Carpe Umbra: Seize the Shadow Part 2

Kimberly Ennico Smith, SOFIA Project Scientist

We took off during the day to hunt down the shadow of a Kuiper Belt object, MU69, as it passed in front of a star. To get in its projected shadow path on Earth, we flew north from Christchurch, New Zealand toward Tahiti.

SOFIA flight path for the MU69 occultation flight. The occultation location is marked by an anchor.
Catching SOFIA’s shadow on the clouds after a rare daytime takeoff.
Flying north over New Zealand’s North Island before sunset.

We had to fly with the telescope door closed until the sun had set. During this time, the NASA New Horizons team went over the plan, rechecked all the computations, and did some time tests to reconcile differences between Coordinated Universal Time (UTC) and GPS time. The usually adjust their timing using the GPS clock, but all the mission and science planning used UTC. GPS is not perturbed by leap seconds so it slowly drifts ahead of UTC. However, GPS timing receivers put in the conversion factor to convert GPS time to UTC, but we had to double check. We also consulted the U.S. National Institute of Standards and Technology’s shortwave radio time signal station in Hawaii.

Manuel Wiedemann (left) and Enrico Pfueller (right), the instrument scientists who operated the high-speed camera, setting up their equipment.

Before the occultation, the flight plan had a short leg planned when we set up the telescope and instruments and then a time holder leg to give the pilots time to get the plane flying at exactly the right speed (adjust for winds etc.).

Sunset from the stratosphere.

After the sun had set we opened the telescope cavity door. Then it was time for the pilots and the mission director, Karina Leppik , to coordinate the plane’s  position to intercept the shadow at 16 degrees south latitude, and 175 degrees west longitude at exactly 07:49:11.

Expectant Astronomers. This picture was taken minutes just before the event.

Don’t Blink!

We were exactly where the center of the shadow was predicted to be, at exactly the right time. But our eyes could not see the event in real time.

We used our high-speed camera to take images at a rate of 20 frames per second, so the dip in the star’s light as MU69 crossed it would only appear in 8-32 images out of the 60,000 we took over 50 minutes.

These observations should enable us to better understand the size of MU69, which is currently not well known. The Hubble Space Telescope images only provide a visual magnitude measurement. So, it’s unclear if MU69 is large and dark, or small and highly reflective because both combinations can provide the equivalent magnitude.

The occultation star is in the bottom middle, marked with the bulls-eye concentric circles. All eyes were on this star during this flight.

We landed back in Christchurch just after midnight. With data in hand, the scientists deplaned SOFIA, took a short nap, and then headed to South America to start preparing for the third of three occultations event by this MU69 on July 17.

Now we wait…

….to learn what the New Horizons team finds as they analyze the data.

Carpe Umbra: Seize the Shadow Part 1

Kimberly Ennico Smith, SOFIA Project Scientist

We’ve teamed up with NASA’s New Horizons mission to observe an astronomical event known as an occultation, when an object passes in front of a background star.

Illustration of SOFIA’s observations of the MU69 occultation on July 10.

An occultation is not the same as an eclipse or a transit. It occurs only when one body completely hides another.  For this event, on July 10, a Kuiper Belt object, MU69, is going to block out a background star.

A transit occurs when the body passing in front of the other body only partially blocks it (like Mercury transiting the sun and all those transiting exoplanets that Kepler has been discovering).

Finally, an eclipse occurs when one body passes into the shadow of another body and disappears, at least partially. During the solar eclipse that will occur on August 21 across North America, the moon will eclipse the sun relative to Earth. The moon has occulted, or passed in front of, the sun. Thus, a solar eclipse could perhaps be called a type of solar occultation.

On July 10 we studied MU69 as it occulted a distant star. Two experts aboard SOFIA, Marc Buie and Simon Porter, of the Southwest Research Institute, used measurements from the Hubble Space Telescope to compute exactly where the shadow of MU69 would fall on Earth’s surface.

Scientists Simon Porter, Marc Buie, and Eliot Young will fly on SOFIA as Guest Observers to catch MU69’s shadow.

