Tuesday, July 25, 2023

SPACE

Older evolved stars passing through a star-forming region could have heated an early Earth

Retired stars join the young stars' party in the sky: how evolved stars contribute to the early heating of Earth
An artist’s impression of an interloping AGB star in a young star-forming region. 
Credit: Mark Garlick

Researchers from the University of Sheffield and Imperial College London have spotted a "retired" asymptotic giant branch (AGB) star passing through a young star-forming region, something which was previously thought not to happen.

The researchers identified this interaction occurred in one of the places where they think stars like our sun must form, using the Gaia satellite, a 740m € mission to map the positions of billions of stars in our galaxy.

The most recent release of data from Gaia, Data Release 3, means that the research team can accurately pinpoint interloping stars. These interlopers are stars that did not form in the region, but are just passing through. The team has previously found young interloping stars, but now has found a much older, evolved star, known as an AGB, passing through a region.

Previous research has shown that these retired AGB stars produce large quantities of radioactively unstable chemical elements, Aluminum-26 and Iron-60. Aluminum-26 and Iron-60 were delivered to our young solar system at the epoch of planet formation, and are thought to dominate the early internal heating of Earth.

Ultimately, Aluminum-26 and Iron-60 may even have indirectly contributed to plate tectonics on our planet, which helps sustain a breathable atmosphere on Earth. The research team has calculated how much Aluminum-26 and Iron-60 from the AGB could be captured by a star like our sun as it formed its planets.

Dr. Richard Parker, a lecturer in Astrophysics in Department of Physics and Astronomy at the University of Sheffield, and the lead author of the study published in The Astrophysical Journal Letters, said, "Until now, researchers have been skeptical that these old, evolved stars could ever meet  that are forming planets, so this discovery reveals much more about the dynamics, relationships and journeys of stars.

"By showing that AGB stars can meet young planetary systems, we have shown that other sources of Aluminum-26 and Iron-60, such as the winds and supernovae of very massive stars, may not be required to explain the origin of these chemical elements in our solar system."

Dr. Christina Schoettler, an Astrophysics research associate in the Department of Physics at Imperial College London, identified the AGB star in the Gaia DR3 data. She says, "Gaia is revolutionizing our ideas about how stars form, and then subsequently move in the galaxy. This discovery of an old, evolved star in close proximity to young planet-forming stars is a wonderful example of the power of serendipity in scientific research."

The next step of this research is to search for other evolved stars in young star-forming regions to establish how common these retired interlopers are.

More information: Richard J. Parker et al, Isotopic Enrichment of Planetary Systems from Asymptotic Giant Branch Stars, The Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/ace24a

Hydrogen peroxide found on Jupiter's moon Ganymede in higher latitudes

Hydrogen peroxide found on Jupiter's moon Ganymede only in higher latitudes
Maps of Ganymede’s 3.5 μm H2O2 absorption compared to those of the 3.1 μm Fresnel 
peaks of water ice and corresponding projections of the U.S. Geological Survey 
Voyager-Galileo imaging mosaic. H2O2 appears constrained to the upper latitudes,
 particularly on the leading hemisphere, which exhibits sharp boundaries at
 approximately ±30° to 35° latitude. These boundaries are roughly coincident with the 
onset of Ganymede’s polar frost caps and with the latitudes at which most of the impinging
 Jovian magnetospheric particles can access the surface. Maps of the Fresnel reflection 
peak of water ice, which generally track the distribution of ice deduced from shorter-
wavelength water bands, also show the areas of greatest H2O2 on the leading hemisphere
 to be enriched in water ice. The trailing hemisphere shows comparatively weak Fresnel 
reflections and, overall, less-icy spectra. This hemispheric dichotomy in water ice may 
help explain the leading/trailing contrast in H2O2, while the overall polar H2O2 distribution
 may reflect a combination of precursor water availability and temperature and/or radiation
 intensity effects. The approximate average boundary between open and closed field lines
 from are included as red dashed lines. The 60°S, 30°S, 0°N, 30°N, and 60°N parallels are
 also included in gray for both hemispheres. The leading-hemisphere map includes the 45°W
, 90°W, and 135°W meridians, while the trailing-hemisphere map shows those for 225°W, 
270°W, and 315°W. 
Credit: Science Advances (2023). DOI: 10.1126/sciadv.adg3724

An international team of space scientists has found evidence that hydrogen peroxide on Ganymede, Jupiter's largest moon, exists only on its higher latitudes. For their research, reported in the journal Science Advances, the group studied data from the James Webb Space Telescope (JWST).

For many years, researchers theorized that hydrogen peroxide existed on Ganymede, but it took a prior team studying data from the JWST to find it. In this new effort, the research team analyzed new data sent back by the telescope to learn more about the  and its hydrogen peroxide.

Ganymede is the largest moon in the solar system, but it has not received nearly the attention given to another of Jupiter's moons, Europa, whose features and characteristics make it far more likely to have harbored life at some point in time. But prior research has shown that the influence of Jupiter's magnetic field on many of its moons could indicate a strong probability of hydrogen peroxide on Ganymede. This is because of its likely impact on the water-ice irradiation process on its surface.

Prior research has shown that both Ganymede and Europa are impacted by radiation from Jupiter's magnetosphere—it bombards the surface of both moons, converting water ice into other compounds such as oxygen, ozone and hydrogen peroxide. In this new effort, the researchers studied data from the JWST NIRSpec Integral Field Unit.

The team found a 3.5-micrometer absorption band showing the presence of hydrogen peroxide in the northern parts of the moon, mostly on the side facing directional orbit. They also observed oxygen mostly seen in lower latitudes and on the opposite side of the moon. The findings show a stark contrast between Ganymede and Europa—on Europa, most of its  is located near its equator.

