Astronomers on the hunt for modest-sized asteroids capable of vaporizing a city or larger beasts that could sterilize the face of the Earth have spotted a new potential threat. However, don’t worry right away… it will be many generations before it poses a danger to our planet.
Detecting space rocks that have never been observed before depends on spotting flashes of sunlight on their surfaces. However, some asteroids occupy corners of the sky where the brightness of the Sun covers them and, like embers fluttering in front of a thermonuclear pyre, they disappear from view.
Last year, hoping to find asteroids blanketed in excess sunlight, an international team of astronomers added a camera designed primarily to probe the universe’s dark energy, which is notoriously elusive. In a Monday announcement based on research first published in September by The Astronomical Journal, researchers announced the discovery of three new light-dipping projectiles.
One of them, 2022 AP7, is approximately 1.5 kilometers long and its orbit crosses that of the Earth around the Sun, so it comes up to 7.08 million kilometers from our planet, an uncomfortable closeness in terms cosmic (although it is much more distant than the Moon from Earth). This makes 2022 AP7 “the largest potentially dangerous asteroid that has been found in the last eight years or so,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington DC and an author of the study.
After the asteroid was discovered in January, other observatories studied its motion and other astronomers retrospectively identified it and placed it in older images. This data set made it clear that it will not visit Earth for the next century or perhaps much longer.
“There is a very low probability of an impact in the near future,” said Tracy Becker, a planetary scientist at the Southwest Research Institute who was not involved in the study.
However, the gravitational pull of objects in the solar system—including our own planet—ensures that Earth-crossing asteroids don’t dance the same way forever. Asteroid 2022 AP7 is no exception. “Over time, this asteroid will get brighter and brighter in the sky as it starts to cross Earth’s orbit and get closer and closer to where our planet actually is,” Sheppard said.
It’s possible that “well into the future, in the next thousand years, it could be a problem for our descendants,” said Alan Fitzsimmons, an astronomer at Queen’s University Belfast, who was not involved in the study.
What if, in the most unfortunate timeline, 2022 AP7 ends up impacting Earth?
“We call them planet killers,” Sheppard mentioned. “If it hits Earth, it would cause planetary destruction. It would be lousy for life as we know it.”
However, since we are safe for many generations, the orbit of this asteroid is not its most notable feature. “The interesting thing about 2022 AP7 is that it is relatively large”said Cristina Thomas, a planetary astronomer at Northern Arizona University, who was not involved in the study. Their existence suggests the disturbing idea that other colossal asteroids, hidden by the Sun’s glare, remain undiscovered.
Currently, astronomers searching for potentially dangerous asteroids—those that come within at least 7.4 million kilometers of Earth and are too large to be incinerated harmlessly in our atmosphere—focus on finding rocks about 140 meters wide. Most likely there are tens of thousands of them and less than half have been identified. They could produce destruction on the scale of a country. Such threats have motivated NASA and other space agencies to develop planetary defense missions like DART, the spacecraft that successfully adjusted the orbit of a small, harmless asteroid in September.
Most asteroids greater than or equal to 1 kilometer long have already been found: much less common, but capable of global devastation. However, “we know there is still more to find,” Fitzsimmons said.
To be sure, there are several sneaking around Mercury and Venus. However, it is “incredibly difficult to discover objects within Earth’s orbit with our current discovery telescopes,” Thomas noted. During most hours of the day, the Sun dazzles telescopes on Earth and objects can only be seen in the few minutes around sunset.
To overcome this limitation, the astronomers who detected 2022 AP7 used the Dark Energy Camera on the Victor M. Blanco 4-meter aperture Telescope in Chile. Not only can this telescope survey large portions of the sky, but it also has the sensitivity to find faint objects that are shrouded in sunlight. So far, the camera has found two other near-Earth objects: one the size of a planet-killer whose orbit never crosses Earth’s, but brings it closer to the Sun than any known asteroid has ever been, for causing its surface to flambé at extreme temperatures that can turn lead into a liquid; and a smaller rock capable of assassinating a country that poses no risk.
Eventually, NASA’s NEO Surveyor mission, which detects near-Earth objects, will dwarf survey capabilities during sunset. Launched this decade, this Earth-orbiting infrared observatory will watch the sun shine and find most of the dangerous asteroids missed by other studies.
“We want to do everything possible not to be surprised”Thomas commented. That’s why these studies exist: to find asteroids capable of impacting Earth long in advance so that, through energetic pinpricks or nuclear explosions, we can return these monsters to the shadows.
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