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A close pass of Comet Wirtanen in 2018 offered researchers an unprecedented opportunity.

Comets are full of surprises. Not only do they often under- or very occasionally over- perform versus expectations, but they also offer a glimpse of the remnants of the very early solar system. In December 2018, astronomers had an unprecedented opportunity to study one of these relics of the early solar system up close as Comet 46P/Wirtanen sped by Earth just 30 times the Earth-Moon distance (7.1 million miles away) on its closest passage for this century.

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The orbit of Comet 46P/Wirtanen. NASA/JPL

Discovered by astronomer Carl A. Wirtanen in 1948, short period Comet 46P Wirtanen orbits the Sun every 5.4 years, on a path that takes it from a perihelion 1.06 AU from the Sun to an aphelion of 5.13 AU, just outside the perihelion of Jupiter.

The 2018 approach past Earth for the comet was an especially favorable one, and this time, astronomers at the W.M. Keck Observatory on Maunakea, Hawai’i were ready. Keck’s Near Infrared Spectrograph (NIRSPEC) just received a major upgrade, featuring more pixels and higher sensitivity, an upgrade that would see first light obtaining spectra of the comet.

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Instruments need hugs, too. Dr. Emily Martin with the newly upgraded NIRSPEC instrument. W.M. Keck Observatory.

And the results, recently published in The Planetary Science Journal were a spectacular success. Not only did the team classify a list of key compounds seen out-gassing from Comet Wirtanen, but they discovered a high alcohol ratio for the comet, along with an anomalous heating mechanism at play.

“46P/Wirtanen has one of the highest alcohol-to-aldehyde ratios measured in any comet to date,” says Neil Dello Russo (JHU/APL) in a recent press release. “This tells us information about how carbon, oxygen, and hydrogen molecules were distributed in the early solar system where Wirtanen formed.”

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Findings from the recent NIRSPEC upgrade. Keck Observatory Astronomy Talk Video

The Keck study also noticed a continuous heating of cometary material sublimating through the coma, the familiar wreath of gas and dust surrounding the nucleus of a comet. The amount of heating is thought to decrease with distance, and was more than what could be explained by simple incoming solar radiation.

“Interestingly, we found that the temperature measured for water gas in the coma did not decrease significantly with the distance from the nucleus, which implies a heating mechanism,” says Erika Gibb (University of Missouri—St Louis) in the recent press release.

One possibility is ionization via sunlight close to the nucleus. “Another possibility is there may be solid chunks of ice flying

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Astronomers Discover a New Meteor Shower. The Source is Comet 46P/Wirtanen

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Like many of you, I love a good meteor shower. I have fond memories of the Leonid meteor storm back in 1999 when several hundred per hour were seen at peak. Sadly meteor storms are not that common unlike meteor showers of which, there are about 20 major showers per year. Wait, there’s another one and this time it comes from the debris left behind from Comet 46P/Wirtanen with an expected peak on December 12. Last year, 23 meteors were seen on that night that matched the location of the comets trail. 

Comets (and some asteroids) leave a trail of debris behind them like a trail of celestial breadcrumbs. If the orbit of a comet crosses the orbit of the Earth then the particles from the debris (that are often no larger than grains of sand) collide with our atmosphere. At the immense speeds (of the order of 60 km per second, the particles falling through the atmosphere cause the gas to glow giving rise to the classic shooting star we see in the sky. Because the orbits of Earth and comets are relatively fixed, this process repeats itself every time we go through the same part of the orbit giving us the familiar annual meteor showers.

One such comet that it seems may become host to a new annual shower is Comet 46P/Wirtanen (46P). It nearly hit the headlines previously when it had been initially selected as the target for the Rosetta mission which, as you may recall, visited 67P/Churyumov-Gerasimenko instead.  46P is known as a short period comet taking 5.4 years to complete one orbit of the Sun. It is among the family of comets known as a Jupiter comet which has a most distant point from the Sun of between 5 and 6 astronomical units (1 AU is the average distance between the Sun and Earth). Observations have suggested it has a diameter of about 1.4km. 

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Comet 67P/Churyumov-Gerasimenko from Rosetta mission (Credit – NASA)

Due to the high levels of ice present in comets, it’s not unusual for active areas on their surface to appear as the ices sublimate into gasses or pockets of gas escape. Observations using the TRAPPIST telescope (The Transiting Planets and Planetesimals Small Telescope) suggest 40% of the surface is active which is higher than the usual 5-10% for Jupiter family comets. A recent study found the presence of mm sized dust particles in the comet’s coma which should be visible upon entering Earth’s atmosphere.

The orbit of 46P has a very low minimum orbit intersection distance (MOID) to Earth of just 0.071AU. The MOID between two objects that orbit a common point is the distance between the closest points of their orbits. The low MOID and the mm sized particles mean there is a high liklihood it could be the source of a meteor shower. Previous observations however have revealed no positive confirmation of peaks in 2017 and 2019.

During the 2017 and 2019 predictions, it seems the low velocity of the particles coupled with the radiant (the point of apparent origin of the shower) below the horizon suggest that visibility may have been severely limited. The radiant of this predicted shower is in the constellation Sculptor and the shower has been dubbed the Lambda Sculptorids.

