Tag Archives: #planet

Astronomers Identified A White Dwarf So Massive That It Might Collapse (Planetary Science)

Astronomers have discovered the smallest and most massive white dwarf ever seen. The smoldering cinder, which formed when two less massive white dwarfs merged, is heavy, “packing a mass greater than that of our Sun into a body about the size of our Moon,” says Ilaria Caiazzo, the Sherman Fairchild Postdoctoral Scholar Research Associate in Theoretical Astrophysics at Caltech and lead author of the new study appearing in the July 1 issue of the journal Nature. “It may seem counterintuitive, but smaller white dwarfs happen to be more massive. This is due to the fact that white dwarfs lack the nuclear burning that keep up normal stars against their own self gravity, and their size is instead regulate­­­d by quantum mechanics.”

The discovery was made by the Zwicky Transient Facility, or ZTF, which operates at Caltech’s Palomar Observatory; two Hawaiʻi telescopes – W. M. Keck Observatory on  Maunakea, Hawaiʻi Island and University of Hawaiʻi Institute for Astronomy’s Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) on Haleakala, Maui – helped characterize the dead star, along with the 200-inch Hale Telescope at Palomar, the European Gaia space observatory, and NASA’s Neil Gehrels Swift Observatory.

White dwarfs are the collapsed remnants of stars that were once about eight times the mass of our Sun or lighter. Our Sun, for example, after it first puffs up into a red giant in about 5 billion years, will ultimately slough off its outer layers and shrink down into a compact white dwarf. About 97 percent of all stars become white dwarfs.

While our Sun is alone in space without a stellar partner, many stars orbit around each other in pairs. The stars grow old together, and if they are both less than eight solar-masses, they will both evolve into white dwarfs.

The new discovery provides an example of what can happen after this phase. The pair of white dwarfs, which spiral around each other, lose energy in the form of gravitational waves and ultimately merge. If the dead stars are massive enough, they explode in what is called a type Ia supernova. But if they are below a certain mass threshold, they combine together into a new white dwarf that is heavier than either progenitor star. This process of merging boosts the magnetic field of that star and speeds up its rotation compared to that of the progenitors.

Astronomers say that the newfound tiny white dwarf, named ZTF J1901+1458, took the latter route of evolution; its progenitors merged and produced a white dwarf 1.35 times the mass of our Sun. The white dwarf has an extreme magnetic field almost 1 billion times stronger than our Sun’s and whips around on its axis at a frenzied pace of one revolution every seven minutes (the zippiest white dwarf known, called EPIC 228939929, rotates every 5.3 minutes).

“We caught this very interesting object that wasn’t quite massive enough to explode,” says Caiazzo. “We are truly probing how massive a white dwarf can be.”

What’s more, Caiazzo and her collaborators think that the merged white dwarf may be massive enough to evolve into a neutron-rich dead star, or neutron star, which typically forms when a star much more massive than our Sun explodes in a supernova.

“This is highly speculative, but it’s possible that the white dwarf is massive enough to further collapse into a neutron star,” says Caiazzo. “It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed.”

If this neutron star formation hypothesis is correct, it may mean that a significant portion of other neutron stars take shape in this way. The newfound object’s close proximity (about 130 light-years away) and its young age (about 100 million years old or less) indicate that similar objects may occur more commonly in our galaxy.

Magnetic and Fast

The white dwarf was first spotted by Caiazzo’s colleague Kevin Burdge, a postdoctoral scholar at Caltech, after searching through all-sky images captured by ZTF. This particular white dwarf, when analyzed in combination with data from Gaia, stood out for being very massive and having a rapid rotation.

“No one has systematically been able to explore short-timescale astronomical phenomena on this kind of scale until now. The results of these efforts are stunning,” says Burdge, who, in 2019, led the team that discovered a pair of white dwarfs zipping around each other every seven minutes.

The team then analyzed the spectrum of the star using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS), and that is when Caiazzo was struck by the signatures of a very powerful magnetic field and realized that she and her team had found something “very special,” as she says. The strength of the magnetic field together with the seven-minute rotational speed of the object indicated that it was the result of two smaller white dwarfs coalescing into one.

Data from Swift, which observes ultraviolet light, helped nail down the size and mass of the white dwarf. With a diameter of 2,670 miles, ZTF J1901+1458 secures the title for the smallest known white dwarf, edging out previous record holders, RE J0317-853 and WD 1832+089, which each have diameters of about 3,100 miles.

The white dwarf ZTF J1901+1458 is about 2,670 miles across, while the moon is 2,174 miles across. The white dwarf is depicted above the Moon in this artistic representation; in reality, the white dwarf lies 130 light-years away in the constellation of Aquila. Credit: Giuseppe Parisi

In the future, Caiazzo hopes to use ZTF to find more white dwarfs like this one, and, in general, to study the population as a whole. “There are so many questions to address, such as what is the rate of white dwarf mergers in the galaxy, and is it enough to explain the number of type Ia supernovae? How is a magnetic field generated in these powerful events, and why is there such diversity in magnetic field strengths among white dwarfs? Finding a large population of white dwarfs born from mergers will help us answer all these questions and more.”

The study, titled “A highly magnetised and rapidly rotating white dwarf as small as the Moon,” was funded by the Rose Hills Foundation, the Alfred P. Sloan Foundation, NASA, the Heising–Simons Foundation, the A. F. Morrison Fellowship of the Lick Observatory, the NSF, and the Natural Sciences and Engineering Research Council of Canada.

