Massive ‘planet killer’ asteroid discovered near Earth, hiding in sun’s glare

Astronomers found three new near-Earth asteroids, and the largest is the biggest “potentially hazardous asteroid” discovered in eight years.

The research team – led by astronomer Scott S. Sheppard of the Carnegie Institution for Science – found these space rocks in the vicinity of the sun and Venus.

The biggest asteroid – 2022 AP7 – measures approximately 1.5 kilometres in diameter and could cross paths with Earth at some point in the future.

Due to this, Asteroid 2022 AP7 has been classified as an Apollo asteroid – meaning it could potentially collide with Earth. It’s therefore also classified as a “potentially hazardous object”.

Asteroid hide-and-seek

The massive space rock has avoided detection because it was hiding in the sun’s glare – specifically in the region between Earth and Venus.

Due to the asteroid’s position, and taking into account how hard it is to study this well-lit area of our solar system, scientists have a very limited understand of 2022 AP7.

To better study 2022 AP7, researchers have to wait until the twilight hours when the sun’s glare is below our planet’s horizon.

Twilight studies

They cannot study it during the day because the glare is too bright. They also cannot study it at night, because there isn’t enough illumination from the sun.

The research team is currently using the Dark Energy Camera with the Blanco 4 m telescope in Chile to look for objects interior to Earth’s and Venus’ orbits.

Catch-22.

But why is the path of the this particular such a cause of concern?

When asteroids sneaks up on Earth

Because it’s not the first time an asteroid sneaked up on Earth using the sun’s glare.

In 2013, a small asteroid measuring only 20 metres arrived in our orbit without warning and exploded above Chelyabinsk, Russia.

It shattered the windows of thousands of buildings. If a space rock measuring 1.5km were to sneak up on us, all life on Earth could be wiped out.

In fact, Sheppard said asteroids bigger than one kilometre across are called “planet killers”.

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Good news about ‘planet killers’

The good news, Sheppard says, is that only a few unknown ‘planet killers’ remain in this “difficult-to-observe” region of space.

“There are likely only a few [Near Earth Objects] 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,” Sheppard said.

That brings us to the other two newly-discovered asteroids – 2021 PH27 and 2021 LJ4.

Two smaller asteroids discovered

The two other asteroids are smaller and less exciting. One’s path will take it closer to the sun and well away from Earth’s orbit, the other is confined within Earth’s orbit.

Asteroid 2021 PH27 has the shortest orbit of any asteroid found to date – it completes a full orbit in just 113 days.

This orbit brings it exceptionally close to the sun. As a result, 2021 PH27 “experiences the largest effects of general relativity among all solar system objects”.

Meanwhile, 2021 LJ4 circles the sun “entirely within Earth’s orbit”. This makes it practically harmless to Earth.

Scientists confirmed that neither 2021 PH27 or 2021 LJ4 pose a risk to Earth because they are Atira asteroids.

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Studying Atira space rocks

Unlike Apollo asteroids which cross Earth’s orbit, the orbit of an Atira space rock is confined within our own orbit, meaning their aphelion_^* is smaller than Earth’s perihelion_^**.

Sheppard said: “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.”

“There are likely only a few near-Earth asteroids 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”.

Sheppard said it is vital to understand the “relative populations of objects with orbits interior to Earth versus exterior to Earth”.

“[It helps] us understand how objects are transported throughout the inner solar system,” he explained.

Sheppard and his research team published a paper describing the three asteroids in The Astronomical Journal.

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_{* An aphelion is the point in the orbit of a planet, comet, or other body most distant from the sun.}

^{** A perihelion is the point nearest to the sun in the path of an orbiting celestial body.}