The prediction for the 2023 shower, which predicted an encounter from a stream of debris from an outburst in 1974, suggested an outburst of meteors on December 12 between 12:08 and 20:06. A further outburst was predicted between 17:05 and 06:26 on December 13. The team who presented their findings in Astronomy and Astrophysics reported meteor activity as predicted and detected 23 meteors from the new shower on the night of December 12 2023. The team are now looking at the models to see what we might expect to see this year and whether Lamba Sculptorids need to be added to our list of annual meteor showers.

Source : Observations of the new meteor shower from comet 46P/Wirtanen

The post Astronomers Discover a New Meteor Shower. The Source is Comet 46P/Wirtanen appeared first on Universe Today.

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The 12 Best Dayhikes in Yosemite

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By Michael Lanza

The natural beauty, variety, pristine quality, and scale of America’s National Park System have no parallel in the world. Still, a handful of flagship parks rise above the rest—including, unquestionably, Yosemite. Created in 1890, our third national park harbors some of the most breathtaking and inspiring wild lands in the entire parks system. And you can reach much of Yosemite’s finest scenery on dayhikes.

This story shares my picks for the 12 best dayhikes in Yosemite, from popular hikes like Half Dome, the Mist Trail, and Upper Yosemite Falls to some trails and peaks you may not have heard of—including the nearly 11,000-foot summit known to have “the best 360 in Yosemite.”

This list of Yosemite’s best hikes is drawn from my numerous trips dayhiking and backpacking all over the park going back more than 30 years, including the 10 years I spent as a field editor for Backpacker magazine and even longer running this blog. Use this story as your guide and you will see the best scenery in Yosemite that’s accessible on a moderate to full day of hiking.

Please share your thoughts on any of these hikes or your own favorites in Yosemite in the comments section at the bottom of this story. I try to respond to all comments.

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Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-books to classic backpacking trips. Click here to learn how I can help you plan your next trip.

May Lake in Yosemite National Park.
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May Lake and Mount Hoffmann

2.4 to 6 miles, 500 to 2,100 feet up and down

From the 10,850-foot summit of Mount Hoffmann (lead photo at top of story) in the geographic center of Yosemite—often described as having “the best 360 in Yosemite”—you’ll look out over virtually the entire park, seeing Half Dome, Clouds Rest, and Yosemite Valley, the Clark and Cathedral Ranges, and the sea of peaks sprawling across northern Yosemite. The hike culminates with a steep, third-class scramble up the final 200 feet to the summit, where you stand at the brink of cliffs with serious exposure (although you don’t have to stand at that dizzying edge).

The summit of Yosemite’s Mount Hoffmann.
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The Kuiper Belt is Much Bigger Than We Thought

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NASA’s New Horizons spacecraft is just over 8.8 billion km away, exploring the Kuiper Belt. This icy belt surrounds the Sun but it seems to have a surprise up its sleeve. It was expected that New Horizons would be leaving the region by now but it seems that it has detected elevated levels of dust that are thought to be from micrometeorite impacts within the belt. It suggests perhaps that the Kuiper Belt may stretch further from the Sun than we thought! 

The Kuiper Belt is found beyond the orbit of Neptune and is thought to extend out to around 8 billion km. Its existence was first proposed in the mid-20th century by Gerard Kuiper after whom the belt has been named. It’s home to numerous icy bodies and dwarf planets and offers valuable insight into the formation and evolution of the Solar System.

Launched by NASA in January 2006 atop an Atlas V rocket, the New Horizon’s spacecraft embarked on its mission to explore the outer Solar System. The primary objective was to perform a close flyby of Pluto, which it did 9.5 years after it launched, and continue on to explore the Kuiper Belt.

New Horizons completed its flyby of Pluto in 2015, and has been travelling through the Kuiper Belt since. As it travels through the outer reachers of the region, almost 60 times the distance from Earth to the Sun, its Venetia Burney Student Dust Counter (SDC) has been counting dust levels. The instrument was constructed by students at the Laboratory for Atmospheric Space Physics at the University of Colorado Boulder. Throughout New Horizon’s journey, SDC has been monitoring dust levels giving fabulous insight into collision rates among objects in the outer Solar System. 

The New Horizons instrument payload that is currently doing planetary science, heliospheric measurements, and astrophysical observations. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
The New Horizons instrument payload that is currently doing planetary science, heliospheric measurements, and astrophysical observations. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The dust particle detections announced in a recent paper published in the Astrophysical Journal Letters by lead author Alex Doner are thought to be frozen remains from collisions between larger Kuiper Belt Objects (KBOs). The results were a real surprise and challenged the existing models that predicted a decline in dust density and KBO population. It seems that the belt extends many billions of miles beyond the current estimates or maybe even that there is a second belt!

The results came from data gathered over a three year period during New Horizon’s journey from 45 to 55 astronomical units (where 1 astronomical unit is the average distance between the Sun and Earth). While New Horizon’s was gathering data about dust, observatories such as the 8.2-meter optical-infrared Subaru Telescope in Hawaii have been making discoveries of new KBOs. Together these findings suggest the Kuiper Belt objects and dust may well extend a further 30 AUs out to about 80 AUs from the Sun.

New Horizons is now in its extended mission and hopefully has sufficient power and propellant to continue well into the 2040s. At its current velocity that will take the spacecraft out to about 100 AU from the Sun so the research team speculate that the SDC could identify the transition point into interstellar space.

Source : NASA’s New Horizons Detects Dusty Hints of Extended Kuiper Belt

The post The Kuiper Belt is Much Bigger Than We Thought appeared first on Universe Today.

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