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Bizarre near-Earth asteroid spins faster each year – and scientists aren't sure why

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An example of the trajectory that the potentially dangerous near-Earth asteroid 3200 Phaethon followed as it passed near Earth in 2017. New research shows that the asteroid’s spin is accelerating.

An example of the trajectory that the potentially dangerous near-Earth asteroid 3200 Phaethon followed as it passed near Earth in 2017.  New research shows that the asteroid's spin is accelerating.

An example of the trajectory that the potentially dangerous near-Earth asteroid 3200 Phaethon followed as it passed near Earth in 2017. New research shows that the asteroid’s spin is accelerating.

An example of the trajectory that the potentially dangerous near-Earth asteroid 3200 Phaethon followed as it passed near Earth in 2017. New research shows that the asteroid’s spin is accelerating. (Image credit: Tom Ruen/Wikimedia)

Close to a potentially dangerous Earth asteroid It spins faster each year, and researchers aren’t sure why.

The space rock, known as 3200 Phaethon, is about 3.4 miles (5.4 kilometers) wide and orbits solar system takes it closer sun Less than any other asteroid reaching a minimum distance of about 13 million miles (20.9 million km) from the sun – less than half the distance Mercury to the sun. During Phaethon’s orbit around the sun, which takes about 524 days, the space rock moves close enough. Soil considered “potentially dangerous”. But the closest Phaethon has ever been to our planet was in 2017, when it passed about 6.4 million miles (10.3 million km) from Earth, or about 27 times further from Earth. moon. The asteroid’s dusty trail is responsible for the Geminid meteor shower, which peaks in early December each year and can be seen around the world.

On October 7, a group of researchers presented at this year’s presentation. Conference of the Planetary Sciences Division of the American Astronomical Society It revealed that Phaethon had an accelerating spin. Space stone takes about 3.6 hours for one full rotation. But each year that spin gets shorter by about 4 milliseconds, the researchers said. It might not sound like much, but over thousands or millions of years, this change could alter the asteroid’s trajectory, the team added.

Related: Could an asteroid destroy Earth?

A visualization (yellow) of Phaethon's orbit around the sun (pink).  Its orbit around the Earth and the sun is colored blue.  At the beginning of the animation, the Phaethon is seen passing by the Earth.

A visualization (yellow) of Phaethon’s orbit around the sun (pink). Its orbit around the Earth and the sun is colored blue. At the beginning of the animation, the Phaethon is seen passing by the Earth.

A visualization (yellow) of Phaethon’s orbit around the sun (pink). Earth and its orbit around the sun are colored blue. At the start of the animation, the Phaethon is seen passing by the Earth. (Image credit: NASA/JPL)

Astronomers first detected Phaethon in 1983 and have been tracking its orbit ever since using light curves (observations of how an object’s brightness rotates over time) and radio telescopes, as well as occasional star occultations when the asteroid blocks light. a distant star. As a result, Phaethon has one of the best-known orbital paths of any asteroid in the solar system. researchers in a statement.

Using decades of datasets, the new team sought to simulate Phaethon’s size, shape, and rotation features in greater detail than ever before.

The team found that the near-Earth asteroid is shaped like a top, meaning it’s somewhat rounded with a bulge around its equator. This shape is common among large asteroids such as 162173 Ryugu. first asteroid landed by spacecraftWhen the Japanese space agency (JAXA) assembled the space rock with a probe and successfully received valuable samples from him.

However, when the researchers began to analyze Phaethon’s rotation, they found that something was wrong.

“Predictions from the shape model did not match the data,” said lead researcher Sean Marshall“The times when the model was brightest were clearly inconsistent with the times when the Phaethon was really bright,” an astronomer from the U.S. National Science Foundation’s Arecibo Observatory in Puerto Rico said in a statement. Marshall added that after reanalyzing the data, the researchers concluded that the only explanation was that Phaethon’s rotation increased from year to year.

These grainy images show how Phaethon's appearance changes over the course of a single turn.

These grainy images show how Phaethon’s appearance changes over the course of a single turn.

These grainy images show how Phaethon’s appearance changes over the course of a single turn. (Image credit: Taylor et al. 2019, Planetary and Space Science 167)

It is very rare for an asteroid’s spins to change. According to the statement, Phaethon is only the 11th asteroid observed with an accelerating spin. In context, there are over 1.1 million known asteroids. NASA.

The Phaethon is unusual in other ways as well. First, it has a comet-like tail made up of pieces of rubble ripped from its rocky surface. These rocky patches produce the spectacular Geminid meteor shower, one of only two known meteor showers to be caused by asteroids. comets. Second, the sunlight reflected from Phaethon has a bluish hue, similar to most comets, but almost unheard of among asteroids. As a result, Phaethon is often referred to by astronomers as a “rocky comet,” according to the description.

Related: Why are asteroids and comets such strange shapes?

It’s not entirely clear why Phaethon’s spin is accelerating. The asteroid’s comet-like tail means its mass is gradually decreasing, but that doesn’t mean its spin will change as a result. But researchers think the asteroid’s unusual tail is the result of overheating its surface as it gets closer to the sun. Thus, the most likely explanation is that the asteroid’s surface is being battered by solar radiation that changes its spin – this is known as the Yarkovsky-O’Keefe-Radzievskii-Paddack effect, Science Alert reported. However, it is difficult to prove this theory with the available data.

Because of Phaethon’s unusual properties, JAXA chose the near-Earth space rock as the target for one of its next asteroid missions. According to the statement, in 2024 the DESTINY+ mission will finally launch a spacecraft that will fly by Phaethon in 2028.

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JAXA’s mission scientists will find the new discovery of Phaethon’s accelerating spin very helpful, the researchers said.

“This is good news for the DESTINY+ team,” Marshall said. “A constant change means that the direction of Phaethon during the flight of the spacecraft can be accurately predicted.” For example, scientists will be able to determine which side of the asteroid will be illuminated by the sun when the spacecraft arrives, which will help them decide which areas to target for their study.

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