Featured image: THIS ILLUSTRATION HIGHLIGHTS A NEWFOUND SMALL WHITE DWARF THAT IS SOMEWHAT LARGER THAN EARTH’S MOON. THE TWO BODIES ARE SHOWN NEXT TO EACH OTHER FOR SIZE COMPARISON. THE HOT, YOUNG WHITE DWARF IS THE MOST MASSIVE WHITE DWARF KNOWN, WEIGHING 1.35 TIMES AS MUCH AS OUR SUN.Credit: Giuseppe Parisi


Provided by W.M. Keck Observatory

Why Do Some Science Instruments Detect the Gas On the Red Planet While Others Don’t? (Planetary Science)

Scientists Closer to Explaining Mars Methane Mystery

Reports of methane detections at Mars have captivated scientists and non-scientists alike. On Earth, a significant amount of methane is produced by microbes that help most livestock digest plants. This digestion process ends with livestock exhaling or burping the gas into the air.

While there are no cattle, sheep, or goats on Mars, finding methane there is exciting because it may imply that microbes were, or are, living on the Red Planet. Methane could have nothing to do with microbes or any other biology, however; geological processes that involve the interaction of rocks, water, and heat can also produce it.

Before identifying the sources of methane on Mars, scientists must settle a question that’s been gnawing at them: Why do some instruments detect the gas while others don’t? NASA’s Curiosity rover, for instance, has repeatedly detected methane right above the surface of Gale Crater. But ESA’s (the European Space Agency) ExoMars Trace Gas Orbiter hasn’t detected any methane higher in the Martian atmosphere.

“When the Trace Gas Orbiter came on board in 2016, I was fully expecting the orbiter team to report that there’s a small amount of methane everywhere on Mars,” said Chris Webster, lead of the Tunable Laser Spectrometer (TLS) instrument in the Sample Analysis at Mars (SAM) chemistry lab aboard the Curiosity rover.

The TLS has measured less than one-half part per billion in volume of methane on average in Gale Crater. That’s equivalent to about a pinch of salt diluted in an Olympic-size swimming pool. These measurements have been punctuated by baffling spikes of up to 20 parts per billion in volume.

“But when the European team announced that it saw no methane, I was definitely shocked,” said Webster, who’s based at NASA’s Jet Propulsion Laboratory in Southern California.

The European orbiter was designed to be the gold standard for measuring methane and other gases over the whole planet. At the same time, Curiosity’s TLS is so precise, it will be used for early warning fire detection on the International Space Station and for tracking oxygen levels in astronaut suits. It’s also been licensed for use at power plants, on oil pipelines, and in fighter aircraft, where pilots can monitor the oxygen and carbon dioxide levels in their face masks.

NASA’s Curiosity rover captured these drifting clouds on May 7, 2019, the 2,400th Martian day, or sol, of the mission. Curiosity used its black-and-white Navigation Cameras to take the photo. Credit: NASA/JPL-Caltech

Still, Webster and the SAM team were jolted by the European orbiter findings and immediately set out to scrutinize the TLS measurements on Mars.

Some experts suggested that the rover itself was releasing the gas. “So we looked at correlations with the pointing of the rover, the ground, the crushing of rocks, the wheel degradation – you name it,” Webster said. “I cannot overstate the effort the team has put into looking at every little detail to make sure those measurements are correct, and they are.”

Webster and his team reported their results today in the Astronomy & Astrophysics journal.

As the SAM team worked to confirm its methane detections, another member of Curiosity’s science team, planetary scientist John E. Moores from York University in Toronto, published an intriguing prediction in 2019. “I took what some of my colleagues are calling a very Canadian view of this, in the sense that I asked the question: ‘What if Curiosity and the Trace Gas Orbiter are both right?’” Moores said.

Moores, as well as other Curiosity team members studying wind patterns in Gale Crater, hypothesized that the discrepancy between methane measurements comes down to the time of day they’re taken. Because it needs a lot of power, TLS operates mostly at night when no other Curiosity instruments are working. The Martian atmosphere is calm at night, Moores noted, so the methane seeping from the ground builds up near the surface where Curiosity can detect it.

The Trace Gas Orbiter, on the other hand, requires sunlight to pinpoint methane about 3 miles, or 5 kilometers, above the surface. “Any atmosphere near a planet’s surface goes through a cycle during the day,” Moores said. Heat from the Sun churns the atmosphere as warm air rises and cool air sinks. Thus, the methane that is confined near the surface at night is mixed into the broader atmosphere during the day, which dilutes it to undetectable levels. “So I realized no instrument, especially an orbiting one, would see anything,” Moores said.

Immediately, the Curiosity team decided to test Moores’ prediction by collecting the first high-precision daytime measurements. TLS measured methane consecutively over the course of one Martian day, bracketing one nighttime measurement with two daytime ones. With each experiment, SAM sucked in Martian air for two hours, continuously removing the carbon dioxide, which makes up 95% of the planet’s atmosphere. This left a concentrated sample of methane that TLS could easily measure by passing an infrared laser beam through it many times, one that’s tuned to use a precise wavelength of light that is absorbed by methane.

