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The idea of avoiding asteroid impacts has featured prominently in the public’s mind for decades – especially since the release of Deep Impact and Armageddon.  But is using a nuclear explosion the best way to deal with potentially hazardous space rocks?  Decidedly not.  If given enough time, there is a much more effective (and safer) way to dealing with any object on a collision course with Earth – a gravity tractor.  Now, Dr. Yohannes Ketema from the University of Minnesota has developed a flight pattern that makes this simplest of all asteroid defense mechanisms that much more effective.

Gravity tractors have been around for a while.  They use the gravity of an artificial body to pull the object toward it and slightly changing its trajectory.  Over long periods, this would pull the hazardous object out of the current trajectory into a safer one.  It also has the advantage of not requiring any direct impact or explosion on the surface of the asteroid itself. Since many asteroids are “rubble piles,” such direct kinetic impactors or nuclear explosions would at best knock apart some of the larger parts of the object, but at worst, it would create a multiple of chaotic trajectory objects that could impact the Earth at an even higher speed.

UT video on different techniques to capture an asteroid.

Designed to avoid such outcomes, gravity tractors come in one of four varieties.  The stationary version parks a relatively heavy probe next to an object and slowly pulls it into a different trajectory.  A halo orbit version has the probe slowly circle the object in a pattern designed to push it in a specific direction.  While the first two techniques would use traditional chemical rockets to reach their targets, a solar sail-equipped gravity tractor could slowly move into position to allow the probe to nudge the object out of the way. Finally, a constellation of probes could work together to push an object into a new path.

Dr. Ketema’s work suggests using a modified version of a stationary and halo orbit.  The new orbit is called “restricted Keplerian motion,” which involves moving a probe back a forth on a specific side of the asteroid to try to force it as much as possible in a particular direction. Initially, Dr. Ketema suggested this solution in a paper back in 2017 and recently released a new one that improves upon the orbit by decreasing the weight required in the probe.

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Mathematical graph of the restricted Keplerian motion orbit suggested by Dr. Ketema in the paper.
Credit – Yohannes Ketema

To do this, he turned to mathematical optimization.  In optimization problems, there are goals and constraints.  In this case, there was one goal (moving the asteroid out of a hazardous orbit) and three constraints: 1) Don’t directly impact the asteroid, 2) Don’t hit the asteroid with thrusters, 3) Give enough time for the gravity tractor to do its work. Best estimates for that third constraint seem to be around ten years. Such long time horizons show the importance of early detection in asteroid defense strategies.

That time factor is also vital due to the amount of time it would take for a gravity tractor to reach it.  Since the weight of the probe is an essential factor in the tool’s effectiveness, the more fuel that burns up with it (i.e., if the probe had to arrive in place quickly), the less effective it will be at pulling the asteroid off course.

Scott Manley’s video describing gravity tractors.
Credit – Scott Manley YouTube Channel

To test his optimization technique, Dr. Ketema simulated his new style gravity tractor on an existing asteroid – 2007 VK184.  While it will pass near to Earth soon, this asteroid will not hit it.  But by placing a gravity tractor next to it about ten years out, calculations show that it could be moved into an even safer orbit.

Even with this real-life simulation, there are still a few kinks to work out.  First, gravity tractors don’t work well on larger objects since their effectiveness depends entirely on how their size compares to the object they are trying to move.  Luckily, most larger asteroids on unsafe orbits are already closely tracked and don’t appear to be heading for Earth anytime soon.  A more specific problem to the modeling done in the paper is that asteroids don’t have a spherical gravitational field, making it harder to calculate the best orbit to deflect them onto a safer course.

Concept for a possible gravity tractor. Did you miss our previous article…

Frontier Adventure

The 12 Best Hikes in Utah’s National Parks

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By Michael Lanza

From natural arches, hoodoos, and hanging gardens to balanced rocks and towering mesas, slot canyons and vast chasms, the desert Southwest holds in its dry, searing, lonely open spaces some of America’s most fascinating and inspiring geology. The writer “Cactus Ed” Abbey no doubt had this region in mind when he said there “are some places so beautiful they can make a grown man break down and weep.” Much of it sits protected within southern Utah’s five national parks: Zion, Bryce Canyon, Arches, Canyonlands, and Capitol Reef.

The good news? Many of the best sights can be reached on dayhikes of anywhere from a couple hours to a full day.

A hiker below the Wall of Windows on the Peek-a-Boo Loop in Bryce Canyon National Park.
” data-image-caption=”Cyndi Hayes hiking below the Wall of Windows on the Peek-a-Boo Loop in Bryce Canyon National Park.
” data-medium-file=”″ data-large-file=”″ src=”″ alt=”A hiker below the Wall of Windows on the Peek-a-Boo Loop in Bryce Canyon National Park.” class=”wp-image-43917″ srcset=” 1024w, 300w, 768w, 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Cyndi Hayes hiking below the Wall of Windows on the Peek-a-Boo Loop in Bryce Canyon National Park.
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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.

The list below of the best dayhikes in southern Utah’s national parks derives from numerous trips I’ve made to each of these parks over the past three decades, including the 10 years I spent as a field editor for Backpacker magazine and even longer running this blog. Use my list as your compass, and I guarantee you will knock off the best hikes in these parks.

