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During the Universe’s Dark Ages, dense primordial gas absorbed and scattered light, prohibiting it from travelling. Only when the first stars and galaxies began to shine in energetic UV light did the Epoch of Reionization begin. The powerful UV light shone through the Universe and punched holes in the gas, allowing light to travel freely.

New observations with the James Webb Space Telescope reveal how it happened. The telescope shows that faint dwarf galaxies brought an end to the darkness.

To reach back in time and answer fundamental questions about our Universe is the James Webb Space Telescope’s greatest gift. The powerful infrared space telescope has peered back into the earliest stages of the Universe’s life and shown astronomers the forces that shaped it. One of our biggest questions about the Universe concerns the Epoch of Reionization (EOR) that occurred several hundred million years after the Big Bang, ending the Universe’s Dark Ages.

An illustration showing the timeline of the Universe. The EOR ended the Cosmic Dark Ages and began about 400 million years after the Big Bang. Credit: NASA, ESA, and A. Feild (STScI)
An illustration showing the timeline of the Universe. The EOR ended the Cosmic Dark Ages and began about 400 million years after the Big Bang. Credit: NASA, ESA, and A. Feild (STScI)

Scientists have been uncertain about the source of light that caused the EOR. The primordial gas that blocked light from travelling prior to the EOR was hydrogen, and it comprised the Intergalactic Medium (IGM). Only higher-energy UV light can ionize hydrogen, so astronomers looked for sources of UV light. (Gamma rays and X-rays can too, but there weren’t enough sources to cause the EOR.) Candidates included Population III stars, the very first stars to form in the Universe. They were massive and luminous and could’ve provided the required UV light.

Quasars were another candidate because they emit so much light above the threshold needed to ionize hydrogen. But there weren’t enough of them to trigger the EOR. Massive galaxies were also a candidate, but astronomers think that they would’ve absorbed much of their own light.

Dwarf galaxies were also a candidate. In fact, they’ve been the prime candidate for a while because they’re small enough for their UV light to easily escape. They need to be what are called Lyman Continuum (LyC)-emitting galaxies. Lyman Continuum Photons have enough energy to ionize hydrogen, so astronomers searched for the LyC dwarf galaxies that emitted them. The Hubble found about 50 of them in 2022, and that helped build the framework for understanding how dwarf galaxies could be responsible for the EOR. But the 50 that Hubble found were local, not ancient.

But now we have the keen-eyed JWST and its piercing infrared gaze. It has the power to see the faintest infrared light from the ancient Universe. Even the powerful JWST needs help to see the very faint dwarf galaxies in the early Universe. Combined with the power of gravitational lensing, the space telescope was able to see some of the earliest galaxies. Among them were LyC dwarf galaxies, some of the faintest objects in the early Universe.

“This discovery unveils the crucial role played by ultra-faint galaxies in the early Universe’s evolution.”

Iryna Chemerynska, Institut d’Astrophysique de Paris in France.

These findings are in a new research article published in Nature titled “Most of the photons that reionized the Universe came from dwarf galaxies.” The lead author is Hakim Atek, an astronomer at the Institut d’Astrophysique de Paris, CNRS, Sorbonne Université, Paris.

Atek and his fellow researchers found eight ultra-faint dwarf galaxies in the early Universe. Contrary to previous thinking, these eight galaxies were prodigious emitters of ionizing Lyman Continuum radiation. Despite their apparent faintness, they emitted four times more ionizing radiation than previously thought. This helps cement their status as the objects responsible for the EOR.

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5 Reasons You Must Backpack in the Grand Canyon

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By Michael Lanza

The Grand Canyon’s appeal to backpackers may seem elusive. It’s hard, it’s dry, it’s often quite hot with little respite from the blazing sun. But while those aspects of hiking there are rarely out of mind, when I recall backpacking in the canyon, I conjure mental images of waterfalls, creeks, and intimate side canyons sheltering perennial streams that nurture lush oases in the desert. I think of wildflowers carpeting the ground for as far as the eye can see. I recall campsites on beaches by the Colorado River and on promontories overlooking a wide expanse of the canyon.

