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Giant planets like Saturn don’t just tilt over all by themselves: something has to knock them over, or tug on them gravitationally, to push them off axis. Scientists expect that when new planets are born, they form with almost no tilt at all, lining up like spinning tops, with their equators level to the orbital plane in which they circle around their sun.

But no planet in our solar system is perfectly level. Jupiter is the closest, boasting an obliquity (tilt) of just 3.12 degrees. Earth’s obliquity is much more substantive at 23.45 degrees, causing us to experience an annual cycle of seasons as our homeworld wobbles on its axis. Saturn’s tilt is more extreme yet, with an obliquity of 26.73 degrees (though it’s nowhere near as extreme as Uranus, which is practically sideways, spinning at a 97.86-degree angle to its orbital plane).

We can learn a lot from these obliquities.

We know, for example, from geological evidence gathered during the Apollo missions, that Earth’s tilt was likely the result of massive impacts with other rocky objects early in the planet’s history, the largest of which broke off and formed our Moon. Just as archeologists examine clay pots and fragments of bone to piece together ancient cultures, physicists can examine planetary tilts to understand the Solar System’s past. Modern-day wobbles are evidence of dramatic events long ago. Or, as a new paper suggests, perhaps not-so-long-ago.

A team of researchers from the Paris Observatory and the University of Pisa, led by Melaine Saillenfest, suggest that the origin of Saturn’s tilt may be much more recent than previously believed, and that its largest moon, Titan, may be to blame.

Astronomers traditionally believed that Saturn’s tilt had nothing to do with its moons, but rather more to do with interactions between it and its fellow gas giants. One mainstream theory of solar system formation, known as the Nice model, suggests that about four billion years ago, a great migration occurred in which the giant planets moved slowly outwards, under the gravitational influence of each other and smaller planetesimals.

*NEW* Final version: FASTER, longer, and corrected thanks to Twitter! ?
Day length (sidereal) & axial tilt for the 8 largest planets in our solar system!

Which planet best represents you? ?

HD Download for educators etc: #SciComm

— Dr. James O’Donoghue (@physicsJ) December 29, 2018Graphic by James O’Donoghue (with imagery from NASA), demonstrating the axial tilt of the planets.

According to this model, the culprit responsible for Saturn’s tilt was Neptune, which tugged the ringed giant over as it swept out towards the Kuiper belt (actually, evidence from the Cassini mission showed that Saturn’s rings are fairly new: they probably weren’t around during the great migration. But I digress). If the Nice model is to be believed, planetary obliquities were set in stone a long time ago, and have remained relatively stable since.

The new theory proposed by Saillenfest and the team disagrees. They suggest instead that a migration of Titan in the recent past (about 1 billion years ago) is equally capable of explaining the tilt Saturn has today. Titan’s orbit may have remained regular for billions of years, but their model shows that an orbital resonance with Saturn could have occurred recently, simultaneously changing the moon’s orbit and forcing a nearly upright Saturn to fall sideways.

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Titan passes in front of Saturn, as seen by the Cassini Spacecraft on June 8, 2015. Credit: NASA/JPL-Caltech/Space Science Institute.

It’s hard to be sure which model is correct without more evidence (maybe the upcoming Dragonfly mission to Titan can turn up something). But the possibility of such a recent migration opens up possibilities for future changes to the Solar System. As the researchers put it, the obliquities of giant planets “are not settled once for all, but continuously evolve as a
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10 Expert Tips for Hiking With Trekking Poles

Tet19 047 Me on Teton Crest Trail copy cropped 28 jpg

Michael Lanza

you’ve opened this story, you probably already recognize this truth: For
backpackers, dayhikers, climbers, mountain runners, and others, trekking poles
noticeably reduce strain, fatigue, and impact on leg muscles and joints, feet,
back—and really on your entire body. And that’s true no matter how much weight
you’re carrying, whether a daypack, an ultralight backpack, or a woefully heavy

if you’ve opened this story, you also probably already have a sense of this
often-overlooked truth: How you use poles matters. If you use them correctly,
you’re gaining their benefits on virtually every step of your hike; if not,
they become dead weight. This story provides 10 highly effective tips on using
poles, from basics like adjusting pole length, gripping the strap, and moving uphill
and downhill on trails, to managing steep terrain, fording streams, advanced
tips for aiding balance, and more.

