Read moreUsing the Very Large Telescope Interferometer (VLTI) in near-infrared light, the team of astronomers observed 92 nearby stars to probe exozodiacal light from hot dust close to their habitable zones and combined the new data with earlier observations. Bright exozodiacal light, created by the glowing grains of hot exozodiacal dust, or the reflection of starlight off these grains, was observed around nine of the targeted stars.
From dark clear sites on Earth, zodiacal light looks like a faint diffuse white glow seen in the night sky after the end of twilight, or before dawn. It is created by sunlight reflected off tiny particles and appears to extend up from the vicinity of the Sun. This reflected light is not just observed from Earth but can be observed from everywhere in the Solar System.
The glow being observed in this new study is a much more extreme version of the same phenomenon. While this exozodiacal light—zodiacal light around other star systems—had been previously detected, this is the first large systematic study of this phenomenon around nearby stars.
In contrast to earlier observations the team did not observe dust that will later form into planets, but dust created in collisions between small planets of a few kilometres in size—objects called planetesimals that are similar to the asteroids and comets of the Solar System. Dust of this kind is also the origin of the zodiacal light in the Solar System.
“If we want to study the evolution of Earth-like planets close to the habitable zone, we need to observe the zodiacal dust in this region around other stars,” said Steve Ertel, lead author of the paper, from ESO and the University of Grenoble in France. “Detecting and characterising this kind of dust around other stars is a way to study the architecture and evolution of planetary systems.”…
By analysing the properties of the stars surrounded by a disc of exozodiacal dust, the team found that most of the dust was detected around older stars. This result was very surprising and raises some questions for our understanding of planetary systems. Any known dust production caused by collisions of planetesimals should diminish over time, as the number of planetesimals is reduced as they are destroyed.
The sample of observed objects also included 14 stars for which the detection of exoplanets has been reported. All of these planets are in the same region of the system as the dust in the systems showing exozodiacal light. The presence of exozodiacal light in systems with planets may create a problem for further astronomical studies of exoplanets.
Exozodiacal dust emission, even at low levels, makes it significantly harder to detect Earth-like planets with direct imaging. The exozodiacal light detected in this survey is a factor of 1000 times brighter than the zodiacal light seen around the Sun. The number of stars containing zodiacal light at the level of the Solar System is most likely much higher than the numbers found in the survey. These observations are therefore only a first step towards more detailed studies of exozodiacal light.
“The high detection rate found at this bright level suggests that there must be a significant number of systems containing fainter dust, undetectable in our survey, but still much brighter than the Solar System’s zodiacal dust,” explains Olivier Absil, co-author of the paper, from the University of Liège. “The presence of such dust in so many systems could therefore become an obstacle for future observations, which aim to make direct images of Earth-like exoplanets.”
planetary formation
Read moreBy reconstructing conditions in the disk of gas and dust in which the Solar System formed, scientists have concluded that the Earth and other planets must have inherited much of their water from the cloud of gas from which the Sun was born 4.6 billion years ago, instead of forming later. The authors say that such interstellar water would also be included in the formation of most other stellar systems, and perhaps of other Earth-like planets. The dense interstellar clouds of gas and dust where stars form contain abundant water, in the form of ice. When a star first lights up, it heats up the cloud around it and floods it with radiation, vaporizing the ice and breaking up some of the water molecules into oxygen and hydrogen. Until now, researchers were unsure how much of the ‘old’ water would be spared in this process. If most of the original water molecules were broken up, water would have had to reform in the early Solar System. But the conditions that made this possible could be specific to the Solar System, in which case many stellar systems could be left dry, says Ilsedore Cleeves, an astrochemist at the University of Michigan in Ann Arbor, who led the new study. But if some of the water could survive the star-forming process, and if the Solar System’s case is typical, it means that water “is available as a universal ingredient during planet formation”, she says.
The Committee to Nuke Elysium 