I’d love to read your thoughts about my list—and your suggestions for dayhikes that belong on it. Please share them in the comments section at the bottom of this story. I try to respond to all comments, and as I continue to explore more trails, I will regularly update this story.

A teenage boy hiking Angels Landing, Zion National Park.
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Frontier Adventure

The View From Mount St. Helens, One of America’s Best Hikes

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By Michael Lanza

Four decades after it last erupted, Washington’s Mount St. Helens has become one of the most sought-after summits in the country—for good reason. Hikers on the standard Monitor Ridge route, on the mountain’s south side, emerge soon from the shady, cool, temperate rainforest onto a stark, gray and black moonscape of volcanic rocks, pumice, and ash, with little vegetation and sweeping views of the Cascade Mountains, including several other snow-covered volcanoes. The views could steal the breath from God.

Tet19 047 Me on Teton Crest Trail copy cropped 35 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.

From atop crumbling cliffs at the crater rim, hikers look out over the vast hole—2,000 feet deep and nearly two miles across—created by the 1980 eruption that decapitated St. Helens. Ice-capped volcanoes dominate three horizons: Rainier, Adams, Hood, and Jefferson. Scroll down to the photo gallery below from my family’s three-generation hike up St. Helens, and you’ll see why I consider it one of “The 10 Best Family Outdoor Adventure Trips.”

A permit is required for every climber above 4,800 feet on Mount St. Helens. It costs $15/person for the permit plus $6 for every permit transaction. For the quota season of April 1 through Oct 31, there are daily limits on the total number of climbers permitted on the mountain.

For each month during the quota season, permits go on sale at at 7 a.m. Pacific Time on the first day of the preceding month; for example, permits for hiking the mountain in July go on sale on June 1. Permits sell out very quickly. See for information.

Read my story “Three Generations, One Big Volcano: Pushing Limits on Mount St. Helens,” about my family’s three-generation hike of Mount St. Helens, with more photos, a video, and tips on how to pull it off yourself.

I can help you plan the best backpacking, hiking, or family adventure of your life.
Click here now to learn more.

Mount Hood from Monitor Ridge.
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Powerful Jets From a Black Hole are Spawning Star Clusters

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Supermassive black holes are messy feeders, and when they’re gorging on too much material, they can hurl high-energy jets into the surrounding Universe. Astronomers have found one of the most powerful eruptions ever seen, emanating from a black hole 3.8 billion light-years away. The powerful jets are blowing out cavities in intergalactic space and triggering the formation of a huge chain of star clusters.

The black hole is part of a massive galaxy cluster, named SDSS J1531, which contains hundreds of individual galaxies, and all these galaxies have huge reservoirs of hot gas and dark matter. Using several telescopes for multiwavelength observations — including the Chandra X-ray Observatory, the Low Frequency Array (LOFAR) radio telescope, the Atacama Large Millimeter and submillimeter Array (ALMA), the Gemini North telescope’s Gemini Multi-Object Spectrograph (GMOS), and the Very Large Array (VLA) — astronomers were able to discern that two of the central galaxies were engaged in a major merger. The merger activated the supermassive black hole in the center of one of the large galaxies, which produced an extremely powerful jet. As the jet moved through space, it pushed the surrounding hot gas away from the black hole, creating a gigantic cavity.

The merger and the resulting jets from the black hole created a remarkable and stunning chain of 19 young stellar superclusters wound the two galaxies like a string of beads.

In their paper, the astronomers said the dynamic environment of SDSS J1531 offers an excellent laboratory to study the interplay between mergers, and their multiwavelength studies allowed them to uncover the origin and evolution of the “beads on a string” star formation complex.

“We’ve reconstructed a likely sequence of events in this cluster that occurred over a vast range of distances and times,” said co-author Grant Tremblay, from the Harvard & Smithsonian Center for Astrophysics CfA). “It began with the black hole a tiny fraction of a light-year across forming a cavity almost 500,000 light-years wide. This single event set in motion the formation of the young star clusters nearly 200 million years later, each a few thousand light-years across.”

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A labeled view of the multiwavelength Image of SDSS J1531. Credit: X-ray: NASA/CXC/SAO/O. Omoruyi et al.; Optical: NASA/ESA/STScI/G. Tremblay et al.; Radio: ASTRON/LOFAR; Image Processing: NASA/CXC/SAO/N. Wolk.

Chandra’s X-ray vision allowed the scientists to see wing-shaped emissions in bright X-rays, which traced dense gas near the center of SDSS J1531. The said these wings make up the edge of the cavity, and then LOFAR revealed radio waves from the remains of the jet’s energetic particles filling in the giant cavity. Together, these data provide compelling evidence of an ancient, massive explosion.

Osase Omoruyi, also from CfA who led the study, compared finding this cavity to unearthing a buried fossil.

“We are already looking at this system as it existed four billion years ago, not long after the Earth formed,” she said. “This ancient cavity, a fossil of the black hole’s effect on the host galaxy and its surroundings, tells us about a key event that happened nearly 200 million years earlier in the cluster’s history.”

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This Hubble Space Telescope image from 2014 shows two galaxies (yellow, center) from the cluster SDSS J1531 found to be merging into one and a “chain” of young stellar super-clusters are seen winding around the galaxies’ nuclei. The galaxies are surrounded by an egg-shaped blue ring caused by the immense gravity of the cluster bending light from other galaxies beyond it. Credit: NASA/ESA/Grant Tremblay

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