1,000th near-Earth asteroid observed by planetary radar since 1968
Seven days after this historic milestone, a massive antenna ">NasaThe Deep Space Network’s Goldstone complex imaged another much larger object.
On August 14, 2021, a small near-Earth asteroid (NEA) designated 2021 PJ1 passed our planet at a distance of over 1 million miles (approximately 1.7 million kilometers). Between 20 and 30 meters wide, the recently discovered asteroid was not a threat to Earth. But the approach to this asteroid was historic, marking the 1,000th NEA to be observed by planetary radar in just over 50 years.
And only seven days later, planetary radar observed the 1001st of these objects, but this one was much bigger.
Since the asteroid’s first radar observation 1566 Icarus in 1968, this powerful technique was used to observe the passage of NEAs and comets (collectively referred to as near-earth objects, or NEOs). These radar detections improve our knowledge of NEO orbits, providing the data that can extend calculations of future motion from decades to centuries and help definitively predict whether an asteroid will strike Earth, or if it will simply pass nearby. For example, recent radar measurements of the potentially dangerous asteroid Apophis have ruled out any possibility that it will impact Earth for the next 100 years.
In addition, they can provide scientists with detailed information on physical properties that could only be matched by sending a spacecraft and observing these objects up close. Depending on the size and distance of an asteroid, radar can be used to image its surface in intricate detail while determining its size, shape, speed of rotation and whether or not it is accompanied by one or more little moons.
In the case of 2021 PJ1, the asteroid was too small and the observation time too short to acquire images. But as the 1,000th NEA detected by planetary radar, this milestone highlights efforts to study NEAs that have passed close to Earth.
“2021 PJ1 is a small asteroid, so when it passed us at a distance of over a million kilometers, we couldn’t get detailed radar images,” said Lance Benner, who heads the program. NASA asteroid radar research at NASA’s Jet Propulsion Laboratory in the South. California. “Yet even at this distance, the planetary radar is powerful enough to detect it and measure its speed with great precision, which has greatly improved our knowledge of its future motion. “
Benner and his team led this effort by using the 70-meter (230-foot) Deep Space Station 14 (DSS-14) antenna at the Deep Space Network’s Goldstone Deep Space Complex near Barstow, Calif., To transmit signals. radio waves to the asteroid and receive radar reflections, or “echoes.”
Capture the waves (radio)
Of all the asteroids seen by planetary radar, well over half were seen by the 305-meter (1,000-foot) large telescope at Arecibo Observatory in Puerto Rico before being damaged and decommissioned in 2020. The antenna collapsed shortly after. Goldstone’s 34-meter (112-foot) DSS-14 and DSS-13 antennas have observed 374 near-Earth asteroids to date. Fourteen NEAs have also been observed in Australia using antennas from the Deep Space Network’s Canberra Deep Space Communication Complex to transmit radio waves to asteroids and the Australian Compact Array Telescope and Observatory CSIRO parks in New South Wales to receive radar reflections.
Explore NASA’s massive 70-meter (230-foot) DSS-14 antenna at the Goldstone Deep Space communications complex in Barstow, Calif. In this 360-degree video. In addition to communicating with spacecraft throughout the solar system, DSS-14 and other DSN antennas can also be used to conduct radio searches. Credit: NASA /JPL-Caltech
Almost three-quarters of all NEA radar observations have been made since NASA’s NEO sightings program, now part of its planetary defense program, increased funding for this work 10 years ago. years.
The most recent asteroid observed by radar did not make its approach to Earth until a week after 2021 PJ1. Between August 20 and 24, Goldstone photographed the 2016 AJ193 as it passed our planet at a distance of 2.1 million miles (approximately 3.4 million kilometers). Although this asteroid is farther away than 2021 PJ1, its radar echoes were stronger because 2016 AJ193 is about 40 times bigger, with a diameter of about three-quarters of a mile (1.3 km). Radar images revealed considerable detail on the object’s surface, including ridges, small hills, flat areas, concavities, and possible boulders.
“The 2016 AJ193 approach provided an important opportunity to study the properties of the object and improve our understanding of its future movement around the Sun,” said Shantanu Naidu, a scientist at JPL who led the 22nd observations. August 2016 AJ193. “It has a cometary orbit, which suggests that it could be an inactive comet. But we knew about it shortly before this pass, other than its size and the amount of sunlight reflected off its surface, so we planned this observation campaign years ago.
NASA’s NEOWISE mission had previously measured the size of the 2016 AJ193, but Goldstone observations revealed more details: it is a very complex and interesting object that spins with a period of 3.5 hours .
Scientists will use these new observations from 2016 AJ193 – the 1001st NEA observed by planetary radar – to better understand its size, shape and composition. As with 2021 PJ1, measurements of its distance and speed during this approach also provided data that will reduce uncertainties in the calculation of its orbit.
“In addition to surveys that use terrestrial and space optical telescopes to detect and track nearly 27,000 near-Earth objects throughout our solar system, planetary radar is an important tool for monitoring approaching asteroids,” said said Kelly Fast, NEO Observations. Program Manager of the Planetary Defense Coordination Office at NASA Headquarters in Washington. “Reaching this milestone of just over 1,000 AEN radar detections underscores the important contribution that has been made to the characterization of this dangerous population, which is fundamental to our planetary defense efforts.”