The large impact craters dotting our planet are powerful reminders that asteroids and comets strike the Earth from time to time. As often said, it’s not a question of “if”; it’s a matter of “when” our planet will face an impending strike from space. But an impact is one existential threat humanity is finally starting to take seriously and wrap its head around.
Seemingly spurred by the success of the Double Asteroid Redirection Test (DART), NASA just released a new planetary defense strategy and action plan, describing its efforts to find and identify potentially hazardous objects to provide an advanced warning, and then even push them off an impact trajectory.
This 10-year strategy looks to advance efforts to protect the Earth from a devastating encounter with a Near Earth asteroid or comet.
“An asteroid impact with Earth has potential for catastrophic devastation, and it is also the only natural disaster humanity now has sufficient technology to completely prevent,” said Lindley Johnson, NASA’s planetary defense officer, in a NASA press release. “The release of this NASA strategy steps up NASA’s intentions for the next 10 years to ensure the agency works both nationally and internationally to protect our planet for the benefit of all.”
The 46-page “NASA Planetary Defense Strategy and Action Plan” (pdf document) was released on April 18, 2023 and follows another document that was put out on April 3 by the White House Office of Science and Technology Policy, “National Preparedness Strategy and Action Plan for Near-Earth Object Hazards and Planetary Defense” (pdf document.)
Each of the reports focuses on enhancing the detection, characterization and responses to impact threats as well as improving international cooperation for coordinating strategies among government agencies.
NASA wants to focus on six key areas for planetary defense over the next decade:
Improving NEO survey, detection, and characterization efforts to work toward a completed catalogue of all NEOs that might pose an impact hazard to EarthDeveloping and demonstrating NEO mitigation technologies similar to the agency’s Double Asteroid Redirection Test (DART) mission, the world’s first planetary defense test mission, which successfully demonstrated one method of asteroid deflection using a kinetic impactor spacecraftFostering international collaboration related to NEO surveying and mitigation to leverage international capabilitiesStrengthening interagency coordination between NASA and other U.S. government agencies to enhance and streamline U.S. government NEO preparedness and response planningReview the agency’s internal planning to maximize the benefits obtained from limited resourcesBetter integrate messaging regarding planetary defense work with the agency’s strategic communications
Each of the strategy objectives are defined into short-term, medium-term, long-term, and ongoing timelines with the goal of meeting all objectives within the next 10 years.
The Near Earth Objects (NEOs) that NASA feels are of most concen range in diameter from 10 m (33 ft.) to more than 10,000 meters (33,000 ft), and that come within 42 million km (30 million miles of the Earth’s orbital path.
NEO size and hazard. (Credit: Johns Hopkins University / Applied Physics Lab)
For decades, scientists and other proponents have been championing the need for humanity to prepare for an what will certainly happen at some point. Apollo astronaut Rusty Schweickart, who helped found the planetary defense nonprofit advocate B612 Foundation has talked with Universe Today numerous times about planetary defense. Even back in 2010, he emphasized that the technology needed to divert an asteroid already existed.
“That is, we do not have to go into a big technology development program in order to deflect most asteroids that would pose a threat of impact,” he said. He also added that coordination and cooperation between countries around the world was essential, and would perhaps be even more difficult to organize than the technology.
“Bureaucracy is the most likely reason we will be hit with an asteroid in the future, not the technology,” said Schweickart. “That is an audacious statement to
Starship | First Integrated Flight Test | Recap
Starship gave us quite a show during the first flight test of a fully integrated Starship (S24) and Super Heavy rocket (B7) from Starbase in Texas.
On April 20, 2023 at 8:33 a.m. CT, Starship successfully lifted off from the orbital launch pad for the first time. The vehicle cleared the pad and beach as Starship climbed to an apogee of ~39 km over the Gulf of Mexico – the highest of any Starship to-date.
With a test like this, success comes from what we learn, and we learned a tremendous amount about the vehicle and ground systems today that will help us improve on future flights of Starship.
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ARABSAT BADR-8 Mission Control Audio
This is the vehicle trajectory and mission control audio without any additional commentary. There may be very long periods of silence. For our full hosted webcast, visit
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When Black Holes Merge, They’ll Ring Like a Bell
When two black holes collide, they don’t smash into each other the way two stars might. A black hole is an intensely curved region of space that can be described by only its mass, rotation, and electric charge, so two black holes release violent gravitational ripples as merge into a single black hole. The new black hole continues to emit gravitational waves until it settles down into a simple rotating black hole. That settling down period is known as the ring down, and its pattern holds clues to some of the deepest mysteries of gravitational physics.
Gravitational wave observatories such as the Laser Interferometry Gravitational-Wave Observatory (LIGO) have mostly focused on the inspiral period of black hole mergers. This is the period where the two black holes orbit ever closer to each other, creating a rhythmic stream of strong gravitational waves. From this astronomers can determine the mass and rotation of the original black holes, as well as the mass and rotation of the merged black hole. The pattern of gravitational waves we observe is governed by Einstein’s general relativity equations, and by matching observation to theory we learn about black holes.
General relativity describes gravity extremely well. Of all the gravitational tests we’ve done, they all agree with general relativity. But Einstein’s theory doesn’t play well with the other extremely accurate physical theory, quantum mechanics. Because of this, physicists have proposed modifications to general relativity that are more compatible with quantum theory. Under these modified theories, there are subtle differences in the way merged black holes ring down, but observing those differences hasn’t been possible. But a couple of new studies show how we might be able to observe them in the next LIGO run.
The modified Teukolsky equation. Credit: Li, Dongjun, et al
In the first work, the team focused on what is known as the Teukolsky Equation. First proposed by Saul Teukolsky, the equations are an efficient way of analyzing gravitational waves. The equations only apply to classical general relativity, so the team developed a way to modify the equations for modified general relativity models. Since the solutions to both the Teukolsky and modified Teukolsky equations don’t require a massive supercomputer to solve, the team can compare black hole ring downs in various gravitational models.
The second work looks at how this would be done with LIGO data. Rather than focusing on general differences, this work focuses on what is known as the no-hair theorem. General relativity predicts that no matter how two black holes merge, the final merged black hole must be described by only mass, rotation, and charge. It can’t have any “hair”, or remnant features of the collision. In some modified versions of general relativity, black holes can have certain features, which would violate the no-hair theorem. In this second work, the authors show how this could be used to test general relativity against certain modified theories.
LIGO has just begun its latest observation run, so it will be a while before there is enough data to test. But we may soon have a new observational test of Einstein’s old theory, and we might just prove it isn’t the final theory of gravity after all.
Reference: Li, Dongjun, et al. “Perturbations of spinning black holes beyond General Relativity: Modified Teukolsky equation.” Physical Review X 13.2 (2022): 021029.
Reference: Ma, Sizheng, Ling Sun, and Yanbei Chen. “Black hole spectroscopy by mode cleaning.” Physical Review Letters 130.2 (2023): 141401.
The post When Black Holes Merge, They’ll Ring Like a Bell appeared first on Universe Today.
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