Radar sees what optical instruments cannot.
When the Arecibo Observatory fell in December 2020, humanity lost one of its most attentive eyes on the cosmos — and the quiet sentinel in California's Mojave Desert stepped forward to fill the silence. NASA's Goldstone Solar System Radar, long content to work in Arecibo's shadow, has since become the world's foremost tool for studying asteroids that pass close to Earth, setting a record of 55 detections in 2024 alone. In a time when more than two hundred new asteroids are discovered each month, the question of which ones might one day find us has never been more pressing — and Goldstone is now the instrument most capable of answering it.
- Arecibo's sudden collapse in 2020 left a dangerous gap in planetary defense, stripping scientists of the world's most powerful asteroid-studying radar almost overnight.
- Goldstone has responded with remarkable momentum — 55 detections in 2024 represent a five-fold increase from fifteen years ago, with 112 of its post-Arecibo finds classified as potentially hazardous asteroids.
- For years, a bureaucratic tangle of more than twenty government and military approvals slowed Goldstone's response time, allowing newly discovered asteroids to slip past its optimal observation window before clearance could be granted.
- That bottleneck has been removed — observers can now pivot targets on the fly, a critical capability as discovery rates surge past 200 new asteroids per month.
- Goldstone is no longer merely keeping pace with Arecibo's legacy; it has corrected it, reclassifying one asteroid system from binary to triple, and now matches Arecibo's historical rate of binary system discoveries.
When the Arecibo Observatory collapsed in December 2020, it left a profound void in planetary defense. For decades, the massive Puerto Rico dish had been the world's premier tool for studying asteroids up close — finding binary asteroid systems at roughly two and a half times the rate of its nearest competitor. That competitor was a solitary antenna in California's Mojave Desert: Goldstone Solar System Radar, which had spent years working quietly in Arecibo's shadow.
Goldstone was built to communicate with spacecraft, sending signals into the void and listening for echoes from the solar system's far reaches. But in the gaps between those deep-space conversations, it hunted asteroids — measuring orbits with precision, calculating collision risks, and revealing details about shape, size, and composition that optical telescopes simply cannot provide. That secondary mission became primary the moment Arecibo fell.
By the end of 2024, Goldstone had detected 55 near-Earth asteroids, a new annual record representing a five-fold increase from fifteen years earlier. Since Arecibo's collapse, the facility has identified 199 near-Earth asteroids, 112 of which were classified as potentially hazardous. Lance Benner, an asteroid hunter at NASA's Jet Propulsion Laboratory, has watched this transformation unfold, noting that Goldstone's binary asteroid discoveries now rival Arecibo's historical output — and have even corrected some of it, reclassifying the asteroid system 1998 ST27 from a binary pair to a triple system.
Radar's power lies in resolution. Where optical telescopes excel at finding asteroids, radar reveals what they are — surface roughness, rotation states, precise orbital trajectories. These details matter both for understanding the solar system's ancient formation and for calculating whether a given rock poses a threat to Earth in the centuries ahead.
Much of Goldstone's surge in productivity traces back to a bureaucratic breakthrough. For years, observers needed clearance from more than twenty government and military agencies before transmitting toward specific parts of the sky — a process that could take days, long enough for a newly discovered asteroid to drift beyond the optimal observation window. That requirement has been eliminated. Observers can now change targets on the fly, an essential capability as more than two hundred new asteroids are discovered each month.
Goldstone itself is a relic with a deepening future. Its first antenna went into operation in December 1958, just months after NASA's creation, and the facility made the first-ever radar observations of an asteroid — the near-Earth object Icarus — in 1968. Now part of NASA's Deep Space Network alongside dishes in Canberra and Madrid, Goldstone maintains contact with the Voyager probes at the edge of interstellar space while simultaneously standing watch over the asteroids that share our cosmic neighborhood. As space missions multiply and asteroid discovery accelerates, its role in both endeavors will only grow.
When the Arecibo Observatory collapsed without warning in December 2020, it left a crater in planetary defense. The massive dish in Puerto Rico had been the world's premier tool for studying asteroids up close—a facility so powerful that it found roughly two and a half times as many binary asteroid systems as its nearest competitor. That competitor was a solitary antenna rising from the Mojave Desert in California, a facility called Goldstone Solar System Radar, which had spent decades in Arecibo's shadow.
Goldstone was built to talk to spacecraft. Its antennas send signals into the void and listen for echoes from the solar system's far corners. But in the gaps between those conversations with distant probes, the facility does something else: it hunts asteroids. When a space rock passes near Earth, Goldstone's radar can measure its orbit with precision, calculate collision risks, and reveal details about its shape, size, and composition—information that optical telescopes simply cannot provide. For decades, this secondary mission was exactly that. Then Arecibo fell, and everything changed.