Based on these calculations, SOFIA needed to be at 16 degrees south latitude, and 175 degrees west longitude at exactly 07:49:11 UTC to catch MU69’s shadow. MU69 and the star lined up for less than 2 seconds because this Kuiper Belt Object is a very tiny (estimated to be between  12-25-miles (20-40-kilometer) across) and approximately 4.1 billion miles from Earth (well past Pluto), so this was a very challenging occultation to capture. But the flight planners and navigators on board can position SOFIA with the precision needed for this brief measurement. We’ve studied occultations of Pluto twice in the past.

The occultation on July 10th predicted ground path.

The event of July 10th had a predicted ground path as described here.

Re-Discovering Our Cosmic Origins

Studying the solar system and beyond using multi-wavelengths of light, including visible, x-ray, and infrared, reveals many different views of the same object. Check out the Milky Way’s Galactic Center in the visible, infrared and x-rays.

A Composite image of the turbulent heart of our Milky Way galaxy, in the visible, infrared and x-ray. courtesy of Hubble, Spitzer and Chandra.

Two recent Guest Observers were aboard to study the infrared universe- Dr. Monica Rubio from the University of Santiago Chile, and Dr. James Jackson, from the University of New Castle, north of Sydney, Australia.

Jackson is a veteran observer on the Kuiper Airborne Observatory (KAO), the predecessor to SOFIA which carried a 36-inch telescope in a converted C-141 military cargo plane. His first remarks about SOFIA were, “It’s big. The instruments are 10x larger than on the KAO. And there is more room for more people and space to walk.” He called the mapping feature of the GREAT instrument on the SOFIA telescope, “phenomenal.” This feature, aptly called “The Translator,” enables efficient communication between the science instrument and the telescope, so that this airborne observatory uses every minute in the sky to its fullest potential.

Panorama image as observations were underway.

The object that Jackson is studying is the Nessie Nebula, named because it looks quite serpentine across the sky. It is a large gas cloud in the spiral arm of our Milky Way, and is a fascinating home to some wacky star-forming regions. Jackson is looking for gas infalling on the cores, which are thought to be forming massive stars. With the data gathered on SOFIA, he hopes to be put together a clearer picture how stars form from collapsing clouds.

James Jackson (standing) talking strategy with Ed Chambers (seated), instrument scientist.

Rubio is studying the Small Magellanic Cloud, or SMC, a neighboring galaxy to ours that is 200,000 light years away. The SMC is very different from our own galaxy, in terms of its chemical makeup. SOFIA is in a prime location to observe this galaxy high in the sky when flying in the Southern Hemisphere. Over multiple nights, Rubio is observing seven different star formation regions in the SMC. She’s studying emission from ionized carbon, which is used as a tracer to measure the star-forming gases in the SMC and better explain the chemistry of the universe. These SOFIA observations give her the infrared view of the chemistry she needs to complete her research, which also includes observations from ground-based, sub-millimeter telescopes.

Monica Rubio discussing her science with GREAT instrument team members Anna Parikka and Denise Riquelme Vasquez.

This flight took us down to 64 degrees south, which also provided a nice glimpse of the Aurora Australis, also known as the southern lights. Aurora are a chemistry of a different kind, a result of Earth’s atmosphere interacting with solar winds.

Southern Lights or Tagu-Nui-A-Rangi, the great burning in the sky.



Our Infrared Eyes

Dr. Kimberly Ennico Smith

Last week aboard SOFIA, our observations included studying star formation regions in the Small Magellanic Cloud, a neighboring galaxy to our own Milky Way, a super-massive black hole, and the center of our Milky Way Galaxy. The method we used for these studies is called spectroscopy, and in more particular, high-resolution spectroscopy. The instrument onboard can isolate the wavelength, or frequency, of a particular atomic or molecular transition, allowing scientists to measure how fast and in which direction the molecule is moving.

When observing on SOFIA, the time spent on each celestial target is planned in advance, taking into account the position of the object in the sky, the direction of the aircraft, and the motion of the sky throughout the observation. When you add in the constraints that the airplane must take off and land at Christchurch International Airport and that the telescope only looks out the left (port) side of the plane, it makes for unique flight plans each night. Often the same targets are observed on multiple flights to get all the data we need.

Updated flight plan.

We, as humans, cannot see infrared light with our eyes. So, we are thankful to have SOFIA’s telescope and instruments which enable us to study the infrared solar system and beyond.

