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exoplanets giant

Giant exoplanets directly observed orbiting Sun-like star – Physics World – physicsworld.com


Image of exoplanets orbiting a Sun-like Star
Caught on camera: This first-ever image of a multi-planet system around a Sun-like star shows the two planets (centre and bottom right) orbiting TYC 8998-760-1 (Courtesy: ESO/Bohn et al.)

The first ever direct image of a young Sun-like star accompanied by two giant exoplanets has been captured by astronomers using the Very Large Telescope (VLT) in Chile. The two planets are orbiting the star TYC 8998-760-1, which lies 300 light-years away from Earth. The star has an almost identical mass to our Sun, but is just 17 million years old compared with 4.6 billion years for our Sun.

Perhaps the most striking feature of this system is the large mass of the planets and their giant orbits. The inner planet has 14 times Jupiter’s mass and the outer one six times. They orbit at distances of roughly 160 and 320 times the Earth–Sun distance respectively, which is more than 30 times larger than the orbits of Jupiter and Saturn.

This discovery is a snapshot of an environment that is very similar to our solar system, but at a much earlier stage of its evolution.

Alexander Bohn, Leiden University

“This discovery is a snapshot of an environment that is very similar to our solar system, but at a much earlier stage of its evolution,” says Alexander Bohn from at Leiden University in the Netherlands, who led the new research, published in Astrophysical Journal Letters.

A turbulent past

Bohn told Physics World that this system might represent the lower mass end of multiple star formation. In other words, had a bit more stuff accreted from the protostellar cloud, then this could have resulted in a binary star system, rather than one star and two huge planets.

Alternatively, these giant planets could be the result of several small planetessimals clustering together into cores, which eventually gained enough gravitational pull to accrete gas from the circumstellar disc. This is the favoured scenario for the formation of the largest planets in our own solar system.

“To explain the large separations of our detected planets, however, some kind of outward migration is required,” says Bohn. “This can be performed by gravitationally scattering off of each other or with another, so far undetected, third object in the system.”

To date, more than 4000 exoplanets have been detected. However, the vast majority of these have been spotted using indirect methods, such as observing the dip in starlight as a planet transits between its parent star and our line of sight.

Only a tiny fraction of these planets has been directly observed, and the direct imaging of two or more exoplanets around the same star is even rarer. Only two such systems have been directly observed so far, both around stars markedly different from our Sun.

Hot young planets

These latest images were possible due to the SPHERE instrument on the VLT at the European Southern Observatory (ESO) in Chile, which uses a coronagraph to block bright starlight, allowing much fainter planets to be seen. While older planets, such as those seen in our solar system, are too cool to be found with this technique, young planets are hotter, and so glow brighter in infrared light.

This discovery still tells us that there is not just one way to form a planetary system.

Carlo Felice Manara, European Southern Observatory

“This discovery still tells us that there is not just one way to form a planetary system, and the outcome of the process can be very different,” says Carlo Felice Manara, an astronomer based at ESO headquarters in Germany, who was not involved in this latest research. “Why in our solar system we only have planets with mass of Jupiter, or less, and no more massive planets is still an open question.”

Further observations of TYC 8998-760-1 system will enable astronomers to better understand its dynamics. ESO’s Extremely Large Telescope – scheduled to capture its first astronomical images in 2025 – could even detect further planets with Neptune or Saturn masses. Unfortunately, even that instrument is  unlikely to detect rocky planets similar to Earth, as these are just too faint.

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giant waves

Giant waves of sand are moving on Mars – Science Magazine

Megaripples near a sand dune on Mars.

NASA/JPL/University of Arizona

By Katherine Kornei

Researchers have spotted large waves of martian sand migrating for the first time. The discovery dispels the long-held belief that these “megaripples” haven’t moved since they formed hundreds of thousands of years ago. They’re also evidence of stronger-than-expected winds on the Red Planet.

It’s pretty staggering that humans can detect these changes on Mars, says Ralph Lorenz, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory who was not involved in the research. “We can now measure processes on the surface of another planet that are just a couple times faster than our hair grows.”

Megaripples are found in deserts on Earth, often between dunes. Waves in the sand spaced up to tens of meters apart, they’re a larger version of ripples that undulate every 10 centimeters or so on many sand dunes.

