Large asteroid coming close, but zero chance of hitting us
An asteroid big enough to wipe out a city will zip harmlessly between Earth and the moon’s orbit this weekend, missing both celestial bodies.
Saturday’s close encounter will offer astronomers the chance to study a space rock from just over 100,000 miles (168,000 kilometers) away. That’s less than half the distance from here to the moon, making it visible through binoculars and small telescopes.
While asteroid flybys are common, NASA said it’s rare for one so big to come so close—about once a decade. Scientists estimate its size somewhere between 130 feet and 300 feet (40 meters and 90 meters).
Discovered a month ago, the asteroid known as 2023 DZ2 will pass within 320,000 miles (515,000 kilometers) of the moon on Saturday and, several hours later, buzz the Indian Ocean at about 17,500 mph (28,000 kph).
“There is no chance of this ‘city killer’ striking Earth, but its close approach offers a great opportunity for observations,” the European Space Agency’s planetary defense chief Richard Moissl said in a statement.
Astronomers with the International Asteroid Warning Network see it as good practice for planetary defense if and when a dangerous asteroid heads our way, according to NASA.
The Virtual Telescope Project will provide a live webcast of the close approach.
The asteroid won’t be back our way again until 2026. Although there initially seemed to be a slight chance it might strike Earth then, scientists have since ruled that out.
© 2023 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.
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NASA's Parker Solar Probe Plunges Into Fast Solar Wind and Discovers Its Mysterious Source – SciTechDaily
NASA’s Parker Solar Probe probe got close enough to sun’s surface to see hidden granular features.
NASA’s Parker Solar Probe (PSP) has flown close enough to the sun to detect the fine structure of the solar wind close to where it is generated at the sun’s surface, revealing details that are lost as the wind exits the corona as a uniform blast of charged particles.
It’s like seeing jets of water emanating from a showerhead through the blast of water hitting you in the face.
In a paper published on June 7 in the journal Nature, a team of scientists led by Stuart D. Bale, a professor of physics at the University of California, Berkeley, and James Drake of the University of Maryland-College Park, report that PSP has detected streams of high-energy particles that match the supergranulation flows within coronal holes, which suggests that these are the regions where the so-called “fast” solar wind originates.
Coronal holes are areas where magnetic field lines emerge from the surface without looping back inward, thus forming open field lines that expand outward and fill most of space around the sun. These holes are usually at the poles during the sun’s quiet periods, so the fast solar wind they generate doesn’t hit Earth. But when the sun becomes active every 11 years as its magnetic field flips, these holes appear all over the surface, generating bursts of solar wind aimed directly at Earth.
Understanding how and where the solar wind originates will help predict solar storms that, while producing beautiful auroras on Earth, can also wreak havoc with satellites and the electrical grid.
“Winds carry lots of information from the sun to Earth, so understanding the mechanism behind the sun’s wind is important for practical reasons on Earth,” Drake said. “That’s going to affect our ability to understand how the sun releases energy and drives geomagnetic storms, which are a threat to our communication networks.”
Based on the team’s analysis, the coronal holes are like showerheads, with roughly evenly spaced jets emerging from bright spots where magnetic field lines funnel into and out of the surface of the sun. The scientists argue that when oppositely directed magnetic fields pass one another in these funnels, which can be 18,000 miles across, the fields often break and reconnect, slinging charged particles out of the sun.
“The photosphere is covered by convection cells, like in a boiling pot of water, and the larger scale convection flow is called supergranulation,” Bale said. “Where these supergranulation cells meet and go downward, they drag the magnetic field in their path into this downward kind of funnel. The magnetic field becomes very intensified there because it’s just jammed. It’s kind of a scoop of magnetic field going down into a drain. And the spatial separation of those little drains, those funnels, is what we’re seeing now with solar probe data.”
Based on the presence of some extremely high-energy particles that PSP has detected — particles traveling 10 to 100 times faster than the solar wind average — the researchers conclude that the wind could only be made by this process, which is called magnetic reconnection. The PSP was launched in 2018 primarily to resolve two conflicting explanations for the origin of the high-energy particles that comprise the solar wind: magnetic reconnection or acceleration by <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="
” data-gt-translate-attributes=”["attribute":"data-cmtooltip", "format":"html"]”>plasma or Alfvén waves.