By the end of 2024, Goldstone had detected 55 near-Earth asteroids, setting a new annual record for the facility. That number represents a five-fold increase from fifteen years earlier, and a fifty percent jump from the average detection rate between 2012 and 2018. The shift is not merely quantitative. Since Arecibo's collapse, Goldstone has identified 199 near-Earth asteroids, with 154 of those being radar observations for the first time. Of those first-time detections, 112 were classified as potentially hazardous—asteroids whose orbits bring them close enough to Earth that they warrant careful monitoring.
Lance Benner, an asteroid hunter at NASA's Jet Propulsion Laboratory, has watched this transformation unfold. He uses Goldstone to observe known asteroids and presented the facility's progress to the planetary science community in March at the Lunar and Planetary Sciences Conference in Houston. According to Benner, the number of binary asteroid systems now identified by Goldstone is comparable to what Arecibo achieved during its operational years. The Mojave facility has even corrected some of Arecibo's work—reclassifying the asteroid system 1998 ST27 from a binary pair into a triple system, a discovery only possible with Goldstone's detailed radar imaging.
Radar's power lies in its resolution. While asteroids are easier to find with optical telescopes, radar sees what optical instruments cannot. The images produced by Goldstone rival the detail captured by spacecraft flybys, revealing surface roughness, rotation states, and the subtle geometry of space rocks tumbling through the void. This matters because asteroids are time capsules from the solar system's formation, and understanding their structure and composition helps scientists reconstruct the conditions of those ancient days. More immediately, precise radar measurements of an asteroid's trajectory allow researchers to calculate whether it poses a collision threat to Earth in the coming centuries.
The surge in Goldstone's productivity stems partly from a bureaucratic breakthrough. For years, observers had to obtain permission from more than twenty government agencies and military units who control the restricted airspace surrounding the Goldstone Deep Space Communications Complex. Approval could take days—long enough for a newly discovered asteroid to move beyond the facility's optimal observation window. That requirement has been eliminated. Observers no longer need advance clearance to transmit toward specific parts of the sky. "This gives us the ability to change targets on the fly," Benner said. The flexibility has proven essential. More than two hundred new asteroids are discovered each month now, and on any given day, multiple targets fall within Goldstone's detection range. Without the ability to pivot quickly, the facility would miss most of them.
Goldstone itself is a relic with a future. The facility's first antenna, an 85-foot polar-mounted dish called the Pioneer Station, went into operation in December 1958, just months after NASA's creation. It supported the Pioneer missions to the moon and later the Apollo program before being shut down in 1981 and declared a National Historic Monument. The asteroid work began in 1968, when Goldstone made the first-ever radar observations of an asteroid—the near-Earth object Icarus, which was making a close approach to our planet. For more than fifty years, that work continued in the background, overshadowed by Arecibo's larger aperture and greater sensitivity. Now, with Arecibo gone and asteroid discovery accelerating, Goldstone has stepped into the foreground. The facility is part of NASA's Deep Space Network, which also includes dishes in Canberra and Madrid, and which continues to maintain contact with the Voyager probes at the edge of interstellar space. As the number of active space missions is expected to double in coming years, Goldstone's role in both deep space communication and planetary defense will only deepen.
Citas Notables
Some images obtained with radar rival the resolutions of spacecraft flyby missions.— Lance Benner, Jet Propulsion Laboratory
This gives us the ability to change targets on the fly, which is really important because more than 200 asteroids are discovered each month.— Lance Benner, Jet Propulsion Laboratory
La Conversación del Hearth Otra perspectiva de la historia
When Arecibo fell, did people immediately understand that Goldstone would have to fill the gap?
Not really. Arecibo was so much larger, so much more capable. Goldstone had been doing this work for decades, but almost as an afterthought. It took time for the community to realize that Goldstone was the only tool left for this particular job.
What makes radar so much better than a telescope for studying asteroids?
A telescope sees the asteroid as a point of light. Radar bounces a signal off it and reads the echo. That echo tells you the shape, the texture, the rotation, even whether there's a companion asteroid orbiting nearby. You get a three-dimensional picture instead of a silhouette.
The approval process sounds like it was strangling the work.
It was. You'd discover an asteroid, want to observe it, and by the time you got permission from twenty different agencies, the asteroid had moved too far away. Now you can just point and shoot. It's changed everything about how much work can get done.
Why does it matter whether an asteroid is binary or single?
It tells you about the asteroid's history—how it formed, whether it's been through collisions. And for planetary defense, it changes how you'd approach deflecting it. A binary system behaves differently than a single rock.
Goldstone was built to talk to spacecraft. Does that mission ever conflict with the asteroid work?
There's scheduling, sure. But asteroid observations are now treated as a priority comparable to space missions. That's the real shift. Goldstone went from being a secondary tool to being essential.