Science
Study: Rough Areas on Moon May Permit Water Ice to Widely Form – VOA Learning English
A new study suggests that rough areas on the moon’s surface block sunlight and permit water ice to form across wide areas.
The U.S. space agency NASA already confirmed last year that results from two studies suggested water ice likely existed across much of the moon’s surface, even during daytime.
One of those studies centered on so-called “cold traps” observed on the moon that hold frozen water. These areas exist in a state of permanent darkness because temperatures are below about minus 160 degrees Celsius.
Until now, scientists have not been sure what was permitting these traps to exist. Especially since the moon does not have a thick atmosphere to help water survive. One theory was that water molecules could be trapped on the lunar surface inside rock or other material that resulted from meteorite strikes.
But a new study by NASA researchers provides another possible explanation for how water ice could remain in many areas of the moon’s surface. It presents evidence that the rough, rocky surface creates shadows that permit water ice to survive.
The researchers note that past observations suggested there were movements of water through the lunar day. A lunar day is the time it takes for one point on the Earth to make one complete rotation and end up at the same point in relation to the moon.
Studies have provided evidence that the amount of water decreased on the moon’s surface when sunlight was brightest and increased with less sunlight.
The latest study was led by Björn Davidsson, a scientist at NASA’s Jet Propulsion Laboratory (JPL) in California. He teamed up with another JPL researcher, Sona Hosseini, to carry out the research.
The team revised past computer modeling to include rough surface areas of the moon that can be seen in images collected from NASA’s Apollo missions from 1969 to 1972. The research results recently appeared in the publication Monthly Notices of the Royal Astronomical Society.
The study suggests that as surface frost that forms in cold areas receives sunlight, it can then be “cycled into the moon’s exosphere.” The exosphere is the thin, outer area that forms around a planet or satellite object, such as the moon.
“Frost is far more mobile than trapped water,” Davidsson said in a statement. “Therefore, this model provides a new mechanism that explains how water moves between the lunar surface and the thin lunar atmosphere.”
The researchers say their study is the first to examine how shadows on the lunar surface can affect the ability of water molecules to survive as frost during the daytime.
They noted that such research is important to help scientists better understand how water enters and leaves the moon’s exosphere.
Hosseini said understanding water as a resource is “essential” for future NASA missions or any possible private space exploration. She added if water ice is available in sunlit areas of the moon, future explorers could use it for fuel and drinking water.
“But first, we need to figure out how the exosphere and surface interact and what role that plays in the cycle,” Hosseini said.
The researchers say they plan to test their theory by leading a team to develop small sensors to measure signals given off by a molecule contained in water ice. The sensing device will be designed to be used on small landers or robotic explorers that could be sent to the moon in future missions.
I’m Bryan Lynn.
Bryan Lynn wrote this report for VOA Learning English, based on reports from NASA and Monthly Notices of the Royal Astronomical Society. Hai Do was the editor.
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Words in This Story
shadow – n. a dark shape that appears on a surface when someone or something moves between the surface and a source of light
revise – v. change something that has already been worked on
mission – n. a flight by an aircraft or spacecraft to perform a specific task
frost – n. a thin layer of ice that forms on surfaces, especially at night when it is cold
mobile – adj. able to move or be moved easily
mechanism – n. a part of a piece of equipment that does a particular job
essential – adj. very important and necessary
figure out – v. to understand or find something, such as a reason or a solution by thinking
Astronomers have discovered hundreds of mysterious cosmic threads that point towards the supermassive black hole at the heart of the Milky Way, after a survey of the galaxy.
The strange filaments, each of which stretches five to 10 light years through space, resemble the dots and dashes of morse code on a vast scale. They spread out from the galactic centre 25,000 light years from Earth like fragmented spokes on an enormous wheel.
Farhad Yusef-Zadeh, an astronomer at Northwestern University in Evanston, Illinois, said he was “stunned” to discover the structures in data taken by the MeerKAT radio telescope in the Northern Cape of South Africa.
The observatory, the most sensitive radio telescope in the world, captured images of the threads during an unprecedented 200-hour survey of the galactic core. Yusef-Zadeh told the Guardian: “They all seem to trace back to the black hole. They are telling us something about the activity of the black hole itself.”
Four decades ago, Yusef-Zadeh found much larger, vertical filaments surrounding Sagittarius A*, the black hole at the centre of the Milky Way, in data gathered by another telescope called the Very Large Array in New Mexico. Those structures dangle perpendicular to the plane of the Milky Way disc and measure 150 light years from top to bottom.
What produced the more numerous vertical filaments is still unclear, but studies have found that they possess strong magnetic fields and emit radio waves as they accelerate particles in cosmic rays to the verge of light speed.
According to Yusef-Zadeh, researchers – himself included – have been so busy grappling with the nature of the giant vertical threads that the existence of the shorter, horizontal filaments which trace back to the centre of the Milky Way almost went unnoticed.
