeh, who earned his Ph.D. while a student in the UT Department of Petroleum and Geosystems Engineering (now the Hildebrand Department of Petroleum and Geosystems Engineering). He currently works as a reservoir engineer with BP America. Soheil was jointly advised by Hesse and Maša Prodanovic, an associate professor in the Hildebrand Department and a co-author.

Planets and planetesimals (small planets and large asteroids) are formed primarily from silicate rocks and metal. Part of the planet formation process involves the initial mass of material separating into a metallic core and a silicate shell made up of the mantle and the crust. For the percolation theory of core formation to work, the vast majority of metal in the planetary body must make its way to the center.

In this study, Ghanbarzadeh developed a computer model to simulate the distribution of molten iron between rock grains as porosity, or melt fraction, increased or decreased. The simulations were perfomed at the Texas Advanced Computing Center. Researchers found that once the metal starts to flow, it can continue flowing even as the melt fraction decreases significantly. This is in contrast to previous simulations that found that once the metal starts flowing, it only takes a small dip in the volume of melt for percolation to stop.

“People have assumed that you disconnect at the same melt fraction at which you initially connected…and it would leave significant amounts of the metal behind,” Hesse said. “What we found is that when the metallic melt connects and when it disconnects is not necessarily the same.”

According to the computer model, only 1 to 2 percent of the initial metal would be trapped in the silicate mantle when percolation stops, which is consistent with the amount of metal in the Earth’s mantle.

The researchers point to the arrangement of the rock grains to explain the differences in how well-connected the spaces between the grains are. Previous work used a geometric pattern of regular, identical grains, while this work relied on simulations using an irregular grain geometry, which is thought to more closely mirror real-life conditions. The geometry was generated using data from a polycrystalline titanium sample that was scanned using X-ray microtomography.

“The numerical model Soheil developed in his Ph.D. thesis allowed for finding three-dimensional melt networks of any geometrical complexity for the first time,” said Prodanovic. “Having a three-dimensional model is key in understanding and quantifying how melt trapping works.”

The effort paid off because researchers found that the geometry has a strong effect on melt connectivity. In the irregular grains, the melt channels vary in width, and the larges ones remain connected even as most of the metal drains away.

“What we did differently in here was to add the element of curiosity to see what happens when you drain the melt from the porous, ductile rock,” said Ghanbarzadeh.

The researchers also compared their results to a metallic melt network preserved in an anchondrite meteorite, a type of meteorite that came from a planetary body that differentiated into discernable layers. X-ray images of the meteorite taken in the Jackson School’s High-Resolution X-Ray CT Facility revealed a metal distribution that is comparable to the computed melt networks. Prodanovic said that this comparison shows that their simulation capture the features observed in the meteorite.

Researchers Present List Of Comet 67P/Churyumov-Gerasimenko Ingredients

The dust that comet 67P/Churyumov-Gerasimenko emits into space consists to about one half of organic molecules. The dust belongs to the most pristine and carbon-rich material known in our solar system and has hardly changed since its birth. These results of the COSIMA team are published today in the journal Monthly Notices of the Royal Astronomical Society. COSIMA is an instrument onboard the Rosetta spacecraft, which investigated comet 67P/Churyumov-Gerasimenko from August 2014 to September 2016. In their current study, the involved researchers including scientists from the Max Planck Institute for Solar System Research (MPS) analyze as comprehensively as ever before, what chemical elements constitute cometary dust.

When a comet traveling along it highly elliptical orbit approaches the Sun, it becomes active: frozen gases evaporate, dragging tiny dust grains into space. Capturing and examining these grains provides the opportunity to trace the “building materials” of the comet itself. So far, only few space missions have succeeded in this endeavor. These include ESA’s Rosetta mission. Unlike their predecessors, for their current study the Rosetta researchers were able to collect and analyze dust particles of various sizes over a period of approximately two years. In comparison, earlier missions, such as Giotto’s Flyby of comet 1P/Halley or Stardust, which even returned cometary dust from comet 81P/Wild 2 back to Earth, provided only a snapshot. In the case of the space probe Stardust, which raced past its comet in 2004, the dust had changed significantly during capture, so that a quantitative analysis was only possible to a limited extent.