The tips below are based on my experience of many thousands of trail miles and more than three decades of backpacking, dayhiking, climbing, trail running, and taking ultra-hikes and ultra-runs—plus a quarter-century of testing and reviewing gear as a past field editor for Backpacker magazine and for many years running this blog. I believe this story will give you expert tips on hiking with trekking poles that you will not find anywhere else.

Tet19 047 Me on Teton Crest Trail copy cropped 29 jpg
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.

A backpacker on the Teton Crest Trail in Grand Teton National Park.
” data-image-caption=”Jeff Wilhelm backpacking the Teton Crest Trail n Grand Teton National Park. Click photo for my e-book “The Complete Guide to Backpacking the Teton Crest Trail.”
” data-medium-file=”″ data-large-file=”″ src=”″ alt=”A backpacker on the Teton Crest Trail in Grand Teton National Park.” class=”wp-image-36371″ srcset=” 1024w, 300w, 768w, 1080w, 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Jeff Wilhelm backpacking the Teton Crest Trail n Grand Teton National Park. Click photo for my e-book “The
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Solar Physics: Why study it? What can it teach us about finding life beyond Earth?

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Universe Today has investigated the importance of studying impact craters, planetary surfaces, exoplanets, and astrobiology, and what these disciplines can teach both researchers and the public about finding life beyond Earth. Here, we will discuss the fascinating field of solar physics (also called heliophysics), including why scientists study it, the benefits and challenges of studying it, what it can teach us about finding life beyond Earth, and how upcoming students can pursue studying solar physics. So, why is it so important to study solar physics?

Dr. Maria Kazachenko, who is a solar astrophysicist and assistant professor in the Astrophysical & Planetary Science Department at the University of Colorado, Boulder, tells Universe Today, “Solar physics studies how our Sun works, and our Sun is a star. Stars are building blocks of our Universe.  We are made of stardust. Stars provide energy for life. The Sun is our home star – it affects our life on Earth (space weather, digital safety, astronauts’ safety). Therefore, to be safe we need to understand our star. If we do not take our Sun into account, then sad things could happen. The Sun is the only star where we could obtain high-quality maps of magnetic fields, which define stellar activity. To summarize, studying the Sun is fundamental for our space safety and for understanding the Universe.”

The field of solar physics dates to 1300 BC Babylonia, where astronomers documented numerous solar eclipses, and Greek records show that Egyptians became very proficient at predicting solar eclipses. Additionally, ancient Chinese astronomers documented a total of 37 solar eclipses between 720 BC and 480 BC, along with keeping records for observing visible sunspots around 800 BC, as well. Sunspots were first observed by several international astronomers using telescopes in 1610, including Galileo Galilei, whose drawings have been kept to this day.

Presently, solar physics studies are conducted by both ground- and space-based telescopes and observatories, including the National Science Foundation’s (NSF) Daniel K. Inouye Solar Telescope located in Hawai’i and NASA’s Parker Solar Probe, with the latter coming within 7.26 million kilometers (4.51 million miles) of the Sun’s surface in September 2023. But with all this history and scientific instruments, what are some of the benefits and challenges of studying solar physics?

Dr. Kazachenko tells Universe Today that some of the scientific benefits of studying solar physics include “lots of observations; lots of science problems to work on; benefits from cross-disciplinary research (stellar physics, exoplanets communities)” with some of the scientific challenges stemming from the need to use remote sensing, sometimes resulting in data misinterpretation. Regarding the professional aspects, Dr. Kazachenko tells Universe Today that some of the benefits include “small and friendly community, large variety of research problems relying on amazing new observations and complex simulations, ability to work on different types of problems (instrumentation, space weather operation, research)” with some of the professional challenges including finding permanent employment, which she notes is “like everywhere in science”.

