When the mainstream media calls an asteroid a “planet killer,” we usually tend to take it with a grain of salt since we know that eye-grabbing headlines like that draw attention. When a noted astronomer using a state-of-the-art ground-based observatory uses that phrase, we should sit up and listen. Well, get that spine straight and those ears perked because a leading astronomer and astrophysicist just released a paper describing two “planet killers” which have been hiding in the glare of the sun and regularly cross the path of the Earth. One of these “killers” is a mile wide and yet has been keeping out of sight in the sun’s bright glare. There is a possibility that more could be hiding there, but this one is the big concern right now because its orbit is slowly moving it to be in sync with Earth. Should we be worried?
“To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo-type Near Earth Object (NEO) that crosses Earth's orbit, 2022 AP7. Two of the discoveries have diameters ≳1 km. 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years.”
In the abstract of the paper, “A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus,” astronomer and lead author Scott Shepherd, an astronomer at the Earth & Planets Laboratory of the Carnegie Institution for Science in Washington, DC, explained three new asteroids have been discovered orbiting the Sun within or almost within the orbit of Earth. Two are Atira or Apohele asteroids -- interior-Earth objects (IEOs) whose orbits have an aphelion (farthest point from the Sun) smaller than Earth's perihelion (nearest point to the Sun), which is 0.983 astronomical units (AU). These IEOs are far more rare than the Aten, Apollo and Amor near-Earth asteroids which are just outside of Earth’s orbit.
“There are likely only a few NEAs with similar sizes left to find, and these large undiscovered asteroids likely have orbits that keep them interior to the orbits of Earth and Venus most of the time. Only about 25 asteroids with orbits completely within Earth’s orbit have been discovered to date because of the difficulty of observing near the glare of the Sun.”
Besides being rare, these IEOs are extremely difficult to see because almost all of their orbit is in front of the Sun, and telescopes have the same ‘don’t look directly at a solar eclipse problem’ as humans – their lenses get fried when pointed too long at old Sol. To avoid this, Shepherd describes in the press release how astronomers seeking Atira asteroids must limit themselves to two 10-minute windows nightly when the asteroids make the turn around the edge of the Sun – a period made more difficult by the Sun being near Earth’s horizon so the asteroids are further hidden or blurred by Earth’s atmosphere. Nonetheless, these intrepid astronomers persist and recently found 2021 LJ4, 2021 PH27 and 2022 AP7. Once the excitement wore off, they realized 2022 AP7 had some unusual and potentially dangerous characteristics.
“One of them, 2022 AP7, is roughly a mile long, and its orbit crosses Earth’s path around the sun, getting as near as 4.4 million miles to Earth itself — uncomfortably close by cosmic standards (although far more distant than Earth’s moon).”
The New York Times is one of the mainstream media sites using the “Planet Killer” headline to describe the deadly potential of 2022 AP7. Let’s start with its size. To put it in perspective, at almost a mile or 1.5 km in diameter, it dwarfs the 525-foot-wide (160 m) asteroid moonlet Dimorphos which was bumped recently by NASA's Double Asteroid Redirection Test (DART) and had its trajectory altered as a test of our still infantile asteroid deflection system. Add to that the recent memory of the tiny 66 feet wide (20 meters) meteorite which exploded in 2013 above the city of Chelyabinsk in southeastern Russia, shattering windows on thousands of buildings – that space rock was also hidden by the glare of the Sun.
Is it time to panic? Do we need a bigger DART?
“Today, AP7 is somewhere between Mars and Jupiter, and given its five-year orbit, spends most of its time out of our way. When it next intersects Earth’s path, we’ll be minding our own business on the opposite side of the Sun.”
Cosmos Magazine gives us a non-mainstream media and more levelheaded perspective on 2022 AP7. Its path-crossing orbit currently has it two astronomical units (AU) away from Earth – that’s twice the distance between Earth and the Sun or just under 300 million km or 186 million miles. That still puts it in the near-Earth category, but calculations show its times crossing through Earth’s orbit in the next 100 years will occur far away from the planet. However, there is plenty of time after that, and they will be making further calculations and models to determine if and when 2022 AP7 will live up to its “Planet Killer” nickname.
“Our DECam survey is one of the largest and most sensitive searches ever performed for objects within Earth’s orbit and near to Venus’s orbit. This is a unique chance to understand what types of objects are lurking in the inner solar system. After 10 years of remarkable service, DECam continues to yield important scientific discoveries while at the same time contributing to planetary defense, a crucial service that benefits all humanity.”
To answer that other question most certainly bothering you … yes, there could be more “Planet Killer” asteroids hiding in the Sun’s glare in an inner-Earth orbit. Scott Shepherd says he’s confident that the Dark Energy Camera (DECam) mounted on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, will find them in the 10 minute periods it opens its lenses to stare at the Sun. Let’s hope he’s right. SInce they can only be seen in the twilight, should this be called "The Twiligt Zone"? Or is that a self-fulfilling prophesy?
In the meantime, it seems like an ironic coincidence that the most dangerous asteroids may come from the inside of our solar system, rather than the outer areas. That is the same thing we’re finding out about our own planet – we need to spend more time studying the oceans and the depths of the mantle where greater dangers to our planet could lurk. Can they point that DECam at the bottom of the Pacific?