“The big conclusion is that it’s magnetic reconnection within these funnel structures that’s providing the energy source of the fast solar wind,” Bale said. “It doesn’t just come from everywhere in a coronal hole, it’s substructured within coronal holes to these supergranulation cells. It comes from these little bundles of magnetic energy that are associated with the convection flows. Our results, we think, are strong evidence that it’s reconnection that’s doing that.”
The funnel structures likely correspond to the bright jetlets that can be seen from Earth within coronal holes, as reported recently by Nour Raouafi, a co-author of the study and the Parker Solar Probe project scientist at the Applied Physics Laboratory at Johns Hopkins University. APL designed, built, manages, and operates the spacecraft.
Plunging into the sun
By the time the solar wind reaches Earth, 93 million miles from the sun, it has evolved into a homogeneous, turbulent flow of roiling magnetic fields intertwined with charged particles that interact with Earth’s own magnetic field and dump electrical energy into the upper atmosphere. This excites atoms, producing colorful auroras at the poles, but has effects that trickle down into Earth’s atmosphere. Predicting the most intense winds, called solar storms, and their near-Earth consequences is one mission of <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="
” data-gt-translate-attributes=”["attribute":"data-cmtooltip", "format":"html"]”>NASA’s Living With a Star program, which funded PSP.
The probe was designed to determine what this turbulent wind looks like where it’s generated near the sun’s surface, or photosphere, and how the wind’s charged particles — protons, electrons, and heavier ions, primarily helium nuclei — are accelerated to escape the sun’s gravity.
To do this, PSP had to get closer than 25 to 30 solar radii, that is, closer than about 13 million miles.
“Once you get below that altitude, 25 or 30 solar radii or so, there’s a lot less evolution of the solar wind, and it’s more structured — you see more of the imprints of what was on the sun,” Bale said.
In 2021, PSP’s instruments recorded magnetic field switchbacks in the Alfvén waves that seemed to be associated with the regions where the solar wind is generated. By the time the probe reached about 12 solar radii from the surface of the sun — 5.2 million miles — the data were clear that the probe was passing through jets of material, rather than mere turbulence. Bale, Drake, and their colleagues traced these jets back to the supergranulation cells in the photosphere, where magnetic fields bunch up and funnel into the sun.
But were the charged particles being accelerated in these funnels by magnetic reconnection, which would slingshot particles outward, or by waves of hot plasma — ionized particles and magnetic field — streaming out of the sun, as if they’re surfing a wave?
The fact that PSP detected extremely high-energy particles in these jets — tens to hundreds of kiloelectron volts (keV), versus a few keV for most solar wind particles — told Bale that it has to be magnetic reconnection that accelerates the particles and generates the Alfvén waves, which likely give the particles an extra boost.
“Our interpretation is that these jets of reconnection outflow excite Alfvén waves as they propagate out,” Bale said. “That’s an observation that’s well known from Earth’s magnetotail, as well, where you have similar kinds of processes. I don’t understand how wave damping can produce these hot particles up to hundreds of keV, whereas it comes naturally out of the reconnection process. And we see it in our simulations, too. ”
The PSP won’t be able to get any closer to the sun than about 8.8 solar radii above the surface — about 4 million miles — without frying its instruments. Bale expects to solidify the team’s conclusions with data from that altitude, though the sun is now entering solar maximum, when activity becomes much more chaotic and may obscure the processes the scientists are trying to view.
“There was some consternation at the beginning of the solar probe mission that we’re going to launch this thing right into the quietest, most dull part of the solar cycle,” Bale said. “But I think without that, we would never have understood this. It would have been just too messy. I think we’re lucky that we launched it in the solar minimum.”
Reference: “Interchange reconnection as the source of the fast solar wind within coronal holes” by S. D. Bale, J. F. Drake, M. D. McManus, M. I. Desai, S. T. Badman, D. E. Larson, M. Swisdak, T. S. Horbury, N. E. Raouafi, T. Phan, M. Velli, D. J. McComas, C. M. S. Cohen, D. Mitchell, O. Panasenco and J. C. Kasper, 7 June 2023, Nature.