But unlike dunes, megaripples are made up of two sizes of sand grains. Coarser, heavier grains cap the crests of megaripples, making it harder for wind to move these features around, says Simone Silvestro, a planetary scientist at Italy’s National Institute of Astrophysics in Naples.

Since the early 2000s, Mars rovers and orbiters have repeatedly spotted megaripples on the Red Planet. But they didn’t seem to change in any measurable way, which led some scientists to think they were relics from Mars’s past, when its thicker atmosphere permitted stronger winds.

Now, using images captured by NASA’s Mars Reconnaissance Orbiter, Silvestro and his colleagues have shown that some megaripples do creep along—just very slowly.

The researchers focused on two sites near the equator of Mars. They analyzed roughly 1100 megaripples in McLaughlin crater and 300 in the Nili Fossae region. They looked for signs of movement by comparing time-lapse images of each site—taken 7.6 and 9.4 years apart, respectively. Megaripples in both regions advanced by about 10 centimeters per year, the team reports in the Journal of Geophysical Research: Planets. That’s about how fast megaripples move in the Lut Desert of Iran.

It’s a surprise that megaripples move at all on Mars, says Jim Zimbelman, a planetary geologist at the Smithsonian Institution’s Air and Space Museum. Just a few decades ago, there was no evidence that sands on Mars were mobile, he says. “None of us thought that the winds were strong enough.”

Winds on Mars might be accelerating small grains of sand, Silvestro and his colleagues suggest. Once these grains start to roll or bounce, they can act like battering rams, knocking into larger grains and setting them in motion. This process, known as impact-driven creep, has been observed on Earth.

Sand dunes on Mars likely donated their grains to the megaripples’ migration, the team concludes, because nearby dunes moved in the same direction as the megaripples.

Atmospheric models of Mars suggest winds capable of moving sand are rare. This discovery of migrating megaripples will force those models to be revised, the team suggests.

Silvestro plans to expand his search for migrating megaripples to the whole planet. He suspects the speediest megaripples will be near Mars’s fastest moving dunes. Megaripples on the move are beacons of windy conditions, which might in turn kick-start dust storms, the researchers suggest. Airborne dust can blanket solar panels, reducing their efficiency, and it can also gum up mechanical parts like gears. That’s bad news for Mars rovers and human habitats alike.

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giant spots

Giant star spots likely cause of Betelgeuse dimming – Phys.org

Betelgeuse—a giant with blemishes
Red Supergiant: An artist’s impression of Betelgeuse. Its surface is covered by large star spots, which reduce its brightness. During their pulsations, such stars regularly release gas into their surroundings, which condenses into dust. Credit: MPIA graphics department

Betelgeuse, the bright star in the constellation of Orion, has been fascinating astronomers in the recent months because of its unusually strong decline in brightness. Scientists have been discussing a number of scenarios trying to explain its behavior. Now a team led by Thavisha Dharmawardena of the Max Planck Institute for Astronomy have shown that most likely unusually large star spots on the surface of Betelgeuse have caused the dimming. Their results rule out the previous conjecture that it was dust, recently ejected by Betelgeuse, which obscured the star.

Red giant stars like Betelgeuse undergo frequent brightness variations. However, the striking drop in Betelgeuse’s luminosity to about 40% of its normal value between October 2019 and April 2020 came as a surprise to astronomers. Scientists have developed various scenarios to explain this change in the brightness of the star, which is visible to the naked eye and almost 500 away. Some astronomers even speculated about an imminent supernova. An international team of astronomers led by Thavisha Dharmawardena from the Max Planck Institute for Astronomy in Heidelberg have now demonstrated that in the photosphere, i.e. the luminous surface of the star, caused the brightness to drop. The most plausible source for such temperature changes are gigantic cool star spots, similar to sunspots, which, however, cover 50 to 70% of the star’s surface.

“Towards the end of their lives, stars become red giants,” Dharmawardena explains. “As their fuel supply runs out, the processes change by which the stars release energy.” As a result, they bloat, become unstable and pulsate with periods of hundreds or even thousands of days, which we see as a fluctuation in brightness. Betelgeuse is a so-called Red Supergiant, a star which, compared to our sun, is about 20 more massive and roughly 1000 times larger. If placed in the center of the solar system, it would almost reach the orbit of Jupiter.