“John predicted that methane should effectively go down to zero during the day, and our two daytime measurements confirmed that,” said Paul Mahaffy, the principal investigator of SAM, who’s based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. TLS’ nighttime measurement fit neatly within the average the team had already established. “So that’s one way of putting to bed this big discrepancy,” Mahaffy said.

While this study suggests that methane concentrations rise and fall throughout the day at the surface of Gale Crater, scientists have yet to solve the global methane puzzle at Mars. Methane is a stable molecule that is expected to last on Mars for about 300 years before getting torn apart by solar radiation. If methane is constantly seeping from all similar craters, which scientists suspect is likely given that Gale doesn’t seem to be geologically unique, enough of it should have accumulated in the atmosphere for the Trace Gas Orbiter to detect. Scientists suspect that something is destroying methane in less than 300 years.

Experiments are underway to test whether very low-level electric discharges induced by dust in the Martian atmosphere could destroy methane, or whether abundant oxygen at the Martian surface quickly destroys methane before it can reach the upper atmosphere.

“We need to determine whether there’s a faster destruction mechanism than normal to fully reconcile the data sets from the rover and the orbiter,” Webster said.

Based on the article “Day-night differences in Mars methane suggest nighttime containment at Gale crater“, by C. R. Webster et al., Published in Astronomy & Astrophysics, 2021, 650, A166

Featured image: This photo was taken on March 19, 2017, by the Mars Hand Lens Imager camera on the arm of NASA’s Curiosity rover. The image helped mission team members inspect the condition of Curiosity’s six wheels. Credit: NASA/JPL-Caltech/MSSS


Provided by NASA JPL

Earth-like Biospheres On Other Planets May be Rare (Planetary Science)

A new analysis of known exoplanets has revealed that Earth-like conditions on potentially habitable planets may be much rarer than previously thought. The work focuses on the conditions required for oxygen-based photosynthesis to develop on a planet, which would enable complex biospheres of the type found on Earth. The study is published today in Monthly Notices of the Royal Astronomical Society.

The number of confirmed planets in our own Milky Way galaxy now numbers into the thousands. However planets that are both Earth-like and in the habitable zone – the region around a star where the temperature is just right for liquid water to exist on the surface – are much less common.

At the moment, only a handful of such rocky and potentially habitable exoplanets are known. However the new research indicates that none of these has the theoretical conditions to sustain an Earth-like biosphere by means of ‘oxygenic’ photosynthesis – the mechanism plants on Earth use to convert light and carbon dioxide into oxygen and nutrients.

Only one of those planets comes close to receiving the stellar radiation necessary to sustain a large biosphere: Kepler−442b, a rocky planet about twice the mass of the Earth, orbiting a moderately hot star around 1,200 light years away.

The study looked in detail at how much energy is received by a planet from its host star, and whether living organisms would be able to efficiently produce nutrients and molecular oxygen, both essential elements for complex life as we know it, via normal oxygenic photosynthesis.

By calculating the amount of photosynthetically active radiation (PAR) that a planet receives from its star, the team discovered that stars around half the temperature of our Sun cannot sustain Earth-like biospheres because they do not provide enough energy in the correct wavelength range. Oxygenic photosynthesis would still be possible, but such planets could not sustain a rich biosphere.

Planets around even cooler stars known as red dwarfs, which smoulder at roughly a third of our Sun’s temperature, could not receive enough energy to even activate photosynthesis. Stars that are hotter than our Sun are much brighter, and emit up to ten times more radiation in the necessary range for effective photosynthesis than red dwarfs, however generally do not live long enough for complex life to evolve.

“Since red dwarfs are by far the most common type of star in our galaxy, this result indicates that Earth-like conditions on other planets may be much less common than we might hope,” comments Prof. Giovanni Covone of the University of Naples, lead author of the study.

He adds: “This study puts strong constraints on the parameter space for complex life, so unfortunately it appears that the “sweet spot” for hosting a rich Earth-like biosphere is not so wide.”

Future missions such as the James Webb Space Telescope (JWST), due for launch later this year, will have the sensitivity to look to distant worlds around other stars and shed new light on what it really takes for a planet to host life as we know it.

Featured image: An artistic representation of the potentially habitable planet Kepler 422-b (left), compared with Earth (right). © Ph03nix1986 / Wikimedia Commons Licence type: Attribution-ShareAlike (CC BY-SA 4.0)


Further information

The new work appears in, “Efficiency of the oxygenic photosynthesis on Earth-like planets in the habitable zone”, G. Covone, R.M. Ienco, L. Cacciapuoti and L. Inno, Monthly Notices of the Royal Astronomical Society (2021), in press (DOI: 10.1093/mnras/stab1357).


Provided by Royal Astronomical Society

World’s Lakes Losing Oxygen Rapidly As Planet Warms (Ecology)

Changes threaten biodiversity and drinking water quality

Oxygen levels in the world’s temperate freshwater lakes are declining rapidly — faster than in the oceans — a trend driven largely by climate change that threatens freshwater biodiversity and drinking water quality.

Research published today in Nature found that oxygen levels in surveyed lakes across the temperate zone have declined 5.5% at the surface and 18.6% in deep waters since 1980. Meanwhile, in a large subset of mostly nutrient-polluted lakes, surface oxygen levels increased as water temperatures crossed a threshold favoring cyanobacteria, which can create toxins when they flourish in the form of harmful algal blooms.

