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When it comes to finding asteroids, we have a blind spot. It may seem counterintuitive, but the most important asteroid discoveries are now being made at dusk, when astronomers can look close to the horizon – and close to the Sun – for obscure objects. asteroids which revolve inside the orbits of the Earth, Venus and even Mercury.
In perspective published In Science Today, asteroid hunter Scott Sheppard of the Carnegie Institute of Science highlights new surveys of the “twilight telescope” and the wealth they are beginning to uncover. This includes the first asteroid with an inner orbit around Venus and one with the shortest known orbital period around the Sun, both of which were discovered in the last two years. It also includes “city killers”, asteroids large enough that, if they collided with Earththe damage will be severe.
“We’re doing a full-scale survey looking for anything that orbits Venus, and that’s somewhere that we haven’t really explored very deeply in the past with anything other than small one-meter telescopes,” Sheppard, who leads the survey twilight using the Dark Energy Camera (DECam) on the 4-meter Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile, reports Space.com. “That’s pretty hard to do, and generally big telescopes don’t have a very large field of view, so you can’t cover much of the sky.”
However, DECam and another telescope make it much easier to explore the previously hidden world of asteroids, which has so far been closed. sunsight.
Connected: How many threatening asteroids are there? It’s Complicated.
Why look for asteroids at dusk
About 30 years of methodical sky surveys have led to the discovery of most asteroids with a diameter of 3 miles (5 kilometers). Models and studies show that more than 90% of “planet killer” near-Earth objects (NEOs) (larger than 0.6 miles or 1 km in size) have been detected, but only about half of the “city killer” NEOs (those larger than 460 feet or 140 meters).
So where are the rest? “There will be other objects either close to the Sun, so they will be difficult to observe, or in orbits that coincide with the Earth, which makes them difficult to detect in a routine survey,” Sheppard said. Their eccentric orbits make them visible only at dusk.
Sheppard’s team has already identified a medium-sized asteroid called 2022 AP7, whose orbit intersects Earth’s orbit, meeting the criteria for a “potentially hazardous asteroid.” But others appear to be yet to be found. “The main reason we haven’t found all the ‘city killers’ is simply because we haven’t looked at the sky at the same depth for years to find them,” Sheppard said.
Asteroid language.
Near-Earth asteroids come in many varieties, all determined by the characteristics of the space rock’s orbit. For example, amors approach the Earth, but never cross its orbital path around the Sun, so they do not pose a danger to us.
The situation is different with the Apollo asteroids, which cross the Earth’s orbit, but are mostly outside it. This category includes things like Apophis as well as Bennuand these space rocks usually orbit the Sun just behind the Earth’s orbital path, meaning that wide-field telescopes operating at night are best suited to detect these asteroids.
Other categories of near-Earth asteroids are much harder to find, such as Athenae (which cross the Earth’s orbit and stay mostly inside it), Athyras (also called Apoheles, which orbit inside the Earth’s orbit), and Vathira (which orbit inside the Earth’s orbit). planets Venus). However, Sheppard’s survey, which uses just 10 minutes of telescope time just after sunset and before sunrise to search close to the sun, does offer some surprises.
The only real “Venus Girl”
So far, astronomers know only one space rock, Vathiras.
Asteroid 2020 AV2 was discovered on January 4 by the Zwicky Transient Facility (ZTF) telescope at the Palomar Observatory near San Diego, California. The object is located in the ancestral lands of the Pauma indigenous group, who were asked to give it a name. They choose ‘Ayló’chaxnim, meaning “Venus girl”. in their language luisegno.
The asteroid is 0.6 to 1.9 miles (1 to 3 km) across, and its orbit is tilted 15 degrees relative to the asteroid’s plane. solar system, and it takes 151 days to orbit the sun. Scientists suspect that the asteroid was likely thrown into the orbit of Venus after a close collision with another planet.
Sun’s nearest neighbor
At dusk on August 13, 2021, Sheppard discovered the asteroid with the shortest orbital period. According to DECam, asteroid 2021 PH27 is about 0.6 miles in diameter, and its surface likely heats up to about 930 degrees Fahrenheit (500 degrees Celsius) — hot enough to melt lead — because its 113-day orbit brings it to 12 million miles (20 million km) from the Sun. Only Mercury has a shorter orbit around the Sun, at 88 days. However, because its orbit intersects both the orbits of Mercury and Venus, this asteroid is classified as Atira.
2021 PH27 may be an extinct comet, scientists say, given that its orbit is tilted 32 degrees from the main plane of the solar system. This tilt suggests that the object may be from the outer solar system, sent into a closer orbit around the Sun after passing near one of the terrestrial planets.
The best “twilight telescopes”
ZTF and DECam are what you need to find asteroids orbiting inside Venus.
You might think that a larger telescope is better for hunting asteroids, but larger telescopes have a smaller field of view. ZTF, which scans the skies quickly, has already detected one Vathira asteroid and several Athir asteroids. DECam, a 570-megapixel CCD scanner designed for dark energy exploration (DES), has detected several Atira asteroids, including 2021 PH27. ZTF has a larger field of view, but DECam can detect objects that are much fainter when measured by magnitude.
“DECam changes everything,” Sheppard said. “Now we’re going a magnitude deeper than people have gone before – we’re opening up a whole new area of space that we can constantly monitor, which hasn’t been tracked very well in the past.”
Expect to hear much more about new asteroids discovered in an uncharted region of our solar system.
Jamie Carter is the author of the bookBeginner Stargazing Program (will open in a new tab)(Springer, 2015) and edits WhenIsTheNextEclipse.com. Follow him on Twitter @jamieacarter. Follow us on Twitter @spacedot.com or at facebook.
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