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Ignorance may seem like a joy, but preparation offers a better chance of surviving what is about to happen. And when it comes to planetary defense, ignorance has become a little more inevitable.
Planetary defense is the art of identifying and mitigating threats to Earth from asteroid impacts. And among its tools is planetary radar, an unusual capability that can give scientists a much better view of a nearby object. The Arecibo Observatory in Puerto Rico was one of the few systems of its kind on the planet, and that instrument’s long tenure is now over after two broken cables made the telescope so unstable that there was no way to even evaluate it. state without risking the lives of workers, according to the US National Science Foundation (NSF), which owns the site. Instead, it will be disabled.
And when it comes to planetary defense, there’s nothing like it.
“There have been claims in the media that, ‘Oh, we have other systems that can replace what Arecibo is doing,’ and I don’t think that’s true,” said Anne Virkki, who leads the planetary radar team at the Arecibo Observatory. Space.com. “It is not outdated and is not easily replaceable with other existing structures and tools.”
Related: Losing the Arecibo Observatory would create a hole that can’t be filled, scientists say
Planetary defense begins with identifying as many asteroids near Earth as possible – nearly 25,000 to date, according to NASA – and estimating their size and orbits around the sun. Arecibo never played a role in the discovery of asteroids; this task is much more easily completed by a myriad of telescopes that see wide swaths of the sky in visible and infrared light and are able to catch the sudden appearance of a bright, fast-moving spot among the stars, telescopes like the observatory PanSTARRS in Hawaii. With those first observations, smaller asteroids and those that are far from Earth can be safely labeled and more or less forgotten.
But larger asteroids with orbits that might get too close for convenience get more studies, and often that work has been done by the Arecibo Observatory. The facility had a powerful radar transmitter capable of bouncing a beam of light off an object in the vicinity of Earth. Then, the observatory’s huge radio antenna could capture the echo of that signal, allowing scientists to decipher precise details about an asteroid’s location, size, shape and surface.
The same telescopes that identify asteroids in the first place can also provide scientists with the data they need to track the orbit of a space rock, but when planetary radar can locate the object, it completes the same job more quickly.
Sometimes that speed will be important, said Bruce Betts, chief scientist at the Planetary Society, a non-profit space exploration advocacy group that includes planetary defense among its key issues. “You want to define an orbit as quickly as possible to figure out if the asteroid will hit Earth,” Betts told Space.com.
This is because with enough warning, humans could theoretically do something to prevent the collision, likely pushing the asteroid off course or breaking it into smaller pieces that wouldn’t wreak as much havoc on the Earth’s surface as a single larger object.
“This is actually a preventable natural disaster if we work hard enough,” Betts said. “While it’s rare, it’s something we can actually do something about, unlike hurricanes or earthquakes in terms of the prevention aspect.”
And radar can offer more details about a space rock more quickly than can inform planetary defense, including vital information such as whether an asteroid is actually a single object or a pair of objects in disguise, as 15% of asteroids near Earth turn out to be be, Betts said. “If you need to deflect it, of course, it is essential to know if there are one or two objects.”
The same with the composition of space rock. “Some are solid metal, others are balls or piles of rubble, so they vary greatly in density,” Betts said. “If you have to actually deflect an asteroid, if it is actually targeting Earth, the techniques may respond differently depending on whether you are dealing with a very dense asteroid or a very soft asteroid.”
So radar is a valuable skill for a planet.
Arecibo wasn’t the only radar facility, but it’s a rare capability given how expensive the technology involved is. With his disappearance, the only remaining radar transmitter is at the Goldstone Deep Space Communications Center in California, operated by NASA’s Jet Propulsion Laboratory. But this facility has a number of additional responsibilities: it is part of the Deep Space Network which manages communications with spacecraft throughout the solar system, and it also has military responsibilities.
“They won’t be as flexible with scheduling these newly discovered target observations as Arecibo has been,” Virkki said. “If you can’t observe those targets when they’re in the window, you could miss the opportunity very quickly, and then you have these asteroids that have more uncertainties in their orbits.” And that uncertainty could make the difference between worrying that a space rock will hit Earth and being certain it won’t.
Goldstone’s radar system is also about 20 times less sensitive than Arecibo’s, and the two systems could see different subsets of space, he said. “So it won’t exactly replace Arecibo.”
Virkki said there are plans underway to add radar capability to the Green Bank Observatory in West Virginia, but even then he will not be able to take control of Arecibo’s work. Green Bank will use a slightly different radar than Arecibo’s and will be more vulnerable to bad weather, he said.
And it will have a narrow radius, making it a little more perceptive in tracking asteroids. “If you have a very narrow range, you need to have a good idea of where your radar is pointing,” Virkki said. “You can’t go, like, look around with that tight beam.” Arecibo was more forgiving when asteroid orbits weren’t so certain.
These factors combine to make the loss of Arecibo a major blow to planetary defense capability, according to Ed Lu, a former NASA astronaut and executive director of the B612 Asteroid Institute, a nonprofit organization focused on asteroid science and deflection studies. “This is a great loss to the community,” he said. “It’s not that we won’t have this capacity, but it will certainly be reduced.”
And then, of course, there is the risk that something else will go wrong. “Radars are, of course, complicated and things break down,” Betts said. “Now you have no redundancy in your system, it’s a single failure with the Goldstone radar. So if it breaks at the wrong time, you don’t get what you need. “
The weakness is coming at a difficult time for planetary defense experts, Lu said. New asteroids are being identified more and more rapidly – a few thousand a year, these days – and this trend will only accelerate when the Vera Rubin Observatory begins. to work within the next year, he said.
“It will discover almost a factor of 10 more asteroids than all other telescopes combined,” said Lu of the Rubin Observatory. “What we’re actually going to have is quite a large number of new asteroid observations, and within that dataset, there will be asteroids that are known to be very close to Earth, and that we initially won’t be able to rule out if to hit or not to hit. “
The risk of an impact is always the same, of course, but increasing our research capacity by losing the capacity for characterization is a recipe for greater uncertainty.
There is no easy way to replace the missing radar capability with Arecibo, all three experts said.
“Obviously, we’d be in favor of finding a way to fix it, rebuild it, whatever happens, upgrade it,” Lu said. “This is a question of money.”
“But sometimes, sometimes, if you don’t make the investment, you’ll regret it later.”
Email Meghan Bartels at [email protected] or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.
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