In the course of the Rosetta mission, COSIMA collected more than 35000 dust grains. The smallest of them measured only 0.01 millimeters in diameter, the largest about one millimeter. The instrument makes it possible to first observe the individual dust grains with a microscope. In a second step, these grains are bombarded with a high-energy beam of indium ions. The secondary ions emitted in this way can then be “weighed” and analyzed in the COSIMA mass spectrometer. For the current study, the researchers limited themselves to 30 dust grains with properties that ensured a meaningful analysis. Their selection includes dust grains from all phases of the Rosetta mission and of all sizes.

“Our analyzes show that the composition of all these grains is very similar,” MPS researcher Dr. Martin Hilchenbach, Principal Investigator of the COSIMA team, describes the results. The scientists conclude that the comet’s dust consists of the same “ingredients” as the comet’s nucleus and thus can be examined in its place.

As the study shows, organic molecules are among those ingredients at the top of the list. These account for about 45 percent of the weight of the solid cometary material. “Rosetta’s comet thus belongs to the most carbon-rich bodies we know in the solar system,” says MPS scientist and COSIMA team member Dr. Oliver Stenzel. The other part of the total weight, about 55 percent, is provided by mineral substances, mainly silicates. It is striking that they are almost exclusively non-hydrated minerals i.e. missing water compounds.

“Of course, Rosetta’s comet contains water like any other comet, too,” says Hilchenbach. “But because comets have spent most of their time at the icy rim of the solar system, it has almost always been frozen and could not react with the minerals.” The researchers therefore regard the lack of hydrated minerals in the comet’s dust as an indication that 67P contains very pristine material.

This conclusion is supported by the ratio of certain elements such as carbon to silicon. With more than 5, this value is very close to the Sun’s value, which is thought to reflect the ratio found in the early solar system.
The current findings also touch on our ideas of how life on Earth came about. In a previous publication, the COSIMA team was able to show that the carbon found in Rosetta’s comet is mainly in the form of large, organic macromolecules. Together with the current study, it becomes clear that these compounds make up a large part of the cometary material. Thus, if comets indeed supplied the early Earth with organic matter, as many researchers assume, it would probably have been mainly in the form of such macromolecules.

Gravitational Waves Could Shed Light On The Origin Of Black Holes

A new study published in Physical Review Letters outlines how scientists could use gravitational wave experiments to test the existence of primordial black holes, gravity wells formed just moments after the Big Bang that some scientists have posited could be an explanation for dark matter.

“We know very well that black holes can be formed by the collapse of large stars, or as we have seen recently, the merger of two neutron stars,” said Savvas Koushiappas, an associate professor of physics at Brown University and coauthor of the study with Avi Loeb from Harvard University. “But it’s been hypothesized that there could be black holes that formed in the very early universe before stars existed at all. That’s what we’re addressing with this work.”

The idea is that shortly after the Big Bang, quantum mechanical fluctuations led to the density distribution of matter that we observe today in the expanding universe. It’s been suggested that some of those density fluctuations might have been large enough to result in black holes peppered throughout the universe. These so-called primordial black holes were first proposed in the early 1970s by Stephen Hawking and collaborators but have never been detected — it’s still not clear if they exist at all.

The ability to detect gravitational waves, as demonstrated recently by the Laser Interferometer Gravitational-Wave Observatory (LIGO), has the potential to shed new light on the issue. Such experiments detect ripples in the fabric of spacetime associated with giant astronomical events like the collision of two black holes. LIGO has already detected several black hole mergers, and future experiments will be able to detect events that happened much further back in time.

