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Astronomie - SOFIA: a telescope on the forefront of astrophysics research

30.10.2020

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From finding organic molecules in distant stars to discovering water on the sunlit surface of the Moon, NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) is at the forefront of scientific research — especially when it comes to the potential for life either developing or being sustained on bodies other than Earth.

The latest studies from SOFIA, both announced this month, confirm the presence of organics and water in protoplanetary discs around young, planet-forming stars as well as the detection of water molecules on the Sun-lit surface of the Moon — indicating that water may be distributed across the lunar surface and not limited to cold, shadowed places.

Organics in distant stars

In a paper published 8 October in the Astrophysical Journal, scientists using data gathered by SOFIA discovered large quantities of water and organic molecules in swirly, dusty discs rotating around two massive newborn stars.

The discovery offers a new understanding of how some of the key ingredients of life are incorporated into planets during the earliest stages of planetary system formation — a process that likely happened during the formation of the Sun and the inner rocky planets of our home solar system. 

“We’re seeing many more molecular signatures than were ever seen before at these wavelengths,” said Andrew Barr, the lead author of the study and a doctoral candidate at Leiden University in the Netherlands.  “It turns out that these stars are like chemical factories churning out molecules important for life as we know it, and we just needed the right kind of observations to see them.”

SOFIA observed clouds around two massive stars approximately 3,000 light-years away in the constellation Cygnus and the Juggler Nebula, respectively.  These clouds are heated from the inside out and contain a chemical soup of organic molecules — including water, ammonia, methane, and acetylene: the chemical building blocks to larger and more complex organic molecules.

The fact that these were observed in the protoplanetary discs from which planets will eventually form provides key evidence for how organics and the building blocks of life might be seeded to planets very early in their development — a very similar process to what is believed to have happened during our solar system’s initial formation 4.5 billion years ago.

“SOFIA’s powerful infrared telescope was able to see the presence of these simple organic compounds that were important for the origin of life on Earth, and possibly other planets,” said Klaus Pontoppidan, project scientist for the Webb telescope at the Space Telescope Science Institute.  “One of the most important goals of both Webb and SOFIA is to understand the origins of stars and planets — and ultimately ourselves.”

SOFIA is a Boeing 747SP aircraft modified to carry a 2.7 meter reflecting telescope.  SP stands for “Special Performance” as the 747 has a shorter fuselage and a greater range.  The aircraft flies at 11.5-13.7 km (38,000-45,000 feet) where there is little to no infrared blocking from the atmosphere, allowing astronomers to study the solar system and beyond with minimal atmospheric distortion. 

Unlike space-based telescopes, SOFIA lands after each flight, so its instruments can be exchanged, serviced, or upgraded to harness new technologies.  Because these new instruments can be tested and adjusted, SOFIA can serve as a testbed for technology that may one day fly in space.

SOFIA’s overall objectives are to: 

  • study the composition of planetary atmospheres and surfaces, 
  • understand the structure, evolution, and composition of comets,
  • determine the physics and chemistry of the interstellar medium, and
  • explore the formation of stars and other stellar objects.

A dusty disc rotating around a massive newborn star about 40 times the size of the Sun. (Credit: NASA / Ames Research Center / Daniel Rutter)

SOFIA’s observations described in the Astrophysical Journal this month indicate that massive star formation is a scaled-up version of what is occurring in smaller, Sun-sized (or main sequence) stars, unambiguously identifying the chemical compositions of molecules glowing brightly around more massive stars and aiding scientists planning to use the James Webb Space Telescope for similar observations.

Right now, SOFIA’s infrared observations offer an unparalleled view of star chemistry as its instruments can detect small details in the chemical fingerprints from the cores of massive young stars, similar to how high-resolution images reveal tiny features. 

Water water… everywhere?

Far away stars were the only thing that made SOFIA shine this month.  Researchers at NASA’s Ames Research Center discovered water molecules in Clavius Crater on the Moon, one of the largest craters visible from the Earth.  While this isn’t the first time water has been detected on the Moon, India’s Chandrayaan-1 mission discovered water-ice in 2008/2009 in shadowy craters, this new research has identified water on the surface that is lit by the Sun — a region long considered to be dry because of the heat and radiation from our nearest star. 

However, data obtained by SOFIA revealed water in concentrations of 100 to 412 parts per million – roughly equivalent to a 12-ounce bottle of water – trapped in a cubic meter of soil spread across the lunar surface.  As a comparison, the Sahara desert has 100 times the amount of water than what SOFIA has detected in the lunar soil.

“We had indications that H2O – the familiar water we know – might be present on the sunlit side of the Moon,” said Paul Hertz, director of the Astrophysics Division in the Science Mission Directorate at NASA.  Hertz added that this research raises intriguing questions about resources relevant for deep space exploration.

Water is a precious resource and will be required for lunar missions and an eventual lunar base under NASA’s Artemis program.  “If we can use the resources at the Moon, then we can carry less water and more equipment to help enable new scientific discoveries,” said Jacob Bleacher, chief exploration scientist for NASA’s Human Exploration and Operations Mission Directorate.

“We knew there was some kind of hydration,” said Casey Honniball, the lead author who published the results from her graduate thesis work at the University of Hawaii at Mānoa in Honolulu.  “But we didn’t know how much, if any, was actually water molecules – like we drink every day – or something more like drain cleaner.”  

Although SOFIA observes the solar system and beyond at mid- and far-infrared wavelengths to gather data about distant, dim objects such as black holes, star clusters, and galaxies, this was its first observation of our nearest neighbor; and the mission was filled with challenges.  Naseem Rangwala, SOFIA’s project scientist at NASA’s Ames Research Center, said “It was, in fact, the first time SOFIA has looked at the Moon, and we weren’t even completely sure if we would get reliable data, but questions about the Moon’s water compelled us to try.”

SOFIA typically uses a guide camera to track stars, keeping the telescope locked steadily on its observation target.  But the Moon is so close and bright that it fills the guide camera’s entire field of view.  With no stars visible, it was unclear if the telescope could reliably track the Moon.  To determine this, operators decided to try a test observation in August 2018.

Additional follow-up flights of SOFIA are planned to look for water in additional sunlit locations and during different lunar phases to learn how the observed water is produced, stored, and moved across the Moon — adding to the work of future Moon missions, such as NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) which will create the first water resource maps of the Moon for future human exploration.

“Incredibly, this discovery came out of what was essentially a test, and now that we know we can do this, we’re planning more flights to do more observations.”

Quelle: NS

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