Using IR to learn about space

Last month, Pluto passed in front of a star and cast a small shadow on the Earth - astronomers from Lowell Observatory were among the scientists and crew who observed the rare occultation event from NASA's newest airborne observatory, SOFIA (Stratospheric Observatory for Infrared Astronomy).

SOFIA has a 100-inch (2.5-meter) telescope aboard a modified 747 SP aircraft, and can fly at an altitude of 45,000 ft., above most of the cloud cover and water vapor in the Earth's atmosphere.

The June 23rd Pluto occultation was observed using HIPO, the High-speed Imaging Photometer for Occultations, and its dual high-speed cameras that record light at two wavelengths simultaneously.

Pluto holds onto a very thin atmosphere of nitrogen, methane, and a few other gases and was first measured directly by astronomers from MIT and Lowell Observatory in 1988 using the stellar occultation technique: monitoring the light from a star as Pluto and its atmosphere pass in front of it. The way in which the starlight dims lets astronomers determine the temperature and density of this tenuous atmosphere. In 1988, astronomers watched from a variety of telescopes in Australia and New Zealand, as well as from the Kuiper Airborne Observatory (KAO), a 36-inch telescope aboard a C-141A transport aircraft, while flying over the Pacific Ocean.

Pluto's tenuous atmosphere exists because of vapor-pressure equilibrium, where a small amount of gas resides above any solid ice surface. The atmosphere in this state is very sensitive to changes in surface temperature, and since 1989 Pluto has been receding from the Sun. Because the Sun is Pluto's prime source of heat, astronomers expect Pluto's surface to become colder and for its atmosphere to become less dense and to finally freeze out onto the surface. However, Pluto's atmosphere is instead becoming more dense, as has been shown through several occultation events observed since 1988.

One goal of continued study is to understand the timescale of the global changes in Pluto's atmosphere; to this end, astronomers have been tracking Pluto occultations across the globe every year from March through October, during Pluto's observing season.

The ability to precisely position SOFIA within the shadow called for a massive prediction effort in the weeks before the event. Telescope time for astrometry (the measurement of precise positions of celestial objects) was secured at Lowell Observatory, the U.S. Naval Observatory--Flagstaff Station, and the Cerro Tololo Inter-American Observatory at La Serena, Chile. Lowell staff members Stephen Levine and Len Bright obtained the observations with the USNO and Lowell telescopes and immediately sent these data to MIT to be analyzed by the astrometry group there.

Dr. Amanda Bosh (MIT,visiting astronomer at Lowell Obs.) reports that astrometric images were appearing at MIT mere minutes after they were acquired. They were processed and Pluto's path toward the star was analyzed by Bosh and colleague Carlos Zuluaga (MIT) to determine where the shadow path would fall on the Earth. Researchers planned a last-minute flight path update, via Iridium satellite phone call between SOFIA and the researchers at MIT. The flightpath was modified by about 125 miles; after the revision, SOFIA flew northwest for 30 minutes, capturing the occultation with both channels of HIPO as well as with the Fast Diagnostic Camera (Jurgen Wolf, Deutsches SOFIA Institut and SOFIA Science Center). The final update put SOFIA within about 65 miles of the exact center of the shadow.

Many ground-based observers also captured the event at locations in Hawaii, southern California,and Flagstaff, AZ. Other teams from the Southwest Research Institute(SwRI) and l'Observatoire de Paris were observing the same event throughout the Pacific basin; the SwRI team included Lowell astronomer Larry Wasserman, who observed from the island nation of Nauru. Data analysis is underway and results will be presented at the Division for Planetary Sciences of the American Astronomical Society fall meeting in October 2011 in Nantes, France.

This Pluto occultation observation continues a long history of occultation science at Lowell Observatory that includes many astronomers, past and present, who have used the technique to study bodies as diverse as asteroids, planets, planetary rings,and stars. Key results include the discovery of the rings around Uranus in 1977, as well as Pluto's atmosphere in 1988.

Funding for this research was provided by grants from USRA for SOFIA and NASA's Planetary Astronomy Program.

Lowell Observatory is a private, non-profit research institution founded in 1894 by Percival Lowell. The Observatory has been the site of many important findings including the discovery of the large recessional velocities (redshift) of galaxies by Vesto Slipher in 1912-1914 (a result that led ultimately to the realization the universe is expanding), and the discovery of Pluto by Clyde Tombaugh in 1930. Today, Lowell's 19 astronomers use ground-based telescopes around the world, telescopes in space, and NASA planetary spacecraft to conduct research in diverse areas of astronomy and planetary science. The Observatory welcomes about 80,000 visitors each year to its Mars Hill campus in Flagstaff, Arizona for a variety of tours, telescope viewing, and special programs. Lowell Observatory currently has four research telescopes at its Anderson Mesa dark sky site east of Flagstaff, and is building a 4-meter class research telescope, the Discovery Channel Telescope.

