- 3274 - ASTEROIDS - a near miss? Is on the way. On April 13, 2029, the asteroid Apophis will pass less than 20,000 miles from our planet's surface, closer than the distance of geosynchronous satellites. During that 2029 close approach, Apophis will be visible to observers on the ground in the Eastern Hemisphere without the aid of a telescope or binoculars.
--------------------- 3274 - ASTEROIDS - a near miss? Is on the way.
- On August 14, 2021, a small near-Earth asteroid (NEA) designated “2021 PJ1” passed our planet at a distance of over 1 million miles. Between 65 and 100 feet wide, the recently discovered asteroid wasn't a threat to Earth. But this asteroid's approach was historic, marking the 1,000th NEA to be observed by planetary radar in the last 50 years.
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- And only seven days later, planetary radar observed the 1,001st such object, but this one was much larger.
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- Since the first radar observation of the asteroid “1566 Icarus” in 1968, this powerful technique has been used to observe passing NEAs and comets, known as near-Earth objects. These radar detections improve our knowledge comet orbits, providing the data that can extend calculations of future motion by decades to centuries and help definitively predict if an asteroid is going to hit Earth, or if it's just going to pass close by.
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- Recent radar measurements of the potentially hazardous asteroid “Apophis” helped eliminate any possibility of it impacting Earth for the next 100 years.
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- Depending on an asteroid's size and distance, radar can be used to image its surface in intricate detail while also determining its size, shape, spin rate, and whether or not it is accompanied by one or more small moons.
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- Asteroid “2016 AJ193” rotates as it was observed by Goldstone’s 70-meter antenna on August 22, 2021. Three-quarters of a mile wide, the object was the 1,001st near-Earth asteroid to be measured by planetary radar since 1968.
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- In the case of 2021 PJ1, the asteroid was too small and the observing time too short to acquire images. 2021 PJ1 as a small asteroid passed us at a distance of over a million miles and we couldn't obtain detailed radar imagery.
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- Yet even at that distance, planetary radar is powerful enough to detect it and measure its velocity to a very high precision, which improved our knowledge of its future motion substantially.
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- NASA’s uses the massive 70-meter DSS-14 antenna at the Goldstone Deep Space Communications Complex in Barstow, California. Along with communicating with spacecraft throughout the solar system, DSS-14 and other DSN antennas can also be used to conduct radio science.
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- Of all the asteroids observed by planetary radar, well over half were observed by the large 305-meter (1,000-foot) telescope at Arecibo Observatory in Puerto Rico before it was damaged and decommissioned in 2020.
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- The antenna collapsed soon after. Goldstone's DSS-14 and 34-meter DSS-13 antennas have observed 374 near-Earth asteroids to date. Fourteen NEAs have also been observed in Australia using antennas at the Deep Space Network's Canberra Deep Space Communication Complex to transmit radio waves to the asteroids and the CSIRO's Australian Telescope Compact Array and Parkes Observatory in New South Wales to receive the radar reflections.
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- Nearly three-quarters of all NEA radar observations have been made since NASA's NEO Observations Program, now a part of its Planetary Defense Program, increased funding for this work 10 years ago. NEO = “near Earth object”, may not yet be identified as an “asteroid“.
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- The most recent asteroid to be observed by radar made its approach by Earth only a week after 2021 PJ1. Between August 20 and 24, Goldstone imaged 2016 AJ193 as it passed our planet at a distance of 2.1 million miles.
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- Although this asteroid was farther away than 2021 PJ1, its radar echoes were stronger because 2016 AJ193 is about 40 times larger, with a diameter of about three-quarters of a mile. The radar images revealed considerable detail on the object's surface, including ridges, small hills, flat areas, concavities, and possible boulders.
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- The 2016 AJ193 approach provided an important opportunity to study the object's properties and improve our understanding of its future motion around the Sun. It has a comet like orbit, which suggests that it may be an inactive comet. But we knew little about it before this pass, other than its size and how much sunlight its surface reflects.
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- 2016 AJ193's turns out to be a highly complex and interesting object that rotates with a period of 3.5 hours.
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- In addition to the surveys that use ground- and space-based optical telescopes to detect and track nearly 27,000 NEOs throughout our solar system, planetary radar is an important tool for monitoring asteroids that come close to Earth.
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- Reaching this milestone of now just over 1,000 radar detections of NEAs emphasizes the important contribution that has been made in characterizing this hazardous population, which is fundamental for our planetary defense efforts.