“The idea is very simple,” Koushiappas said. “With future gravitational wave experiments, we’ll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we’ll know that those black holes are not of stellar origin.”

Cosmologists measure how far back in time an event occurred using redshift — the stretching of the wavelength of light associated with the expansion of the universe. Events further back in time are associated with larger redshifts. For this study, Koushiappas and Loeb calculated the redshift at which black hole mergers should no longer be detected assuming only stellar origin.

They show that at a redshift of 40, which equates to about 65 million years after the Big Bang, merger events should be detected at a rate of no more than one per year, assuming stellar origin. At redshifts greater than 40, events should disappear altogether.

“That’s really the drop-dead point,” Koushiappas said. “In reality, we expect merger events to stop well before that point, but a redshift of 40 or so is the absolute hardest bound or cutoff point.”

A redshift of 40 should be within reach of several proposed gravitational wave experiments. And if they detect merger events beyond that, it means one of two things, Koushiappas and Loeb say: Either primordial black holes exist, or the early universe evolved in a way that’s very different from the standard cosmological model. Either would be very important discoveries, the researchers say.

For example, primordial black holes fall into a category of entities known as MACHOs, or Massive Compact Halo Objects. Some scientists have proposed that dark matter — the unseen stuff that is thought to comprise most of the mass of the universe — may be made of MACHOs in the form of primordial black holes. A detection of primordial black holes would bolster that idea, while a non-detection would cast doubt upon it.

The only other possible explanation for black hole mergers at redshifts greater than 40 is that the universe is “non-Gaussian.” In the standard cosmological model, matter fluctuations in the early universe are described by a Gaussian probability distribution. A merger detection could mean matter fluctuations deviate from a Gaussian distribution.

“Evidence for non-Gaussianity would require new physics to explain the origin of these fluctuations, which would be a big deal,” Loeb said.

The rate at which detections are made past a redshift of 40 — if indeed such detections are made — should indicate whether they’re a sign of primordial black holes or evidence for non-Gaussianity. But a non-detection would present a strong challenge to those ideas.

Blowing In The Stellar Wind: Scientists Reduce The Chances Of Life On Exoplanets In So-Called Habitable Zones

Is there life beyond Earth in the cosmos? Astronomers looking for signs have found that our Milky Way galaxy teems with exoplanets, some with conditions that could be right for extraterrestrial life. Such worlds orbit stars in so-called “habitable zones,” regions where planets could hold liquid water that is necessary for life as we know it.

However, the question of habitability is highly complex. Researchers led by space physicist Chuanfei Dong of the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and Princeton University have recently raised doubts about water on — and thus potential habitability of — frequently cited exoplanets that orbit red dwarfs, the most common stars in the Milky Way.

Impact of stellar wind

In two papers in The Astrophysical Journal Letters, the scientists develop models showing that the stellar wind — the constant outpouring of charged particles that sweep out into space — could severely deplete the atmosphere of such planets over hundreds of millions of years, rendering them unable to host surface-based life as we know it.

“Traditional definition and climate models of the habitable zone consider only the surface temperature,” Dong said. “But the stellar wind can significantly contribute to the long-term erosion and atmospheric loss of many exoplanets, so the climate models tell only part of the story.”

To broaden the picture, the first paper looks at the timescale of atmospheric retention on Proxima Centauri b (PCb), which orbits the nearest star to our solar system, some 4 light years away. The second paper questions how long oceans could survive on “water worlds” — planets thought to have seas that could be hundreds of miles deep.

Two-fold effect

The research simulates the photo-chemical impact of starlight and the electromagnetic erosion of stellar wind on the atmosphere of the exoplanets. These effects are two-fold: The photons in starlight ionize the atoms and molecules in the atmosphere into charged particles, allowing pressure and electromagnetic forces from the stellar wind to sweep them into space. This process could cause severe atmospheric losses that would prevent the water that evaporates from exoplanets from raining back onto them, leaving the surface of the planet to dry up.