During the June 28 flight, we observed a target called Sagittarius A, or SgrA (pronounced ‘Sag A-Star’), which when viewed from Earth is in the constellation Sagittarius. Evidence has been mounting that SgrA is a supermassive black hole, as telescopes have measured the speeds of stars orbiting that point in space at much higher speeds than any other star in the galaxy.

Using the powerful instruments on SOFIA, we are studying atomic oxygen in the gas surrounding the black hole, which can only be studied with far-infrared wavelengths of light that do not reach Earth’s surface. The researchers onboard are trying to measure the amount of neutral (not ionized) gas that is falling into the black hole. With SOFIA they can actually determine how fast the gas is moving and its direction of motion using the high-resolution instrument onboard. Combining measurements of both the gas’s velocity and mass will help us understand how the black hole at the center of our galaxy is accumulating mass from its surroundings, due to its large gravitational pull.

Image from the visible light guide camera on SOFIA. SgrA is in the center.



Southern Lights Just Take Your Breath Away

Dr. Kimberly Ennico Smith

What’s up tonight for this flying observatory? We’re looking at the Central Molecular Zone, the region around the center of our Milky Way Galaxy, young protostars, massive young stellar objects, and the “stuff between the stars,” called the Diffuse Interstellar Medium.

The Center of the Milky Way Galaxy as seen while flying at 40,000 feet.

As with any SOFIA flight, there is a timeline of preparation activities that must be followed to prepare the plane for an observing mission: the aircraft items refuel and coordinate transferring the onboard instruments from ground-based power to the aircraft’s power; the pilots meet to go over departure and arrival options; the scientists discuss the observations planned for the flight. Everyone flying has to be present for the head count at the final mission meeting.

The team meeting before the flight.

Soon it’s time to board and the clock is ticking. I sat in the cockpit for takeoff, this time for departure, and pilots Paul & Dean with flight engineer Moose (Marty) certainly were kept busy with air traffic control. For SOFIA, taking off within a narrow time window is crucial for the flight’s success in because each turn of the flight is planned to the minute to facilitate our scientific observations. If there are delays with takeoff, the mission directors need to work with the pilots to alter our path to get back on schedule. It was a fine balance and Paul & Dean handled it smoothly.

The flight plan showing where we flew during our observations.

This flight plan took us very south — we reached 64.534 degrees south latitude and were delighted to see a show of the southern lights, the Aurora Australis!

Southern Lights, seen from SOFIA while flying at 63 degrees south and 170 degrees east. (Kimberly Ennico Smith)

At the end of the 10+ hour flight, the science team disembarked with high-quality data thanks to the very low water vapor at 43,000 feet. Water vapor blocks infrared light from reaching the ground, but SOFIA flies above 99% of it. This data should provide new insights into the role of atomic gas in extreme conditions, like those at our galactic center, in jets and outflows of protostars, and in the regions of massive young stellar objects.


The Journey Down to Southern Astronomical Skies

Dr. Kimberly Ennico Smith, SOFIA Project Scientist

SOFIA, the world’s only flying observatory, is in Christchurch, New Zealand for the next few weeks, to enable unique infrared observations from the Southern Hemisphere. From here, we can study our galaxy’s center and nearby galaxies, the Magellanic Clouds, which will feature prominently in our observations in the weeks to come.

I flew onboard SOFIA on the journey south from its home base at NASA’s Armstrong Flight Research Center, in southern California. We stopped in Honolulu, Hawaii, to refuel and change crews on the way to New Zealand.

During the flight, I got a chance to hang out in the cockpit and spend time with the flight engineer. He explained what all the dials and buttons do — some monitor the temperature of the engines and control the engine heaters, others monitor the airplane’s elevation.

The pilots and flight engineer aboard SOFIA. (NASA Photo)

The rest of my fellow passengers were a mixture of mechanics, software engineers, telescope operators, and avionics technicians. We got to chatting about all sorts of avionics systems and swapped stories. They know the world of aircraft inside and out and it was truly a pleasure to pick their brains over the two long flights down south.

SOFIA landing at Christchurch International Airport.

We are ready to observe the solar system and beyond from the National Science Foundation’s Antarctic Program Facility at Christchurch Airport!