On August 14, 2021, while the world watched Haiti, punished for a violent earthquake —the umpteenth to shake the region—, NASA was writing a new chapter in space history. Maybe not a tremendous one and the height of that first moonwalk by Neil Armstrong and Buzz Aldrin from the late 1960s, but certainly revealing of the silent work carried out in the agency to achieve a goal that is not much less ambitious: keep an eye on asteroids and comets that pass close to Earth. Or what is the same, to guarantee that we can anticipate an impact like the one that triggered an episode of mass extinction 66 million years ago.
That day in mid-August, Saturday, the antenna of the Deep Space Station 14 (DSS-14), at the Goldstone Deep Space Communications Complex, followed in the footsteps of 2021 PJ1, an asteroid between 20 and 30 meters wide that was traveling at a speed of about 9.25 kilometers per second (km/s). It is not a huge rock, but it is relevant for another reason: it became the near-Earth asteroid -or NEA (Near-Earth Asteroid)-. number 1,000 observed by a planetary radar since in 1968 the 1566 Icarus launched the list.
2021 PJ1 whizzed by at around 1.7 million kilometers, which didn’t make it a real threat to our planet; but it did make him enter the radar —pun intended— of the vigilantes who are dedicated to controlling NEOs —Near-Earth Objects, a label that also includes comets— that orbit the Sun and can approach Earth. In fact, about 75% of NEA radar observations have been made within the framework of NASA’s NEO Observations Program, which is itself part of the Planetary Defense Program.
On the hunt for the lost “projectiles”
Using its ground-based and space-based telescopes, the program’s experts can calculate the NEOs’ orbits, characteristics, and—perhaps most importantly—the future trajectories. The goal, like specifies the US agency itself: “Early detection of potentially dangerous objects”, close to our planet and that will come within 5 million miles —8 million km— of the Earth’s orbit. In terms of size, it focuses on those bodies “large enough – from 30 to 50 m – to cause significant damage” to the planet.
On their side they have tools as powerful as Goldstone’s 34-meter DSS-14 and DSS-13 antennas, which by September last year had observed 374 near-Earth asteroids, or other resources, such as the Canberra Deep Space Communication Complex, of the Deep Space Network; or the Parkes Observatory, in New South Wales. Before collapsing, one of the key supports was the great telescope of 305 meters of the Arecibo Observatory. Another key support is ATLAS, which just updated to search the entire night sky every 24 hours.
The good thing is that the effort, at least for now, doesn’t look bad at all. Since in 1993 astronomers detected fragments of a comet that was heading towards Jupiter and understood the great damage it could cause if its “target” were to Earth, scientists and politicians have turned to keep these space projectiles well guarded. The first step was taken by NASA in 1998, when the goal was marked to find at least 90% of asteroids and comets a kilometer or more wide that approached the orbit of our planet.
NASA estimates that there are about a thousand NEA of more than one kilometer and approximately 15,000 that exceed 140 meters. Today, the agency and its partners they claim to have controlled 95% of which, it is believed, could pass within 48.2 million kilometers of the planet and the largest objects; but, despite that percentage, there is still work ahead. Especially when it comes to smaller rocks.
“Researchers still lack sufficient data and models. Smaller NEOs that qualify as ‘big enough’ to penetrate Earth’s atmosphere and cause surface damage are difficult to capture and monitor because they are too dark to see.” acknowledge the agency, which explains that the Asteroid Threats Project (ROOF), for example, uses simulations with NASA supercomputers to assess threats.
Precisely to meet this complex challenge, in 2005 Congress raised the bar again NASA and gave it a new task: to detect, track and identify 90% of space rocks larger than 140 meters close to Earth. The mission, however, got off to a slow start. During a debate in the US House in March 2013, almost a decade later, a presenter from the Committee on Science, Space and Technology acknowledged that NASA had located 10%.
Its size – 140 meters – may not seem too threatening, but the Chelyabinsk meteor, which hit Russia that same year, measured just 20 meters and caused a shock wave that left a thousand and a half injured and damaged thousands of buildings spread over half a dozen cities. And that, despite the protective effect of the Earth’s atmosphere. The object, on that occasion, approached the Earth undetected before entering the atmosphere.
To deal with similar threats, scientists and space agencies have different initiatives on the table. Within a couple of years, in 2026, NASA plans to launch the space telescope Near-Eart Object Surveyor (NEO Surveyor), designed precisely to “advance planetary defense efforts to discover and characterize the majority of potentially dangerous asteroids and comets” located about 48.2 million kilometers from Earth’s orbit.
In order to achieve this, it is equipped with a 50 cm diameter telescope that operates in two heat-sensitive infrared wavelengths. “It will be able to detect both bright and dark asteroids, which are the hardest to find,” they need from the space agency.
NEO Surveyor will start with the ambitious goal of locating during its first five years of work at least two thirds of the NEOs of more than 140 m, “objects large enough to cause significant regional damage in case of impact with the Earth”, the technicians of NASA itself add: “You can make precise measurements of the sizes of NEO and obtain valuable information about its composition, shapes, rotational states and orbits.”
It is not his only strategy. at the end of last year NASA announced a new tool, Sentry-II, a monitoring algorithm that allows to improve the calculation of the probabilities of impact of all known NEA. The system will make it easier for scientists to get more out of observations and orbit calculations such as those made by the Center for Near Earth Object Studies (CNEOS), whose workload increases year after year. According to the agency, to date they have located nearly 28,000 near-Earth asteroids thanks to the exploration telescopes. Every year, on average, 3,000 new discoveries are added to the list.
Detect, control… and more
Although monitoring NEOs is the first step, it is of little use to anticipate a threat if, in the event, we cannot do anything to protect ourselves from an asteroid capable of passing through the atmosphere and impacting the Earth. For this reason, scientists work in parallel on other lines of study. Perhaps with solutions not as spectacular as those shown by the Hollywood industry in ‘Armageddon’ or ‘Deep Impact’, but fascinating from a technical point of view.
Just a few months ago, in November, the DART (Double Asteroid Redirection Test) spacecraft was launched, which has set out for space with a pioneering objective: to hit Dimorphos, an asteroid the size of a football field that orbits around something else major, Didymos, and check if, if necessary, we could divert the trajectory of a threatening object.
Another of the most surprising missions that scientists have underway, NEA Scout, seeks to bring a small CubeSaT the size of a shoebox to 2020 GE, a NEA asteroid of less than 18 meters, to analyze it closely, observe its size, shape, rotation, surface properties… Everything with the object, he details NASA, to provide information for future missions and “gain important planetary defense knowledge about this class of NEA”.
For now, on our side we have the protective effect of the atmosphere, against which they end up disintegrating most objects and the estimate that larger ones, such as those that first drew NASA’s attention, hit the planet every hundreds of thousands of years.
Cover image | NASA