Category Archives: Astronomy

ESO: VLT captures sharpest images yet of a “dog-bone” asteroid

A new report from the European Southern Observatory (ESO):

ESO captures best images yet of peculiar “dog-bone” asteroid

These eleven images are of the asteroid Kleopatra, viewed at different angles as it rotates. The images were taken at different times between 2017 and 2019 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s VLT.  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”.

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.

This image provides a size comparison of the asteroid Kleopatra with northern Italy.  The top half of the image shows a computer model of Kleopatra, a “dog-bone” shaped asteroid which orbits the Sun in the Asteroid Belt between Mars and Jupiter. End to end, Kleopatra is 270 kilometres long.  The bottom half of the image gives an aerial view of northern Italy, with the footprint Kleopatra would have if it were hovering above it.

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.

Notes

[1] The newly calculated density is 3.4 grams per cubic centimetre, while previously Kleopatra was believed to have a mean density of about 4.5 grams per cubic centimetre.

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Night sky highlights for September 2021

** What’s Up: September 2021 Skywatching Tips from NASA – NASA JPL

What are some skywatching highlights in September 2021? Mercury provides a challenging target to spot in the fading light after sunset at the beginning of the month. Enjoy spotting two “fast” stars all month long: speedy Arcturus and fast-spinning Altair. Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/whats-up….

** Tonight’s Sky: SeptemberSpace Telescope Science Institute

In September, Pegasus becomes increasingly prominent in the southeastern sky, allowing stargazers to locate globular star clusters and a nearby double star, Alpha Capricorni. Keep watching for space-based views of densely packed, spherical collections of ancient stars in visible and X-ray light.

** What to see in the night sky: September 2021BBC Sky at Night MagazineStar Diary Podcast | What’s in the night sky, September 2021 – BBC Sky at Night Magazine

What can you see in the night sky tonight? Astronomers Pete Lawrence and Paul Abel guide us through September’s night-sky highlights.

** What’s in the Night Sky September 2021 #WITNS | Meteors | Milky Way Core Alyn Wallace

** Night Sky Notebook September 2021 – Peter Detterline

** See also:

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ESO: Rocky exoplanet with half the mass of Venus detected with VLT

Latest report from the European Southern Observatory (ESO):

New ESO observations show rocky exoplanet
has just half the mass of Venus

This artist’s impression shows L 98-59b, one of the planets in the L 98-59 system 35 light-years away. The system contains four confirmed rocky planets with a potential fifth, the furthest from the star, being unconfirmed. In 2021, astronomers used data from the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on ESO’s VLT to measure the mass of L 98-59b, finding it to be half that of Venus. This makes it the lightest planet measured to date using the radial velocity technique.

A team of astronomers have used the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile to shed new light on planets around a nearby star, L 98-59, that resemble those in the inner Solar System. Amongst the findings are a planet with half the mass of Venus — the lightest exoplanet ever to be measured using the radial velocity technique — an ocean world, and a possible planet in the habitable zone.

“The planet in the habitable zone may have an atmosphere that could protect and support life,” 

says María Rosa Zapatero Osorio, an astronomer at the Centre for Astrobiology in Madrid, Spain, and one of the authors of the study published today in Astronomy & Astrophysics.

The results are an important step in the quest to find life on Earth-sized planets outside the Solar System. The detection of biosignatures on an exoplanet depends on the ability to study its atmosphere, but current telescopes are not large enough to achieve the resolution needed to do this for small, rocky planets. The newly studied planetary system, called L 98-59 after its star, is an attractive target for future observations of exoplanet atmospheres. Its orbits a star only 35 light-years away and has now been found to host rocky planets, like Earth or Venus, which are close enough to the star to be warm.

With the contribution of ESO’s VLT, the team was able to infer that three of the planets may contain water in their interiors or atmospheres. The two planets closest to the star in the L 98-59 system are probably dry, but might have small amounts of water, while up to 30% of the third planet’s mass could be water, making it an ocean world.

This infographic shows a comparison between the L 98-59 exoplanet system (top) with part of the inner Solar System (Mercury, Venus and Earth), highlighting the similarities between the two. L 98-59 contains four confirmed rocky planets (marked in colour in the top panel), orbiting a red-dwarf star 35 light-years away. The planet closest to the star is around half the mass of Venus, making it the lightest exoplanet ever detected using the radial velocity technique. Up to 30% of the third planet’s mass could be water, making it an ocean world. The existence of the fourth planet has been confirmed, but scientists don’t yet know its mass and radius (its possible size is indicated by a dotted line). The team also found hints of a potential fifth planet, the furthest from the star, though the team knows little about it. If confirmed, it would sit in the system’s habitable zone where liquid water could exist on its surface. The distances from the stars and between the planets in the infographic are not up to scale. The diagram has been scaled to make the habitable zone in both the Solar System and in L 98-59 coincide. As indicated by the infographic, which includes a temperature scale (in Kelvin [K]), the Earth and the fifth (unconfirmed) planet in L 98-59 receive similar amounts of light and heat from their respective stars. Assuming their atmospheres are similar, this fifth planet would have a similar average surface temperature to Earth and would support liquid water at its surface.
Furthermore, the team found “hidden” exoplanets that had not previously been spotted in this planetary system. They discovered a fourth planet and suspect there is a fifth, in a zone at the right distance from the star for liquid water to exist on its surface.