From science20.com July 19th 2011

MOFFETT FIELD, Calif. - Researchers using NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) have captured infrared images of the last exhalations of a dying sun-like star.

The object observed by SOFIA, planetary nebula Minkowski 2-9, or M2-9 for short, is seen in this three-color composite image. The SOFIA observations were made at the mid-infrared wavelengths of 20, 24, and 37 microns. The 37-micron wavelength band detects the strongest emissions from the nebula and is impossible to observe from ground-based telescopes.

Objects such as M2-9 are called planetary nebulae due to a mistake made by early astronomers who discovered these objects while sweeping the sky with small telescopes. Many of these nebulae have the color, shape and size of Uranus and Neptune, so they were dubbed planetary nebulae. The name persists despite the fact that these nebulae are now known to be distant clouds of material, far beyond our solar system, that are shed by stars about the size of our sun undergoing upheavals during their final life stages.

Although the M2-9 nebular material is flowing out from a spherical star, it is extended in one dimension, appearing as a cylinder or hourglass. Astronomers hypothesize that planetary nebulae with such shapes are produced by opposing flows of high-speed material caused by a disk of material around the dying star at the center of the nebula. SOFIA's observations of M2-9 were designed to study the outflow in detail with the goal of better understanding this stellar life cycle stage that is important in our galaxy's evolution.

"The SOFIA images provide our most complete picture of the outflowing material on its way to being recycled into the next generation of stars and planets," said Michael Werner of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., principal investigator of these observations. "We were gratified to see the lobes so clearly using SOFIA. These early results demonstrate the scientific potential of this important new observatory."

The observations were made using the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST) instrument in June 2011 by a team consisting of astronomers from JPL, the California Institute of Technology, the University of California at Los Angeles, Cornell University and Ithaca College, Ithaca, N.Y. Preliminary analyses of these data were first presented in January 2012 at the American Astronomical Society meeting in Austin, Texas.

The SOFIA observatory combines an extensively modified Boeing 747SP aircraft and a 17-metric-ton reflecting telescope with an effective diameter of 2.5 meters (100 inches) that is capable of reaching altitudes as high as 45,000 feet (14 km), above more than 99 percent of the water vapor in Earth's atmosphere that blocks most infrared radiation from celestial sources.

SOFIA is a joint project of NASA and the German Aerospace Center (DLR), and is based and managed at NASA's Dryden Aircraft Operations Facility in Palmdale, Calif. NASA's Ames Research Center in Moffett Field, Calif., manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association (USRA), headquartered in Columbia, Md., and the German SOFIA Institute (DSI) at the University of Stuttgart.

From nasa.gov March 29, 2012

NASA has announced the discovery of water on a sunlit surface of the Moon. The discovery could have major implications both for piecing together the history of the Solar System but also for future human spaceflight.

The discovery was made by NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA), and is particularly surprising because it suggests water can survive the extremities of the lunar day.

It could also mean that more water is available across the surface of the Moon.

The water was discovered in the Clavius crater (pictured at the top of this page) of the Moon's southern hemisphere.

Previous observations of the lunar surface had detected hydrogen, but SOFIA's infrared spectrometer was able to confirm the hydrogen detected is unique to the water molecule H20, indicating the presence of water.

The water does not exist in puddles, but in concentrations of 100 to 412 parts per million. This is about the same as a 350ml bottle of water trapped in a cubic metre of soil spread across the surface of the Moon.

The Sahara desert, as a comparison, has 100 times the amount of water detected by SOFIA detected in the lunar soil.

It was already known that water exists in the darker, colder craters of the Moon, but finding water in a sunlit region suggests water could be more abundant on the Moon than thought, while the presence of water in more easily accessible regions of the Moon could have major implications for human spaceflight.

NASA scientists have suggested the water may be delivered by micrometeorites impacting the Moon and depositing the water on the lunar surface.

Or, it could have been delivered to the Moon by the solar wind, which is a stream of charged particles emanating from the Sun.

This could deliver hydrogen to the lunar surface, and a subsequent chemical reaction with oxygen-bearing minerals in the lunar soil could create hydroxyl. Radiation from micrometeorites might then transform that hydroxyl into water.

But how the water remains on the Moon is a mystery, as water on the sunlit surface of the Moon should be lost to space. It could be trapped within glass beads deposited by micrometeorite impacts, say NASA scientists.

The discovery has major implications for our understanding of the role played by water in the creation and evolution of the Solar System, but also for NASA's Artemis program to establish a human presence on the Moon.

“Prior to the SOFIA observations, we knew there was some kind of hydration,” says Casey Honniball, lead author of the study 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.

“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space, yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”

“Water is a valuable resource, for both scientific purposes and for use by our explorers,” says Jacob Bleacher, chief exploration scientist for NASA’s Human Exploration and Operations Mission Directorate.

“If we can use the resources at the Moon, then we can carry less water and more equipment to help enable new scientific discoveries.”

From Sky at Night Magazine By Iain Todd

Published: October 26, 2020