On Proxima Centauri b, the model indicates that high stellar wind pressure would cause the atmosphere to escape and prevent atmosphere from lasting long enough to give rise to surface-based life as we know it. “The evolution of life takes billions of years,” Dong noted. “Our results indicate that PCb and similar exoplanets are generally not capable of supporting an atmosphere over sufficiently long timescales when the stellar wind pressure is high.”

“It is only if the pressure is sufficiently low,” he said, “and if the exoplanet has a reasonably strong magnetic shield like that of the Earth’s magnetosphere, that the exoplanet can retain an atmosphere and has the potential for habitability.”

Evolution of habitable zone

Complicating matters is the fact that the habitable zone circling red stars could evolve over time. So high stellar wind pressure early on could increase the rate of atmospheric escape. Thus, the atmosphere could have eroded too soon, even if the exoplanet was protected by a strong magnetic field like the magnetosphere surrounding Earth, Dong said. “In addition, such close-in planets could also be tidally locked like our moon, with one side always exposed to the star. The resultant weak global magnetic field and the constant bombardment of stellar wind would serve to intensify losses of atmosphere on the star-facing side.”

Turning to water worlds, the researchers explored three different conditions for the stellar wind. These ranged from:

Winds that strike the Earth’s magnetosphere today.
Ancient stellar winds flowing from young, Sun-like stars that were just a toddler-like 0.6 billion years old compared with the 4.6 billion year age of the Sun.
The impact on exoplanets of a massive stellar storm like the Carrington event, which knocked out telegraph service and produced auroras around the world in 1859.
The simulations illustrated that ancient stellar wind could cause the rate of atmospheric escape to be far greater than losses produced by the current solar wind that reaches the magnetosphere of Earth. Moreover, the rate of loss for Carrington-type events, which are thought to occur frequently in young Sun-like stars, was found to be greater still.

“Our analysis suggests that such space weather events may prove to be a key driver of atmospheric losses for exoplanets orbiting an active young Sun-like star,” the authors write.

High probability of dried-up oceans

Given the increased activity of red stars and the close-in location of planets in habitable zones, these results indicate the high probability of dried-up surfaces on planets that orbit red stars that might once have held oceans that could give birth to life. The findings could also modify the famed Drake equation, which estimates the number of civilizations in the Milky Way, by lowering the estimate for the average number of planets per star that can support life.

Authors of the PCb paper note that predicting the habitability of planets located light years from Earth is of course filled with uncertainties. Future missions like the James Webb Space Telescope, which NASA will launch in 2019 to peer into the early history of the universe, will therefore “be essential for getting more information on stellar winds and exoplanet atmospheres,” the authors say, “thereby paving the way for more accurate estimations of stellar-wind induced atmospheric losses.”

Scientists spot potentially habitable worlds with regularity. Recently, a newly discovered Earth-sized planet orbiting Ross 128, a red dwarf star that is smaller and cooler than the sun located some 11 light years from Earth, was cited as a water candidate. Scientists noted that the star appears to be quiescent and well-behaved, not throwing off flares and eruptions that could undo conditions favorable to life.

Collaborating with Dong on the PCb paper were physicists from Harvard University, the Harvard-Smithsonian Center for Astrophysics, the University of California, Los Angeles, and the University of Massachusetts. Support for the work came from a NASA Jack Eddy postdoctoral fellowship for Dong through the Princeton Center for Heliophysics, led by Prof. Amitava Bhattacharjee, head of the PPPL Theory Department who serves as Dong’s postdoctoral advisor, and the Max Planck-Princeton Research Center for Plasma Physics, jointly financed by the DOE Office of Science and the National Science Foundation. Collaborating on the water world research were scientists from the University of Michigan, the Harvard-Smithsonian Center for Astrophysics and Harvard University. The NASA Jack Eddy postdoctoral fellowship supported Dong.