“All complex life depends on oxygen. It’s the support system for aquatic food webs. And when you start losing oxygen, you have the potential to lose species,” said Kevin Rose , author and professor at Rensselaer Polytechnic Institute. “Lakes are losing oxygen 2.75-9.3 times faster than the oceans, a decline that will have impacts throughout the ecosystem.”

Researchers analyzed a combined total of over 45,000 dissolved oxygen and temperature profiles collected since 1941 from nearly 400 lakes around the globe. Most long-term records were collected in the temperate zone, which spans 23 to 66 degrees north and south latitude. In addition to biodiversity, the concentration of dissolved oxygen in aquatic ecosystems influences greenhouse gas emissions, nutrient biogeochemistry, and ultimately, human health.

Although lakes make up only about 3% of Earth’s land surface, they contain a disproportionate concentration of the planet’s biodiversity. Lead author Stephen F. Jane, who completed his Ph.D. with Rose, said the changes are concerning both for their potential impact on freshwater ecosystems and for what they suggest about environmental change in general.

“Lakes are indicators or ‘sentinels’ of environmental change and potential threats to the environment because they respond to signals from the surrounding landscape and atmosphere. We found that these disproportionally more biodiverse systems are changing rapidly, indicating the extent to which ongoing atmospheric changes have already impacted ecosystems,” Jane said.

Watch a video about this research.

Although widespread losses in dissolved oxygen across the studied lakes are linked to climate change, the path between warming climate and changing freshwater oxygen levels is driven by different mechanisms between surface and deep waters.

Deoxygenation of surface waters was mostly driven by the most direct path: physics. As surface water temperatures increased by .38 degrees Centigrade per decade, surface water dissolved oxygen concentrations declined by .11 milligrams per liter per decade.

“Oxygen saturation, or the amount of oxygen that water can hold, goes down as temperatures go up. That’s a known physical relationship and it explains most of the trend in surface oxygen that we see,” said Rose.

However, some lakes experienced simultaneously increasing dissolved oxygen concentrations and warming temperatures. These lakes tended to be more polluted with nutrient-rich runoff from agricultural and developed watersheds and have high chlorophyll concentrations. Although the study did not include phytoplankton taxonomic measurements, warm temperatures and elevated nutrient content favor cyanobacteria blooms, whose photosynthesis is known to cause dissolved oxygen supersaturation in surface waters.

“The fact that we’re seeing increasing dissolved oxygen in those types of lakes is potentially an indicator of widespread increases in algal blooms, some of which produce toxins and are harmful. Absent taxonomic data, however, we can’t say that definitively, but nothing else we’re aware of can explain this pattern,” Rose said.

The loss of oxygen in deeper waters, where water temperatures have remained largely stable, follows a more complex path most likely tied to increasing surface water temperatures and a longer warm period each year. Warming surface waters combined with stable deep-water temperatures means that the difference in density between these layers, known as “stratification,” is increasing. The stronger this stratification, the less likely mixing is to occur between layers. The result is that oxygen in deep waters is less likely to get replenished during the warm stratified season, as oxygenation usually comes from processes that occur near the water surface.

“The increase in stratification makes the mixing or renewal of oxygen from the atmosphere to deep waters more difficult and less frequent, and deep-water dissolved oxygen drops as a result,” said Rose. Water clarity losses were also associated with deep-water dissolved oxygen losses in some lakes. However, there was no overarching decline in clarity across lakes.

Oxygen concentrations regulate many other characteristics of water quality. When oxygen levels decline, bacteria that thrive in environments without oxygen, such as those that produce the powerful greenhouse gas methane, begin to proliferate. This suggests the potential that lakes are releasing increased amounts of methane to the atmosphere as a result of oxygen loss. Additionally, sediments release more phosphorous under low oxygen conditions, adding nutrients to already stressed waters.

“Ongoing research has shown that oxygen levels are declining rapidly in the world’s oceans. This study now proves that the problem is even more severe in fresh waters, threatening our drinking water supplies and the delicate balance that enables complex freshwater ecosystems to thrive,” said Curt Breneman, dean of the School of Science. “We hope this finding brings greater urgency to efforts to address the progressively detrimental effects of climate change.”

“Widespread deoxygenation of temperate lakes” was published with support from the National Science Foundation. Rose and Jane were joined by dozens of collaborators in GLEON, the Global Lake Ecological Observatory Network, and based in universities, environmental consulting firms, and government agencies around the world.

Featured image: Oxygen levels in the world’s temperate freshwater lakes are declining faster than in the oceans. © Gretchen Hansen, University of Minnesota


Reference: Jane, S.F., Hansen, G.J.A., Kraemer, B.M. et al. Widespread deoxygenation of temperate lakes. Nature 594, 66–70 (2021). https://doi.org/10.1038/s41586-021-03550-y


Provided by Rensselaer Polytechnic Institute

Astronomers Discover Circumbinary Planet TIC 172900988b (Planetary Science)

A team of international astronomers reported on the discovery of the first TESS circumbinary planet (CBP), “TIC 172900988 b”, using the multiple-transits-in-one-conjunction technique. Their study recently appeared in Arxiv.

A circumbinary planet is a planet that orbits two stars instead of one. Finding transiting planets around binary stars is much more difficult than around single stars. The transits are shallower (due to the constant ‘third-light’ dilution from the binary companion), noisier (due to starspots and stellar activity from two stars), and can be blended with the stellar eclipses.

