Update (12.01.20) Arecibo Observatory platform collapses. The Arecibo Observatory radio telescope platform collapsed in the morning (7:50 am) today, December 1, due to faults in its structure, confirmed Francisco Córdoba, director of the scientific center. For his part, scientist Jonathan Friedman, from the Arecibo Observatory, described that the collapse caused a sound like "tremors, like a train or an avalanche."
Paul Chodas of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. Chodas is a leading authority on the dynamics of asteroid orbits and the impact probabilities from small solar system bodies. He is the primary creator of the orbital calculation and impact probability software used by NASA. Chodas reminds us that just some years ago, we had two unrelated encounters with small bodies passing close to or striking Earth during the same day.
On February 15, 2013, a small asteroid, perhaps measuring 20 meters across, came down over the southern Urals of Russia, barreling in at about 19 km/s, and exploded over Chelyabinsk Oblast, near the town of Chelyabinsk. With a mass greater than that of the Eiffel Tower, the asteroid exploded in an airburst, unleashing energy equal to about 500 kilotons of TNT, some 20 or 30 times the energy released in the Hiroshima atomic explosion. The enormous resulting shock wave shattered glass in the town’s buildings, injuring nearly 1,500 people. The 2013 Chelyabinsk meteor streaked through the Russian skies and exploded only 30 kilometers from the surface. Though it wasn’t a direct impact, the force of 444,000 tons of TNT damaged buildings for 500 kilometers. The same day, within 24 hours, 2012 DA14, a space rock about 30 meters across, whizzed past Earth at a distance of some 27,700 kilometers, some 2.2 times Earth’s diameter.
Wake up call?
Earth has a long history of impacts from other bodies in the solar system, one that is almost entirely hidden because of our planet’s continual resurfacing — from erosion, plate tectonics, volcanism, and more. In the early solar system, Earth was struck frequently and by large objects.
Most planetary scientists believe the Moon formed as the result of a very early collision between Earth and a planetesimal some 4.53 billion years ago. During the so-called Late-Heavy Bombardment, about 4.1 to 3.8 billion years ago, numerous large objects impacted Earth. The Moon, which does not hide its scars so effectively, shows this impressive battering.
Most travelers to northern Arizona are familiar with Meteor Crater near Winslow, and walking the perimeter of the 1-kilometer rim. Some 50,000 years ago, a 30- to 50-meter iron meteorite, part of the core of an asteroid, hurtled into the desert plain, striking with the force of 15 megatons.
Chicxulub Crater, a subsurface scar lying underneath the Yucatán Peninsula in Mexico. In the late 1970s, two geophysicists working for the Mexican oil giant Pemex discovered a huge underwater arc in a ring some 40 kilometers across. They soon found another arc and then discovered the feature formed a circle, suggestive of an ancient impact crater.
Nobel Prize-winning physicist Luis Alvarez, along with his son Walter and other collaborators, had stumbled into a shock. They found evidence of a massive impact on Earth coinciding with the boundary between the Cretaceous and Paleogene geological eras, some 66 million years ago. The Alvarez team discovered high levels of iridium and osmium, and four years later scientists found shocked quartz and micro diamonds associated with an extraterrestrial impact. This coincided with the disappearance of the dinosaurs, and the K-Pg Impact (first called K-T before the redoing of geological nomenclature) was held responsible. Moreover, geological evidence ties the Chicxulub Crater with the impact, giving geologists a place on Earth where the impactor struck. This was no small rock, either, but a roughly 10-kilometer asteroid.
In 2008, for the first time, astronomers discovered a small asteroid that was heading toward Earth, before it impacted. Designated 2008 TC3, the tiny space rock was a 4-meter-wide object weighing some 80 tons, on October 7 of that year, the small rock hurtled into Earth’s atmosphere and exploded over the Nubian Desert in Sudan.
Just five years later, on New Year’s Day 2014, Richard Kowalski again discovered a small asteroid, 2014 AA, some 2 to 4 meters across, bound for Earth. Some 21 hours after discovery, the small rock entered Earth’s atmosphere somewhere along a line between northern South America and western Africa, quite probably into the ocean.
On Thursday 25 July 2019 an asteroid 57-130 meters across missed our planet by just one-fifth of the distance to the moon. In astronomical terms, that’s a hair’s breadth. Had it hit us, the devastation would have been staggering. Astronomers call asteroids of this size “city killers”. We have explained that experience in the preceding note and Arecibo's role was vital.
