Ground-based radar systems could have a unique role to play in planetary defense, helping humanity protect Earth by spotting asteroids and comets on potentially devasting collision courses with our planet.
This was the conclusion reached by National Academies in their 2023-2032 Planetary Science and Astrobiology Decadal Survey. Currently, only one radar system on Earth concentrates on detecting threatening space rocks: NASA's Goldstone Solar System Radar, which is part of the Deep Space Network (DSN).
On Saturday (Feb. 17) at the American Association for the Advancement of Science’s annual conference in Denver, Colorado, scientists revealed results that suggest ground-based radar that could significantly impact asteroid detection, and thus planetary defense.
Future efforts in this vein include the National Radio Astronomy Observatory's (NRAO) next-generation RADAR (ngRADAR) system, which uses the National Science Foundation’s Green Bank Telescope (GBT) and other facilities to expand humanity's capability to detect asteroids and comets in the vicinity of Earth using radar.
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Scientists are aware of over 1.1 million asteroids in the solar system, and over 30,000 of these are so-called Near-Earth Objects (NEOs). NASA's Center of Near Earth Object Studies (CNEOS) estimates that around 90% of NEOs wider than around 0.62 miles (1 kilometer) have been discovered.
Additionally, CNEOS has determined no NEO orbits presently threaten Earth, at least within the next century. But that doesn't mean that, within the remaining 10% of NEOs yet undiscovered, there isn't an object that could threaten our planet.
Radar, a word that comes from the acronym radio detection and ranging, uses radio waves to determine the distance and velocity of targets. Radar systems are composed of sender antennas, which beam out radio waves, and receiver antennas, which pick them up as they are reflected back. Radio waves bounced back by space rocks could help uncover asteroids or comets as well as help to study the nearby solar system and in unprecedented detail.
"There are many applications for the future of radar, from substantially advancing our knowledge of the solar system to informing future robotic and crewed spaceflight and characterizing hazardous objects that stray too close to Earth," Tony Beasley, NRAO's director, said in a statement.
Radar could give DART an early heads up
Earth's geological history is littered with examples of the destructive impact asteroids have had on our planet and its species. The most striking example of this is the 120-mile (200-kilometer) wide Chicxulub crater located in the Yucatán Peninsula, Mexico. This crater was created by the impact of a 6.2-mile (10-kilometer) wide asteroid 66 million years ago.
That asteroid impact triggered the Cretaceous-Tertiary (K–T) extinction event, which wiped out three-quarters of plant and animal species on the planet, including non-avian dinosaurs.
So, to ensure that humanity doesn't go the same way as the dinosaurs, space agencies are developing strategies to divert asteroids and comets in orbits that could impact Earth someday. Arguably, the most striking example of this defense mechanism is NASA's Double Asteroid Redirection Test (DART) mission. In September 2022, DART slammed into the smaller body of the double asteroid system, Didymos and Dimorphos. The aim of this was to see if a kinetic impact can reorientate the orbit of an asteroid enough to steer it off a collision course. In short, it worked.
Other asteroid diversion methods include the obvious — detonating a nuclear device at its surface — the sublime — towing an asteroid away with a solar sail — and even the plain strange — painting one side of an asteroid black so it absorbs more sunlight, thereby shifting its center of mass and altering its orbit. Though it sounds extremely far-fetched, that last one has some foundational research behind it.
However, one thing all of these potential diversion methods require is time.
The lead times needed by asteroid diversion missions can vary from many years to many decades. That means space agencies need a great deal of prior warning before implementing a method to adjust an asteroid's orbit.
The GBT is suggested as an important tool in the effort to detect asteroids that impinge on Earth's orbit because it is the world’s largest fully steerable radio telescope. This means it can observe around 85% of the sky over Earth and quickly track objects that race through its field of view. Such capability would allow space agencies to determine the location, size and speed of potentially hazardous NEOs on quicker timelines, scientists say.
"Most recently, the GBT helped confirm the success of NASA's DART mission, the first test to see if humans could successfully alter the trajectory of an asteroid," Patrick Taylor a scientist at the NRAO and ngRADAR's project director, said in the statement.
Radar is already unveiling the solar system
During initial testing, the GBT's ngRADAR system already demonstrated its capability to reveal denizens of the solar system in incredible detail.
"With the support of Raytheon Technologies, ngRADAR pilot tests on the GBT — using a low-power transmitter with less output than a standard microwave oven — have produced the highest-resolution images of the moon ever taken from Earth," Taylor added. "Imagine what we could do with a more powerful transmitter."
Thus, in addition to spotting and tracking asteroids and comets, radar could help planetary scientists study the geology of relatively nearby planets and moons. This could give us a hint as to how these bodies have evolved over the 4.6 billion-year history of the solar system.
Not bad for a technology that has been around since 1935, when the first working radar system was erected in the form of six wooden towers — two for transmitting antennae and four for receiving antennas. That system was built in Orford Ness in the Suffolk region of the U.K., and as scientists explain, NASA's Goldstone facility hasn't evolved much since just after this, in fact.
"The public might be surprised to learn that the technology we use in our current radar at Goldstone hasn’t changed much since World War II. For 99% of our observations, we transmit and receive from this one antenna," NASA's Marina Brozović said in the statement. "New radar transmitter designs, like ngRADAR on the GBT, have the potential to significantly increase the output power and waveform bandwidth, allowing for even higher resolution imaging.
"It will also produce a scalable and more robust system by using telescope arrays to increase the collecting area."
"NRAO is an ideal organization to lead these efforts because of the instruments we have available to receive radar signals as the Very Long Baseline Array has done in our pilot ngRADAR project," NRAO director of science communications Brian Kent said in the statement. "Future facilities like the next generation Very Large Array, as a receiver, will create a powerful combination for planetary science."
