NASA has released an image obtained by the New Horizons spacecraft that appears to show a frozen lake on Pluto.
The photograph is of a mountainous area north of Sputnik Planum and shows details as small as 130 meters in size.
The substance in the lake is not water. It is instead, in all likelihood, frozen nitrogen. If you look closely, you can also see features around the lake that may have once carried liquids.
Pluto must have had a thicker atmosphere that exerted greater pressure and conditions on the dwarf planet’s surface must have been warmer in the past if liquids flowed there.
NASA released the image on March 24.
In recent years humanity has learned that oceans are not unique to Earth. Discoveries of them on Saturn’s moons Enceladus and Titan and Jupiter’s moon Europa indicate that oceans may actually be ubiquitous in our solar system.
Now, it seems, it is possible that an ocean once existed on a satellite of the dwarf planet Pluto.
NASA said Friday that images obtained by the New Horizons probe suggest that Charon once had a subsurface sea that expanded outward as it froze, cracking the surface of the moon.
The photographs show tectonic faults, including some valleys more than 6.5 kilometers deep, that indicate an expansion of Charon sometime in the past.
Here’s how it likely happened:
The outer-most layer of Charon, including its surface, is now water ice. But the satellite’s internal heat would have caused that ice to melt deep under the surface, which would have resulted in a subsurface ocean. As the decay of radioactive elements that constitute Charon’s structure subsided, and as the rocky object cooled as the time since its formation passed, that ocean would have frozen. Just as the change of water’s state from liquid to solid on Earth causes an increase in the the compound’s volume, ice formation under the surface of Charon would have pushed the surface outward, resulting in the valleys and also numerous ridges and scarps.
The New Horizons spacecraft won’t arrive in the vicinity of Pluto until 2015, but it is close enough now to obtain images of some Kuiper Belt objects.
NASA has released images of Charon, Pluto’s largest moon, taken by New Horizons earlier this month. The images of Charon are somewhat fuzzy because the spacecraft is still about 550 million miles (900 million kilometers) away from Pluto, which is farther away from the dwarf planet than Earth is from Jupiter. From the perspective of the spacecraft, Charon’s location is about 0.01 degrees from Pluto.
Nevertheless, the detail they provide about Charon is a significant improvement over that obtained from Earth-based observation.
“The image itself might not look very impressive to the untrained eye, but compared to the discovery images of Charon from Earth, these ‘discovery’ images from New Horizons look great!”, Hal Weaver, a New Horizons project scientist affiliated with The Johns Hopkins University Applied Physics Laboratory said. “We’re very excited to see Pluto and Charon as separate objects for the first time from New Horizons.”
The photographs were obtained by the spacecraft’s Long Range Reconnaissance Imager in less than one second.
Charon is not Pluto’s only satellite. However, the images obtained by LORRI (an acronym for New Horizons’ photographic apparatus) indicate just how tiny the other moons of Pluto are. Pluto is about 2,300 kilometers across and Charon is about half that large (1,200 kilometers). None of the other moons of Pluto exceed about 170 kilometers across. Some may be as small as 10 kilometers (that’s about 6.2 miles) across!
This composite image of Charon is an amalgamation of six images. Pluto is the bright object near the center of the frame, while Charon is the dimmer object to the upper left of Pluto. Image courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
New Horizons is beyond the orbit of Uranus and is traveling at a velocity of about 15 kilometers per second. That’s about 32,000 miles per hour! Despite that amazing speed, the spacecraft won’t arrive at Pluto until July 2015. By the time it gets there it will have been traveling in the cosmos for about nine and one-half years.
If that causes you to wonder just how big the solar system is, it should. Think of it this way: the solar system is so enormous that even the two Voyager spacecraft that were launched 36 years ago, which are still moving as fast as New Horizons is, have not yet left it.
Two newly-discovered moons of Pluto now have names.
The International Astronomical Union announced Tuesday that the fourth and fifth satellites of the solar system’s former ninth planet will be known as Kerberos and Styx.
Like moons of most of Earth’s other planetary neighbors, the names relate to the gods of Greek and Roman mythology.
Kerberos is the name of the dog that guards the underworld in the ancient Greek tales, while Styx is the name of the river that separated Earth and the underworld in those tales.
Both moons are recent discoveries.
“They were both discovered in images from the Hubble Space Telescope,” Mark Showalter, an astronomer associated with the Carl Sagan Center for Study of Life in the Universe at California’s SETI Institute and the leader of the research team that discovered them, said. “P4, which is now Kerberos, was found in 2011, late June or July, and P5 was found about this time in 2012. The discovery of P4 was actually in a short Hubble program to search for dust rings around Pluto. We were doing that by taking longer exposures of Pluto than anyone had attempted before.”
Researchers subsequently decided to look for more evidence of additional satellites of Pluto.
The two moons are very small, on the order of about 100 times smaller than Charon, Pluto’s largest satellite.
“They’re just dots in the sky,” Showalter explained. “The estimates we have are on the order of 10-15 miles in diameter. Three billion miles away, and that’s how big they are. Just to illustrate, P5 is about 100,000 times fainter than Pluto itself. They’re separated on the sky by, basically, a hair’s breadth.”
Charon has a diameter of about 1,200 kilometers.
Kerberos and Styx almost certainly move in synchronous rotation with Pluto, just as Earth’s moon does in relation to our planet.
“Every satellite in the solar system, except Saturn’s moon Hyperion, has been shown to be tidally locked,” Showalter said.
The Hubble Space Telescope was used to find Pluto’s two other known satellites, Nix and Hydra, in 2005. Those moons are named, respectively, for the Greek goddess of darkness and night and the nine-headed serpent that fought Hercules in the ancient myths.
The system of naming moons for characters of Greek and Roman mythology is commonly employed by astronomers in naming the moons of the solar system’s planets.
“Moons of Neptune are named for creatures associated with the oceans in Greek and Roman mythology because Neptune was the god of the ocean,” Showalter said.
Similarly, eight moons of Saturn are named for titans of Greek mythology, while many of Jupiter’s moons – notably excluding Callisto, Europa, Ganymede, and Io – are named for lovers and descendants of Zeus. Mars’ two moons are named for children of Ares, the Greek god of war.
The moons of Uranus are named for characters from English literature, particularly Shakespeare’s plays.
Kerberos and Styx may not be the last moons of Pluto to be discovered. The New Horizons spacecraft is scheduled to arrive in the vicinity of Pluto in 2015, allowing scientists a close-up look at the dwarf planet and its satellites.
“I would be frankly surprised if we don’t find a P6 and a P7 and a P8,” Showalter said. “Whatever is going on in the Pluto system that created this family of moons probably didn’t stop at five.”
He explained that it’s not likely the IAU will have any problem finding names for any newly-discovered Plutonian moons that fit the existing theme.
“I can assure you that is not a concern,” Showalter said. “We had 30,000 write-in candidates put in. There’s a long list. I still have that list. I’d like to think we’ll be returning to that list come 2015 when we find other rocks out there.”
Graphic courtesy Wikimedia