Asteroid impact expert Alan Harris, estimates that 200 million objects equal to or greater than 6 meters across are in Earth-crossing orbits.
A 140-meter asteroid will impact Earth on average every 20,000 years, according to Harris, and will unleash 300 megatons of energy, causing regional scale devastation. A 300-meter asteroid will impact Earth roughly every 70,000 years, unleashing 2,000 megatons of energy and creating continent-wide devastation.
The risk from asteroids impacting Earth and causing widespread damage, death, and catastrophe is real and present every day of our lives.
Do we need to worry about an asteroid strike? Probably not. But that is changing as planetary scientists discover more objects and rocks, the fact remains that the risk is still slightly greater from the remaining undiscovered big objects. Be they comets or asteroids on peculiar orbits, could pass into the inner solar system and be on a collision course with Earth’s orbit, too.
The risk to Earth from impacts is clearly significant from the near-Earth object population, present, and possible.
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and large enough to cause significant regional damage in the event of an impact. Most of these objects are potentially hazardous asteroids (PHAs), and a few are comets.
Near-Earth objects (NEOs) are asteroids and comets with orbits that come within 28 million miles of Earth's path. In 1994, Congress directed NASA to develop a plan to discover, characterize and catalog potentially hazardous NEOs larger than 1 kilometer in size.
In 2005, Congress again directed NASA to find at least 90 percent of potentially hazardous NEOs sized 140 meters or larger by the end of 2020.
In 2012 NASA estimated 20 to 30 percent of these objects have been found. In 2005, Congress passed a bill requiring NASA to find and track at least 90% of all near-Earth objects (NEOs) 140 meters or larger by 2020.
At the start of 2019, the number of discovered near-Earth asteroids totaled more than 19,000. An average of 30 new discoveries are added each week. There are currently over 822,000 known asteroids.
As of September 2020 there are 2,116 known PHAs (about 9% of the total near-Earth population), of which 157 are estimated to be larger than one kilometer in diameter. To date, astronomers have spotted more than 8,000 near-Earth asteroids that are at least 460 feet (140 meters) wide — big enough to wipe out an entire region, only about one-third of the 25,000 such space rocks that are thought to be in Earth's neighborhood. NASA knows about only a fraction of near-Earth objects (NEOs). "There's still two-thirds of this population out there to be found," Lindley Johnson, planetary defense officer at NASA headquarters in Washington, D.C., said.
Before we can quantify the threat an object poses, we first need to know that the object is there. But finding asteroids is hard. Understanding the risks from asteroid impacts on Earth is a pretty young science, like much of astronomy and planetary science.
NASA believes it will find just 50 percent of those objects by 2033 and that assessment was before the closing of asteroid investigation in Arecibo, the most important scientific instrument in that respect.
Lindley Johnson, NASA's planetary defense officer, on the topic of finding 140-meter-plus asteroids, said NASA likely needed "additional capability." Once again before Arecibo ceased to function as the primary asteroid finding system. An inbound asteroid's exact impact location will be harder to predict without Arecibo, that is without a doubt.
There are swarms of millions of asteroids in the Solar System. Most orbit the Sun between Mars and Jupiter. But, a subset of these asteroids, have orbits that come in a little too close and cross the orbit of Earth around the Sun, some astronomers think it’s only a matter of time before one will crash into the planet.
Asteroid 2019 OK wasn’t even on any of the detection programs when it passed a mere 73,000 kilometers from Earth on 26 July 2019, this asteroid once detected was properly studied and its route traced by, of course, Arecibo.
With Arecibo functional, it is possible to evaluate the structure, movement, speed and map the route of an asteroid much earlier than another system and with an unmatched degree of accuracy. Arecibo’s capacities are not possessed by any other facility in the would including the new Chinese FAST telescope.
How real is the threat?
Let's stick to facts: just seven years ago, an asteroid entered Earth's atmosphere over Chelyabinsk, Russia. It exploded in the air, releasing 20 to 30 times more energy than that of the first atomic bombs and generating brightness greater than the sun. It damaged more than 7,000 buildings and injured more than 1,000 people. The shock wave caused damage 58 miles away.
So tell me if we are right on insisting on the priority is that Arecibo be reconstructed.
