NASA’s Double Asteroid Redirection Test (DART) spacecraft successfully hit its target Sept. 26, and now scientists are analyzing to what degree the kinetic impact changed the trajectory of Dimorphos, the asteroid moonlet of Didymos.
The mission is a test to see if hitting a body headed for Earth with a small spacecraft could redirect the threat away from us.
Five Planetary Science Institute scientists, Jian-Yang Li, Eric Palmer, Steven Schwartz, Amanda Sickafoose and Jordan Steckloff are working on the DART mission.
The mission will attempt to slightly change an asteroid’s motion in a way that can be accurately measured using ground-based telescopes. DART’s target Dimorphos is approximately 530 feet (160 meters) in diameter, and orbits Didymos, approximately 2,560 feet (780 meters) in diameter. Since Dimorphos orbits Didymos at much a slower relative speed than the pair orbits the Sun, the result of DART’s kinetic impact within the binary system can be measured much more easily than a change in the orbit of a single asteroid around the Sun.
“This is the first time that humans have tried to actually alter the path of an asteroid. This is the type of thing that blockbusters movies are made of!” said Sickafoose, a DART Investigation Team member.
Sickafoose’s team has been taking six-hour blocks of images using a 1-meter telescope in Sutherland, South Africa to derive Didymos’ light curve on the days leading up to the impact, the impact itself, and will then take more light-curve observations following impact. “Our site is also well placed to observe the impact itself. Changes in brightness near the impact time can be compared with models to help determine the physical properties of Dimorphos. Combining light-curve observations from many sites over a long period of time will allow accurate determination of changes to Dimorphos’ orbit as a result of the impact,” Sickafoose said.
“By observing the Didymos system before and after the impact, we are supporting the primary goal of determining how much the path of the satellite is altered. Right now, Dimorphos has an orbital period of roughly 11.9 hours. Changes to this orbital period after the impact would indicate the effect of the spacecraft,” Sickafoose said. “Taking images of the impact itself can be used to compare with models of ejecta formation and distribution, which should help constrain the physical properties of the asteroid.”
“The DART mission is a test to see how effective a kinetic impact is in changing the orbit of an asteroid. We are using this binary asteroid system for this test because it provides a clear and accurate technique to measure the change in orbit,” Palmer said.
“I will be building the digital terrain model for Didymos, the binary asteroid system’s primary. Additionally, I am responsible for updating and testing the software needed to generate the shape model,” Palmer said. “My part supports our scientific understanding of asteroids, especially binary asteroids.”
Li is leading the NASA Hubble Space Telescope observations of the impact, and also participating in the analysis of the images of Didymos and Dimorphos to be collected by the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO) onboard DART and the LEIA camera onboard the Light Italian CubeSat for Imaging Asteroids (LICIACube) to study the surface albedo of the asteroids.
“I’m currently a Participating Scientist on the mission, but I’ve been involved with it for a while,” Schwartz said. “It was conceived as a more coordinated set of two missions, NASA’s DART and the European Space Agency’s Asteroid Impact Mission.”
Steckloff is on the mission’s investigative team. “My main interest is in the behavior of the asteroid regolith and topography in response to the DART impact. Are we going to trigger landslides and landscape evolution? How will any impact-induced seismic activity contribute to landscape evolution? What are the physical properties of the asteroid material – for example, cohesive strength?
“In short, my interests are on changes to a rubble pile in response to a known impact. This has less to do with the primary goal of the DART mission to determine the efficacy of current kinetic deflection technology, but more to do with what we can learn from a known impact into a rubble pile asteroid,” Steckloff said.
The spacecraft, about the size of a golf cart and weighing 1,210 pounds, or 550 kilograms, slammed into Dimorphos at roughly 4 miles per second (6 kilometers per second). Scientists estimate the kinetic impact will shorten Dimorphos’ orbit around Didymos by several minutes.
Direct impact or nuclear weapons? How to save Earth from an asteroid
Laurel, United States (AFP) Sept 26, 2022 –
NASA’s DART mission to test deflecting an asteroid using “kinetic impact” with a spaceship is just one way to defend planet Earth from an approaching object — and for now, the only method possible with current technology.
The operation is like playing billiards in space, using Newton’s laws of motion to guide us.
If an asteroid threat to Earth were real, a mission might need to be launched a year or two in advance to take on a small asteroid, or decades ahead of projected impact for larger objects hundreds of kilometers in diameter that could prove catastrophic to the planet.
Or, a larger object might require hits with multiple spacecraft.
“This demonstration will start to add tools to our toolbox of methods that could be used in the future,” said Lindley Johnson, NASA’s planetary defense office, in a recent briefing.
Other proposed ideas have included a futuristic-sounding “gravity tractor,” or a mission to blow up the hypothetical object with a nuclear weapon — the method preferred by Hollywood.
– Gravity tractor –
Should an approaching object be detected early — years or decades before it would hit Earth — a spaceship could be sent to fly alongside it for long enough to divert its path via using the ship’s gravitational pull, creating a so-called gravity tractor.
This method “has the virtue that the method of moving the asteroid is totally well understood — it’s gravity and we know how gravity works,” Tom Statler, a DART program scientist at NASA said at a briefing last November when DART launched.
The mass of the spacecraft however would be a limiting factor — and gravity tractors would be less effective for asteroids more than 500 meters in diameter, which are the very ones that pose the greatest threat.
In a 2017 paper, NASA engineers proposed a way to overcome this snag: by having the spacecraft scoop material from the asteroid to enhance its own mass, and thus, gravity.
But none of these concepts have been tried, and would need decades to build, launch and test.
– Nuclear detonation –
Another option: launching nuclear explosives to redirect or destroy an asteroid.
“This may be the only strategy that would be effective for the largest and most dangerous ‘planet-killer’ asteroids (more than one kilometer in diameter),” a NASA article on the subject says, adding such a strike might be useful as a “last resort” in case the other methods fail.
But these weapons are geopolitically controversial and technically banned from use in outer space.
Lori Glaze, NASA’s planetary science division director said in a 2021 briefing that the agency believed the best way to deploy the weapons would be at a distance from an asteroid, in order to impart force on the object without blowing it into smaller pieces that could then multiply the threat to Earth.
A 2018 paper published in the “Journal of Experimental and Theoretical Physics” by Russian scientists looked at the direct detonation scenario.
E. Yu. Aristova and colleagues built miniature asteroid models and blasted them with lasers. Their experiments showed that blowing up a 200-meter asteroid would require a bomb 200 times as powerful as the one that exploded over Hiroshima in 1945.
They also said it would be most effective to drill into the asteroid, bury the bomb, then blow it up — just like in the movie Armageddon.
Related Links
DART at APL
Planetary Science Institute
DART’s Final Images Prior to Impact
Asteroid and Comet Mission News, Science and Technology
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Tenoumer Crater, Mauritania
Paris (ESA) Jul 01, 2022
Deep within the Sahara Desert lies one of the best-preserved craters on Earth. On Asteroid Day, the Copernicus Sentinel-2 mission takes us over the almost-perfectly circular Tenoumer Crater in Mauritania.
Zoom in to explore this image in its full 10 m resolution.
Tenoumer Crater, visible in the centre of the image, is 1.9 km wide. The rims of the crater rise some 110 m high above the base, but the bottom of the crater is covered with approximately 200 to 300 m thick layer of sediments.
