Chasing the Shadow of Neptune’s Moon Triton

Our Flying Observatory

Our flying observatory, called SOFIA, carries a 100-inch telescope inside a Boeing 747SP aircraft. Scientists onboard study the life cycle of stars, planets (including the atmosphere of Mars and Jupiter), nearby planetary systems, galaxies, black holes and complex molecules in space.

AND on Oct. 5, SOFIA is going on a special flight to chase the shadow of Neptune’s moon Triton as it crosses Earth’s surface!

In case you’re wondering, SOFIA stands for: Stratospheric Observatory for Infrared Astronomy.


Triton is 1,680 miles (2,700 km) across, making it the largest of the 13 moons orbiting Neptune. Unlike most large moons in our solar system, Triton orbits in the opposite direction of Neptune, called a retrograde orbit. This backward orbit leads scientists to believe that Triton formed in an area past Neptune, called the Kuiper Belt, and was pulled into its orbit around Neptune by gravity. 

The Voyager 2 spacecraft flew past Neptune and Triton in 1989 and found that Triton’s atmosphere is made up of mostly nitrogen…but it has not been studied in nearly 16 years!

Occultations are Eclipse-Like Events

An occultation occurs when an object, like a planet or a moon, passes in front of a star and completely blocks the light from that star. As the object blocks the star’s light, it casts a faint shadow on Earth’s surface

But unlike an eclipse, these shadows are not usually visible to the naked eye because the star and object are much smaller and not nearly as bright as our sun. Telescopes with special instruments can actually see these shadows and study the star’s light as it passes near and around the object – if they can be in the right place on Earth to catch the shadow.

Chasing Shadows

Scientists have been making advanced observations of Triton and a background star. They’ve calculated exactly where Triton’s faint shadow will fall on Earth! Our SOFIA team has designed a flight path that will put SOFIA (the telescope and aircraft) exactly in the center of the shadow at the precise moment that Triton and the star will align. 

This is no easy feat because the shadow is moving at more than 53,000 mph while SOFIA flies at Mach 0.85 (652 mph), so we only have about two minutes to catch the shadow!! But our SOFIA team has previously harnessed the aircraft’s mobility to study Pluto from inside the center of its occultation shadow, and is ready to do it again to study Triton!

What We Learn From Inside the Shadow

From inside the shadow, our team on SOFIA will study the star’s light as it passes around and through Triton’s atmosphere. This allows us to learn more about Triton’s atmosphere, including its temperature, pressure, density and composition! 

Our team will use this information to examine if Triton’s atmosphere has changed since our Voyager 2 spacecraft flew past it in 1989. That’s a lot of information from a bit of light inside a shadow! Similar observations of Uranus in 1977, from our previous flying observatory, led to the discovery of rings around that planet!

International Ground-Based Support

Ground-based telescopes across the United States and Europe – from Scotland to the Canary Islands – will also be studying Triton’s occultation. Even though most of these telescopes will not be in the center of the shadow, the simultaneous observations, from different locations on Earth, will give us information about how Triton’s atmosphere varies across its latitudes. 

This data from across the Earth and from onboard SOFIA will help researchers understand how Triton’s atmosphere is distorted at different locations by its high winds and its strong tides!

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“Ethereal Explosion”

An explosion of pastel colours paints the sky, as the sun sets over the frozen and snow dusted Little Cranberry Lake.
I made this time stack by combining 242 photos into one image.

Astronomy From 45,000 Feet

What is the Stratospheric Observatory for Infrared Astronomy, or SOFIA, up to?

SOFIA, the Stratospheric Observatory for Infrared Astronomy, as our flying telescope is called, is a Boeing 747SP aircraft that carries a 2.5-meter telescope to altitudes as high as 45,000 feet. Researchers use SOFIA to study the solar system and beyond using infrared light. This type of light does not reach the ground, but does reach the altitudes where SOFIA flies.

 Recently, we used SOFIA to study water on Venus, hoping to learn more about how that planet lost its oceans. Our researchers used a powerful instrument on SOFIA, called a spectrograph, to detect water in its normal form and “heavy water,” which has an extra neutron. The heavy water takes longer to evaporate and builds up over time. By measuring how much heavy water is on Venus’ surface now, our team will be able to estimate how much water Venus had when the planet formed.

We are also using SOFIA to create a detailed map of the Whirlpool Galaxy by making multiple observations of the galaxy. This map will help us understand how stars form from clouds in that galaxy. In particular, it will help us to know if the spiral arms in the galaxy trigger clouds to collapse into stars, or if the arms just show up where stars have already formed.

We can also use SOFIA to study methane on Mars. The Curiosity rover has detected methane on the surface of Mars. But the total amount of methane on Mars is unknown and evidence so far indicates that its levels change significantly over time and location. We are using SOFIA to search for evidence of this gas by mapping the Red Planet with an instrument specially tuned to sniff out methane.

Next our team will use SOFIA to study Jupiter’s icy moon Europa, searching for evidence of possible water plumes detected by the Hubble Space Telescope. The plumes, illustrated in the artist’s concept above, were previously seen in images as extensions from the edge of the moon. Using SOFIA, we will search for water and determine if the plumes are eruptions of water from the surface. If the plumes are coming from the surface, they may be erupting through cracks in the ice that covers Europa’s oceans. Members of our SOFIA team recently discussed studying Europa on the NASA in Silicon Valley Podcast.

This is the view of Jupiter and its moons taken with SOFIA’s visible light guide camera that is used to position the telescope.  

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