Pluto’s moon Charon has giant canyon; New Horizons studies small KBO
Argo Chasma, a huge canyon located on the eastern limb of Pluto’s largest moon, Charon, is longer, deeper, and more complex than the Grand Canyon on Earth.
A newly-released image was taken by NASA’s New Horizons spacecraft using its Long Range Reconnaissance Imager (LORRI) from a distance of 289,000 miles (466,000 kilometers) 9 hours and 22 minutes before the spacecraft’s closest approach to Charon, with a resolution of 2.33 kilometers per pixel.
The four observations of 1994 JR1 that New Horizons made in November 2015. The KBO is the dot in the center, and the stars are moving past in the background. Credits: NASA/JHUAPL/SwRI
Released alongside the image is a magnified version of the inset region where the canyon runs along Charon’s limb.
Mission scientists estimate Argo Chasma to be about 430 miles (700 kilometers) long. In contrast, the Grand Canyon in Arizona has a length of 280 miles (450 kilometers).
The magnified image shows a section of the canyon running approximately 185 miles (300 kilometers) in length.
Because the LORRI image shows the canyon edge-on, it reveals significant details, including the canyon’s depth and the presence of steep cliffs rising several miles high in various areas along the canyon’s length.
The cliffs could be as tall or even taller than the Solar System’s tallest known cliffs – Verona Rupes on Uranus’s moon Miranda.
Verona Rupes are estimated to have a height of three miles (five kilometers).
From this photo and others, mission scientists estimate Argo Chasma to have a depth as great as 5.5 miles (9 kilometers), about five times that of the Grand Canyon.
The “Super Grand Canyon” was likely created when an ancient subsurface ocean inside Charon froze, in the process stretching and fracturing the large moon’s surface.
Today, Charon has a complex network of tectonic faults, which account for its deep chasms, ridges, and scarps.
While data from the Pluto flyby is still being returned from the spacecraft, New Horizons has already observed another object, Kuiper Belt Object (KBO) 1994 JR1, in “distant flybys” conducted in November 2015 and April 2016.
Above, the first two of the 20 observations that New Horizons made of 1994 JR1 in April 2016. The Kuiper Belt object is the bright moving dot indicated by the arrow. The dots that do not move are background stars. The moving feature in the top left is an internal camera reflection (a kind of selfie) caused by illumination by a very bright star just outside of LORRI’s field of view; it shows the three arms that hold up LORRI’s secondary mirror. Credits: NASA/JHUAPL/SwRI
Simon Porter, a New Horizons postdoctoral researcher based at the Southwest Research Institute (SwRI) in Boulder, Colorado, in a June 24 blog entry titled “New Horizons: Getting to Know a KBO“, describes how LORRI was used to image the small object from a distance of about 66 million miles (106.2 million kilometers).
In November 2015, four sets of 10 images of 1994 JR1, spaced one hour apart, were taken from a distance of 172 million miles (276.8 million kilometers); the images were used to create the animated GIF shown above.
At the same time that New Horizons was imaging the small KBO, the Hubble Space Telescope was turned toward it for a simultaneous observation from Earth.
Combining data from both observations enabled scientists to better determine the object’s orbit.
That knowledge was used when the second set of photos was taken in April 2016.
No orbiting moons were detected by New Horizons or by Hubble.
A “ghostly circular pupil image” and tiny dots that appear to move around in the background of the animated GIF (shown on the left) are the effects of scattered light from a nearby star, Porter explains.
Observations conducted in April 2016 focused on 1994 JR1’s changing brightness over time, identified its rotational period as 5.47 hours, and found it to have a rugged surface similar to that of Saturn’s moon Phoebe, which is thought to be a captured KBO.
The April data allowed scientists to compute the object’s current orbit with much greater proficiency and conduct a computer simulation to determine its long-term future orbit.
If New Horizons’ extended mission proposal for a 2019 close flyby of the smaller KBO 2014 MU69 is formally approved, the spacecraft will be able to conduct distant flybys of several more KBOs during the journey.
Laurel Kornfeld
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.