And, of course, I picture the endless vistas stretching for miles in every direction, where impossibly immense stone towers loom thousands of feet above an unfathomably vertiginous and complex landscape.

After several backpacking trips in the Big Ditch, I find that the more I go there, the more I need to go back again. This place really hooks you (see reason no. 5, below). And my perspective is shaped by more than three decades of backpacking all over the United States, including formerly as the Northwest Editor of Backpacker magazine for 10 years and even longer running this blog. I’ve taken many of the best multi-day hikes out there—some of them multiple times.

Tet19 047 Me on Teton Crest Trail copy cropped 21
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-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

A backpacker on the Tonto Trail on the Grand Canyon’s Royal Arch Loop.
” data-image-caption=”David Ports backpacking the Tonto Trail on the Grand Canyon’s Royal Arch Loop.
” data-medium-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg?fit=900%2C600&ssl=1″ src=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy-1024×683.jpg?resize=900%2C600&ssl=1″ alt=”A backpacker on the Tonto Trail on the Grand Canyon’s Royal Arch Loop.” class=”wp-image-23908″ srcset=”https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg 1024w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg 300w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg 768w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg 1080w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg 200w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg 670w, https://tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2017/06/06235057/Gran6-137-Ports-Tonto-Trail-Royal-Arch-Loop-Grand-Canyon-copy.jpg 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />David Ports backpacking the Tonto Trail on the Grand Canyon’s Royal Arch Loop. Click photo to read about that trip.

See my lists of “America’s Top 10 Best Backpacking Trips,” “The 10 Best National Park Backpacking Trips,” and “The

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8 Epic Grand Canyon Backpacking Trips You Must Do

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By Michael Lanza

This is, in a way, a story about addiction. Or a love affair. Or both. Those metaphors best describe how the Grand Canyon constantly lures me back when I’m thinking about spring and fall hiking and backpacking trips.

It is that rare kind of natural environment that exists on a scale of its own, like Alaska or the Himalaya. There’s something soul-stirring and hypnotic about its infinite vistas, the deceptive immensity of the canyon walls and stone towers, and the way the foreground and background continually expand and shrink as you ascend and descend elevation gradients of a vertical mile or more—all of which validates enduring the wilting heat and trails that sometimes seem better suited to rattlesnakes and scorpions than bipedal primates.

For backpackers seeking adventure, challenge, and incomparable natural beauty, the canyon stands alone.

This story will show you, in words and photos, why one or more of these Big Ditch backpacking trips deserves top priority as you’re planning your next trip. I think you will quickly understand why the Grand Canyon has increasingly become one of my favorite places over more than three decades (and counting) of backpacking, including the 10 years I spent as a longtime field editor for Backpacker magazine and even longer running this blog.

Tet19 047 Me on Teton Crest Trail copy cropped 19
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-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

A backpacker at Ooh-Ah Point on the South Kaibab Trail in the Grand Canyon.
” data-image-caption=”Todd Arndt at Ooh-Ah Point on the South Kaibab Trail. Click on the photo to see my e-book “The Best Backpacking Trip in the Grand Canyon.”
” data-medium-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?fit=900%2C600&ssl=1″ src=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?resize=900%2C600&ssl=1″ alt=”A backpacker at Ooh-Ah Point on the South Kaibab Trail in the Grand Canyon.” class=”wp-image-36039″ srcset=”https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?resize=900%2C600&ssl=1 1200w, https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?resize=900%2C600&ssl=1 300w, https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?resize=900%2C600&ssl=1 768w, https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?resize=900%2C600&ssl=1 1024w, https://i0.wp.com/tbo-media.sfo2.digitaloceanspaces.com/wp-content/uploads/2019/10/06231753/Gran8-003-Todd-Arndt-at-Ooh-Ah-Point-South-Kaibab-Trail-Grand-Canyon..jpg?resize=900%2C600&ssl=1 1080w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Todd Arndt at Ooh-Ah Point on the South Kaibab Trail. Click on the photo to see my e-book “The Best Backpacking Trip in the Grand Canyon.”