The team notes that their findings are part of a larger process geared toward better understanding how Ganymede's  influences its own surface chemistry.

More information: Samantha K. Trumbo et al, Hydrogen peroxide at the poles of Ganymede, Science Advances (2023). DOI: 10.1126/sciadv.adg3724


Journal information: Science Advances 


© 2023 Science X NetworkNASA's Juno exploring Jovian moons during extended mission

Webb detects water vapor in rocky planet-forming zone

Peer-Reviewed Publication

NASA/GODDARD SPACE FLIGHT CENTER

Artist’s concept portrays the star PDS 70 and its inner protoplanetary disk 

IMAGE: THIS ARTIST’S CONCEPT PORTRAYS THE STAR PDS 70 AND ITS INNER PROTOPLANETARY DISK. NEW MEASUREMENTS BY NASA’S JAMES WEBB SPACE TELESCOPE HAVE DETECTED WATER VAPOR AT DISTANCES OF LESS THAN 100 MILLION MILES FROM THE STAR – THE REGION WHERE ROCKY, TERRESTRIAL PLANETS MAY BE FORMING. THIS IS THE FIRST DETECTION OF WATER IN THE TERRESTRIAL REGION OF A DISK ALREADY KNOWN TO HOST TWO OR MORE PROTOPLANETS, ONE OF WHICH IS SHOWN AT UPPER RIGHT. view more 

CREDIT: CREDITS: NASA, ESA, CSA, J. OLMSTED (STSCI) DOWNLOAD THE FULL-RESOLUTION VERSION FROM THE SPACE TELESCOPE SCIENCE INSTITUTE.




Water is essential for life as we know it. However, scientists debate how it reached the Earth and whether the same processes could seed rocky exoplanets orbiting distant stars. New insights may come from the planetary system PDS 70, located 370 light-years away. The star hosts both an inner disk and outer disk of gas and dust, separated by a 5 billion-mile-wide (8 billion kilometer) gap, and within that gap are two known gas-giant planets.

 

New measurements by NASA’s James Webb Space Telescope’s MIRI (Mid-Infrared Instrument) have detected water vapor in the system’s inner disk, at distances of less than 100 million miles (160 million kilometers) from the star – the region where rocky, terrestrial planets may be forming. (The Earth orbits 93 million miles from our Sun.) This is the first detection of water in the terrestrial region of a disk already known to host two or more protoplanets.

 

“We’ve seen water in other disks, but not so close in and in a system where planets are currently assembling. We couldn’t make this type of measurement before Webb,” said lead author Giulia Perotti of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany.

 

“This discovery is extremely exciting, as it probes the region where rocky planets similar to Earth typically form,” added MPIA director Thomas Henning, a co-author on the paper. Henning is co-principal investigator of Webb’s MIRI (Mid-Infrared Instrument), which made the detection, and the principal investigator of the MINDS (MIRI Mid-Infrared Disk Survey) program that took the data.

 

A Steamy Environment for Forming Planets

 

PDS 70 is a K-type star, cooler than our Sun, and is estimated to be 5.4 million years old. This is relatively old in terms of stars with planet-forming disks, which made the discovery of water vapor surprising.

 

Over time, the gas and dust content of planet-forming disks declines. Either the central star’s radiation and winds blow out such material, or the dust grows into larger objects that eventually form planets. As previous studies failed to detect water in the central regions of similarly aged disks, astronomers suspected it might not survive the harsh stellar radiation, leading to a dry environment for the formation of any rocky planets.

 

Astronomers haven’t yet detected any planets forming within the inner disk of PDS 70. However, they do see the raw materials for building rocky worlds in the form of silicates. The detection of water vapor implies that if rocky planets are forming there, they will have water available to them from the beginning.

 

“We find a relatively high amount of small dust grains. Combined with our detection of water vapor, the inner disk is a very exciting place,” said co-author Rens Waters of Radboud University in The Netherlands.

What is the Water’s Origin?

 

The discovery raises the question of where the water came from. The MINDS team considered two different scenarios to explain their finding.

 

One possibility is that water molecules are forming in place, where we detect them, as hydrogen and oxygen atoms combine. A second possibility is that ice-coated dust particles are being transported from the cool outer disk to the hot inner disk, where the water ice sublimates and turns into vapor. Such a transport system would be surprising, since the dust would have to cross the large gap carved out by the two giant planets.

 

Another question raised by the discovery is how water could survive so close to the star, when the star’s ultraviolet light should break apart any water molecules. Most likely, surrounding material such as dust and other water molecules serves as a protective shield. As a result, the water detected in the inner disk of PDS 70 could survive destruction.

 

Ultimately, the team will use two more of Webb’s instruments, NIRCam (Near-Infrared Camera) and NIRSpec (Near-Infrared Spectrograph) to study the PDS 70 system in an effort to glean an even greater understanding.

 

These observations were taken as part of Guaranteed Time Observation program 1282. This finding has been published in the journal Nature.

 

A spectrum of the protoplanetary disk of PDS 70, obtained with Webb’s MIRI (Mid-Infrared Instrument), displays a number of emission lines from water vapor. Scientists determined that the water is in the system’s inner disk, at distances of less than 100 million miles from the star – the region where rocky, terrestrial planets may be forming. Download the full-resolution version from the Space Telescope Science Institute.

CREDIT

Credits: NASA, ESA, CSA, J. Olmsted (STScI) Download the full-resolution version from the Space Telescope Science Institute.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

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