The unusual asteroid Cleopatra is shaped like a dog bone and has two moons: researchers have now discovered amazing things about the celestial body and its moons.
The dog bone asteroid Cleopatra is half the length of the English Channel.
Photo: ESO / M. Kornmeiser / Marchis et al
Exotic Cleopatra. The asteroid, named after the legendary Egyptian pharaoh, orbits the sun in the asteroid belt between Mars and Jupiter, and, as a celestial body, is completely different from other known asteroids. Now the asteroid has made an unusual astronomical discovery.
Investigations with strangers regularly lead to major scientific developments. This must also be the case with Cleopatra. If we better understand this complex asteroid system, we can learn a lot about our solar system,” says Frank Marchis, an astronomer at the SETI Institute in the US Mountain View. He is the head of the study on the asteroid Cleopatra, which they also call the dog bone asteroid.
The dog bone Cleopatra asteroid has at least two moons
Cleopatra is unusually shaped: an elongated asteroid, which is 200 million km from Earth, has two thick ends, a thin conductor and resembles a stylized chewing bone of dogs. In addition, two moons orbit the asteroid, Marches and his colleagues discovered: they bear the names of Cleopatra’s sons: AlexHelios and CleoSelene. The researchers have now discovered how reasonable this assignment is.
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Because astronomers have succeeded in the most accurate 3D modeling of Cleopatra to date, which is now used as the basis for studies on the mass and density of the dog bone asteroid. For this purpose, Marchis and his team used images of the asteroid taken between 2017 and 2019 with the SPHERE (Polarization Spectral High Contrast Exoplanet Research) instrument on the European Southern Observatory’s Very Large Telescope (VLT).
The asteroid Cleopatra is shaped like a dog bone. As it rotates, the images of the VLT, taken over the course of two years, show it from different perspectives.
Photo: this
The VLT in the Chilean Atacama Desert has adaptive optics. These help correct distortions caused by Earth’s atmosphere and make objects appear out of focus. It is precisely because of this effect that the stars that we observe with the naked eye from Earth seem to twinkle. Such a sharp image of a distant asteroid was only possible with the help of these corrections. Since the dog bone asteroid is rotating, the high-resolution images show it from different angles. Cleopatra is about 270 kilometers long: half the length of the English Channel. And one of these two fish at the ends is larger than the other.
Researchers recalculate lunar orbits
In a second study, led by Miroslav Proch of Charles University in Prague, Czech Republic, a team used Sphere observations to study Cleopatra’s lunar orbiter. Scientists have tried to predict trajectories before. However, this speculation did not match the new observations made by astronomers using the VLT. “We had to resolve this contradiction,” says Miroslav Broch. “Because if the moons’ orbits were wrong, everything was wrong, including Cleopatra’s mass.” With the help of new observations and detailed 3D modeling, researchers are now able to describe exactly how Cleopatra’s gravity affects the moons’ movements. This enabled them to recalculate the mass of the asteroid. According to this, this is 35% lower than previous estimates.
Asteroid, meteorite, comet: what are the differences?
- Celestial bodies differ mainly in size, composition and distance from the Sun.
- a asteroid They usually consist of solid materials and contain little or no volatile matter, which is why they do not have a tail.
- a comet It is largely composed of volatile substances such as water. Because the distance from the sun is large, the volatiles are frozen. As comets approach warmer regions, the ice melts and a typical comet tail emerges.
- Meteorites are the smallest things. They often arise from comet tail particles or when larger celestial bodies collide. If they enter the Earth’s atmosphere, they can be considered a meteor or a falling star.
Using the new values for size and mass, the research team was also able to derive a new value for the asteroid’s density. With less than half the density of iron, this is lower than previously assumed. Cleopatra probably has a mineral composition and a porous structure. In fact, the asteroid is now thought to be a loose pile of rubble, made up of pieces that clump together again after a massive collision.
The asteroid Cleopatra is spinning at top speed and almost flying away
This allows conclusions to be drawn about the composition of the two moons. The asteroid is spinning roughly at its claimed critical speed: this is the speed of rotation at which the material the asteroid is made of is volatilized. Say: Cleopatra is completely unstable. Therefore, even small effects can loosen the material from the surface. Possibly the unusual situation is that the asteroid has two moons of its own: AlexHelios and CleoSelene may have formed from melted matter. To stay in the picture: Cleopatra gave birth to her own moons.
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In the future, the search for asteroids must make significant progress again: ESO’s Very Large Telescope (ELT), currently still under construction, has more advanced adaptive optical systems. “I can’t wait to direct the ELT to Cleopatra to see if there are more moons and to accurately measure the moon’s orbits so that even small changes can be detected,” Frank Marches says.
Asteroids often come from the asteroid belt, which lies between the planetary orbits of Mars and Jupiter. It was assumed that the asteroid belt must have resulted from a catastrophic collision between a planet and an asteroid: a now-dead planet, called Phaeton, was thought to have given off debris after the collision as the asteroid orbits the Sun. This thesis has now been refuted. Because the total mass of all asteroids is less than the mass of the Earth’s moon – it is too little for a planet. Alternatively, it is possible that the asteroid belt originated from minor planets, i.e. from planetary components, in the early stage of our solar system. However, due to Jupiter’s gravitational force, they could never have combined to form a planet.
NASA calculates the date of the collision of the asteroid Bennu
Sometimes asteroids erupt from the belt, for example after colliding with other debris. Then they draw their own paths and can theoretically get close to Earth – like asteroid benno. The orb with a height of 500 meters frequently crosses the Earth’s orbit and gets very close to our planet. Even the impact cannot be ruled out: on September 24, 2182, this scenario could become a reality. This is the result of the latest analyzes of the asteroid that astronomers have long seen in their sights. Bennu is considered one of the most dangerous asteroids of all, although the probability of an impact is relatively low: the odds that Bennu will collide with Earth by 2300 are 1: 1750. However, the asteroid Cleopatra, discovered in 1880, cannot expose the Earth Danger: It moves its orbits in the distant asteroid belt.
The comet from a completely unknown world
Some of the celestial bodies moving in our solar system have nothing to do with the asteroid belt – they come from a much farther region, such as Comet 2I / Borisov. Most comets come from the so-called Oort cloud, a group of astronomical bodies at the edge of the solar system – at least that’s the theory, because no one has seen this cloud yet. However, Borisov comes from a more unknown region: it is an interstellar comet from the infinite expanses of the Milky Way, which crossed our solar system, but probably never returned.
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