“We have hints of the presence of a terrestrial planet in the habitable zone of this system,”

explains Olivier Demangeon, a researcher at the Instituto de Astrofísica e Ciências do Espaço, University of Porto in Portugal and lead author of the new study.

The study represents a technical breakthrough, as astronomers were able to determine, using the radial velocity method, that the innermost planet in the system has just half the mass of Venus. This makes it the lightest exoplanet ever measured using this technique, which calculates the wobble of the star caused by the tiny gravitational tug of its orbiting planets.

The team used the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on ESO’s VLT to study L 98-59.

“Without the precision and stability provided by ESPRESSO this measurement would have not been possible,” says Zapatero Osorio. “This is a step forward in our ability to measure the masses of the smallest planets beyond the Solar System.”

The astronomers first spotted three of L 98-59’s planets in 2019, using NASA’s Transiting Exoplanet Survey Satellite (TESS). This satellite relies on a technique called the transit method — where the dip in the light coming from the star caused by a planet passing in front of it is used to infer the properties of the planet — to find the planets and measure their sizes. However, it was only with the addition of radial velocity measurements made with ESPRESSO and its predecessor, the High Accuracy Radial velocity Planet Searcher (HARPS) at the ESO La Silla 3.6-metre telescope, that Demangeon and his team were able to find extra planets and measure the masses and radii of the first three.

“If we want to know what a planet is made of, the minimum that we need is its mass and its radius,” Demangeon explains.

The team hopes to continue to study the system with the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST), while ESO’s Extremely Large Telescope (ELT), under construction in the Chilean Atacama Desert and set to start observations in 2027, will also be ideal for studying these planets.

“The HIRES instrument on the ELT may have the power to study the atmospheres of some of the planets in the L 98-59 system, thus complementing the JWST from the ground,”

says Zapatero Osorio.

“This system announces what is to come,” adds Demangeon. “We, as a society, have been chasing terrestrial planets since the birth of astronomy and now we are finally getting closer and closer to the detection of a terrestrial planet in the habitable zone of its star, of which we could study the atmosphere.”

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Night sky highlights for August 2021

** What’s Up: August 2021 Skywatching Tips from NASA – NASA JPL

What are some skywatching highlights in August 2021? The best-known meteor shower of the year should be a good time this year on the peak night of Aug. 11, with no bright Moon to interfere. Jupiter and Saturn are at their best all month long. And on Aug. 22, the full moon will be a “seasonal blue moon.” Additional information about topics covered in this episode of What’s Up, along with still images from the video, and the video transcript, are available at https://solarsystem.nasa.gov/whats-up….

** Tonight’s Sky: August Space Telescope Science Institute

In August, a flock of star-studded figures soars overhead. Look for the Vega and Lyra constellations, which point to Epsilon Lyrae and the Ring Nebula. You can also spot three bright summer stars: Vega, Deneb, and Altair, which form the Summer Triangle. Keep watching for space-based views of these and other stars and nebulas.

About this Series “Tonight’s Sky” is a monthly video of constellations you can observe in the night sky. The series is produced by the Space Telescope Science Institute, home of science operations for the Hubble Space Telescope, in partnership with NASA’s Universe of Learning. This is a recurring show, and you can find more episodes—and other astronomy videos—at [Tonight’s Sky].

** What to see in the night sky: August 2021BBC Sky at Night Magazine

What can you see in the night sky tonight? Astronomers Pete Lawrence and Paul Abel guide us through August’s night-sky highlights.

** What’s in the Night Sky August 2021 #WITNSAlyn Wallace

** Night Sky Notebook August 2021Peter Detterline

** See also:

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ESO: Moon-forming disk observed around exoplanet

A new report from the European Southern Observatory (ESO):

Astronomers make first clear detection of a moon-forming disc around an exoplanet

This image, taken with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, shows wide (left) and close-up (right) views of the moon-forming disc surrounding PDS 70c, a young Jupiter-like planet nearly 400 light-years away. The close-up view shows PDS 70c and its circumplanetary disc centre-front, with the larger circumstellar ring-like disc taking up most of the right-hand side of the image. The star PDS 70 is at the centre of the wide-view image on the left. Two planets have been found in the system, PDS 70c and PDS 70b, the latter not being visible in this image. They have carved a cavity in the circumstellar disc as they gobbled up material from the disc itself, growing in size. In this process, PDS 70c acquired its own circumplanetary disc, which contributes to the growth of the planet and where moons can form. This circumplanetary disc is as large as the Sun-Earth distance and has enough mass to form up to three satellites the size of the Moon.