Because of its size, the gravitational pull on the surface of the star is less than on a star of the same mass but with a smaller radius. Therefore, pulsations can eject the outer layers of such a star relatively easily. The released gas cools down and develops into compounds that astronomers call dust. This is why are an important source of heavy elements in the Universe, from which planets and living organisms eventually evolve. Astronomers have previously considered the production of light absorbing dust as the most likely cause of the steep decline in brightness.

Betelgeuse—a giant with blemishes
Light and dark: These high-resolution images of Betelgeuse show the distribution of brightness in visible light on its surface before and during its darkening. Due to the asymmetry, the authors conclude that there are huge stars pots. The images were taken by the SPHERE camera of the European Southern Observatory (ESO). Credit: ESO / M. Montargès et al.

To test this hypothesis, Thavisha Dharmawardena and her collaborators evaluated new and archival data from the Atacama Pathfinder Experiment (APEX) and the James Clerk Maxwell telescope (JCMT). These telescopes measure radiation from the spectral range of submillimeter waves (terahertz radiation), whose wavelength is a thousand times greater than that of visible light. Invisible to the eye, astronomers have been using them for some time to study interstellar dust. Cool dust in particular glows at these wavelengths.

“What surprised us was that Betelgeuse turned 20% darker even in the submillimeter wave range,” reports Steve Mairs from the East Asian Observatory, who collaborated on the study. Experience shows that such behavior is not compatible with the presence of dust. For a more precise evaluation, she and her collaborators calculated what influence dust would have on measurements in this spectral range. It turned out that indeed a reduction in brightness in the sub-millimeter range cannot be attributed to an increase in dust production. Instead, the star itself must have caused the brightness change the astronomers measured.

Physical laws tell us that the luminosity of a star depends on its diameter and especially on its surface temperature. If only the size of the star decreases, the luminosity diminishes equally in all wavelengths. However, temperature changes affect the radiation emitted along the electromagnetic spectrum differently. According to the scientists, the measured darkening in and submillimeter waves is therefore evidence of a reduction in the mean surface temperature of Betelgeuse, which they quantify at 200 K (or 200 °C).

“However, an asymmetric temperature distribution is more likely,” explains co-author Peter Scicluna from the European Southern Observatory (ESO). “Corresponding high-resolution images of Betelgeuse from December 2019 show areas of varying brightness. Together with our result, this is a clear indication of huge star spots covering between 50 and 70% of the visible surface and having a lower temperature than the brighter photosphere.” Star spots are common in giant stars, but not on this scale. Not much is known about their lifetimes. However, theoretical model calculations seem to be compatible with the duration of Betelgeuse’s dip in brightness.

We know from the sun that the amount of spots increases and decreases in an 11-year cycle. Whether giant have a similar mechanism is uncertain. An indication for this could be the previous brightness minimum, which was also much more pronounced than those in previous years. “Observations in the coming years will tell us whether the sharp decrease in Betelgeuse’s is related to a spot cycle. In any case, Betelgeuse will remain an exciting object for future studies,” Dharmawardena concludes.



More information:
Thavisha E. Dharmawardena et al. Betelgeuse Fainter in the Submillimeter Too: An Analysis of JCMT and APEX Monitoring during the Recent Optical Minimum, The Astrophysical Journal (2020). DOI: 10.3847/2041-8213/ab9ca6

Citation:
Giant star spots likely cause of Betelgeuse dimming (2020, June 29)
retrieved 29 June 2020
from https://phys.org/news/2020-06-giant-star-betelgeuse-dimming.html

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giant Young

Young Giant Planet Offers Clues to Formation of Exotic Worlds – NASA

Young Giant Planet Offers Clues to Formation of Exotic Worlds – NASA
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Asian giant

Asian giant hornet invasion becomes latest 2020 concern – NBC News

An invasion of Asian giant hornets became the latest 2020 worry — and internet sensation — as the term “murder hornet” began to trend over the weekend.

The first spotting of the 2-inch Asian giant hornet, or vespa mandarinia, was verified in the United States in December, according to the Washington state Agriculture Department. The insect does not generally target people or pets, but it is a deadly threat to at-risk honeybee hives.

Giant hornets of this species apparently enter a “slaughter phase” during which they decapitate honeybees and destroy entire hives in the span of a few hours, according to the department.

