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New sun-hugging asteroids: ‘Biggest in 8 years’

New sun-hugging asteroids: Space rock barely visible with brilliant sun glaring in the distance.
Twilight observations with a special camera have enabled astronomers to spot 3 new sun-hugging asteroids. They’re part of an elusive population of asteroids that lurks inside the orbits of Earth and Venus. One is the largest potentially hazardous asteroid to be discovered in the last 8 years. Image via NOIRLab.

New sun-hugging asteroids

NSF’s NOIRLab, based in Tucson, Arizona, said on Monday (October 31, 2022) that astronomers used a special camera on a telescope in Chile to discover three new near-Earth asteroids hiding in the inner solar system. Why hiding? It’s because they’re talking about the part of the solar system closer to the sun than Earth or Venus. And that’s a realm of space where asteroids are tough to spot, because – when astronomers look that way – they’re also looking into our sun’s glare.

These astronomers said they took advantage of the “brief yet favorable observing conditions during twilight” – when the sun was just below the horizon, blocked from view – to find the sun-hugging asteroid trio. So their special camera was capable of picking faint objects out of the bright twilight.

One of the asteroids – a 1.5-kilometer-wide (about 1-mile-wide) asteroid called 2022 AP7 – is likely the biggest potentially hazardous asteroid found in eight years. It is not known to be aimed toward Earth now. But its orbit might someday place it in Earth’s path.

The other asteroids – called 2021 LJ4 and 2021 PH27 – have orbits that safely remain closer to the sun than Earth’s orbit. But 2021 PH27 is of interest for another reason. It’s now the closest known asteroid to the sun, with a surface hot enough to melt lead. What’s more, it endures the largest effects of any known body in our solar system of the curved space near our sun. These effects – described early in the 20th century by Albert Einstein in his theory of general relativity – also cause what’s known as the perihelion precession of the innermost planet Mercury.

It’ll be interesting to watch the orbit of 2021 PH27, to see if its perihelion (closest point to the sun) also precesses (moves) over time.

The special camera, called DECam

The astronomers used the Dark Energy Camera (DECam) mounted on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, which is a program of NSF’s NOIRLab.

DECam is a wide-field survey camera, designed for another project, the Dark Energy Survey. Dark energy is a weird property of our universe, in which the expansion rate of the universe – the rate at which the galaxies are fleeing apart from each other – isn’t just constant, but accelerating. The camera worked on that project from 2013 to 2019, and the team has published mounds of data on the universe at large.

So now the camera is being used for other purposes. It’s particularly sensitive in the red part of the visible spectrum and in the near infrared, which makes it excellent for faint asteroid searches.

What’s the danger?

We’ve just seen a successful test of a way to deflect asteroids on a possible collision course with Earth. Just what is the danger from asteroids?

The biggest known near-Earth asteroid is 1036 Ganymede with a diameter of nearly 25.5 miles (41 km). And the asteroid that wiped out the dinosaurs is thought to have had a diameter of about 6 miles (10 km). But no known asteroids in those size ranges are due to strike Earth, at least not in the coming 100 years.

But smaller asteroids do take aim at Earth regularly, only to meet Earth’s blanket of protective atmosphere and vaporize, explosively. No harm done, usually. They mostly fall over the ocean. On the other hand, in 2013, a nearly 60-foot (18-meter) meteor exploded with the force of 30 atomic bombs more than 14 miles above Chelyabinsk, Russia. More than 1,000 people were injured from flying glass from windows blown out by the shock wave.

That same year, a large asteroid, 1.6 miles (2.5 km) in diameter, flew by Earth at only seven times the moon’s distance (3.6 million miles, or about 5.8 million km). As reported in the Washington Post:

‘Had an object this size struck the Earth, the resulting debris would likely have contaminated the Earth’s atmosphere, causing partial obstruction of sunlight, acid rain, and firestorms,’ NASA’s Inspector General said in a report.

City destroyers and planet killers

You often see the number 140 meters (460 feet) in diameter as the size for city-destroying asteroids. That’s assuming the asteroid took dead aim on an earthly city (unlikely since our world is mostly ocean). Still, it’s clear that asteroids can wreak havoc even when they don’t reach the ground. And it’s thought that about 60% of near-Earth asteroids 140 meters or smaller are still unknown.

Not only that, but many of the unknown ones must be in the realm of space that DECam is studying, the innermost part of the solar system, closer to the sun than Earth or Venus, where the sun’s dazzle keeps them mostly hidden from view.

Scott S. Sheppard, an astronomer at the Earth and Planets Laboratory of the Carnegie Institution for Science and the lead author of the paper describing the new DECam survey of the inner solar system said in a statement:

Our twilight survey is scouring the area within the orbits of Earth and Venus for asteroids. So far we have found two large near-Earth asteroids that are about 1 kilometer [.6 mile] across, a size that we call planet killers.

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.

Watch a video comparing the sizes of asteroids

How they find them

The astronomers’ statement went on to say:

Finding asteroids in the inner solar system is a daunting observational challenge. Astronomers have only two brief 10-minute windows each night to survey this area and have to contend with a bright background sky resulting from the sun’s glare. Additionally, such observations are very near to the horizon, meaning that astronomers have to observe through a thick layer of Earth’s atmosphere, which can blur and distort their observations.

Discovering these three new asteroids despite these challenges was possible thanks to the unique observing capabilities of DECam. The state-of-the-art instrument is one of the highest-performance, wide-field CCD imagers in the world, giving astronomers the ability to capture large areas of sky with great sensitivity.

Astronomers refer to observations as ‘deep’ if they capture faint objects. When hunting for asteroids inside Earth’s orbit, the capability to capture both deep and wide-field observations is indispensable.

Bottom line: Using a special camera designed to study the universe at large, astronomers have found several new sun-hugging asteroids, including the biggest potentially hazardous asteroid in eight years.

Source: A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus

Via NOIRLab

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