ESA – Cheops explores mysterious warm mini-Neptunes – European Space Agency
ESA’s exoplanet mission Cheops confirmed the existence of four warm exoplanets orbiting four stars in our Milky Way. These exoplanets have sizes between Earth and Neptune and orbit their stars closer than Mercury our Sun.
These so-called mini-Neptunes are unlike any planet in our Solar System and provide a ‘missing link’ between Earth-like and Neptune-like planets that is not yet understood. Mini-Neptunes are among the most common types of exoplanets known, and astronomers are starting to find more and more orbiting bright stars.
Mini-Neptunes are mysterious objects. They are smaller, cooler, and more difficult to find than the so-called hot Jupiter exoplanets which have been found in abundance. While hot Jupiters orbit their star in a matter of hours to days and typically have surface temperatures of more than 1000 °C, warm mini-Neptunes take longer to orbit their host stars and have cooler surface temperatures of only around 300 °C.
The first sign of the existence of these four new exoplanets was found by the NASA TESS mission. However, this spacecraft only looked for 27 days at each star. A hint to a transit – the dimming of light as a planet passes in front of its star from our viewpoint – was spotted for each star. During its extended mission, TESS revisited these stars and the same transit was seen again, implying the existence of planets.
Scientists calculated the most likely orbital periods and pointed Cheops at the same stars at the time they expected the planets to transit. During this hit-or-miss procedure Cheops was able to measure a transit for each of the exoplanets, confirming their existence, discovering their true orbital periods and taking the next step in their characterisation.
The four newly discovered planets have orbits between 21 and 53 days around four different stars. Their discovery is essential because it brings our sample of known exoplanets closer to the longer orbits that we find in our own Solar System.
One of the outstanding questions about mini-Neptunes is what they are made of. Astronomers predict that they have an iron-rocky core with thick outer layers of lighter material. Different theories predict different outer layers: Do they have deep oceans of liquid water, a puffy hydrogen and helium atmosphere or an atmosphere of pure water vapour?
Discovering the composition of mini-Neptunes is important to understand the formation history of this type of planet. Water-rich mini-Neptunes probably formed far out in the icy regions of their planetary system before migrating inwards, while combinations of rock and gas would tell us that these planets stayed in the same place as they formed.
The new Cheops measurements helped determine the radius of the four exoplanets, while their mass could be determined using observations from ground-based telescopes. Combining the mass and radius of a planet gives an estimate of its overall density.
The density can only give a first estimate of the mass of the iron-rocky core. While this new information about the density is an important step forward in understanding mini-Neptunes, it does not contain enough information to offer a conclusion for the outer layers.
The four newly confirmed exoplanets orbit bright stars, which make them the perfect candidates for a follow-up visit by the NASA/ESA/CSA James Webb Space Telescope or ESA’s future Ariel mission. These spectroscopic missions could discover what their atmospheres contain and provide a definitive answer to the composition of their outer layers.
A full characterisation is needed to understand how these bodies formed. Knowing the composition of these planets will tell us by what mechanism they formed in early planetary systems. This in turn helps us better understand the origins and evolution of our own Solar System.
The results were published in four papers: ‘Refined parameters of the HD 22946 planetary system and the true orbital period of the planet d’ by Z. Garai et al. is published in Astronomy & Astrophysics. https://www.aanda.org/10.1051/0004-6361/202345943
‘Two Warm Neptunes transiting HIP 9618 revealed by TESS & Cheops’ by H. P. Osborn et al. is published in the Monthly Notices of the Royal Astronomical Society. https://doi.org/10.1093/mnras/stad1319
‘TESS and CHEOPS Discover Two Warm Sub-Neptunes Transiting the Bright K-dwarf HD15906’ by A. Tuson et al. is published in the Monthly Notices of the Royal Astronomical Society. https://doi.org/10.1093/mnras/stad1369
‘TOI-5678 b: a 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS’ by S. Ulmer-Moll et al. is published in Astronomy & Astrophysics. https://www.aanda.org/10.1051/0004-6361/202245478
Brightest gamma-ray burst ever seen, the largest known explosion since Big Bang, has a unique jet structure unlike any other – Space.com
Scientists may finally know what made the largest explosion in the universe ever seen by humankind so powerful.