“The emphasis has been on understanding the vertical filaments. The horizontal structures somehow didn’t register,” Yusef-Zadeh said. “It was a surprise to suddenly find a new population of structures that seem to be pointing in the direction of the black hole. I was actually stunned when I saw these.”
“If it wasn’t for MeerKAT these wouldn’t have been detected,” he added. “We’ve never been able to dedicate that amount of time to the centre of the galaxy.
The shorter, horizontal threads that spread out from the centre of the Milky Way came into focus when the scientists removed the background and filtered noise from the MeerKAT images. Yusef-Zadeh believes the structures, described in the Astrophysical Journal Letters, formed through a different process to the larger, vertical filaments.
He suspects that an outburst of material from the black hole about 6m years ago slammed into surrounding stars and gas clouds, creating streaks of hot plasma that point back towards the black hole. The effect is akin to blowing blobs of paint across a canvas with a hairdryer.
“The outflow from the black hole interacts with the objects it meets and distorts their shape,” Yusef-Zadeh said. “It’s sufficient to blow everything in the same direction.”
By studying the cosmic threads, astronomers hope to understand more about the spin of the Milky Way’s central black hole and the accretion disc of infalling material that whirls around it.
“These are not going to be the last images of the centre of the galaxy,” said Yusef-Zadeh. “Our galaxy is rich in lots of structures that we can’t explain. There’s still a lot to be learned.”
The James Webb Space Telescope has found traces of water vapor in the atmosphere of a super-hot gas giant exoplanet that orbits its star in less than one Earth day.
The exoplanet in question, WASP-18 b, is a gas giant 10 times more massive than the solar system‘s largest planet, Jupiter. The planet is quite extreme, as it orbits the sun-like star WASP-18, which is located some 400 light-years away from Earth, at an average distance of just 1.9 million miles (3.1 million kilometers). For comparison, the solar system’s innermost planet, Mercury, circles the sun at a distance of 39.4 million miles (63.4 million km).
Due to such close proximity to the parent star, the temperatures in WASP-18 b’s atmosphere are so high that most water molecules break apart, NASA said in a statement. The fact that Webb managed to resolve signatures of the residual water is a testament to the telescope’s observing powers.
“The spectrum of the planet’s atmosphere clearly shows multiple small but precisely measured water features, present despite the extreme temperatures of almost 5,000 degrees Fahrenheit (2,700 degrees Celsius),” NASA wrote in the statement. “It’s so hot that it would tear most water molecules apart, so still seeing its presence speaks to Webb’s extraordinary sensitivity to detect remaining water.”
WASP-18 b, discovered in 2008, has been studied by other telescopes, including the Hubble Space Telescope, NASA’s X-ray space telescope Chandra, the exoplanet hunter TESS and the now-retired infrared Spitzer Space Telescope. None of these space telescopes, however, was sensitive enough to see the signatures of water in the planet’s atmosphere.
“Because the water features in this spectrum are so subtle, they were difficult to identify in previous observations,” Anjali Piette, a postdoctoral fellow at the Carnegie Institution for Science and one of the authors of the new research, said in the statement. “That made it really exciting to finally see water features with these JWST observations.”
In addition to being so massive, hot and close to its parent star, WASP-18 b is also tidally locked. That means one side of the planet constantly faces the star, just like the moon‘s near side always faces Earth. As a result of this tidal locking, considerable differences in temperature exist across the planet’s surface. The Webb measurements, for the first time, enabled scientists to map these differences in detail.
The measurements found that the most intensely illuminated parts of the planet can be up to 2,000 degrees F (1,100 degrees C) hotter than those in the twilight zone. The scientists didn’t expect such significant temperature differences and now think that there must be some not yet understood mechanism in action that prevents the distribution of heat around the planet’s globe.
“The brightness map of WASP-18 b shows a lack of east-west winds that is best matched by models with atmospheric drag,” co-author Ryan Challener, of the University of Michigan, said in the statement. “One possible explanation is that this planet has a strong magnetic field, which would be an exciting discovery!”
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To create the temperature map, the researchers calculated the planet’s infrared glow by measuring the difference in the glow of the parent star during the time the planet transited in front of the star’s disk and then when it disappeared behind it.
“JWST is giving us the sensitivity to make much more detailed maps of hot giant planets like WASP-18 b than ever before,” Megan Mansfield, a Sagan Fellow at the University of Arizona and one of the authors of the paper describing the results. said in the statement. “This is the first time a planet has been mapped with JWST, and it’s really exciting to see that some of what our models predicted, such as a sharp drop in temperature away from the point on the planet directly facing the star, is actually seen in the data.”
The new study was published online Wednesday (May 31) in the journal Nature.
When astronomers discovered WASP-18b in 2009, they uncovered one of the most unusual planets ever found. It’s ten times as massive as Jupiter is, it’s tidally locked to its Sun-like star, and it completes an orbit in less than one Earth day, about 23 hours.
Now astronomers have pointed the JWST and its powerful NIRSS instrument at the ultra-Hot Jupiter and mapped its extraordinary atmosphere.