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- A University of Hawaiʻi Institute for Astronomy (IfA) astronomer has revealed critical new findings announcing the detection of “Yarkovsky acceleration” on the near-Earth asteroid “Apophis“. This acceleration arises from an extremely weak force on an object due to “non-uniform thermal radiation“. This force is particularly important for the asteroid Apophis, as it affects the probability of an Earth impact in 2068.
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- All asteroids need to reradiate as heat the energy they absorb from sunlight in order to maintain thermal equilibrium, a process that slightly changes the orbit of the asteroid. Prior to the detection of Yarkovsky acceleration on Apophis, astronomers had concluded that a potential impact with Earth in 2068 was impossible. The detection of this effect acting on Apophis means that the 2068 impact scenario is still a possibility.
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- Apophis is noteworthy because of its extremely close approach to the Earth on, April 13, 2029, when the 300 meter-sized asteroid will become visible to the unaided eye as it passes within the belt of communications satellites orbiting the Earth.
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- We have known for some time that an impact with Earth is not possible during the 2029 close approach. Astronomers have been accurately tracking the motion of Apophis in the sky since 2004.
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- The new observations we obtained with the Subaru telescope earlier this year, 2021, were good enough to reveal the Yarkovsky acceleration of Apophis, and they show that the asteroid is drifting away from a purely gravitational orbit by about 170 meters per year, which is enough to keep the 2068 impact scenario in play.
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- Further observations to refine the amplitude of the Yarkovksy effect and how it affects Apophis' orbit are underway. Astronomers will know well before 2068 if there is any chance of an impact.
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- After its discovery in 2004, Apophis had been identified as one of the most hazardous asteroids that could impact Earth. Estimated to be about 1,100 feet across, Apophis quickly gained notoriety as an asteroid that could pose a serious threat to Earth when astronomers predicted that it would come uncomfortably close in 2029.
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- Thanks to additional observations of the near-Earth object (NEO), the risk of an impact in 2029 was later ruled out, as was the potential impact risk posed by another close approach in 2036.
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- When Apophis made a distant flyby of Earth around March 5, 2021, astronomers took the opportunity to use powerful radar observations to refine the estimate of its orbit around the Sun with extreme precision, enabling them to confidently rule out any impact risk in 2068 and long after.
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- A 2068 impact is not in the realm of possibility anymore, and our calculations don't show any impact risk for at least the next 100 years. With the support of recent optical observations and additional radar observations, the uncertainty in Apophis' orbit has collapsed from hundreds of kilometers to just a few kilometers when projected to 2029.
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- The orbital trajectory of Apophis as it zooms safely past Earth on April 13, 2029 is calculated. Earth’s gravity will slightly deflect the trajectory as the 1,100-foot-wide near-Earth object comes within 20,000 miles of our planet’s surface.
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- To arrive at the latest Apophis calculations, astronomers turned to the 70-meter radio antenna at the Deep Space Network's Goldstone Deep Space Communications Complex near Barstow, California, to precisely track Apophis' motion.
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- Although Apophis made a recent close approach with Earth, it was still nearly 10.6 million miles away. Even so, we were able to acquire incredibly precise information about its distance to an accuracy of about 150 meters.
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- Goldstone also worked in a collaboration with the 100-meter Green Bank Telescope in West Virginia in order to enable imaging of Apophis; Goldstone was transmitting while Green Bank was receiving a "bistatic" experiment that doubled the strength of the received signal.
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- Although the radar imagery of Apophis appears pixelated, the images have a resolution of 38.75 meters (127 feet) per pixel, which is a remarkable resolution, considering the asteroid was 17 million kilometers away, or about 44 times the Earth-Moon distance.
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- If we had binoculars as powerful as this radar, we would be able to sit in Los Angeles and read a dinner menu at a restaurant in New York.
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- As the radar team further analyzes their data, they also hope to learn more about the asteroid's shape. Previous radar observations have suggested that Apophis has a "bilobed," or peanutlike, appearance. This is a relatively common shape among the near-Earth asteroids larger than 660 feet in diameter; at least one in six have two lobes.
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- Astronomers are also working to develop a better understanding of the asteroid's rotation rate and the axis it spins around, its spin state. That knowledge will enable them to determine the orientation the asteroid will have with Earth as it encounters our planet's gravitational field in 2029, which could change that spin state and even cause "asteroid quakes."
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- On April 13, 2029, the asteroid Apophis will pass less than 20,000 miles from our planet's surface, closer than the distance of geosynchronous satellites.
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- During that 2029 close approach, Apophis will be visible to observers on the ground in the Eastern Hemisphere without the aid of a telescope or binoculars.
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- September 13, 2021 - ASTEROIDS - a near miss? Is on the way. 3274
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