ESO captures best images yet of peculiar ‘dog-bone’ asteroid

Astronomers have obtained the sharpest and most detailed images yet of the asteroid Kleopatra. The observations have allowed the team to constrain the 3D shape and mass of this peculiar asteroid, which resembles a dog bone, to a higher accuracy than ever before. Their research provides clues as to how this asteroid and the two moons that orbit it formed.

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Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), a team of astronomers have obtained the sharpest and most detailed images yet of the asteroid Kleopatra. The observations have allowed the team to constrain the 3D shape and mass of this peculiar asteroid, which resembles a dog bone, to a higher accuracy than ever before. Their research provides clues as to how this asteroid and the two moons that orbit it formed.

“Kleopatra is truly a unique body in our Solar System,” says Franck Marchis, an astronomer at the SETI Institute in Mountain View, USA and at the Laboratoire d’Astrophysique de Marseille, France, who led a study on the asteroid — which has moons and an unusual shape — published today in Astronomy & Astrophysics. “Science makes a lot of progress thanks to the study of weird outliers. I think Kleopatra is one of those and understanding this complex, multiple asteroid system can help us learn more about our Solar System.”

Kleopatra orbits the Sun in the Asteroid Belt between Mars and Jupiter. Astronomers have called it a “dog-bone asteroid” ever since radar observations around 20 years ago revealed it has two lobes connected by a thick “neck.” In 2008, Marchis and his colleagues discovered that Kleopatra is orbited by two moons, named AlexHelios and CleoSelene, after the Egyptian queen’s children.advertisementMotegrity® (Prucalopride) – Official Physician SiteSee Motegrity Dosing and Administration Information at the Official Physician

To find out more about Kleopatra, Marchis and his team used snapshots of the asteroid taken at different times between 2017 and 2019 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s VLT. As the asteroid was rotating, they were able to view it from different angles and to create the most accurate 3D models of its shape to date. They constrained the asteroid’s dog-bone shape and its volume, finding one of the lobes to be larger than the other, and determined the length of the asteroid to be about 270 kilometres or about half the length of the English Channel.

In a second study, also published in Astronomy & Astrophysics and led by Miroslav Brož of Charles University in Prague, Czech Republic, the team reported how they used the SPHERE observations to find the correct orbits of Kleopatra’s two moons. Previous studies had estimated the orbits, but the new observations with ESO’s VLT showed that the moons were not where the older data predicted them to be.

“This had to be resolved,” says Brož. “Because if the moons’ orbits were wrong, everything was wrong, including the mass of Kleopatra.” Thanks to the new observations and sophisticated modelling, the team managed to precisely describe how Kleopatra’s gravity influences the moons’ movements and to determine the complex orbits of AlexHelios and CleoSelene. This allowed them to calculate the asteroid’s mass, finding it to be 35% lower than previous estimates.

Combining the new estimates for volume and mass, astronomers were able to calculate a new value for the density of the asteroid, which, at less than half the density of iron, turned out to be lower than previously thought [1]. The low density of Kleopatra, which is believed to have a metallic composition, suggests that it has a porous structure and could be little more than a “pile of rubble.” This means it likely formed when material reaccumulated following a giant impact.

Kleopatra’s rubble-pile structure and the way it rotates also give indications as to how its two moons could have formed. The asteroid rotates almost at a critical speed, the speed above which it would start to fall apart, and even small impacts may lift pebbles off its surface. Marchis and his team believe that those pebbles could subsequently have formed AlexHelios and CleoSelene, meaning that Kleopatra has truly birthed its own moons.

The new images of Kleopatra and the insights they provide are only possible thanks to one of the advanced adaptive optics systems in use on ESO’s VLT, which is located in the Atacama Desert in Chile. Adaptive optics help to correct for distortions caused by the Earth’s atmosphere which cause objects to appear blurred — the same effect that causes stars viewed from Earth to twinkle. Thanks to such corrections, SPHERE was able to image Kleopatra — located 200 million kilometres away from Earth at its closest — even though its apparent size on the sky is equivalent to that of a golf ball about 40 kilometres away.