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Image of the Sun obtained by NASA’s Solar Dynamics Observatory (SDO) on June 20, 2013, with a solar flare discharging on the left side. (Credit: NASA/SDO)

As noted, the study of solar physics involves investigating space weather, which is when the solar wind interacts with the Earth, specifically with our magnetic field, resulting in the beautiful auroras observed in the high northern and southern latitudes. On occasion, the solar wind is strong enough to wreak havoc on satellites and even knock out power grids across the Earth’s surface. This was demonstrated with the Carrington Event on September 1-2, 1859, when fires at telegraph stations were reported across the globe, along with several strong aurora observations, as well. While this event occurred with the Earth’s magnetic field largely deflecting the incoming solar wind, life on this planet could be doomed without our magnetic field protecting us. Therefore, what can solar physics teach us about finding life beyond Earth?

Dr. Kazachenko tells Universe Today, “The Sun can tell us about stellar activity, including flares and coronal mass ejections that might be crucial
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Gravastars are an Alternative Theory to Black Holes. Here’s What They’d Look Like

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One of the central predictions of general relativity is that in the end, gravity wins. Stars will fuse hydrogen into new elements to fight gravity and can oppose it for a time. Electrons and neutrons exert pressure to counter gravity, but their stability against that constant pull limits the amount of mass a white dwarf or neutron star can have. All of this can be countered by gathering more mass together. Beyond about 3 solar masses, give or take, gravity will overpower all other forces and collapse the mass into a black hole.

While black holes have a great deal of theoretical and observational evidence to prove their existence, the theory of black holes is not without issue. For one, general relativity predicts that the mass compresses to an infinitely dense singularity where the laws of physics break down. This singularity is shrouded by an event horizon, which serves as a point of no return for anything devoured by the black hole. Both of these are problematic, so there has been a long history of trying to find some alternative. Some mechanism that prevents singularities and event horizons from forming.

One alternative is a gravitational vacuum star or gravitational condensate star, commonly called a gravastar. It was first proposed in 2001, and takes advantage of the fact that most of the energy in the universe is not regular matter or even dark matter, but dark energy. Dark energy drives cosmic expansion, so perhaps it could oppose gravitational collapse in high densities.

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Illustration of a hypothetical gravastar. Credit: Daniel Jampolski and Luciano Rezzolla, Goethe University Frankfurt

The original gravastar model proposed a kind of Bose-Einstein condensate of dark energy surrounded by a thin shell of regular matter. The internal condensate ensures that the gravastar has no singularity, while the dense shell of matter ensures that the gravastar appears similar to a black hole from the outside. Interesting idea, but there are two central problems. One is that the shell is unstable, particularly if the gravastar is rotating. There are ways to tweak things just so to make it stable, but such ideal conditions aren’t likely to occur in nature. The second problem is that gravitational wave observations of large body mergers confirm the standard black hole model. But a new gravastar model might solve some of those problems.

The new model essentially nests multiple gravastars together, somewhat like those nested Matryoshka dolls. Rather than a single shell enclosing exotic dark energy, the model has a layers of nested shells with dark energy between the layers. The authors refer to this model as a nestar, or nested gravastar. This alternative model makes the gravastar more stable, since the tension of dark energy is better balanced by the weight of the shells. The interior structure of the nestar also means that the gravitational waves of a nestar and black hole are more similar, meaning that technically their existence can’t be ruled out.

That said, even the authors note that there is no likely scenario that could produce nestars. They likely don’t exist, and it’s almost certain that what we observe as black holes are true black holes. But studies such as this one are great for testing the limits of general relativity. They help us understand what is possible within the framework of the theory, which in turn helps us better understand gravitational physics.

Reference: Jampolski, Daniel and Rezzolla, Luciano. “Nested solutions of gravitational condensate stars.” Classical and Quantum Gravity 41 (2024): 065014.

The post Gravastars are an Alternative Theory to Black Holes. Here’s What They’d Look Like appeared first on Universe Today.

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