And the time to start planning your
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Juno Reveals a Giant Lava Lake on Io

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NASA’s Juno spacecraft came within 1,500 km (930 miles) of the surface of Jupiter’s moon Io in two recent flybys. That’s close enough to reveal new details on the surface of this moon, the most volcanic object in the Solar System. Not only did Juno capture volcanic activity, but scientists were also able to create a visual animation from the data that shows what Io’s 200-km-long lava lake Loki Patera would look like if you could get even closer. There are islands at the center of a magma lake rimmed with hot lava. The lake’s surface is smooth as glass, like obsidian.

“Io is simply littered with volcanoes, and we caught a few of them in action,” said Juno principal investigator Scott Bolton during a news conference at the European Geophysical Union General Assembly in Vienna, Austria. “There is amazing detail showing these crazy islands embedded in the middle of a potentially magma lake rimmed with hot lava. The specular reflection our instruments recorded of the lake suggests parts of Io’s surface are as smooth as glass, reminiscent of volcanically created obsidian glass on Earth.”

This animation is an artist’s concept of Loki Patera, a lava lake on Jupiter’s moon Io, made using data from the JunoCam imager aboard NASA’s Juno spacecraft. With multiple islands in its interior, Loki is a depression filled with magma and rimmed with molten lava. Credit: NASA/JPL-Caltech/SwRI/MSSS

Just imagine if you could stand by the shores of this lake – which would be a stunning view in itself. But then, you could look up and see the giant Jupiter looming in the skies above you.

Juno made the two close flybys of Io in December 2023 and February 2024. Images from Juno’s JunoCam included the first close-up images of the moon’s northern latitudes. Undoubtedly, Io looks like a pizza – which has been the conclusion since our first views of this moon, when Voyager 1 flew through the Jupiter system in March 1979. The mottled and colorful surface comes from the volcanic activity, with hundreds of vents and calderas on the surface that create a variety of features. Volcanic plumes and lava flows across the surface show up in all sorts of colors, from red and yellow to orange and black. Some of the lava “rivers” stretch for hundreds of kilometers.

JNCE 2024034 58C00025 V01.point 1
Io’s sub-Jovian hemisphere is revealed in detail for the first time since Voyager 1 flew through the Jupiter system in March 1979, during the Juno spacecraft’s 58th perijove, or close pass, on February 3, 2024. This image shows Io’s nightside illuminated by sunlight reflected off Jupiter’s cloud tops. Several surface changes are visible include a reshaping of the compound flow field at Kanehekili (center left) and a new lava flow to the east of Kanehekili. This image has a pixel scale of 1.6 km/pixel. Credit : NASA/SwRI/JPL/MSSS/Jason Perry.

Juno scientists were also able to re-create a spectacular feature on Io, a spired mountain that has been nicknamed “The Steeple.” This feature is between 5 and 7 kilometers (3-4.3 miles) in height. It’s hard to comprehend the type of volcanic activity that could have created such a stunning landform.

Created using data collected by the JunoCam imager aboard NASA’s Juno during flybys in December 2023 and February 2024, this animation is an artist’s concept of a feature on the Jovian moon Io that the mission science team nicknamed “Steeple Mountain.” Credit: NASA/JPL-Caltech/SwRI/MSSS

Speaking of volcanic activity, two recent papers have come to a jaw-dropping conclusion about Io: this moon has been erupting since the dawn of the Solar System.

All the volcanic on Io is activity is driven by tidal heating. Io is in an orbital resonance with two other large moons of Jupiter, Europa and Ganymede.

“Every time Ganymede orbits Jupiter once, Europa orbits twice, and Io orbits four times,” explained the authors of a paper published in the Journal of Geophysical Research: Planets, led by Ery Hughes of GNS Science in New Zealand. “This situation causes tidal heating in Io (like how the Moon causes ocean tides on Earth), which causes the volcanism.”

However, scientists haven’t known how long this resonance has been occurring and whether what we observe today is what has always been happening in the Jupiter system. This is because volcanism renews Io’s surface almost

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