ESO’s upcoming Extremely Large Telescope (ELT), with its advanced adaptive optics systems, will be ideal for imaging distant asteroids such as Kleopatra. “I can’t wait to point the ELT at Kleopatra, to see if there are more moons and refine their orbits to detect small changes,” adds Marchis.

Habitable Planets That Received Our Radio Signals And May Know We’re Here

We have been broadcasting for over 100 years. Now a new 3D map of the galaxy reveals the stars these signals have reached that can also see Earth.

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When Guglielmo Marconi made the first “long-distance” radio broadcasts in 1895, his assistant tuned into from a less than a kilometer away. Marconi went on to develop the world’s first commercial radio system and, by the time of his death in 1937, radio signals were routinely used to communicate across the world.

These broadcasts have also travelled into space, signaling to all who care to tune in, that humanity has emerged as a technologically advanced species. The first signals have now been travelling for over hundred years, reaching distances that would have been unimaginable to Marconi.

That raises some interesting questions about the stars these signals have already reached. What kind of stars are they, do they host exoplanets and if so, are any potentially Earth-like and in the habitable zone? How many of these exoplanets might also be able to see us?about:blankabout:blank

Now we get an answer thanks to the work of Lisa Kaltenegger at Cornell University in Ithaca and Jackie Faherty at the American Museum of Natural History in New York City. These astronomers have calculated the size of the sphere that our radio signals have covered since they left Earth, counted the stars that sit inside it and worked out which of them should also be able to see Earth transiting the Sun.

3D Star Map

All this is made possible by the Gaia Catalogue, a new 3D map of our galaxy showing the distance and motion of more than 100 million stars. The data comes from the European Space Agency’s Gaia spacecraft that was launched in 2013 and is mapping the position and motion of some 1 billion astronomical objects.

The resulting map is giving astronomers an entirely new way to study our galactic environment. Kaltenegger and Faherty’s project is a good example. Since Gaia measures how these stars are moving relative to one another, the researchers can work out for how long we have been visible to them and for how much longer.

Kaltenegger and Faherty say 75 stars systems that can see us, or soon will, sit within this 100 light year sphere. Astronomers have already observed exoplanets orbiting four of them.

These systems are generally well studied. The researchers say, for example, that the Ross128 star system is the 13th closest to the Sun and the second closest with a transiting Earth-size exoplanet. Then there is Teegarden’s Star, with at least two Earth-mass exoplanets and the Trappist-1 star system with seven Earth-sized planets, of which four are in the habitable zone.about:blankabout:blank

Our signals continue to radiate away from us. So Kaltenegger and Faherty also pick out at the star systems set to receive our signals in the next 200 years or so and will also be able to see us. “1,715 stars within 326 light-years are in the right position to have spotted life on a transiting Earth since early human civilization, with an additional 319 stars entering this special vantage point in the next 5,000 years,” they say.

Rocky Exoplanets

Exoplanet statistics suggest that at least 25 per cent of these stars will have rocky exoplanets. So there should be at least 508 rocky planets in this population with a good view of earth. “Restricting the selection to the distance radio waves from Earth have traveled- about 100 light-years – leads to an estimated 29 potentially habitable worlds that could have seen Earth transit and also detect radio waves from our planet,” say Kaltenegger and Faherty.

Of course, the possibility of life on these worlds is entirely unknown. The next generation of space telescopes should allow astronomers to study these worlds in more detail, to determine their atmospheric make up and perhaps see continents and oceans.

To similarly equipped alien eyes, Earth will have long looked an interesting target. Life first emerged here some 4 billion years ago, ultimately giving our atmosphere its rich oxygen content and its other biomarkers, such as methane. If astronomers find similar conditions elsewhere, that will pique their interest.

It could even prompt searches for radio signals that may already be reaching us from these places. Marconi would surely have been amazed.