Astronomers have discovered that the brightest gamma-ray burst (GRB) ever seen had a unique jet structure and was dragging an unusually large amount of stellar material along with it.
This might explain the extreme properties of the burst, believed to have been launched when a massive star located around 2.4 billion light-years from Earth in the direction of the constellation Sagitta underwent total gravitational collapse to birth a black hole, as well as why its afterglow persisted for so long.
The GRB officially designated GRB 221009A but nicknamed the BOAT, or the brightest of all time, was spotted on October 9, 2022, and stood out from other GRBs due to its extreme nature. It was seen as an immensely bright flash of high-energy gamma-rays, followed by a low-fading afterglow across many wavelengths of light.
Related: A tiny Eastern European cubesat measured a monster gamma-ray burst better than NASA. Here’s how
“GRB 221009A represents a massive step forward in our understanding of gamma-ray bursts and demonstrates that the most extreme explosions do not obey the standard physics assumed for garden variety gamma-ray bursts,” George Washington University researcher and study lead author Brendan O’Connor said in a statement. O’Connor led a team that continued to monitor the BOAT GRB with the Gemini South Telescope in Chile following its initial discovery in Oct 2023.
Northwestern University doctoral candidate Jillian Rastinejad, who was also part of a team that observed the BOAT on Oct. 14 after its initial discovery,told Live Science that GRB 221009A is thought to be brighter than other highly energetic GRBs by a factor of at least 10.
“Photons have been detected from this GRB that has more energy than theLarge Hadron Collider (LHC) produces,” she said.
Even before the BOAT was spotted, GRBs were already considered the most powerful, violent, and energetic explosions in the universe, capable of blasting out as much energy in a matter of seconds as the sun will produce over its entire around ten billion-year lifetime. There are two types of these blasts, long-duration, and short-duration, which might have different launch mechanisms, both resulting in the creation of a black hole.
Further examination of the powerful GRB has revealed that it is unique for its structure as well as its brightness. The GRB was surprisingly wide. So wide, in fact, that astronomers were initially unable to see its edges.
“Our work clearly shows that the GRB had a unique structure, with observations gradually revealing a narrow jet embedded within a wider gas outflow where an isolated jet would normally be expected,” co-author and Department of Physics at the University of Bath scientist Hendrik Van Eerten said in a statement.
Thus, the jet of GRB 221009A appears to possess both wide and narrow “wings” that differentiate it from the jets of other GRBs. This could explain why the afterglow of the BOAT continued to be seen by astronomers in multiple wavelengths for months after its initial discovery.
Van Eerten and the team have a theory as to what gives the jet of the BOAT its unique structure.
“GRB jets need to go through the collapsing star in which they are formed,” he said. “What we think made the difference in this case was the amount of mixing that happened between the stellar material and the jet, such that shock-heated gas kept appearing in our line of sight all the way up to the point that any characteristic jet signature would have been lost in the overall emission from the afterglow.”
Van Eerten also points out the findings could help understand not just the BOAT but also other incredibly bright GRBs.
“GRB 221009A might be the equivalent of the Rosetta stone of long GRBs, forcing us to revise our standard theories of how relativistic outflows are formed in collapsing massive stars,” O’Connor added.
The discovery will potentially lay the foundation for future research into GRBs as scientists attempt to unlock the mysteries still surrounding these powerful bursts of energy. The findings could also help physicists better model the structure of GRB jets.
“For a long time, we have thought about jets as being shaped like ice cream cones,” study co-author and George Washington University associate professor of physics Alexander van der Horst said. “However, some gamma-ray bursts in recent years, and in particular the work presented here, show that we need more complex models and detailed computer simulations of gamma-ray burst jets.”
The team’s research is detailed in a paper published in the journal Science Advances.
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