Ever since its discovery, astronomers have been keenly interested in WASP-18b. For one thing, it’s massive. At ten times more massive than Jupiter, the planet is nearing brown dwarf territory. It’s also extremely hot, with its dayside temperature exceeding 2750 C (4900 F.) Not only that, but it’s likely to spiral to its doom and collide with its star sometime in the next one million years.
For these reasons and more, astronomers are practically obsessed with it. They’ve made extensive efforts to map the exoplanet’s atmosphere and uncover its details with the Hubble and the Spitzer. But those space telescopes, as powerful as they are, were unable to collect data detailed enough to reveal the atmosphere’s properties conclusively.
Now that the JWST is in full swing, it was inevitable that someone’s request to point it at WASP-18b would be granted. Who in the Astronomocracy would say no?
In new research, a team led by a Ph.D. student at the University of Montreal mapped WASP-19b’s atmosphere with the JWST. They used the NIRISS instrument, one of Canada’s contributions to the JWST. The paper is “A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b.” It’s published in Nature, and the lead author is Louis-Philippe Coulombe.
The researchers trained Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) on the planet during a secondary eclipse. This is when the planet passes behind its star and emerges on the other side. The instrument measures the light from the star and the planet, then during the eclipse, they deduct the star’s light, giving a measurement of the planet’s spectrum. The NIRISS’ power gave the researchers a detailed map of the planet’s atmosphere.
With the help of NIRISS, the researchers mapped the temperature gradients on the planet’s dayside. They found that the planet is much cooler near the terminator line: about 1,000 degrees cooler than the hottest point of the planet directly facing the star. That shows that winds are unable to spread heat efficiently to the planet’s nightside. What’s stopping that from happening?
“JWST is giving us the sensitivity to make much more detailed maps of hot giant planets like WASP-18 b than ever before. This is the first time a planet has been mapped with JWST, and it’s really exciting to see that some of what our models predicted, such as a sharp drop in temperature away from the point on the planet directly facing the star, is actually seen in the data!” said paper co-author Megan Mansfield, a Sagan Fellow at the University of Arizona.
The lack of winds moving the atmosphere around and regulating the temperature is surprising, and atmospheric drag has something to do with it.
“The brightness map of WASP-18 b shows a lack of east-west winds that is best matched by models with atmospheric drag,” said co-author Ryan Challener, a post-doctoral researcher at the University of Michigan. “One possible explanation is that this planet has a strong magnetic field, which would be an exciting discovery!”
In our Solar System, Jupiter has the strongest magnetic field. Scientists think that swirling conducting materials deep inside the planet, near its bizarre liquid, metallic hydrogen core generates the magnetic fields. The fields are so powerful that they protect the three Galilean moons from the solar wind. They also generate permanent aurorae and create powerful radiation belts around the giant planet.
But WASP-18 b is ten times more massive than Jupiter, and it’s reasonable to think its magnetic fields are even more dominant. If the planet’s magnetic field is responsible for the lack of east-west winds, it could be forcing the winds to move over the North Pole and down the South Pole.
The researchers were also able to measure the atmosphere’s temperature at different depths. Temperatures increased with altitude, sometimes by hundreds of degrees. They also found water vapour at different depths.
At 2,700 Celsius, the heat should tear most water molecules apart. The fact that the JWST was able to spot the remaining water speaks to its sensitivity.
CREDIT: NASA/JPL-CALTECH/R. HURT
“Because the water features in this spectrum are so subtle, they were difficult to identify in previous observations. That made it really exciting to finally see water features with these JWST observations,” said Anjali Piette, a postdoctoral fellow at the Carnegie Institution for Science and one of the authors of the new research.
But the JWST was able to reveal more about the star than just its temperature gradients and its water content. The researchers found that the atmosphere contains Vanadium Oxide, Titanium Oxide, and Hydride, a negative ion of hydrogen. Together, those chemicals could combine to give the atmosphere its opacity.
All these findings came from only six hours of observations with NIRISS. Six hours of JWST time is precious to astronomers, and that’s all the researchers needed. That’s not only because the JWST is so powerful and capable, but also because of WASP-18 b itself.
At only 400 light-years away, it’s relatively close in astronomical terms. Its proximity to its star also helped, and the planet is huddled right next to its star. Plus, WASP-18 b is huge. In fact, it’s one of the most massive planets accessible to atmospheric investigation.
The planet’s atmospheric properties also provide clues to its origins. Comparisons of metallicity and composition between planets and stars can help explain a planet’s history. WASP-18 b couldn’t have formed in its current location. It must have migrated there somehow. And while this work can’t answer that conclusively, it does tell us other things about the giant planet’s formation.
“By analyzing WASP-18 b’s spectrum, we not only learn about the various molecules that can be found in its atmosphere but also about the way it formed. We find from our observations that WASP-18 b’s composition is very similar to that of its star, meaning it most likely formed from the leftover gas that was present just after the star was born,” Coulombe said. “Those results are very valuable to get a clear picture of how strange planets like WASP-18 b, which have no counterpart in our Solar System, come to exist.”
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