Pachi Ortizfeliciano
#RebuildAreciboObservatory
#WhatAreciboMeansToMe
Postdata: Scientists talk Arecibo
Planetary defense is the art of identifying and mitigating threats to Earth from asteroid impacts. And among its tools is planetary radar, an unusual capability that can give scientists a much better look at a nearby object. Arecibo Observatory in Puerto Rico was one of only a couple such systems on the planet. And when it comes to planetary defense, there's nothing like it.
"There's been statements in the media that, 'Oh we have other systems that can kind of replace what Arecibo is doing,' and I don't think that's true," Anne Virkki, who leads the planetary radar team at Arecibo Observatory, told Space.com. "It's not obsolete and it's not easily replaceable by other existing facilities and instruments."
Planetary defense begins with spotting as many near-Earth asteroids as possible — nearly 25,000 to date, according to NASA — and estimating their sizes and their orbits around the sun.
But larger asteroids with orbits that might bring them too close for comfort get additional study, and often, that work has been Arecibo Observatory's. The facility sported a powerful radar transmitter that could bounce a beam of light off an object in Earth's neighborhood. Then, the observatory's massive radio dish could catch the echo of that signal, letting scientists decipher precise details about an asteroid's location, size, shape and surface, when planetary radar can spot the object, it completes the work more quickly.
Sometimes that speed will matter, said Bruce Betts, chief scientist at the Planetary Society, a nonprofit space-exploration advocacy group that includes planetary defense among its key issues. "You want to define an orbit as quickly as you can to figure out whether the asteroid is going to hit Earth," Betts told Space.com.
That's because with enough warning, humans could theoretically do something to prevent the collision — likely by nudging the asteroid off track or by breaking it into smaller pieces that wouldn't wreak as much havoc.
And radar can more quickly offer other details about a space rock that can inform planetary defense, including such vital information as whether an asteroid is actually a single object or a pair of objects in disguise, as 15% of near-Earth asteroids turn out to be, Betts said. "If you needed to deflect it, obviously, it's crucial to know whether there's one or two objects."
Same with the composition of the space rock. "Some are solid metal, some are fluff balls or rubble piles, so they vary considerably in density," Betts said. So radar is a valuable skill for a planet to have.
Arecibo wasn't the only radar facility, but it's a rare capacity given how expensive the technology involved is. With its demise, the only remaining radar transmitter is at the Goldstone Deep Space Communications Center in California, run by NASA's Jet Propulsion Laboratory. But this facility has a host of additional responsibilities — it's part of the Deep Space Network that manages communication with spacecraft throughout the solar system and it has military responsibilities as well.
"They are not going to be as flexible with scheduling these recently discovered target observations as Arecibo has been," Virkki said. "If you don't get to observe those targets when they are in the window, then you might lose the opportunity very quickly, and then you have these asteroids that have higher uncertainties in their orbits."
Goldstone's radar system is also about 20 times less sensitive than Arecibo's was, and the two systems could see different subsets of space, she said. "So it's not exactly going to be replacing Arecibo."
And it will have a narrow beam, making it a bit more persnickety in tracking down asteroids. "If you have a very narrow beam, you have to have a very good idea of where you are pointing your radar," Virkki said. "You can't go, like, looking around with that narrow beam." Arecibo was more forgiving when the asteroids' orbits weren't as certain.
Those factors combine to make Arecibo's loss a major blow to the planetary defense capability, according to Ed Lu, a former NASA astronaut and executive director of the B612 Asteroid Institute, a nonprofit organization focused on asteroid science and deflection studies. "This is a big loss to the community," he said. The weakness is coming at a tricky time for planetary defense experts, Lu said. New asteroids are being identified ever more quickly — a few thousand a year, these days.
The risk of an impact is always the same, of course, but increasing our search capacity while losing characterization capacity is a recipe for greater uncertainty.
There's no easy way to replace the radar capacity that is being lost with Arecibo, all three experts said.
"Obviously, we'd be in favor of finding a way to either repair it, rebuild it, whatever that happens to be, update it," Lu said.
"But sometimes, sometimes, if you don't make the investment, you're sorry about it later."
https://www.space.com/arecibo-observatory-loss-for-planetary-defense-asteroids
The Arecibo conundrum
http://ortizfeliciano.blogspot.com/2020/11/the-arecibo-conundrum-english-text.html
Pdd: The news is headline throughout the world, reconstruction is the option that Puerto Rico and the scientific field acclaim
#RebuildAreciboObservatory
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