Category Archives: Astronomy

This image depicts 42 of the largest objects in the asteroid belt, located between Mars and Jupiter. Most of them are larger than 100 kilometres, with the two biggest asteroids being Ceres and Vesta, which are around 940 and 520 kilometres in diameter, and the two smallest ones being Urania and Ausonia, each only about 90 kilometres. The images of the asteroids have been captured with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s Very Large Telescope.

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile, astronomers have imaged 42 of the largest objects in the asteroid belt, located between Mars and Jupiter. Never before had such a large group of asteroids been imaged so sharply. The observations reveal a wide range of peculiar shapes, from spherical to dog-bone, and are helping astronomers trace the origins of the asteroids in our Solar System.

The detailed images of these 42 objects are a leap forward in exploring asteroids, made possible thanks to ground-based telescopes, and contribute to answering the ultimate question of life, the Universe, and everything [1].

“Only three large main belt asteroids, Ceres, Vesta and Lutetia, have been imaged with a high level of detail so far, as they were visited by the space missions Dawn and Rosetta of NASA and the European Space Agency, respectively,”

explains Pierre Vernazza, from the Laboratoire d’Astrophysique de Marseille in France, who led the asteroid study published today in Astronomy & Astrophysics.

“Our ESO observations have provided sharp images for many more targets, 42 in total.”

The previously small number of detailed observations of asteroids meant that, until now, key characteristics such as their 3D shape or density had remained largely unknown. Between 2017 and 2019, Vernazza and his team set out to fill this gap by conducting a thorough survey of the major bodies in the asteroid belt.

Most of the 42 objects in their sample are larger than 100 km in size; in particular, the team imaged nearly all of the belt asteroids larger than 200 kilometres, 20 out of 23. The two biggest objects the team probed were Ceres and Vesta, which are around 940 and 520 kilometres in diameter, whereas the two smallest asteroids are Urania and Ausonia, each only about 90 kilometres.

These images have been captured with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s Very Large Telescope as part of a programme that surveyed 42 of the largest asteroids in our Solar System. They show Ceres and Vesta, the two largest objects in the asteroid belt between Mars and Jupiter, approximately 940 and 520 kilometres in diameter. These two asteroids are also the two most massive in the sample.

By reconstructing the objects’ shapes, the team realised that the observed asteroids are mainly divided into two families. Some are almost perfectly spherical, such as Hygiea and Ceres, while others have a more peculiar, “elongated” shape, their undisputed queen being the “dog-bone” asteroid Kleopatra.

By combining the asteroids’ shapes with information on their masses, the team found that the densities change significantly across the sample. The four least dense asteroids studied, including Lamberta and Sylvia, have densities of about 1.3 grams per cubic centimetre, approximately the density of coal. The highest, Psyche and Kalliope, have densities of 3.9 and 4.4 grammes per cubic centimetre, respectively, which is higher than the density of diamond (3.5 grammes per cubic centimetre).

This large difference in density suggests the asteroids’ composition varies significantly, giving astronomers important clues about their origin.

“Our observations provide strong support for substantial migration of these bodies since their formation. In short, such tremendous variety in their composition can only be understood if the bodies originated across distinct regions in the Solar System,”

explains Josef Hanuš of the Charles University, Prague, Czech Republic, one of the authors of the study. In particular, the results support the theory that the least dense asteroids formed in the remote regions beyond the orbit of Neptune and migrated to their current location.

These findings were made possible thanks to the sensitivity of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s VLT [2].

“With the improved capabilities of SPHERE, along with the fact that little was known regarding the shape of the largest main belt asteroids, we were able to make substantial progress in this field,”

says co-author Laurent Jorda, also of the Laboratoire d’Astrophysique de Marseille.

Astronomers will be able to image even more asteroids in fine detail with ESO’s upcoming Extremely Large Telescope (ELT), currently under construction in Chile and set to start operations later this decade.

“ELT observations of main-belt asteroids will allow us to study objects with diameters down to 35 to 80 kilometres, depending on their location in the belt, and craters down to approximately 10 to 25 kilometres in size,”

says Vernazza.

“Having a SPHERE-like instrument at the ELT would even allow us to image a similar sample of objects in the distant Kuiper Belt. This means we’ll be able to characterise the geological history of a much larger sample of small bodies from the ground.”

This poster shows 42 of the largest objects in the asteroid belt, located between Mars and Jupiter (orbits not to scale). The images in the outermost circle of this infographic have been captured with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s Very Large Telescope. The asteroid sample features 39 objects larger than 100 kilometres in diameter, including 20 larger than 200 kilometres. The poster highlights a few of the objects, including Ceres (the largest asteroid in the belt), Urania (the smallest one imaged), Kalliope (the densest imaged) and Lutetia, which was visited by the European Space Agency’s Rosetta mission.

Notes

[1] In The Hitchhiker’s Guide to the Galaxy by Douglas Adams, the number 42 is the answer to the “Ultimate Question of Life, the Universe, and Everything.” Today, 12 October 2021, is the 42^nd anniversary of the publication of the book.

[2] All observations were conducted with the Zurich IMaging POLarimeter (ZIMPOL), an imaging polarimeter subsystem of the SPHERE instrument that operates at visible wavelengths.

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Night sky highlights for October 2021

October 3, 2021 TopSpacer

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

What are some skywatching highlights in October 2021? See several groupings of the Moon, planets, and stars at sunrise and sunset. Then get to know two bright stars that are part of a special group: along with a handful of others, they take turns with Polaris as North Star over thousands of years. Plus, Oct. 16 is International Observe the Moon Night! Details: https://moon.nasa.gov/observe 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: March – Space Telescope Science Institute – Tonight’s Sky

Crisp, clear October nights are full of celestial showpieces. Find Pegasus, the flying horse of Greek myth, to pinpoint dense globular star clusters and galaxies, and keep watching for space-based views of M15, NGC 7331, and the Andromeda Galaxy.

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

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

** What’s in the Night Sky October 2021 #WITNS | Orionid Meteor Shower | Draconid Meteor Shower – Alyn Wallace

** Night Sky Notebook October 2021 – Peter Detterline

** See also:

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

September 9, 2021 TopSpacer

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

September 1, 2021 TopSpacer

** 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: September – Space 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 2021 – BBC Sky at Night Magazine – Star 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

August 5, 2021 TopSpacer

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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