Using the Atacama Large Millimetre/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, astronomers have unambiguously detected the presence of a disc around a planet outside our Solar System for the first time. The observations will shed new light on how moons and planets form in young stellar systems.

“Our work presents a clear detection of a disc in which satellites could be forming,”

says Myriam Benisty, a researcher at the University of Grenoble, France, and at the University of Chile, who led the new research published today in The Astrophysical Journal Letters.

“Our ALMA observations were obtained at such exquisite resolution that we could clearly identify that the disc is associated with the planet and we are able to constrain its size for the first time,”

she adds.

The disc in question, called a circumplanetary disc, surrounds the exoplanet PDS 70c, one of two giant, Jupiter-like planets orbiting a star nearly 400 light-years away. Astronomers had found hints of a “moon-forming” disc around this exoplanet before but, since they could not clearly tell the disc apart from its surrounding environment, they could not confirm its detection — until now.

In addition, with the help of ALMA, Benisty and her team found that the disc has about the same diameter as the distance from our Sun to the Earth and enough mass to form up to three satellites the size of the Moon.

But the results are not only key to finding out how moons arise.

“These new observations are also extremely important to prove theories of planet formation that could not be tested until now,”

says Jaehan Bae, a researcher from the Earth and Planets Laboratory of the Carnegie Institution for Science, USA, and author on the study.

Planets form in dusty discs around young stars, carving out cavities as they gobble up material from this circumstellar disc to grow. In this process, a planet can acquire its own circumplanetary disc, which contributes to the growth of the planet by regulating the amount of material falling onto it. At the same time, the gas and dust in the circumplanetary disc can come together into progressively larger bodies through multiple collisions, ultimately leading to the birth of moons.

This image, taken with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, shows a close-up view on the moon-forming disc surrounding PDS 70c, a young Jupiter-like gas giant nearly 400 light-years away. It shows this planet and its disc centre-front, with the larger circumstellar ring-like disc taking up most of the right-hand side of the image. The dusty circumplanetary disc is as large as the Sun-Earth distance and has enough mass to form up to three satellites the size of the Moon.

But astronomers do not yet fully understand the details of these processes.

“In short, it is still unclear when, where, and how planets and moons form,”

explains ESO Research Fellow Stefano Facchini, also involved in the research.

“More than 4000 exoplanets have been found until now, but all of them were detected in mature systems. PDS 70b and PDS 70c, which form a system reminiscent of the Jupiter-Saturn pair, are the only two exoplanets detected so far that are still in the process of being formed,”

explains Miriam Keppler, researcher at the Max Planck Institute for Astronomy in Germany and one of the co-authors of the study [1].

“This system therefore offers us a unique opportunity to observe and study the processes of planet and satellite formation,”

Facchini adds.

PDS 70b and PDS 70c, the two planets making up the system, were first discovered using ESO’s Very Large Telescope (VLT) in 2018 and 2019 respectively, and their unique nature means they have been observed with other telescopes and instruments many times since [2].

The latest high resolution ALMA observations have now allowed astronomers to gain further insights into the system. In addition to confirming the detection of the circumplanetary disc around PDS 70c and studying its size and mass, they found that PDS 70b does not show clear evidence of such a disc, indicating that it was starved of dust material from its birth environment by PDS 70c.

An even deeper understanding of the planetary system will be achieved with ESO’s Extremely Large Telescope (ELT), currently under construction on Cerro Armazones in the Chilean Atacama desert.

“The ELT will be key for this research since, with its much higher resolution, we will be able to map the system in great detail,”

says co-author Richard Teague, a researcher at the Center for Astrophysics | Harvard & Smithsonian, USA. In particular, by using the ELT’s Mid-infrared ELT Imager and Spectrograph (METIS), the team will be able to look at the gas motions surrounding PDS 70c to get a full 3D picture of the system.

Notes

[1] Despite the similarity with the Jupiter-Saturn pair, note that the disc around PDS 70c is about 500 times larger than Saturn’s rings.

[2] PDS 70b was discovered using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument, while PDS 70c was found using the VLT’s Multi Unit Spectroscopic Explorer (MUSE). The two-planet system has been investigated using the X-shooter instrument too, also installed on ESO’s VLT.

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