In the current study, astronomers detected planet, “TIC 172900988 b” from a single sector of TESS data. They found that, during Sector 21, the planet TIC 172900988b transited the primary star and then 5 days later it transited the secondary star i.e. it produced just two transits.

They also revealed, a prominent apsidal motion of the binary orbit, caused by the dynamical interactions between the binary and the planet, from an extensive archival data from multiple surveys like ASAS-SN, Evryscope, KELT, and SuperWASP.

In addition, they found, binary star is itself eclipsing, with an orbital period of 19.7 days and an eccentricity of 0.45. Moreover, stellar masses of 1.24 and 1.2 M respectively, and stellar radii of 1.38 and 1.31 R have been found for the primary and secondary stars respectively.

Upper panels, from left to right: the TESS data for the primary eclipse, the secondary eclipse, the planet transit of the primary, and the planet transit of the secondary. Lower panels: Configuration of the system at the times of the two transits. © Veselin Kostov

For a circumbinary planet, the radius is found to be 11.07 R (1.009 RJup). However, they couldn’t able to determine the planet’s mass and orbital properties uniquely—there are six solutions with nearly equal likelihood. Specifically, they found that the planet’s mass is in the range of 820-980 M, its orbital period could be in between 190-205 days, and the eccentricity is in between 0.02 and 0.09.

“Follow-up observations from other instruments are key for strongly constraining the orbit and mass of the CBP. In particular, observing the predicted 2022 February-March conjunction of the CBP is critical for solving the currently-ambiguous orbit of the planet.”

Finally, they concluded that, as a relative bright target (V=10.141 mag), the system is accessible for high resolution spectroscopy, e.g. Rossiter-McLaughlin effect, transit spectroscopy.

Featured image: The inset image is of the primary target to within 300 of the target, with an arrow marking the position of the detected companion. © Veselin Kostov


Reference: Veselin B. Kostov, Brian P. Powell, Jerome A. Orosz, William F. Welsh, William Cochran, Karen A. Collins, Michael Endl, Coel Hellier, David W. Latham, Phillip MacQueen, Joshua Pepper, Billy Quarles, Lalitha Sairam, Guillermo Torres, Robert F. Wilson, Serge Bergeron, Pat Boyce, Robert Buchheim, Caleb Ben Christiansen, David R. Ciardi, Kevin I. Collins, Dennis M. Conti, Scott Dixon, Pere Guerra, Nader Haghighipour, Jeffrey Herman, Eric G. Hintz, Ward S. Howard, Eric L. N. Jensen, Ethan Kruse, Nicholas M. Law, David Martin, Pierre F. L. Maxted, Benjamin T. Montet, Felipe Murgas, Matt Nelson, Greg Olmschenk, Sebastian Otero, Robert Quimby, Michael Richmond, Richard P. Schwarz, Avi Shporer, Keivan G. Stassun, Denise C. Stephens, Amaury H. M. J. Triaud, Joe Ulowetz, Bradley S. Walter, Edward Wiley, David Wood, Mitchell Yenawine, Eric Agol, Thomas Barclay, Thomas G. Beatty, Isabelle Boisse, Douglas A. Caldwell, Jessie Christiansen, Knicole D. Colon, Magali Deleuil, Laurance Doyle, Daniel Fabrycky, Michael Fausnaugh, Gabor Furesz, Emily A. Gilbert, Guillaume Hebrard, David J. James, Jon Jenkins, Stephen R. Kane, Richard C. Kidwell Jr., Ravi Kopparapu, Gongjie Li, Jack J. Lissauer, Michael B. Lund, Steve Majewski, Tsevi Mazeh, Samuel N. Quinn, George Ricker, Joseph E. Rodriguez, Jason Rowe, Alexander Santerne, Joshua Schlieder, Sara Seager, Matthew R. Standing, Daniel J. Stevens, Eric B. Ting, Roland Vanderspek, Joshua N. Winn, “TIC 172900988: A Transiting Circumbinary Planet Detected in One Sector of TESS Data”, Arxiv, pp. 1-64, 2021. https://arxiv.org/abs/2105.08614


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Astronomers Discovered Neptune-sized Planet Orbiting Dwarf Star TOI-1231 (Planetary Science)

A team of international astronomers reported on the discovery of a Neptune-sized exoplanet, “TOI-1231 b” orbiting TOI-1231 (NLTT 24399, L 248-27, 2MASS J10265947-5228099), a V = 12.3 mag M3V dwarf star in the Vela constellation at distance 27.493 pc. Their study recently appeared in Arxiv.

TOI-1231 was first reported as a high proper motion star (0″.35 yr¯1) by Luyten in 1957, and later in the Revised NLTT catalog. Over the past decade, the star has appeared in several surveys of high proper motion 2MASS and WISE stars and nearby M dwarfs.

In the current study, astronomers detected the planet using photometric data from the Transiting Exoplanet Survey Satellite and followed up with observations from the Las Cumbres Observatory and the Antarctica Search for Transiting ExoPlanets program.

Combining the photometric data sets, they found that the newly discovered planet has a radius of 3.65 R, and an orbital period of 24.246 days. While, radial velocity measurements obtained with the Planet Finder Spectrograph on the Magellan Clay telescope confirm the existence of the planet and lead to a mass measurement of 15.5 M. In addition, they found that the planet has a bulk density of 1.74 g cm¯3 which makes it slightly denser than Neptune (ρNep = 1.638 g cm¯3) .