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The Asian giant hornet is the world’s largest species of hornet.Washington State Department of Agriculture

Although the species was first spotted months ago, the term “murder hornet” circulated on Twitter over the weekend after a New York Times report Saturday on efforts to stop the species from annihilating honeybees.

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As the globe reels with the upheaval of normal life during the coronavirus pandemic, the internet latched onto “murder hornets” as yet another strange development of 2020.

“Murder hornets. Sure thing, 2020,” actor and comedian Patton Oswalt tweeted Saturday. “Give us everything. Hypno-frogs. Fecal blizzards. Toilet tsunamis. A CATS sequel. We can take it.”

Murder hornets. Sure thing, 2020. Give us everything. Hypno-frogs. Fecal blizzards. Toilet tsunamis. A CATS sequel. We can take it. https://t.co/DSDpgKhKzQ

— Patton Oswalt (@pattonoswalt) May 2, 2020

An invasion could have severely negative impacts on the environment and public health, the Washington Agriculture Department warned.

The species has longer stingers with more toxic venom that could pose a danger to people if the insects feel threatened. And unlike honeybees, the Asian giant hornets can sting repeatedly, entomologist Chris Looney said in a video posted to the department’s YouTube page last month.

Authorities are working to find nests and destroy them before they can reproduce, according to Looney.

Looney warned people against trying to kill the hornets themselves and to avoid their nests entirely. Instead, the public is encouraged to report a possible sighting to local authorities.

Image: Doha MadaniDoha Madani

Doha Madani is a breaking news reporter for NBC News. 

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asteroid giant

This giant asteroid will fly by Earth Wednesday, close enough to see by telescope, but it won’t hit us, experts say – CNN

(CNN)An asteroid estimated to be 1.2 miles wide will fly by Earth early Wednesday morning, but it’s not expected to collide with our planet.

The asteroid is called 52768 (1998 OR2), and it was first spotted in 1998. On April 29, it will pass within 3,908,791 miles of Earth, moving at 19,461 miles per hour. That’s still 16 times farther than the distance between Earth and the moon.
The flyby is expected to occur at 5:56 a.m. ET, according to NASA’s Center for Near-Earth Object Studies. The center tracks Near-Earth Objects, or NEOs, that could collide with Earth. They have been tracking this particular asteroid for 20 years, according to NASA.
You can watch it live on The Virtual Telescope’s website. Gianluca Masi, founder and scientific director of The Virtual Telescope in Italy, has been tracking and imaging it for some time.
If it did impact Earth, the asteroid is “large enough to cause global effects,” according to NASA, back when the asteroid was first discovered.
And if an asteroid could be aware of such things, it appears to be wearing a face mask in deference to the pandemic, according to new images from Arecibo Observatory in Puerto Rico.
“The small-scale topographic features such as hills and ridges on one end of asteroid 1998 OR2 are fascinating scientifically,” said Anne Virkki, head of planetary radar at Arecibo Observatory, in a statement. “But since we are all thinking about Covid-19, these features make it look like 1998 OR2 remembered to wear a mask.”
Arecibo Observatory is a National Science Foundation facility managed by the University of Central Florida. A team of experts has been monitoring this near-Earth asteroid, among others. The observatory is supported by NASA’s Near-Earth Object Observations Program and has been analyzing asteroids since the mid-’90s.
During the pandemic, scientists at Arecibo are continuing to make their observations on behalf of planetary defense. In line with social distancing, they have limited the number of scientists and radar operators at the facility, and they’re wearing masks during observations.
The asteroid was classified as a potentially hazardous object because it’s bigger than 500 feet and comes within 5 million miles of Earth’s orbit. The experts at Arecibo can monitor the asteroids and use observations to determine their path in the future to see if they pose a risk to Earth.
“The radar measurements allow us to know more precisely where the asteroid will be in the future, including its future close approaches to Earth,” said Flaviane Venditti, a research scientist at the observatory, in a statement. “In 2079, asteroid 1998 OR2 will pass Earth about 3.5 times closer than it will this year, so it is important to know its orbit precisely.”
It’s the largest asteroid expected to zip by Earth within the next two months, but it’s not the largest ever.
That honor belongs to the asteroid 3122 Florence (1981 ET3), which flew by and luckily missed colliding with Earth on September 1, 2017. It will make another pass again on September 2, 2057. That asteroid is estimated to be between two and a half and five and a half miles wide.

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