(opens in a new tab)
A potentially dangerous near-Earth asteroid spins faster and faster every year, and researchers don’t know why.
The space rock, known as 3200 Phaethon, is about 3.4 miles (5.4 kilometers) wide and orbits through the solar system brings it closer to Sun than any other named asteroid, reaching a minimum distance of about 13 million miles (20.9 million km) from the sun – less than half the distance of Mercury under the sun. During Phaethon’s orbit around the sun, which lasts about 524 days, the space rock moves close enough to Earth be considered “potentially dangerous”. But the closest Phaethon to ever arrive on our planet was in 2017, when it passed about 10.3 million km from Earth, or about 27 times farther than the moon. The asteroid’s dusty trail is responsible for the Geminid meteor shower, which peaks in early December each year and is visible around the world.
On October 7, a group of researchers presenting at this year’s conference Conference of the Division of Planetary Sciences of the American Astronomical Society (opens in a new tab) revealed that Phaethon has accelerated rotation. The space rock takes about 3.6 hours for a full rotation. But every year, that spin shortens by about 4 milliseconds, the researchers say. It may not seem like much, but over thousands or millions of years, the change could alter the asteroid’s orbit, the team added.
Related: Could an asteroid destroy the Earth?
(opens in a new tab)
Astronomers first detected Phaethon in 1983 and have been tracking its orbit ever since using lightcurves – observations of an object’s brightness over time that show how it rotates – and radio telescopes, as well as occultations occasional starlight, when the asteroid blocks light from a distant star. As a result, Phaethon has one of the best-known orbital paths of any asteroid in the solar system, the the researchers said in a statement (opens in a new tab).
Using the decades-old dataset, the new team attempted to simulate Phaethon’s size, shape and rotational properties in greater detail than ever before.
The team found that the near-Earth asteroid is shaped like a spinning top, meaning it’s somewhat rounded with a bulge around its equator. This shape is common among large asteroids, such as 162173 Ryugu, which in 2018 became the first asteroid on which a spacecraft landedwhen the Japanese space agency (JAXA) mounted the space rock with a probe and succeeded in extracting valuable samples.
However, when the researchers began to analyze Phaethon’s rotation, they discovered that something was wrong.
“The shape model predictions did not match the data,” the lead researcher said. Sean Marshall (opens in a new tab), an astronomer at the US National Science Foundation’s Arecibo Observatory in Puerto Rico, said in the statement. “The times when the model was brightest were clearly out of sync with the times when Phaethon was actually observed to be brightest.” After reanalyzing the data, the researchers concluded that the only explanation was that Phaethon’s rotation was increasing year on year, Marshall added.
(opens in a new tab)
It is very rare for an asteroid’s spins to change. Phaethon is only the 11th asteroid observed with accelerated rotation, according to the statement. For context, there are over 1.1 million known asteroids, according to Nasa (opens in a new tab).
Phaethon is also unusual in other ways. First, it has a comet-like tail made up of chunks of rubble that stick out from its rocky surface. These rocky chunks produce the spectacular Geminids meteor shower, which is one of only two known meteor showers that are caused by asteroids and not comets. Second, sunlight reflected from Phaethon has a bluish tint, which is similar to most comets but almost unheard of among asteroids. As a result, Phaethon is often dubbed the “rocky comet” by astronomers, the statement said.
Related: Why do asteroids and comets have such strange shapes?
It is unclear exactly why Phaethon’s rotation is accelerating. The asteroid’s comet-shaped tail means its mass is gradually decreasing, but that doesn’t necessarily mean its rotation will change accordingly. However, researchers believe the asteroid’s unusual tail is the result of its surface overheating as it approaches the sun. Therefore, the most likely explanation is that the asteroid’s surface is battered by solar radiation, which changes its rotation – this is called a Yarkovsky-O’Keefe-Radzievskii-Paddack effect, Scientific alert (opens in a new tab) reported. But this theory is difficult to prove with the available data.
Due to Phaethon’s unusual properties, JAXA has chosen the near-Earth space rock as a target for one of its upcoming asteroid missions. In 2024, the DESTINY+ mission will launch a spacecraft that will eventually fly by Phaethon in 2028, according to the release.
JAXA mission scientists will likely find the new discovery of Phaethon’s accelerated spin very useful, the researchers said.
“This is great news for the DESTINY+ team,” said Marshall. “Constant change means Phaethon’s orientation at the time of the spacecraft’s flyby 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 studies, he added.
#strange #nearEarth #asteroid #spinning #faster #year #scientists #dont