Stellar and planetary parameters © Burt et al.

Moreover, it has been suggested that, TOI-1231 b has an equilibrium temperature of just 330K, which makes it one of the coolest small planets accessible for atmospheric studies so far. In addition, its volatile rich atmosphere, long transit duration and small host star, makes it one of the most promising small exoplanets for transmission spectroscopy with HST and JWST detected by the TESS mission. Finally, its high systemic radial velocity makes it a particularly attractive target for atmospheric escape observations via the H I Lyman α, and possibly the meta-stable He I line.

“Future atmospheric observations would enable the first comparative planetology efforts in the 250-350 K temperature regime via comparisons with K2-18 b.”

— concluded authors of the study

Reference: Jennifer A. Burt, Diana Dragomir, Paul Mollière, Allison Youngblood, Antonio García Muñoz, John McCann, Laura Kreidberg, Chelsea X. Huang, Karen A. Collins, Jason D. Eastman, Lyu Abe, Jose M. Almenara, Ian J. M. Crossfield, Carl Ziegler, Joseph E. Rodriguez, Eric E. Mamajek, Keivan G. Stassun, Samuel P. Halverson, Steven Jr. Villanueva, R. Paul Butler, Sharon Xuesong Wang, Richard P. Schwarz, George R. Ricker, Roland Vanderspek, David W. Latham, S. Seager, Joshua N. Winn, Jon M. Jenkins, Abdelkrim Agabi, Xavier Bonfils, David Ciardi, Marion Cointepas, Jeffrey D. Crane, Nicolas Crouzet, Georgina Dransfield, Fabo Feng, Elise Furlan, Tristan Guillot, Arvind F. Gupta, Steve B. Howell, Eric L. N. Jensen, Nicholas Law, Andrew W. Mann, Wenceslas Marie-Sainte, Rachel A. Matson, Elisabeth C. Matthews, Djamel Mékarnia, Joshua Pepper, Nic Scott, Stephen A. Shectman, Joshua E. Schlieder, François-Xavier Schmider, Daniel J. Stevens, Johanna K. Teske, Amaury H.M.J. Triaud, David Charbonneau, Zachory K. Berta-Thompson, Christopher J. Burke, Tansu Daylan, Thomas Barclay, Bill Wohler, C. E. Brasseur, “TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399”, Arxiv, pp. 1-20, 2021. https://arxiv.org/abs/2105.08077


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Where On Earth is All The Water? (Earth Science)

There may be up to 70 times more hydrogen in Earth’s core than in the oceans

High-temperature and high-pressure experiments involving a diamond anvil and chemicals to simulate the core of the young Earth demonstrate for the first time that hydrogen can bond strongly with iron in extreme conditions. This explains the presence of significant amounts of hydrogen in the Earth’s core that arrived as water from bombardments billions of years ago.

Given the extreme depths, temperatures and pressures involved, we are not physically able to probe very far into the earth directly. So, in order to peer deep inside the Earth, researchers use techniques involving seismic data to ascertain things like composition and density of subterranean material. Something that has stood out for as long as these kinds of measurements have been taking place is that the core is primarily made of iron, but its density, in particular that of the liquid part, is lower than expected.

Left. A metal cylinder with colored dots on its top. Right. Two jewels meeting at a point.
Diamond anvil. The outer metal casing and inner diamond teeth of the high-pressure anvil. © 2021 Hirose et al.

This led researchers to believe there must be an abundance of light elements alongside the iron. For the first time, researchers have examined the behavior of water in laboratory experiments involving metallic iron and silicate compounds that accurately simulate the metal-silicate (core-mantle) reactions during Earth’s formation. They found that when water meets iron, the majority of the hydrogen dissolves into the metal while the oxygen reacts with iron and goes into the silicate materials.

“At the temperatures and pressures we are used to on the surface, hydrogen does not bond with iron, but we wondered if it were possible under more extreme conditions,” said Shoh Tagawa, a Ph.D. student at the Department of Earth and Planetary Science at the University of Tokyo during the study. “Such extreme temperatures and pressures are not easy to reproduce, and the best way to achieve them in the lab was to use an anvil made of diamond. This can impart pressures of 30–60 gigapascals in temperatures of 3,100–4,600 kelvin. This is a good simulation of the Earth’s core formation.”

A large office of electronic items. A man sitting at a computer desk.
Isotope imaging lab at Hokkaido University. The research was a collaboration between institutions, including Hokkaido University. © 2021 Hisayoshi Yurimoto

The team, under Professor Kei Hirose, used metal and water-bearing silicate analogous to those found in the Earth’s core and mantle, respectively, and compressed them in the diamond anvil whilst simultaneously heating the sample with a laser. To see what was going on in the sample, they used high-resolution imaging involving a technique called secondary ion mass spectroscopy. This allowed them to confirm their hypothesis that hydrogen bonds with iron, which explains the apparent lack of ocean water. Hydrogen is said to be iron-loving, or siderophile.

