Astronomers plan to track more potential ‘planet-killer’ asteroids near Earth

Most asteroids are harmless. But a frightening number of these remnants of the formation of the solar system are “planet killers”.

The nightmarish possibilities of a collision with Earth motivate space agencies like Nasa and the European Space Agency to sweep the night in search of their revealing reflections. A mysterious population of rocks, however, drifts where the sun shines and hides in plain sight.

“There is a whole half of the sky which is not observed. These asteroids may have orbits that approach Earth from the daylight side. So they are dangerous asteroids in their own right,” Scott Shepardastronomer at the Carnegie Institute for Science in Washington DC, says Reverse.

To combat the obscuring effect of glare from the Sun, Sheppard will harness the sensitivity of a particular telescope in South America to hopefully detect inner asteroids when starlight fades at dusk. A paper describing the investigation was published in the journal Science Thursday.

“It is very unlikely that something [dangerous] is hiding out there,” Sheppard says to allay major concerns.

“But that’s always good to know, isn’t it?”

A moving image of asteroid 2021 PH27. Scott Sheppard discovered this near-Earth object last year. It is about 1 km long and crosses the orbits of Mercury and Venus in an unstable trajectory. Scott S. Sheppard/Carnegie Science

Here’s the background — Sheppard pivoted from his work observing objects beyond Pluto to search for veiled asteroids in the inner solar system for ten minutes at dusk and ten minutes at dawn. Less is known about rocks orbiting near the Sun; there is a population that could exist in Mercury’s orbit, called Vulcanoids. Although these have not been confirmed and only appear in models of solar system physics, there are “thousands” of other inner asteroids that astronomers know exist.

Astronomers classify near-Earth objects (NEOs) based on their general location. They classify those that fly closer to the Sun than Venus as “Vatiras” and those whose orbits are inside the Earth as “Atiras”. Other populations that come close to our planet’s orbit include “Atens”, “Amors”, and “Apollos”.

An illustration showing the orbits of near-Earth objects. V. Cary, AAAS/Science

How they will do it – To detect currently unknown members of these groups, Sheppard and his colleagues will use the 4-meter Victor M. Blanco Telescope in Chile. This National Science Foundation observatory includes sensitive equipment — the Dark Energy Camera (DECam) — that will be crucial to Sheppard’s work.

DECam can detect the faintest objects that elude the instrumentation of one of the best observatories, the 48 inch Zwicky Transitional Facility telescope camera in California. Zwicky has the advantage of covering a lot of sky thanks to its large size and has detected a Vatira asteroid and several Atira. Zwicky and DECam are “the two main games in town right now looking for these items,” says Sheppard.

Why is it important – Most asteroids have stable orbits, which Sheppard describes as ships sailing through the night. It is highly unlikely that Earth and a NEO will be in the same place at the same time that their orbits intersect.

The rocks that cause major concern are randomly trajectory asteroids that change direction.

Some rocks experience a sort of gravitational ricochet. It begins when energy from the Sun strikes a spinning rock, heating one side and triggering a very slow change. These asteroids are prime targets for tugs from large planets like Jupiter. It is therefore difficult for astronomers to predict where they will go in the future.

And after – The next asteroid-planet collision we know of doesn’t involve Earth, but our neighbor. Sheppard tells Reverse on the particular case of an asteroid discovered last year, called 2021 PH27.

In about a thousand years, this asteroid will encounter Venus and drastically alter its orbit. 2021 PH27 might just crash into the planet – doing what, we don’t know. Models suggest the asteroid will come extremely close to the planet, but that’s all that can be detailed at this time.

“What happens after that, we can’t predict,” Sheppard said.

“But,” he adds optimistically, “there is nothing in the catalogs now that is a danger.”

Hopefully they keep watching the sky to make sure it stays that way.

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