“This finding allows us to explore something that affects us in quite a profound way,” said Hirose. “That hydrogen is siderophile under high pressure tells us that much of the water that came to Earth in mass bombardments during its formation might be in the core as hydrogen today. We estimate there might be as much as 70 oceans’ worth of hydrogen locked away down there. Had this remained on the surface as water, the Earth may never have known land, and life as we know it would never have evolved.”

Featured image: Sample from high-pressure experiment. High-resolution chemical analyses with secondary ion mass spectroscopy showed the abundance of water left in silicate melt after compressing with liquid iron metal. © 2021 Tagawa et al.


Paper

Shoh Tagawa, Naoya Sakamoto, Kei Hirose, Shunpei Yokoo, John Hernland, Yasuo Ohishi, and Hisayoshi Yurimoto, “Experimental evidence for hydrogen incorporation into Earth’s core.,” Nature Communications: May 11, 2021, doi:10.1038/s41467-021-22035-0.
Link (Publication)


Provided by University of Tokyo

He Was Looking For A Planet, Found A Gamma-ray Burst (Planetary Science)

NASA’s Transiting Exoplanet Survey Satellite, designed to locate worlds around stars other than the Sun, recorded the entire optical afterglow evolution of an intense gamma-ray burst, Grb 191016A. The result demonstrates how Tess’s capabilities can produce useful results also for high energy astrophysics

In space as in sport, there are triathlon telescopes – capable of setting record after record in multiple fields – and telescopes specialized in only one discipline. The extremely versatile Hubble, for example, is undoubtedly a champion of the first type: there is no area of ​​astrophysics in which it has not won a few medals. The exoplanet hunter of NASA Tess , on the other hand, as stated by the acronym ( Transiting Exoplanet Survey Satellite ), was born with a very specific purpose: to discover new exoplanets using the photometric method of transit.. But when you are a champion of observing transits – that is, the partial mini-eclipses produced by the passage of a planet in front of the star you are observing – it means that you do very well in all situations where the required skill is to measure minimums. brightness variations lasting a few hours. Situations that do not arise only during planetary transits: also the optical afterglow following the explosion of a gamma ray burst ( Grb, in English), for example, is such a phenomenon – albeit on the contrary, since it does not produce a decrease but an increase in brightness. And it is precisely by exploiting this extraordinary sensitivity to light variations that Tess was able to add the observation of a Grb to her medal collection.

The event dates back to October 16, 2019, the day on which another space hunter, the Nasa Swift telescope , specialized precisely in detecting gamma-ray bursts, intercepts the unequivocal signal of a Grb with its rapid alert instrument Bat : name in code 191016A . Under normal circumstances Swift would immediately initiate a standard sequence to turn – and no space telescope is as agile as he is in this maneuver – in the direction the signal is coming from and to observe its evolution in detail. But that day there is an obstacle: the Moon, with its cumbersome presence, is right there where Swift should be looking, thus precluding observation.

The region observed by Tess before (left) and during the Grb afterglow (the signal is indicated by the arrow in the central panel). On the right, the portion of the sky where the explosion occurred. Credits: Krista Lynne Smith et al., ApJ, 2021

By pure chance, however, that October 16, Tess’s eye is also oriented in that direction, and from her point of view the Moon does not create any particular problems. Thus, in the archive of the planet hunter, the afterglow of the GRB is recorded for its entire duration, or at least until Tess’s sensitivity is sufficient to trace it: a good seven thousand seconds, over two hours, with a peak of intensity at 2589.7 seconds after the explosion. Nothing particularly brilliant, it must be said: with a magnitude of 15.1, at its maximum it is a glare ten thousand times lessintense than that of the faintest star that can be observed with the naked eye. But considering that these are photons that have traveled for 11.7 billion years, it is a very powerful signal: it is one of the brightest gamma-ray bursts ever detected. It is also the first time that a Grb has been observed in this way, from space, with a telescope designed to track down planets.

Tracing those seven thousand seconds of recording from Tess’s archive was an astronomer from Southern Methodist University, Krista Lynne Smith , first author of the article reporting the discovery, published last month in The Astrophysical Journal . “Our results show that Tess is useful not only for finding new planets, but also for high-energy astrophysics,” says Smith. “Having the burst reached its peak of brightness with some delay, and being a peak of intensity higher than that of most gamma-ray bursts, Tess was able to make multiple observations before the burst.vanished below the telescope’s detection limit. We were thus able to obtain the only optical follow-up from space of this exceptional Grb ».

Featured image: Artistic impression of Tess, NASA’s Transiting Exoplanet Survey Satellite. Credits: Nasa


To know more:

  • Read on The Astrophysical Journal the article ” GRB 191016A: A Long Gamma-Ray Burst Detected by TESS “, by Krista Lynne Smith, Ryan Ridden-Harper, Michael Fausnaugh, Tansu Daylan, Nicola Omodei, Judith Racusin, Zachary Weaver, Thomas Barclay , Péter Veres, D. Alexander Kann and Makoto Arimoto

Provided by INAF

Hubble Watches How a Giant Planet Grows (Planetary Science)

NASA’s Hubble Space Telescope is giving astronomers a rare look at a Jupiter-sized, still-forming planet that is feeding off material surrounding a young star.

“We just don’t know very much about how giant planets grow,” said Brendan Bowler of the University of Texas at Austin. “This planetary system gives us the first opportunity to witness material falling onto a planet. Our results open up a new area for this research.”

Though over 4,000 exoplanets have been cataloged so far, only about 15 have been directly imaged to date by telescopes. And the planets are so far away and small, they are simply dots in the best photos. The team’s fresh technique for using Hubble to directly image this planet paves a new route for further exoplanet research, especially during a planet’s formative years.

This huge exoplanet, designated PDS 70b, orbits the orange dwarf star PDS 70, which is already known to have two actively forming planets inside a huge disk of dust and gas encircling the star. The system is located 370 light-years from Earth in the constellation Centaurus. 

“This system is so exciting because we can witness the formation of a planet,” said Yifan Zhou, also of the University of Texas at Austin. “This is the youngest bona fide planet Hubble has ever directly imaged.” At a youthful five million years, the planet is still gathering material and building up mass. 

Hubble’s ultraviolet light (UV) sensitivity offers a unique look at radiation from extremely hot gas falling onto the planet. “Hubble’s observations allowed us to estimate how fast the planet is gaining mass,” added Zhou.

The European Southern Observatory’s Very Large Telescope caught the first clear image of a forming planet, PDS 70b, around a dwarf star in 2018.
The European Southern Observatory’s Very Large Telescope caught the first clear image of a forming planet, PDS 70b, around a dwarf star in 2018. The planet stands out as a bright point to the right of the center of the image, which is blacked out by the coronagraph mask used to block the light of the central star.Credits: ESO, VLT, André B. Müller (ESO)

The UV observations, which add to the body of research about this planet, allowed the team to directly measure the planet’s mass growth rate for the first time. The remote world has already bulked up to five times the mass of Jupiter over a period of about five million years. The present measured accretion rate has dwindled to the point where, if the rate remained steady for another million years, the planet would only increase by approximately an additional 1/100th of a Jupiter-mass.

Zhou and Bowler emphasize that these observations are a single snapshot in time – more data are required to determine if the rate at which the planet is adding mass is increasing or decreasing. “Our measurements suggest that the planet is in the tail end of its formation process.” 

The youthful PDS 70 system is filled with a primordial gas-and-dust disk that provides fuel to feed the growth of planets throughout the entire system. The planet PDS 70b is encircled by its own gas-and-dust disk that’s siphoning material from the vastly larger circumstellar disk. The researchers hypothesize that magnetic field lines extend from its circumplanetary disk down to the exoplanet’s atmosphere and are funneling material onto the planet’s surface.

“If this material follows columns from the disk onto the planet, it would cause local hot spots,” Zhou explained. “These hot spots could be at least 10 times hotter than the temperature of the planet.” These hot patches were found to glow fiercely in UV light. 

Hubble observations pinpoint planet PDS 70b.
Hubble observations pinpoint planet PDS 70b. A coronagraph on Hubble’s camera blocks out the glare of the central star for the planet to be directly observed. Though over 4,000 exoplanets have been cataloged so far, only about 15 have been directly imaged to date by telescopes. The team’s fresh technique for using Hubble to directly image this planet paves a new route for further exoplanet research, especially during a planet’s formative years.Credits: Joseph DePasquale (STScI)

These observations offer insights into how gas giant planets formed around our Sun 4.6 billion years ago. Jupiter may have bulked up on a surrounding disk of infalling material. Its major moons would have also formed from leftovers in that disk. 

A challenge to the team was overcoming the glare of the parent star. PDS 70b orbits at approximately the same distance as Uranus does from the Sun, but its star is more than 3,000 times brighter than the planet at UV wavelengths. As Zhou processed the images, he very carefully removed the star’s glare to leave behind only light emitted by the planet. In doing so, he improved the limit of how close a planet can be to its star in Hubble observations by a factor of five.

“Thirty-one years after launch, we’re still finding new ways to use Hubble,” Bowler added. “Yifan’s observing strategy and post-processing technique will open new windows into studying similar systems, or even the same system, repeatedly with Hubble. With future observations, we could potentially discover when the majority of the gas and dust falls onto their planets and if it does so at a constant rate.”

The researchers’ results were published in April 2021 in The Astronomical Journal.

Featured image: This illustration of the newly forming exoplanet PDS 70b shows how material may be falling onto the giant world as it builds up mass. By employing Hubble’s ultraviolet light (UV) sensitivity, researchers got a unique look at radiation from extremely hot gas falling onto the planet, allowing them to directly measure the planet’s mass growth rate for the first time. The planet PDS 70b is encircled by its own gas-and-dust disk that’s siphoning material from the vastly larger circumstellar disk in this solar system. The researchers hypothesize that magnetic field lines extend from its circumplanetary disk down to the exoplanet’s atmosphere and are funneling material onto the planet’s surface. The illustration shows one possible magnetospheric accretion configuration, but the magnetic field’s detailed geometry requires future work to probe. The remote world has already bulked up to five times the mass of Jupiter over a period of about five million years, but is anticipated to be in the tail end of its formation process. PDS 70b orbits the orange dwarf star PDS 70 approximately 370 light-years from Earth in the constellation Centaurus.Credits: NASA, ESA, STScI, Joseph Olmsted (STScI)


Reference: Yifan Zhou, Brendan P. Bowler, Kevin R. Wagner et al., “Hubble Space Telescope UV and Hα Measurements of the Accretion Excess Emission from the Young Giant Planet PDS 70 b”, The Astronomical Journal, 161(5), 2021. Link to paper


Provided by NASA